Tandem gyro plans

[joe nelson]

Monday, I received plans for a tandem rotor rc gyro. Being a big fan of the H46 and 47 I was excited to see how the designer controlled the rotor. Unfortunately, they were fixed. All control was by engine power, elevators and rudders on the tail. The rotors, themselves, were set at -4 degrees...no lift here!

The designer has the mast angle for both rotors set at +4 deg. and the blades set at -4deg. making flight questionable. If it flew at all it would be from engine power and maybe a small amount of newton's lift from the rotors.:rant:

[joe nelson]

This morning, I cut the heads out of 1/8 inch ply and drilled an 1/8 inch hole for the rotor shaft. This was sleved with a 5/32 brass tube and glued in place. A flairing tool was then used to lock the sleve in place on the head.

The plans didn't specify the type of airfoil but it looks as if it was an 8H12 or Clark Y...both being flat bottomed and 12 "in length. I went to the r/c webpage to poach a few ideas on rotor blade construction. Building blade is the next task list.

[Jazzenjohn]

Do the rotors intermesh or are they completely separate? side by side or front and back? do they spin in opposite directions?

[joe nelson]

John,

In the plans there is overlap of about 30% and the rotors turn in the same direction. I intend to have them turn in the opposite direction and like the Chinook an overlap of 34% which agrees with the formula in Stan Dzik's book. The front rotor, in the plans, is set at 4 degrees but I'll set them at 9 drees like a real gyro and the rear set with two or three more for the airframe interfrence ( that's Joe's best guess). The rotors are separated in height by the height of the pylons.

Yesterday, I found a rotor blade at the hobby store which might save me some time in construction but they are symetrical rather than the flat bottom blades in the plans. They look like that they may be 0012 airfoils. This will save a lot of work in building blades that turn in opposite directions...just turn them updown for the counter-rotating rotor. The front rotor turn ccw and the rear turns cw... I don't known if that makes any difference?

[joe nelson]

Sorry John,

I didn't answer your question. The blades overlap but do not intermesh. There is no linkage between rotor for separation. The rear rottor is about two inches higher than the front.

[joe nelson]

Today, I'm using an idea from Chuck B. in using a small door hinge to allow the blades to cone a few degrees. I'm thinking of attaching them at a 20 degree angle as an offset but I'm not sure if I have the best understanding of this process.

Over the weekend I'll begin work on the airframe.. it'll be as simple as possible. Most likely, just a few sticks of blasa and some control surfaces (elevator and rudders).

[joe nelson]

Well, the first spin tests were failures! The rotors mast angles were set at 4 degrees(per plans) with no success, then 9 and 12 degrees...no luck. The blades are set a zero pitch and they would'nt even rotate. I'll try adding a few degrees of pitch and try again. I thought they would autorotate at zero pitch but I guess I was wrong! In the plans, the blade angle was set at -4 degrees with a 8H12 airfoil which 2 degrees below zero lift. I'm using an 0012 airfoil set at zero pitch which, I thought, would give me the same result...wrong.

[HobbyCAD]

Joe,

Go to AeroBalsa, look at the gyro rotorblades here (http://www.aerobalsa.com/rotorblade.php). They have a perfect little reflex trailing edge, you won't find that anywhere else. Dirt cheap for a set of 4 blades.

They are SUPER DOOPER model autogyro blades, simply the BEST. When I used to play with R/C autogyro's, I only used these. They spin up in an instant, very durable as well. They come in different chord size and lengths.

Also go to a very informative R/C gyro site here (http://www.autogyro.com/).

Dont forget this site here (http://www.mickeynowell.com).

[joe nelson]

Thanks Francois,

I've been a regular visitor to the r/c website...lotsa good info there. I will order a couple of sets of blades on Monday morning with luck.

The model that I'm working on is a way to educate myself on varios types of rotorcraft without the large expense of building the real thing. My goal is to build a gyro with 1000 pound payload. Now, I'm working on a tandem (chinook type) gyro configuration.

[joe nelson]

Today was a big letdown. The aerobalsa blades were all sold out! However, I've been working on a new rotorhead. This is a fully articulated one with pitch control only. Keep your fingers crossed.

[GrantR]

Joe,

The symmetrical blade will not hand start. You can make blades out of house insulation foam using a hot wire and airfoil template to guide the wire. These will work pretty good but not as good as the AB blades.

You can also hand sand balsa planks into blades.

[joe nelson]

Thanks Grant,

I had two large fans trying get the 0012 airfoil rotors to turn but with no luck. The diameter is about two feet and I'd even considered mounting them on my truck to get enough relative wind.

Do gyro blades need some amount of reflex to behave normally?

[joe nelson]

Bingo!!

Finally, it works as it should even though with low rrpm. My guess is that I still have to much pitch in the blades. Presently, I have zero pitch and later I'll reduce this to -2 degrees.

The head, that I've just finish, has two hinges but only one works as of now. The drag hinge is locked down until I can make it work as it should. This will be addressed when the blade pitch issue is resolved.

[joe nelson]

The pitch was changed to -4 degrees as the plans indicated...who's the dummy? The blades turned up without effort in front of my large fan. Later, I try to add some washout on the last 10% of the blades. I'll try setting the root at -4 and the tips at -2 degrees for my first attempt...wish me luck!

[brett s]

I'm also building a tandem r/c model - but helicopter, not gyro. One of these:

http://tech-mp.com/twinn_rexx.htm

Using 3 bladed rotors too :)

[joe nelson]

Brett,

The model gyro is a way to educate myself on several things that I'm having a problem with. First will be the problems of a sas-less tandem. Could I mount a rudder on the aft pylon with a horizontal stabs to minimize the need for a sas? Second is the amount of airframe interference with the blades around the airframe itself? Does the rotors have to turn in the same direction as on the model? Both turn ccw!

The rotor blades are one inch in cord and 12 inches long giving it about 72 sq. inches of lifting surface and 3-4 pounds in weight it should fly.

[brett s]

The biggest issue on a tandem is lots of body surface area ahead of the cg & nowhere to place stabilizers on a long arm, and there's not a lot you can do about that.

A real CH-47 is a handful in yaw in particular with the artificial stability off, the blunt aft pylon & the strakes on the lower fuselage & ramp that were added starting with the B models supposedly helped out quite a bit.

Having the rotors turning in the same direction seems like it would be asking for a blade strike if they overlap at all, it'd be hard to have sufficient clearance to make it impossible. I suppose you avoid the gearing & driveshafting that way though.

That weight sounds high for a model gyro that size - my helicopter should be less than 4 lbs ready to fly, with 2 ~28" 3 bladed rotors (blades are 24x320mm). You sure it'll weigh that much?

[joe nelson]

Brett,

I'm not sure of the weight. The weight range was on the plans and dependant on the engine used.

The blades are separated by two inches by the height on the front and rear pylons. I also thought the rotors should be counter-rotating but there's no torque to contend with.

Do you think horizonal stabs like on the H-21 and H-25's would help?...That was my first thought. On the plans, to climb or descend is by the application of power and left or right is by rotor tilt on the aft pylon. It also said to land with power... maybe it's a rock when unpowered.

I don't want to get ahead of myself here. I still have to build the front rotor. One thing I've discovered is the 1/4 inch aluminum shaft is too weak and I'm switching to music wire for now.

[brett s]

If there's only throttle + yaw for controls that would explain why they say to land power-on, you've got no way to flare - landing without power probably only works once :)

That's how they get away with so little clearance between the rotors too.

Seems like you'd learn a lot more from the experiment if you set it up with full controls, but that sure does make it a lot more complicated. Be easier to start off with r/c helicopter parts, steal the whole drivetrain!

[joe nelson]

Brett,

You're probably right about my approach to the gyro! I have'nt built the pylons yet so it's not to late to put full controls on it.

Today, I have to disassemble the aft rotor to use it as a pattern for the front. I have heavily modified the aft head so I can't use the plans for this. Besides, I have a few ideas how I can make them fully articulated... cross my fingers lol

[joe nelson]

I've finished cutting out the front rotor hub but I've ran out of screws (2-56x5/8). This will slow me down a little until I can get to the hobby store. Today, I'll draw up some plans on a fully functioning rotor system and make a parts list.

[joe nelson]

The new articulated hub was cut out this morning. It seems to have all the axis of movements on the dry fit. Now comes the hard part of making the swash plate. I do have a small one, made of UHMW plastic, that I build last year. I'll give it a try before making a new one.

[brett s]

You can always buy ones built for 450 scale r/c helicopters, all sorts available (plastic/metal/good/bad) anywhere from about $25 & up.

They'll be sized for a 5mm shaft and you could of course use one of their rotor heads & all too, would also give you the option of easily changing collective pitch.

I'm using two of these on my CH-47 model:
http://www.scaleflying.com/product_p/klw-rca4503b.htm

Comes with everything you see there, swashplate, shaft & all linkages - the only negative is they are rigid heads, best off using some flexible blades with them.

[joe nelson]

Thank you Brett,

The enjoyment of doing this is the learning process. I'm a gearhead who likes to work on projects that are difficult. My flying days are over so I reverse engineer things...that's fun!

I found that building full scale components gets expensive and travelling 4 hours to my farm for testing is time consuming as well. Building small is the best solution because I can do testing in my backyard and change components several time a day.

My plans are to build two full size gyros. The first is one to test my rotors systems...single place glider/trainer. This is for L/D varification and system testing.

[joe nelson]

P.S.

That website is cool! I already have a couple of rotorheads that I got when I was working on my UHMW plastic swash plate, last year.

The system in the video looks good. I may try it if this system fails.

By the way, how's your building project coming?

You're right! flexible blades are a must since I don't see any ability to cone. I've noticed a bit of vibration at low rrpm.

[joe nelson]

Brett,

I was just reviewing the info that you have posted and I noticed two things of interest. One is the model that you are working on has a semi-rigid rotor system. The only tandem in memory was the Bell tandem, in the late 1940's, with this system and the Navy replaced it quickly with the H-25 with the three bladed system...the model was flying OK. I guess that mast bumping was not an issue. Next was the model has a gyroscope. Is this in lew of the SAS?

[joe nelson]

The UPS man came today and it's time get back to work! I should be able to test my articulated head this week. I've also found a four bladed system, on the web, with a delta 3 configuration that I might try. It looks easy to make... it uses packing tape for hinges.:puke:

[brett s]

Mine will have a 3 bladed rigid rotor heads, with fairly flexible blades. Couldn't find an off-the-shelf 3 bladed head with flapping hinges at that scale, there is a 4 bladed one though...

The standard setup is two bladed w/flybar but it's most definitely not a typical teetering rotor like a full-sized ship uses - these things (like almost all r/c helicopters these days) are for all practical purposes rigid, they don't teeter at all & only have very firm dampers inside the grips. They have huge effective flapping hinge offsets, that's why they can do all the crazy aerobatics & inverted stuff - the flybars keep them much easier to fly.

[joe nelson]

Good Morning Brett,

I have wondered what the effect the airframe has on the rotor system since it obviously blocks some of the air up through the rotors. I think the aft rotor would be the most affected...maybe the height of the aft pylon plays a role in it efficiency? Hopefully, I'll find out as soon as I build my airframe.

I've seen videos of the two bladed chinooks, that you are talking about, and they fly well! It appears that the rrpm is very high making the semi-rigid not move much. The three bladed system might not turn as fast.

You said your dampers are very stiff. My take on this is very crude because I'm using two very small springs one on the leading edge of the blade and one on the trailing edge connected just ahead of the vertical hinge. I'll let you know if it works.

[brett s]

I'll probably be running mine at 1800-2000 rpm, have to see what it likes best but that should be in the ballpark.

Are you talking about lead-lag dampers? If so, they aren't needed at this scale, at least on helicopters. Most people leave the blades loose enough so they can hunt & find their own position - if you tilt the head on it's side the blades should be just tight enough to hold position.

I was talking about flapping - those typical 2 bladed flybar heads don't teeter at all, just have some flapping allowed in the grips. My 3 bladed ones don't even have that, totally rigid.

[joe nelson]

Thanks for that info!

I am working on the lead lag dampers with the springs and the coning is zero degrees down and up to whatever the rpm allows.

I've just finished the articulated head..it's very crude but it seems to work. When I put it in front of the fan it spun up very quickly. Now for the swash plate. To make it simple I'm only going to work with collective pitch changes. I'll refine it later when I feel more confident in what I'm doing.

[Arnie Madsen]

Joe Nelson. I have always liked all your experiments and the input from various guy's that help you. I do not have any knowledge to benefit you but I enjoy reading this thread. It is like you are building something that we all wanted to build at one time or another. Much appreciated.

Arnie.

[joe nelson]

Arnie,

Thank you for your kind words. You have always been great at giving me a lot of moral support!!

Now that I've fully retired it will give me much more time to spend in my shop. Doing this stuff is so much fun!!

God Bless!!!!

P.S. Maybe, one day I'll bring all of this tinkering together in something useful...lol

[joe nelson]

Over the weekend I finished the front rotor. It's identical to the aft rotor with the exception of turning in the opposite direction. Also, I've found a new material for the airframe and it's lighter than balsa. It is 3mm foam and it comes in a large sheet so I can screw up without running to the hobby store so frequently. If it works OK I might try it out as rotor blade material.

During a web search, I found another 4 blade rotor system used on rc gyros. It has a Delta 3 configuration that looks interesting if not promising. Again, I like Chuck B's idea of using a mini door hinges on this rotor. I haven't measured the angle used on the flapping hinge but it looks to be around 45 degrees or so.

In retrospect, I may change the rotor shafts to use 1/8 inch carbon fibre rods in lew of the 1/8 inch music wire in anticipation of vibration in the system.

[brett s]

I'm interested in seeing photos as this progresses :)

Here's what my Chinook looks like as of yesterday - getting ready to start setting up the controls...

[joe nelson]

Brett,

I'm having trouble getting the pictures over to the forum...I've had trouble since the format was changed a year or so ago. It seems to have a problem with my account on photobucket.

P.S. This has happened before!!

[joe nelson]

It looks like you do great work! My project is much less refined...crude. I make too many changes to make it pretty. LOL

[brett s]

Mine is also a kit though & not scratch-built like yours - big difference in the level of difficulty there! I'm just bolting stuff together for the most part, you're making it :)

Where I'm doing something unusual are the 3 bladed rotors, plus a few minor things - I cut down & re-drilled the main shafts to reduce rotor clearance from the body, mounting the body a bit higher to also help there (the rotors will still be a bit higher than I'd like but nothing I can do about that without totally redesigning things), and I'll shorten the gear legs a touch as well.

I'll have it flying without the body in the next couple of weeks depending on how much time I get to work on it, should be fun :)

[joe nelson]

:usa2:Brett,

Do you use c/v joints on your drive shaft or gearboxes? I don't need them on my plans but I might experiment with a driveshaft later. At the hobby stores, I've been looking for some beveled gears and small univeral joints but I haven't found what I need yet. Working on this scale gives you a good idea if what you are doing will work or not.

I have a few ideas on the controls that I'm looking foreward to working on. Differential pitch between the front and rear rotor (no cyclic control) and tilt for roll control. If it fails...can we say CA glue. LOL :wave:

[brett s]

One of the compromises in this model are both rotors being at the same angle (something like 6 degrees nose down), so a straight shaft & bevel gears is used - makes things a lot simpler.

In a perfect world I'd really like the Chinook model here:
http://www.rc2rotors.co.uk/9.html

Correct shaft tilt, flapping hinges on the rotors, a lot more scale than the one I'm building - but much more expensive too!

[joe nelson]

That website was a great bit of help!! I think I understand the controls enough to do the job. The cyclic stick controls the differential collective input between the front and rear rotors...up pitch on the front and down on the rear ect. The collective (torque) controls collective pitch in the rotors at the same time. The pedals control the aft rotor left and right and the front cyclic controls the front rotor left and right. I think and hope that's right.

This morning was a little slow for me but I did take some time to work on that Delta 3 rotor I was thinking about. I've measured the hinge angles and they are 45 degrees. My understanding of these angles are extremely weak. Do the blades climb while advancing with decreasing pitch? On the retreating side the blades fall and increase pitch? I haven't seen this configuration on newer rotor designs so I have to conclude that it has some shortfalls but it's fun to play with the idea.

The chinook on your website was impressive. The mechanics were beautiful and "beefy". I did see a couple pillar block bearings, a c/v joint and coupling just as you expect in the real thing. It also appeared to have a wankel engine mount at the CG. Some of the components looked like they were made of carbon fibre and others parts look as if they are aluminum.

[brett s]

Right, that's how the controls work - both my model & that other one use electronic mixers to deal with it. Mine also uses a bit of fwd/aft cyclic in addition to differential collective, it's all adjustable.

45 degrees delta 3 is pretty common on tail rotors, where the idea is to keep flapping to a minimum - would be a bad thing if you intended to use cyclic pitch for control, but probably a good thing if you want a super stable rotor & you're tilting the entire shaft.

Both ships use a small brushless electric motor, those things have come a long ways as have LiPo batteries.

[joe nelson]

Brett,

Have you checked out the chinook-helicopter website? There's a picture of a "hook" with some nose art that I really liked... it was called the Dumpster!! LOL

[joe nelson]

My Delta 3 rotorhead folded up in my hillbilly wind tunnel. The head was made of a 1/8 inch thick plywood hub with a 5/32 brass tube for a bushing. The blades were 3mm foam 12 inches in span and 1.5 inches in cord ca glued to a 45 degree hinges at the hub. The head was mounted on a 1/8 music wire shaft at 9 degrees to the floor on a 2x4 taped in front of an industrial fan four feet away. The fan was started on the lowest setting (approx 800 cfm). It made about 3 revolutions when the blades went vertical and broke the blades at the hinges.:sorry:

[brett s]

Yep, lots of good Chinook stuff on that website - do you remember the tailnumber of the "Dumpster"? Had a ship in my old unit in the mid 80's with that on it :)

Sounds like you had too much airspeed at low rpm there!

[joe nelson]

Brett,

I looked for the Dumpster last night but can't remember where it was on that website...it's larger than I thought. I'll keep looking till I find it!

I did find some rotor info about the chinooks blades. They have a twist of -12degree on the outboard part of the blades and has two different types of airfoils. Inboard is a VH7 airfoil and I can't remember the other one but it's symmetrical.

Today, I'll put the Delta 3 head back together and re-do yesterday's test with the head several feet away from the fan. I'll also add some weight to the tips of the blades for good measure.

[brett s]

The current composite blades (in use since the mid 80's) are VR-7 at the root & out to the 85% point (I think?), VR-8 at the tip - neither are symmetrical though.

[joe nelson]

Sorry for the bad info, Brett. Pain meds do that to you some times!

I did test the delta 3, 4 bladed rotor yesterday...it turns much slower than the three bladed ones. Slower rrpm was expected but I'm thinking that the brass bushing had some effect too. I'll try some 1/8 inch bearings later. The conning movement looks odd, a bit like some old videos of Kellets. The angle on the advancing side is very steep to the point of making no lift, I think!

[joe nelson]

Today was spent researching mold making and vacuforming. I need to make parts that can't be found readily or is not available. I want to use vacuforming to build my airframe. It seems that this would be done with little time invested...quicker to flight. With the ability to mold parts to the exact dimension would give greater function to the design and not make for a "Rube Goldberg award."

The next few days will be used for construction of a simple vacuform machine. I've looked on line and they appear to be fairly easy to build.

[joe nelson]

The hobby store didn't stock the components for making molds so I had to order them. While waiting for the brown UPS truck to arrive I've been working on my articulated head. I'm finding the pitch horns and links are difficult to get to work smoothly. At first, I wanted the swashplate to be down toward the nose of the model so I might use gyro-style control so I would only need two servos per head. When adjusting for precession, the links wanted to bind-up. Adjusting the swashplate movement appears to be the easier solution and using shorter links.:boom:

[joe nelson]

Here are some pictures of the rotors that I've been working on. They are small but fun to build!

The first picture is one of two that I'd built for my tandem gyro project. It has only two axises of movement... lag and flapping. They have -4 degrees of pitch with no washout...I'll change this later!

Picture#2 is an experiment in full articulation and I spend too much time in putzing around with it. I've made a crude swashplate but I'm having trouble with the links binding.

Picture #3 is another experiment in elastomerics but haven't had time to fiddle with it yet. Abs from a plastic yard sign was used for the hinges.

[joe nelson]

Today is rotor blade day. After reading a post by Chuck B. I'm going to put some pitch (washout) in a set of blades just to see how it works. The blades that are on my present project is set at -4 degrees... that's where they spin up the best but it seems not to generate much lift. The airfoil that I'm using is an 8H12 or as close to it that a 12 inch blade can be. I know that this airfoil produces lift at -2 degrees of pitchbut doesn't spin-up well. I'll put -4 degrees on the driving portion of the blade ( inter 75%) and +4 on the outer 25% on my first attempt.:wacko:

[joe nelson]

This is an update on my progress.

Picture #1 is the elastomeric head with the addition of more abs plastic to the hinge. This brings it up to .065 inch of abs at the hinge. I have also added a pitch block of -4 degrees. It turns up quickly and does have a bit of vibration probably due to the blades being unbalanced. The airfoil is an 0012 (?) which seems to work as well as the 8H12.

Picture #2 is a 8H12 blade with the outer 25% of the blade cut to +4 degrees and the inter part of the blade attached to the head with a -4 degree block. The overall result is zero degrees at the blade tip... With an 8H12 airfoil this should be lifting (?) I think. It spins up slowly but it eventually has good rrpm. Tomorrow, I'll put the tip pitch down 4 degrees so I'll have -4 at the head and -8 degrees at the tip.

Picture #3 is the crude articulated head that I'm fiddling with. I'll get some better pitch links on my next visit to th hobby shop.

[joe nelson]

Today, I'm still working on the different washout angles on my blades. It is difficult to get accurate washout angles working on this scale but I'm determined to get it right. My last test the -4 degree pitch blocks were removed and the articulated head was set to -2 degrees giving me -2 at the hub and +6 at the driven part of the blades. The results were good with a good spin up but one thing was confusing. I'd removed the blades and put the head back on the stand. It was set at -2 degrees and it spun up without the blades....Confusing!:wacko:

[joe nelson]

The only conclusion to the head spinning up without blades is the blade grip cuff provide enough motive force to turn the head...well duh! They were set at -2 degrees.

This morning, I was playing with the delta/ four bladed head which I added brass weights to each blade with good results. Spin up was quick and the flapping angles were small unlike my eariler test. The blade angle was set at zero and I could feel lift in the system. I'll add weight to the articulated systems blades (four degree washout) and retry my tests. This will be set at -2 at the hub and I'll have +2 at the tip.

Tomorrow, I'll build another set of blades with ability to change the angle in the driven portion of the blades so that I might change angles quicker.

[joe nelson]

I was watching one test and I noticed that the positive coning angle might be too much. I think that it may be low rrpm with the blade angle set at -2 degrees. I'm going to limit the drup to 0 and +5 degree for the cone with the blades back to -4 degrees. This should give me better rrpm and I'll watch the outcome.:puke:

[joe nelson]

After talking to Chuck B., I have come to the conclusion that my tests need to be more accurate. I'm going to build a small test stand (whirl tower) with the ability to measure the outcome of my tests. Also, my fans are swirlling the air which affects the testing. I'll put together a group of pvc tubes, glued in a way to straighten my airflow on the fans and add a way to measure the wind speed. Mast angle will need to measured accurately as well.

Chuck also pointed out to me that the reynold's numbers are low! I do understand that a one inch cord doesn't displace as many molecules of air as a 8" cord. He said that because of this washout or twist is uneffective at this scale. Well, now I'm really confused! I'm sitting here looking at my AirHogs. Surprisingly, they both have washout and taper with a span of 6" and a cord of 1/2".:noidea:

P.S. Please understand that I'm not trying to start a debate here! I would certainly lose but I just don't understand and I'm eager to learn. Unfortunately, information is scant in the gyro community!!!!

[joe nelson]

This morning, while waiting for some glue to dry, I pulled out my calculator and worked up the numbers for this rotor system. As Chuck B. pointed out the reynold's number was very low at 272,300. I guesstemated the rrpm and figured all stations on the blade at the same speed. As you might have guessed the total lift was .25 pound...less than the weight of the blades themselves! This is why I wasn't feeling sensible lift! Another mistake I made was with the difference between aerodynamic pitch and geometric pitch.:der:

[joe nelson]

New rotor system and test.

#1 is the three bladed delta 3 system with 1/16th plywood blades. Each blade is reenforce with a cf rod of 3/32nd inch along the leading edge. I've also ca'ed a weight at each blade tip. As you can see the blades are connected to the hub by small door hinges set at 45 degrees. This hinge setup give me both flapping and pitch movement.

#2 is a wider view of the delta 3 configuration.

#3 is my test where it rotated and accelerated on it's own...no help from me! The flapping is set at -1 degree down and unlimited up ( by cf only). The blades have no pitch when static. The trailing edges are truncated to induce rotation in the right direction.

[joe nelson]

I 've forgotten the tests...all were good with some vibrations, alot of sensible lift and good rrpm!!!! Now, on to the airframe.

[joe nelson]

This morning, I've made the "airflow straighteners" on my test fans. They are made of 2liter soda bottles and thin walled pvc pipe hot glued together.

My first airframe test was to put the two rotors on a peice of wood approx. the size of the airframe called for in the plans. The front mast angle was 9 degrees and the aft was 10. There was 2 inches vertically between the rotors with a 34% overlap. Coning of the front rotor was an issue but I reduced the angle 2 degrees and all was OK. The front rotor's rrpm was good but the rear was very slow. At this point, I don't know if it is airframe interference or mast angle.:noidea:

[barnstorm2]

don't forget to post some photos!

[joe nelson]

Sorry for the time delay, Tim. I've been in Gatlinburg,Tn. for the last week with the family.

I'll certainly post some pictures after my next addition to my test rig. I'm going to mount a pivot to test angles of attack on my tandem rotored stick. LOL I've found my delta 3 head gives the best results so far!

[joe nelson]

I've just been down in the shop.

#1 picture is the tandem stick with two different types of rotors. The front is the hub with flapping only and the rear is the delta 3 hub.

#2 is the fan set on the lowest setting (800cfm). The front rotor is very slow due to excess drag and low aoa... I think!
#3 is with the fan at 1600 cfm with the delta 3 hub turning well and the front rotor approx. half as fast.

[joe nelson]

I think that I'll build another delta 3 hub for the front rotor and make some pylons for the stick. The rear rotor turns up good rrpm at a mast angle of 20 degrees and some work needs to be done on the front pylon and rotor. The delta 3 has no washout and I'll continue with this for the time being. In the future, I would like to try to make some blades by bending the wood in forms to have a washout of 8 degrees ( -2 to +6 at the tip).

From what I can gather, the stick will only fly when it reaches translation speeds not from the rotors themselves....I think! You know, "with proper application of power a brick will fly". lol:boom:

[joe nelson]

Last night, I visited several websites and found a few bits of information useful to my project. The first point that was discovered was the small gyros have very few thing in common with full size craft! Aspect ratios, in models, are very low. They are normally 8-10 to one and disc loading is 5 oz. per square foot. This is in contrast to the AR of 16/1 in the real gyros. Washout in models is not worth the effort and makes little difference in performance. Blade thickness of 6% is acceptable in models as compared to 12-14% in the big guys. Mast angles of 10-15 degrees is workable in models as well.

I will go back and apply this information to my project to see if I can get a better outcome.

One thing that has worked is the delta hub. However, I have found distortion in the hub's nylon hinges trailing edges. They will replaced with metal ones and if this distortion continues I'll add a drag hinge.

[joe nelson]

Well, I started working on the pylons but was side-tracted by something that I'd overlooked. Controls! I need to devise a plan to control this beastie. First, a gimballed head on both sets of rotors...giving me a way to feed inputs to the blades. Next, collective mast angle control. This input will change the lift in both rotors at the same time. Then, differential angle control... front up and aft down ect. The front rotor will tilt left and right with cyclic stick input. The rear rotor will tilt left and right with pedal or rudder control input. I'll draw a schematic and post it to unmuddy my explanation. If this plan works it should fly with normal control inputs:eek:

[davh12]

Joe,

I'm really intreagued by what you're doing w/ the delta 3 hinge in a tandem gyro. Interesting & resourceful wind tunnel.

Regards,

Dav

[joe nelson]

Dav,

Sometimes I feel that I take two steps backward for every step forward! Since I've retired, I have plenty of time to experiment with this project though.

I've tested several types of delta 3 heads with various angles at the hinge. The 45 degree hinge seems to work well at this scale. The values of these tests are much different from the real thing... which I'll begin testing in the future.

Things are somewhat crazy here due to the wounding of my 11B son in Afghanistan Sunday. He's was protected by his body armor and is doing OK! Thank God! When I spoke to him, all he wanted was a icy cold beer...HOOAH! I'm going to give the gyro stuff a rest for a few days until the dust settles a bit.

[davh12]

Joe,

I feel the same way, but I only get to tweak my experimental helo on week ends. Trying to go Army full time and build/ test a muckup & carbon fiber RC prototype is time consuming. If it fails...I'll still post the crash video. I'll breath a prayer for your son. My step son and I both did 2 tours in Iraq. We both are 11B as well. There has been more than one incident where I should not be alive....a couple missed sniper bullets, 1 RPG and a hand full of IEDs. We both lost a little hearing, but not a scratch. Son got hit with an AT mine.....he got jacked pretty good. This last and most recent deployment I lost one of my AGs in a rocket attack, but I've learned if it's not your time and the Old Man upstairs is not ready for ya..........you'll be fine. Some of the true incidents I could tell you about........I quess God says no a time or two with regard to dying..gotta be a reason for sticking around. Take care. Godspeed.

Dav

[joe nelson]

Dave,

This my first time on this side of a deployment...It's was always me that was leaving not one of my kids. That gives me a new respect for all who stay behind. My young 11B was extremely lucky in that his IBA took the hits and his M249 protected his face from the IED. His team leader wasn't so lucky. He has a concussion and burns... both suffered hearing lose. He and his team leader are now being treated for concusive injuries at their FOB.

By the way, thank you for your and your son's service.

[davh12]

Joe,

Thanks to you as well. IEDs are nasty. I got most of my hearing back, but I cannot tune my guitar with the right ear....can't hear the tones clearly. I have a bad dream or two and wake up feeling the "after blast" again. The brain does not forget what over pressure does to it. I usual feel it about 30 seconds after I'm awake behind my eyes, ears, and sinus. It only comes every now and then.

Dav

[joe nelson]

Sad to say, that I was injured more in training than two tours in Viet Nam. God willing, I'll get my son back in one whole piece and the rest we can fix! He's very headstrong so I'm sure he'll be OK.

Yesterday, when I was trying not to think about my son's plight I did some work on my tandem. I put together a prototype front control system. It was made of UHMW plastic and it seems to have good articulation. I'll post a picture or two when I get back from the post office.

[joe nelson]

As promised here's the pictures.

#1 is a side view. You can see the cheek plates as on a standard gyro and upper winged part is where the control input mechanism is attached. All components are connected with #4-40 bolts.

#2 is the front view. The cheek plates will be attached to the front pylon and control will be through CF push-pull tubes. The mast, the black part, will be shorten a bit after installation.

The rear head is the same with the exception of the cheek plate will be mounted backwards on a higher pylon.

One thing that I've noticed is the rear rrpm is much higher than the front. I think that it is due to the higher aoa of the rear rotor. I'll try to correct this after I finish the front pylon...fan testing continues.:eek:

[joe nelson]

Dave, I've just found a "reuseable" cold cloth and I've tested it under 120 degree water then snapped it as per instructions. It turned cold as advertised!!! I'm going back to buy enough for my son's whole platoon...it was 111 degrees in Khanahar, Sunday!

HOOAH!

[davh12]

Joe,

It's always the small things we forget how much they mean until it's not avaiable. I remember doing Humanitarian aid drops in 127 degress. They'll appreciate what you send. Had an Uncle who served in Vietnam, Army Field Arty ...he made it back and I also had a 4th cousin who was a Infantry, Marines and he was killed in the Quang Tri Province. Most of my family have always been Infantry, but sometimes I think I should've been an aircraft mechanic since I love tinkering with mechnical stuff so much. Unscented baby wipes are good to send too. We call it taking a "Whore's bath"...wipe and powder your balls, change your socks...keep moving. Nice rotor pylons. The airframe I tinkering with has an offset axis gimbal joint, similar to a Gyro, but the axises are like your pylon axises, except my fore/aft axsis is above the lateral axsis. The airframes "morph", but it's mechanical to vector the thrust. I'm not looking for speed records and retreating blade stall still has an effect. Take care.

Dav

[joe nelson]

Dave,

It sounds like you are far ahead of me since your prototype has flown already even though they've crashed. I've just ordered a set of plan and spent a long time trying to make it fly. At this scale, the numbers are much different from the real thing. My main objective is to see if a tandem gyro will fly and fly without a bunch of bandaids like the real thing ie...SAS. I like the K.I.S.S. approach to aircraft. Make it simple, make it strong and make it light as possible. Dave, this whole building project is just one big learning exercise. I've learned more in the last few months than over years of flying. As a pilot you learn mostly "WHY"& "WHEN" it works but rarely "HOW." As a designer, you must know "HOW" to make the aircraft do what you want. That's where I am now...learning HOW! To date, I have three notebooks of what doesn't work and 3/4 of another on what does work. Luckily, I love to experiment with this stuff.:wacko:

[joe nelson]

Today's tests were encouraging. I was able to get the front rotor rrpm up to where it might fly. The new plastic head enabled me to set the proper angle of attack resulting in much better rrpm! A balsa 1/2 x 1/2 inch mast was made and attached to my test stick. I put it back in front of the fan with the same good results. Unfortunately, the stick picked up and rolled to the left destroying two plastic flapping hinges...just a small step back!

The aft pylon will be borrowed from the CH-46 in that it is longer that the one employed by the chinook. I'm hoping the length will add longitudenal stability since tandems are directionally challenged by nature.

If all goes well, next week may bring my first tow tests. I have a shopping center parking lot picked out already. A fishing scale will be used to measure total drag when it's pulled behind my truck so I might determine the HP needed for its' motors.:wacko:

[phantom]

I have built a few twin rotor model gyros and in some I tied the rotors together with a loop of speedometer cable without the outer housing and in another I used a cog belt out of some kind of cash register with a twist, both systems worked well to keep the blades in phase. I have also made multi blade rotor hubs with small hydraulic hose, it gives lead/lag and flapping but is very ridgid in pitch.

[joe nelson]

Norm,

Any suggestions are appreciated. I like to experiment with this stuff so I will give your ideas a try! How did your tandems fly? I'm just getting to the point of flying now and I sure hope for some success. My rotors overlap and do not intermesh to save weight since I'm bless with short blades (12"x1.25"per plans).

I like the hydaulic hose idea. Can you tell me more about the set-up. I think the elastomeric hinges are way to go but had'nt ever thought of hose. I'd tested some conveyer belt, last year, but that would need to be on some larger scale. Also, I have worked with .018 inch thck 316 stainless steel laminae for hinges like on the Hughes 500. Again, that's on a larger scale.

[davh12]

Joe,

I call it a flying RC prototype, but so far, just "hand tethered". I powered it up enough to a point when it's "light on the skids (hand) and so far it has allowed me to feel out the airframes' tendency to dift & that the gyro/receiver, motor and reduction gear are too high on the upper airframe that is nothing more than the modified frame the helo came with. Since it is a little top heavy, I scratched that and I'm in the process of building a new carbonfiber upper airframe. Joints held together w/ gorilla glue and carbonfiber pegs....like in wood working. It's not too slow, but have to sand & clean before adhesive is applied. Getting there.

Regards,

Dave

[joe nelson]

Hey Dave,

I heard from my young 11B last night! He has been returned to duty but his team leader has been evaced to better medical facilities. He started to have memory issues and the docs decided to ship him to a more capable facilites in Germany. I have met him on several occasions in the last year and he's surely in my prayers.

Yesterday, I tried my first tow test with no results. There is several modifications that needs to be made. The airframe need to be strengthened because when the rotors come up to speed it oscilates badly. I'm going to improve the ballance of the blade and add bearing not bushings. Two front rotors were tested. One turned in the same direction of the aft rotor. There was definately resonance with airframe shaking wildly. The second rotor turned in an opposite direction with better results. With adding a basswood doubler to the balsa may solve some of the shaking. The landing gear is spring wire and adds to any resonance generated by the rotor imbalance and weak airframe. It will need to be changed but not now.

Dave, keep me posted on how your carbonfiber works. I used CF on my masts but seems to add to the resonance problem.

[davh12]

Joe,

Glad to hear your son is doing better. We'll keep him in our prayers as well.
Finished the CF lower airframe.....brain stormin on the upper....may need to order more CF. Both airframes joined will still keep the CG low and I'm hoping that is enough to at least help w/ stability. I post everything on a web site that I started: www.envisionhelicopters.com

I'm trying to keep up w/ an aluminum mockup as well as get a small scale flying. I still want to start w/ a forward/aft tilting axis only and then as I tweak the CG more, free up the lateral axis of the gimbal joint. I'm a bit concerned that the torque created by the rotors may be a little too much for the gimbal joint w/ regard to material failure. I may lengthen the gimbal joint a little, but then again, the upper airframe is attached at 3 points to the lower airframe....we'll see. Take care.

Regards,

Dave:yo:

[joe nelson]

After a bit of tinkering I put the stick back in front of the fan with the delta 3 rotor on the front mast. To my surprize, the nose lifted off to the point of the rear rotor striking the ground. The rear rotor was much heavier than the delta 3 so I'm concluding that was caused by an aft CG. I'll make adjustment to the CG where it will be half way between the rotors to maybe 1/4 toward the front. I'll build another delta 3 head that turns the opposite direction. Even a small success is sweet!:whoo:

[joe nelson]

Today, I've been working on a new set of delta 3 heads. Both will be configured with metal hinges since the plastic ones are showing wear.

At the hobby store, I saw a 1/24 scale rock crawler with very interesting coil over shocks. They were just the right size for blade dampers on my project...just a thought. The shocks would be mounted on the front of the blade to maintain the 25% blade balance.

[brett s]

You don't need lead-lag dampers at this scale - you can leave the blades loose enough to hunt as they desire (which is usually what I do) or crank them down tight as long as you've got the position correct.

[joe nelson]

Thanks Dave,

Your website looks great! It looks like you're going for the commercial end of your project. I'm just a hobbyist who is retired and loves to tinker.

[joe nelson]

Brett,

Yes, I know but I'm just tinkering. I think at you and I talked about that a while ago. BTW, how's your project coming? It was much more complex than my tinkering!

[brett s]

Mine has been gathering dust for the last month or so, too much other stuff going on - mechanics are assembled, it's ready for final control rigging then firing it up. Maybe this weekend I'll get a chance to get some of that done...

[davh12]

Joe,

Yep, but just nickel and dime money is all I am trying to get. I have several more airframes w/ respective rotor systems I want to build... & 3 are ready for the patent office, but maintenance fees will add up if I move any further. I'm just a tinkerer too, but need a better machine shop........a mill and new lathe. I told the guy at Bell that I understood about acquisition costs, prototyping, etc....just need a little residual income to tinker more, so fingers crossed. I'm a bit obsessed w/ figuring stuff out...find a better way and all...keeps the mind busy. Take care..

Dave:confused:

[joe nelson]

Dave,

I think your venture is great! I wish you much success in your project even if just for nickels and dimes...HOOAH!

[davh12]

Joe,

Thanx. I keep trying, but the best part is just tinkering. I love to test stuff out. Even if it fails. It will be a small machine shop "setup".....ie my basement/man cave. I actually thought of using a drill press for a mill. Have to pull the spring on the rotary handle and use a two axis swivel vise. I'm all about cutting costs if the end product is still sound.

Dave

[joe nelson]

Dave,

I love my man-cave! The only machinery I need to make it perfect is a mill and a cnc router! I have a couple of lathes...one for wood and the other is for metal. It is generally a woodworking shop since I build furniture as a hobby. I have built most of the furniture in my two oldest children's homes. They tell me, Dad you use "real" wood. What are they sitting on...cardboard?

Today, was a good day in the shop! I was able to get good rrpm on both rotors with the fan at it's lowest setting. Two things were changed from yesterday's test. Both heads are delta 3's with no pitch blocks and I reduced the blade finess to approx. 6% from 12%. Unfortunately, the plastic hinge on the front rotor failed. The hinges on the aft rotor is metal and the front will need to be changed to the same.

[davh12]

Joe,

CNC is great, but I always jacked up the tool bit because I was never good at programming, so my Precision Machining Teacher told me to "Stay Manuel". That was a little over 20 years ago. Had to work half a day today. Little over 30 LT's failed Land Nav..retested today, so I'm behind on this week-ends' tinkering. I should have the upper airframe and canopy done tomorrow. I ordered new rotor blades and a rotor head, but I may not attach the fly paddles as my airframe does not have a swash. I may use just the blades grips and machine a quick hub out of industrial nylon. I still want the hub to teeter a bit, but the sp blades should have a slight flapping action w/ just blade bending. We'll see. Take care,

Dave

[joe nelson]

Dave,

I watched a demo video of a CNC router making perfect little rotor blades all identical! If you could see the pile of rotor blades in my shop then you'd understand. I have blades of all description. Some are tappered, some have berp tips and some are made of various materials. Your nylon hud sounds interesting. I have used UHWM plastic for hub parts but it tends to be be a bit heavy. Phantom, on a previous posting, suggested that iI use hydraulic tubing to connect my blades. He says that it's ridgid enough to support the blades but flexible enough to give some flapping and dragging movement. I have some 1/4 inch plastic tube here but that's a little large for my scale.

Dave, I'm sure the young Lt's are in good hands! But if they fail... the army will give you 30 more to train. lol The troops will appreciate having good leadership.

[davh12]

Joe,

Got the rotor blades balanced & started the upper airframe. Pics posted later this week. I was covered in carbon dust. Quick machined the new rotor mast. This one will be a bit longer for a bit lower CG. We'll see. The rotor blades on this carbon frmae will be fixed pitch and I believe it will also be just forward/aft tilting....small steps. The larger gas operated heli will have lateral in addition to forward/aft tilt. Should be with in the next month for a test flight...fingers crossed. What's the best way to post a vid?

Regards,

Dave

[joe nelson]

Good morning Dave,

I've tried using a 3/32 carbon fiber tube as a mast/shaft but it was too weak. It allowed too much torsional bending which generated a frequency that shook the whole airframe. With the combination of the spring landing gear it would jump side to side until it fell over. I rebalanced the rotors, reenforce the airframe and incerted a piece of music wire in the CF tubes. The following tests were much improved. The front gear would rise smoothly until the aft rotor would strike the floor. I thought that this was a CG problem. The CG was located aft of the center point between the rotors. I am going to reposition the CG to the center between the rotors and retest. If the lift axis for both rotors are perpendicular to the rotation of the blades and the aft rotor is set at 14* and the front rotor is 12* then the "center" should be slightly forward of the center between the rotors...just a guess! Cross your fingers.:noidea:

[davh12]

Joe,

Just keep tweaking it. Is there any way to "hang" test it from the ceiling? Not sure about the dual tandem rotor set up. I'm using 1/8" stainless steel rod for main mast. I've got to eliminate the aluminum brackets and "SS" fasteners on the lower airframe along w/ the nylon spacer blocks....cut weight...cut weight....cut weight. Hope to finish the upper airframe and attach a thin canopy this week end and start a hang test to tweak the CG. Good luck w/ yours.

Regards,

Dav

[joe nelson]

Dave,

What I use is two 2" spring clamps with a piece of beveled wood between. I slide the airframe until it is balanced. Unfortunately, it's very top heavy with the two rotors being the heaviest parts. I'm going to take your suggestion and replace the CF masts with 1/8 inch music wire. I'm hoping to do the tow test this Sunday morning at the local shopping center.

[davh12]

Joe,

I don't know if you have heard of this company, but I get a lot of "odd" parts that I use for tinkering from there. Google "small parts". Their prices are pretty good. They have rare components, even smaller power tranmission parts. They also have titanium rod as well, so if the 1/8" music wire is still too heavy, try titanium..... 1/8" and a bit larger diameters are not that expensive. CP grade 2 titanium is a good choice.My first failed RC airframe, I used titanium rod for tail rotor power transmission. It never got off the ground because a CG problem halted everything. Had to redesign. Depending on the length, you may need an additional bearing at the top of your pylons. If there is too much length between the airframe & hub, the forces affecting your rotor head will increase negative effects like vibration, etc because titanium is a bit more "springy". I also used titanium for my tail rotor out put shaft. A couple of inches should be ok and the fact that a gryo is rotating from relative wind passing up through your blades and not from a power plant connected to the rotor hub causing torque....titanium should be perfect for your tandem rotor masts. I had a CP grade 2 titanium plate that I tried to bend into a right angle for a mounting plate for power transfer to the tail rotor input shaft....well I had it clamped to the "I" beam in my basement. I was doing chin ups on it and the plate only flexed and went back to it's original flat form. It was only 1/8" thick. I finally got it bent......took a whole afternoon. When you machine/cut titanium, use a lower RPM and constant applied pressure along with cutting oil. Any lub oil will be good.....bearing oil works well too. But, as with all new things......test test test.........you already know. Good luck. I am still interested in you design. I have never seen a tandem gyro. Good mechanical challenge.

Regards,

Dav

[joe nelson]

Dave,

I 've just looked at that website...thanks for the help! I've been using a company called Micro Fasteners. Their prices for 4-40 and 2-56 bolts and nut are far more reasonable than most hobby and hardware stores.

I took today to reevaluate my tandem. I've come to the conclusion that it's too heavy! I'm going to rebuild the hubs...not the blades they're OK. The UHMW plastic needs to go and be replaced with 1/16" ply. The landing gear needs to be smaller and changed to a taildragger configuration... three wheels instead of four. The aft pylon needs to lightened by changing to a stick and fabric construction. When A final weight has been determined the I can size the rotor discs to the correct dimension. Also, my observations as to the 5-6 ounce per square foot of disc loading may have been too much. I'll try 3-4 oz. disc loading next.:usa2:

[davh12]

Joe,

Today I'll be busy changing the carbon fiber lower airframe w/ regard to fastening the joints and finishing the upper airframe, attaching the tail boom and tail rotor. I've got an idea about interlocking the CF parts by cutting slots & attaching with adhesive. Should be strong enough and allow the elimination of the nylon spacer bocks, aluminum brakets, & ss fasteners.......another week-end cover in carbon dust. I'll PM the pics to you when it's done. Still need to finish attaching the rotor mast. Where will your pusher propeller go on your tandem gyro? Just curious. Still intreagued by your delta 3 flapping hinges. Good design. Have a good week-end
.........never stop thinking & reasoning...innovate........don't sit down for a coffee break.......drink coffee and fabricate at the same time. :rant:

Regards,

Dave

[joe nelson]

Dave,

I went out to the hobby store this morning and bought some 1.5mm CF rod for reenforcement...man-o-man it was expensive! Ten bucks for two 610mm x 1.5mm (.060 x 24") CF rod. Ooch!

The delta 3 hinge isn't of my design. In fact, it's probably one of the oldest types of hubs. The main problem with it is the nylon hinges only last for a short time then fail. The metal hinges are too heavy. When I was researching on-line there was one that used packing tape for the hinge with foam blades. I found it interesting since the blade used a blade tip like you find on a blackhawk. I have been tempted to duplicate this design or maybe something like the cartercopter tips. Until I get something flying those will be on my bucket list.:wave:

[davh12]

Joe,
I had never seen a delta 3 in a 3 bladed flapping hinge. I've seen delta 3 flapping axises in 2 bladed hubs where the teetering axsis is at 45 degrees. Just never seen individual 45 degree flapping hinges. (0% lower airframe complete and 80% complete on the upper airframe. Have a good week.

Regards,

Dave

[joe nelson]

Thanks Dave,

This rebuild is taking a little longer than I'd anticipated. I think alot as to do with my fat fingers. LOL

[davh12]

Joe,

My airframe/fastener rebuild or lack of fasteners has set me back. The CF bonding is slow, but I want it to set right for balance and all:usa:. More to follow.

Dave

[joe nelson]

Dave,

I've gotten your PM and your work looks great. I wish that I had your skill-set! My work looks like a 10 year old Revell model builder.

[davh12]

Joe,

You made sound delta3 flapping hinges......and tested them on a wind tunnel that you made............you're doing ok in the innovation department.

Dav

[joe nelson]

Thanks Dave,

You're too kind!

I've been working on another project this week. We're getting ready to ship 41 care packages to my son's platoon. It's like trying to stuff 10 pounds into a 5 pound box. You always want to send more than the box is big. HOOAH!

[davh12]

Joe,

Found this on the net from our British & French tinkerers. Dual gyrocopter, but in an outrig configuration instead of tandem. I wonder if they're using too many blades?

http://3d-synthesis.com/17-Gyrocopter.html

:rolleyes:

[joe nelson]

Dave,

That craft has driven rotors. If it were a gyro the controls beneath rotors would'nt be there. The air flows in the opposite direction on a gyro and the disc diameter is too small to be undriven . Other than the technical points, it's a cool concept. It looks like something straight out of the movie "Avatar". I think those aircraft are very inspirational...a project for my future!

I'm still working on getting a gyro with a 1000# payload. Something like the Cennsa 172 but with a rotor. A craft that you could throw the wife and kids into with a little camping gear then head to Mentone or Wachula for the week! It's a goal and a work in progress.

[joe nelson]

Last night, I was doing a bit of reading and I found an old design from the mid-fifties. It was very simple but the thing that stood out was the connection between the hub and blade grips. Norm "Phantom" had suggested the use of hydraulic tubing since it would give two axises of movement in the blades. I thought that this idea had merrit! The design that I'd found, last night, used the same idea but used 1/16 music wire. The hub was very light as was the whole aircraft. This is my main problem...WEIGHT!

Another design I'd studied was called the "HUP Tandem Autogyro". It was a beautiful little bird with good craftsmanship. When the builder tried to fly it he remarked, " It fell straight to the ground". After reading this I looked a little closer at the design specs. to find it's weight was 60 oz. with 1.9 sq.ft. of disc area. With what I've found in experimenting that all you would get in lift is about 4-6 oz. per sq.ft. (1.9x6oz.=11.4oz lift.) It was just too fat.:whip:

[joe nelson]

I ran out of map gas this morning which stopped me for a few hours. The new rotor hub that I found on the internet this weekend requires some sodering in lew of the 2-56 bolts. The design requires 1/16th inch wire to connect to the grips. I didn't have this particular guage wire so I am using a 1/32nd inch music wire instead. If this has too much slop I'll go to the hobby store later this week and get the bigger wire. The hud on this design is very small and simple... I'll post some pictures when it's finshed.

[davh12]

Joe,

Sounds like you're still rolling through succesfully. My wife called last night and said that I got a letter from Northrop Grumman yesterday. They said that my rotor system was "interesting", but did not want to move on it. They kept the disc w/ the video clip of the CG hang test on the aluminum mockup for certain and I think the DARPA stuff as well, but returned the patent docs. I have to wait and see the letter and what was returned for myself. My wife only sees "greek" when she looks at the helicopter stuff and quickly associates it with the patent, even though it may not be.... lol. It only took them 6 months. Oh well, I'm still waiting on Bell. If they turn it down there are a few UAV tech companies I want to hit. Any more tow test flights scheduled for your gyro? Take care,

Regards,

Dave

[joe nelson]

Dave,

I think it's great that these companies are talking to you. I have never considered anything that I make worthy of their comment! Good show ole man!!

Your UAV approach sounds very interesting in that DARPA has been looking for a low cost method of resuppling combat troops in the field. They have been testing GPS guided parachutes and UAV helicopters (A-160). Why not a gyro delivery system? Grunts already have embeds flying their UAV's. They would be able to steer a small resupply gyro accurately into someplace as small as a COP or FARP with a near vertical landing! Well, it was just a thought.

I didn't get to the hardware store yesterday...my wife had me doing honey-dos. She want another chair for her dining room. The bad part is that I can't remember the specifics of how I built the other chairs 15 years ago. She said, "you're a crafty guy." My reply was, "you know what craft means?...Can't Remember A F'g Thing!" LOL:whoo:

[davh12]

Joe,

Yeah, my wife already has a job for me to do when I get home next week-end.........cap the chimney. We had a squirrel living in it over the winter. I had intended to re-pour a new chimney inner wall, but my wife is from New Jersey and is afraid of squirrels.............stands her ground with people. Just not with tree rats. Pending how this smaller CF helo flies, I want to build a larger gas powered version and put one of those "flip it" cams in the nose. Time will tell. Have fun with the chairs.

Dave

[joe nelson]

This morning, while my glue was drying, I put together the head with the 1/32nd music wire connecting the grips. The plans called for 1/16th wire but I didn't have it available.
It was placed in front of the fan and it came up to good rrpm. As you could've guessed the blades were sloppy until the rrpm came up to speed. The blades were flapping and dragging with relatively smooth operation since I did't take the time to balance them properly. The hub was made from two 3/4 inch wood wheels. The blades were 16 inches long with a cord of 1.5 inches spanning 18 inches from the hub to the tip. It was a Clark Y airfoil with a 6% finess. I had a 4* washout in the blades attached to the grips at -3* and +1* at the tip. The washout was set in the last 20% of the blades.

The major problem that I experienced was sodering the 1/32nd wire to the grips...It wouldn't bond to the wire for some reason even with the use of flux. I tried both a soder gun and torch!:help:

[davh12]

Joe,

Got the forward / aft servo mounted and the airframes attached. Did the 1st linkage & CG test this past Sunday. I tried to distribute the weight between both airframes so that the lower airframe does not just tilt forward / aft while the helo is in a hover..... not going anywhere. It had + 1 degree mast tilt forward and right about the same -1 degree aft, so my theory about the weight between both airframes appears ok. I had the battery on the lower airframe and the gyro/receiver on the upper...the weight was not equally distributed, but it was the best I can do until I get the hinged suspension "cradle" for the batt/ gyro finished. Started it last night. It should allow the batt & gyro to pivot within the inside area of the canopy. Shoot me a PM w/ your email & I drop a couple more pics. Have not updated my web site w/ them yet. Too busy. I also cut away a little more CF from the lower airframe. Godspeed

Regards,

Dave

[joe nelson]

Dave,

I'm trying to juggle two projects at once...chairs and gyro. The chairs are going great because I've found some spare parts in the garage. Now I remember making them because at the time my kids could break a solid steel ball without trying. This saves me a lot of lathe work and all I need to make is the seats.

[joe nelson]

I've just uploaded these pictures.

#1 is the grip that I can't seem to soder. It keeps breaking under a load.

#2 is the hub and 1/32nd wire detail.

#3 is a screw-up that I've just found on my chair project. The color is off a little and my spindle turning was not accurate!

#4 is another project that's on the back burner until I can come up to speed on my construction and understanding of servo flap control.

[joe nelson]

This morning, while having my morning coffee, I thought by adding a second 1/32nd inch wire to the hub the pitch of the blades woud be more stable. The blade would flap OK but not drag. A drag hinge would have to be added which is no problem. The benefit of this would be the addition of a small pitch change mechanism between the two 1/32nd inch wires.

[joe nelson]

Here's some pictures to help clarify my thought.

#1 is the two 1/32nd wires connecting the hub to the grip. My idea was to attach a pitch horn to add pitch control. In adding this feature the drag hinge must be moved to the outer part of the grip.

#2 this detail show how the single wire set-up attaches from the hub to the grip. As you can see the droop is extreme but when the rrpm comes up it goes aways to a more normal position. The grips attaches to the pitch block(-3*). The blades are made with a 4 degree washout at the 20% outboard section. A piece of 1/8 inch ply was steamed until it was soft and clapped in a jig until dry to get the desired washout. Foam was glued to the top of the blade and sanded to get the Clark Y airfoil.

#3 is the set of plans that gave me the idea for this experiment. The tandem is a 1950's vintage U/control model that flew successfully.

[joe nelson]

This morning, I'm testing a variation of the previous head. It differs in that the 1/32nd music wire has been replaced by 1/16th inch carbon fibre rod. My goal is to improve the droop and make for easier construction. The CF rod is flexible enough to allow for dragging and flapping but hopefully not resonance. This system is four bladed so I'll need to build a new set of blades. This time the washout will be increased to 8* and cord of 2 inches by 12 inches in length. The aspect ratio is lower on models than the real... 6-10 to 1 is model standards.

[davh12]

Joe,

Rotor hubs look good. Is the music wire rigid enough? Pictures are difficult to tell the stiffness of materials. I had a set back w/ a thinner rotor blade causing too much coning angle.

Dave

[joe nelson]

Dave,

The 1/32nd music wire isn't stiff enough. The droop is excessive but does come up to a normal position when the rrpm goes up. I have put together two more heads made with CF rods.The 4 bladed hub has .070 inch rod and the three bladed one has .060 inch rod. Also, I'm using electrical connectors as grips to save time in production. I haven't gotten to the blades yet because of the shipping of "care packages" to my son's platoon. Tomorrow, I have a helicopter seminar to go to so it'll be Sunday before starting on the blades. I'm sure the CF rods will yield better results because of their weight and strength. I just thought that I could try shortening the 1/32nd wire to stiffen it a bit...well it was just a thought.

[joe nelson]

I went down to the shop and took these pictures.

#1 is the three bladed head with .060 inch CF rod. I have made an effort to keep the head as light and simple as possible.

#2 Is the 4 blade head with the .070 CF rod and electrical connectors as grips.

#3 is the detail of the connector as it will be used on the 3 and 4 bladed heads

#4 is the head with the 1/32nd music wire. As you can see, I need to shorten the wire to improve the stiffness and improve the droop.

One thing that I need to improve my camera work is to put a piece of paper behind the heads for better contrast.

[joe nelson]

Last weekend, I attended a helicopter seminar presented by Ray Prouty. Ray has been in the helicopter industry for nearly 60 years employed by most of the major rotarywing manufacturers. His class was excellent turning helicopter mathimatical vodoo into understandable math. The most interesting portion of the class was a film made by Jan Drees,made in 1950, called the smoke movie. A model helicopter was placed in a wind tunnel with smoke injected around the model. The movie explored several conditions that are common in rotary wing flight. All of these conditions were made possible by changing the direction of the air flow in the tunnel. In the hover, you could see the eddies and vortices around the blade tips all around the disc. One thing that I saw was the vortices turned inboard rather than outboard like I had thought. In the autorotative state, I could see why that I was having trouble with the rear rotor rrpm. The rear pylon needs to be lowered so it's not flying into distrubed air. The rear rotor needs to be on or lower than the plane of the front rotor or maybe farther back( less overlap). All in all, I found the film and the class to be what the doctor ordered.:yo:

[joe nelson]

This morning, I finished the four bladed hub with -4 degrees pitch. It was mounted on the tandem airframe then placed in front of the small fan. At the lowest setting (800cfm) it came up to speed and the front wheels lifted off. The aft rotor, as I suspected, was slow to come to rpm and never reaching a good rrpm. The aft pylon is a few inches above the front rotor disc and it is probably stuck in the rotor wash of the front rotor. It also has 34% overlap rear rotor over the front. As a quick test to verify my assumptions I'll will turn it around so the relative wind is coming from the rear. This with have the aft rotor higher than the other rotor. If all rotors come up to speed the airframe will be rebuilt to have both rotors on the same plane.

The new rotor has .070 inch by 4 inch carbon fibre flexbeams, 10 inch store-bought 0012 blades that bring the total up to 14 inches long. If my math is correct, that gives me approx. 4.28 square feet in disc area and at 5-6 ounces of lift per sq.ft. or approx 21.4 to 25.68 ounces of lift (1.0 blade merit).

[joe nelson]

The position of the rotors doesn't seem to be the problem. Now, the rotor shafts will be replaced with another material other than carbon fibre. I'll try aluminum shafts to see if the shaft friction is the problem. However, the new hub worked well. I think the .070 inch carbon fibre flexbeam seems to have done the trick as far as the coning and flapping.

With watching the Jan Drees smoke movie I felt that the wash above the front rotor was causing the low rrpm in the aft rotor by starving it of clean airflow but at this point I don't know! This afternoon I changed the tandem's configuration a bit and both the rotors turned up nicely. I lowered the aft rotor pylon and it worked well...I am certainly confused.:wacko:

[joe nelson]

This morning, I had the same problem with low rrpm on the aft rotor. The shafts have been changed with little or no improvement in the aft rotor rpm. What I observed was, at the low setting on the fan, the aft rotor seems to stall or get choked and rrpm decreased. I still think that it's the wash from the front rotor. At higher fan settings this doesn't happen or it is not obvious. The aft pylon is still a bit higher than the front and is not coplanar. The next test will be extending the airframe to accomodate the coplanar rotors and retry. The present configuration the rotors have an 34% overlap of the blades and will be reduced to zero overlap...no intermessing.:noidea:

[RotoPlane]

I am wondering about the torsional stiffness of your blade and wire combination. If it is too flexible in pitch, depending on the blades CP and chord balance, your blades may be hunting for a comfortable pitch that only torsional stiffness can dampen (as constructed in the pictures).

[joe nelson]

Ed,

I have changed from the 1/32nd wire to .070 carbon fibre rod... it's stiff stuff. The low rrpm only happens on the aft rotor. The front rotor is made the same way and it works great. Unless, the wash off the front rotor is causing the pitch instability in the aft rotor blades. I'm thinking that by lowering the aft pylon to a coplanar position the aft rotor would be in clean air and will, hopefully, function as it should. My reasoning behind the lowering of the aft pylon is that nothing is driving the aft rotor. It could be starved for air by the front rotor or operating in the wash of the front rotor. It maybe blade pitch instability...the only way to find out is to test. Thanks Ed for you input!

[brett s]

Tie them together with a belt or driveshaft perhaps?

My tandem helicopter kit is just about ready to test fly - discovered the main gear was out of round enough to be a problem with both gear mesh & balancing when testing it without blades a couple days ago, waiting on the replacement.

[joe nelson]

Brett,

I have given the idea of tying them together a lot of thought! It would make life simpler. The connection would have to be very light!

I'm glad you are nearly ready with your tandem...good show ole man! Bet you can't wait!

Over the next couple of weeks, if I can't iron some of the problems out I'll go to another route with my tandem...maybe converting it into a helicopter not a gyro. I feel that I'm real close especally when the front landing gear is off the ground and the rear gear is very light and bouncing!

[RotoPlane]

When you have the rpm problem again with the aft rotor, try turning the frame (or the fan) 90° so both rotors get clean air at the same AoA. On a helicopter like an H21, you want the aft rotor higher than the front one to keep both rotors in clean air in forward flight…..I would think just the opposite would be true for a gyro…..

[joe nelson]

I think that you are right, Ed. The aft rotor needs to be lower. This morning, I've changed the aft rotor from the new carbon fibre flexbeam one to an older one to eliminate the blade instability question. The same low rrpm condition happened to the older rotor. With this, I think it would be safe to say that the problem is aerodynamic not mechanical. The flexbeam rotor is OK and the aft pylon needs to be lowered. Thanks!

[joe nelson]

I think that this may help visualize things better. In the old setup, the wash from the front rotor chokes the aft rotor. It has no clean air to drive it and this problem is compounded by the 34% overlap. The new configuration is what Ed has suggested. It looks good to me! I'll let you know how it works in a couple of days.

[joe nelson]

This is the result of removing the overlap of the fore and aft rotors. As you can see the airframe was lenghten by 8 inches and the results were amazing. The rrpm of both rotors came up to a good speed and the airframe was very active on the floor. One thing that I noticed was the tendancy of the aft rotor to move the tail to the right. I changed the direction of the rotors and the movement was still there.:eek:

[barnstorm2]

I am enjoying this very much, thank you for posting you work Joe.

[RotoPlane]

Outstanding....you don't mess around Joe ;). Looking at your setup, the aft R/H movement may be caused by that horizontal stab-like thingy (more lift on the left side) or some swirling air flow from the fan or a little of both. Also the aft RTV may be pointing slightly to the right. No torque, so that shouldn't be a factor......

[joe nelson]

Thank you for your kind words, TimO!

Ed, The elevator-thingy was just a passing thought and doesn't serve any purpose at this point. It was there to support an elevator for trim and additional rudders for directional control. I should remove it! Life is so easy when you have a coping saw and CA glue.LOL

Two weeks ago, I met a gentleman who flies r/c helicopters. When I explained that I was working on a tandem gyro, he became interested in the project and will be helping me with the servos and electronics. That's good since I know nothing about this!

[joe nelson]

This is what, I think, is happening with the relative air flow (RAF) through the rotors.:noidea:

[RotoPlane]

This is what, I think, is happening with the relative air flow (RAF) through the rotors.:noidea:

Yep! Of course once you start moving this craft forward, the incoming airflow will become more horizontal and this flow interference may reduce the aft rotors lift somewhat.....but that is what testing is all about ;). I think you will find that the fore and aft rotors will need some differential RTV control....depending on fwd speed. You enjoy tough projects, huh.....I mean you could have gone the easy way and positioned the rotors side by side.....;).

[joe nelson]

Ed,

I agree that the RAF will become more horizonal in forward flight. I'll have to test to see what affect it will have on the aft rotor in this condition. My testing approach is by taking baby steps or trial & error. No educated strategy here, Ed. I would like to build a smoke chamber to be able to see what is physically happening around the rotors. Maybe, that will be my next project.

The controls have been the point of my reading over the last year or so. I'm interested in two approaches. The first is a two servo control where the front and aft rotors are connected differentially both in the lateral and longitudinal axises. The other is more simple and lighter in weight. Again, it has two servos but only connected to the front rotor and the aft rotor is used only for trim. I'll build both systems and see which is the better of the two.:twitch:

[davh12]

Joe,

Your project is looking real good. Love the pictures. I have a drawing that I did for a tandem powered helo, but I did not want to mesh with gear sync, so I spaced it to where the rotor blade tips have about 2" to clear one another.

Dave

[joe nelson]

Dave,

Overlap is OK in helicopter because of the direction of air through the rotors but not in gyros. By not putting gears in the helicopter, you will save weight and that's the name of the game! Make it the lightest you can. The tough part is ballancing the thrust between the two rotors without gearing.

Today, I will test an idea that I had while watching my 2 year old grandson playing with his birthday ribbon. Maybe, I can visualize the airflow around my rotors by using the ribbon!

I got a letter from my son's team leader, today. He told me that my son has been recommended for a bronze star for his actions in the IEA attack last month...hooah! God bless them all!

[joe nelson]

Well, I tried the ribbon but it was too stiff so I'll change it to yarn. I think that this may work even on this scale. I'm trying to make tell-tails to see the airflow around the blades. I'll post some pictures if I'm successful.

[joe nelson]

These are the results of the tell-tales.

#1 shows the present configuration and the theoretical airflow. This was Ed's suggestion last week.

#2 the air straightener has been removed because the diameter of the tubes were to large and was ineffective. The rotation is clockwise on the front rotor. The tell-tales show the airflow, on the advancing blade, is strong by the tuff angle toward the blades.

#3 is the tell-tales at the upper rear of the front rotor. I was expecting to see more desturbed airflow here. The only other thing of interest here is the flow pattern just aft of the center of the rotor. It seems to separate as you can see by the tuffs. I did this test twice with the same results.

#4 is a closer study of the flow of the front rotor.

[joe nelson]

The aft rotor airflow is still a little weak as the tuffs show.

#1 is the flow below the aft rotor as compared to picture #2 which is the front rotor. You still see the "v" pattern in the middle of the stick but the flow is still weak.

#3 Is the area between the two rotors. It is more turbulent here and what I was expecting closer to the front rotor. You can see more "v" patterns here. My best guess is that it is caused by the air flow from the fan or vortices generated by the front rotor.:twitch:

[RotoPlane]

Since you like to experiment, are not afraid of time and work and you are retired….think of the fun you could have and the knowledge you could accumulate if you built a good sized wind tunnel. Look at this one for an idea on the flow straightener grid…..and then we could ask you to test some stuff…..;).

From Jim O'Donnell: http://www.fi.edu/flights/first/makebigger/index.html

[joe nelson]

Ed,

The only restriction to your suggestion would be the size of my shop. The way that it would need to be built is portable and collapsable. I would want the ability to inject smoke on to the model as in the Jan Drees "smoke movie". With this feature you can see all the airflow and vortices. Any ideas on how a smoke generator is made?

[RotoPlane]

This is a cold smoker idea for one that seems to work well…..you could make something similar....

YouTube - VENTURA COLD SMOKE GENERATOR (http://www.youtube.com/watch?v=KRacXT9EeEA&feature=related)
http://smokemate.blogspot.com/

[joe nelson]

Ed,

That sounds like a good project for next year. I'm getting close to the time that I'll start my Christmas furniture projects for my kids. After that I'll get started.

[joe nelson]

This morning, I tried to refine the carbon fibre rod between the hub and the grips. Each rod (flexbeam) was filed to have flat spots to get the blades to have the same flapping and drag axis. The rotors were reinstalled on the model and placed in front of the fan. The results were small with the front wheels rising about 1/8 of an inch off the floor. The aft wheels danced about but didn't lift off. I don't know if this was because of the added degree of freedom in the blades or some other reason. However, this was the best test so far.

[davh12]

Hey Joe,

Found this web site. It's not bad. Google "Rotor Space". Kinda like myspace, but without the stupid high school BS. Serious site...not "he said she said". Another interesting site is this one:

http://www.linvents.com/01_3-Rotors_Compound_Heli-Linn/Problems_of_existing_rotorcraft/problems_of_existing_rotorcrafts.htm

It is a tandem helicopter/gyrocopter. You may have already seen this site. Have a good week-end.

Regards,

Dave

[joe nelson]

Thanks Dave,

I will certainly take a look at you websites. I've been down in my shop working on a pitch change idea that I had. I'm using the CF rods ability to twist to effect pitch change in the rotor blades.

[davh12]

Joe,

Sounds interesting. I never thought about using torsion that way.....flapping sure, but pitch change......It should work well. CF has enough twist flex and good "return" back to is original form......like a composite bow. I'm curious to see what you come up with. Good luck and have a good week-end.

Dave:usa:

[joe nelson]

Dave,

Here's a quick drawing of what I had in mind.:wave:

[joe nelson]

Today, I've spent a very informative and enjoyable afternoon with a young man who explained how the servos and linkages work on R/C helis. He gave me a demo of very extreme rotary wing flight and needless to say, I was impressed. He was actually cutting the grass at the small R/C field with his helicopter. My enthusiasm has been restored!

[joe nelson]

This is a quick prototype of what I was thinking about on Friday. You can see the .070 inch CF rod used as a flexbeam. I hope it works!

[davh12]

Hey Joe,

Got a question for you. On the bottom of the electric motor for my helo there are a couple "radio" style chip components. If I cut those little things off will it turn faster or burn it up?

Dave

[joe nelson]

Dave,

Honestly, I don't know! I'm not as far along as you and only starting to work with the electrical components. In fact, I was going to the hobby store on Saturday to pick up servos and the like. I was told that I can get a mini ball joint there which should save a few grams.

I now have a duplicating machine. It's not one of the fancy ones (CNC) but a manual one. I'll be able to make accurate blades...only flat bottom ones until I the hang of using this thing. I'll post some pictures when it's all together.:twitch:

[davh12]

Joe,

Sounds good...and there is nothing wrong with manuel hand operated machining........to be honest my machine shop teacher did not want me touching his CNC mill and lathe after I broke 2 or 3 tool bits....he said" some folks are better with manuel lathes".......the small ball joints are a time saver. I've used them as small as 2 oe 3 mm wide to pencil eraser size to nickel size all steel. Look forward to the pics.

Dave

[joe nelson]

Dave,

Can CF rod be threaded? I'm going to get some more when I go to the hobby store and was thinking about using threaded ball joints. Maybe 2/56 ball joints.

[Countach]

Joe-I don't know of a process to thread CF rod,you would be cutting into the uni directional thread.This is a link to what I believe you need.Been using these titanium rod ends for years as tail rotor pushrods on my rc nitro helis.
http://www.centralhobbies.com/control_linkage/pushrod3.htm
Central sells alot of unique products,mosty oriented towards pattern fliers.

[davh12]

Joe,

I do not believe so, but I'm not an expert. I do know from my own experience that when machining small pieces, the fibers can seperate easily if too much pressure is applied. That being said, I would guess that the small threads cut into a rod with a die is possible, but I do not think it will have good load bearing qualities. If a small part does have fiber seperation, a little glue and pressing it back into place works ok. Usually sanding, cleaning with cotton ball/alcohol and then glue works well in rod ends. Just make sure it is the right length because once the glue sets....you're not getting the rod end off the CF rod. I'll dig around my PC. I have a pic of rod ends on CF rod when I used them as support struts.

Dave

[davh12]

Countach,

Thanx for the web site for the titanium ball joints.

Dave

[joe nelson]

Countach and Dave,

Thanks for the input. It does make sense that the fibres are on the outside of the rod and threating it would cut the fibre. When you working with grams of weight every parts weight is crucial. The Central Hobbies website was much help! It is not only for parts that I need but for what parts are available.

[joe nelson]

These pictures shows my new duplicator and the hub prototype.

#1 is the duplicator and as you can see I still need to make fixtures to hold the blade blanks. The fixture is placed on the bed to the left under the router and the blade master is on the right under the stylus. For now, it will be just flat bottomed blades like 8H12 and Clark Y airfoils.

#2 shows the blade at a negitive pitch and #3 shows a neutral pitch. I think this system will give me all 3 degrees of freedom:feathering, dragging and flapping.

Feather is possible through a small ball that rides on a flat part filed off the shaft eliminating the need for scissors. Dragging and flapping is made possible though the material charactistic of the CF rod.

[davh12]

Joe,

Nice pics. Will a servo hold the pitch?...taking in to account the stored torsion energy in a CF rod with a slight twist. I had to tweak my servo a bit because if the balance in weight is not just perfect you hear a slight buzzing in the servo as if it wants to extend further or it is having trouble maintaining. I got it worked out for the most part. May need a bit larger servo.

Dave

[joe nelson]

Good morning Dave,

I'm hoping that the servo will hold the pitch...I'm still unsure about the size of the servo or how much throw it needs. I'm also hoping that the pitch horn will improve pitch stability in the rotor blades while using the CF rod. I think it'll reduce the torsion in the rod while letting it drag and flap...we'll see!

[Countach]

Digital servos have much more holding power than analog.Look for a standard size digital with around 80 oz/in torque.Good Luck Jason ex.Futaba,JR,Airtronics,Hitec Call Heliproz and ask for Todd or Larry
www.heliproz.com

[joe nelson]

Countach,

Thanks for the information...that really helps! I have a young gentleman who is going to help me set up the radios and servos early next week. I'll keep every one posted.

[davh12]

Joe,
Hope to see pics of the set of your servos and rotor system once you get everything linked.

I got my Grade 5 titanium rod yesterday. The Stainless steel mast bent slightly from the torque during the power up. It bent right where the reduction gear cross lock pin goes through the mast. New rotor mast hopfully before the week-end is out. Good luck this week-end. Still prayers going out for your son. Hope he's doing ok. Seen a Hational Geographic thing on DARPA last night. It was cool putting a face to the guy who sent me my "no thanx" letter. It will not keep me down.....tinker till I die.

Best Regards,

Dave

[joe nelson]

Dave,

I think that this phase of my project is going to be both challenging and expensive! I'm going to have to make some parts on my lathe which I've haven't used in a while. Then I have to work out the programing on the radio. I want to get a Futaba 2.4 Ghx radio because the ease of use. The young gentleman who has been helping me with the setup has one and I was impressed with it. I never knew how advanced this new stuff was. I'll surely post some pictures when I'm far enough along to show more than bits and pieces.

Thanks for asking about my son. He was knocked down again by an IED two Thursdays ago. in a sweep west of Kandahar. The guy in front of him took most of the blast and lost his right leg. The kid behind my son was struck by a log kicked up the AP mine. My son was bruised but uninjured...our prayers must be working! His platoon is now combat ineffective and he's working with another one. He says, he's nervous about working with guys he doesn't know...all I have to say is god bless them all!

Dave, keep up the good work and DARPA will come around! hooah

[joe nelson]

Well, here's a little success.

Picture #1 shows the front of the tandem off the floor about two inches.
Picture#2 is a differnt perspective.

The rotor is a two bladed 8H12 airfoil set at -4 degrees pitch on a semi-rigid hub. The semi-rigid set-up seemed to have worked much better than the other rotor configurations. The aft rotor was removed for this test. Rotor rrpm was measured at 327 rpm, in the picture, and some vibration was present but not excessive.

[davh12]

Joe ,

I love these pics. Was the -4 degrees pitch blade pitch with respect to the hub or rotor disc/ mast tilt with regard to the airframe or a vertical reference line......sorry.....it's just that I am gyrocopter stupid...hehehe!

Regards,

Dave

[joe nelson]

Morning Dave,

The blade pitch is in reference to the hub or plane of rotation. In a gyro, I have found, that the pitch is backward to a heli. At the hub, in a model gyro, it will have negative pitch and at the blade tips it will be a positive pitch. In a helo, the pitch is positive at the hub and negative at the tips. On my model, the mast angle and shaft angle are the same due to the design. I don't know what the angle is because I've always adjusted it in front of the fan to get max rrpm...I'll measure it and get back to you later.

[davh12]

Joe,

Sounds good................at least your model has been light on the wheels and actually off the ground. Had another set back last night. The new center spindle hub that I was fabing for the reduction gear was drilled too large for the mast diameter....my fault....I miss my lathe. Center drilling was so easy and on point. I'll get it eventually. Have a good week-end.

Dave

[joe nelson]

Dave,

I have just gotten my radio. It is a Spektrum DX6i, 6 channel on 2.4Ghz. It will take a while to read the instructions and get it working. I also picked up a couple of ST47 servos on my trip.

I'm going to start replacing all of the HMWP parts and replace them with something lighter. 1/16th ply is what I had in mind for the cheek plates and control arms.

[joe nelson]

This is how I'll set up the controls for the first attempt. It is a two servo system with right and left connections being the same. I'm using JR Sport ST 47 servos with 47 oz/in capability. This configuration works the front and aft rotors moving opposite to each other.

[joe nelson]

Today, I had a bit more success. I had tinkered with the aft rotor trying to get it to pick up. The rotor diameter was increased, the number of blades were increased and the shaft angle was increased with no improvement. Then I remembered an article that I'd read about a tandem gyro where the aft rotor was smaller in diameter than the front. The blades on the aft rotor was cut down to 18 inches from the 24 inch original. The aft rotor rrpm was improved and rear was dancing as it became lighter. It didn't get airborne but I consider it a success. I'll cut a half inch off each blade and retest.

[davh12]

Keep at it Joe. You'll get it. I'm on Con leave. Bone spur in left foot. Too many years of Infantry stuff...catches up with you.

David

[joe nelson]

Dave,

That not good news when a grunt has L.P.C. (leather personel carrier) problems! I know you'll take full advantage of your con leave with your project. lol

I heard from my young 11B this morning. He's excited about making E-4 and the extra money he'll earn. It's already burning a hole in his pocket and he has nowhere to spend it. lol

Get well soon.

[davh12]

Yep I've already started. That's good to hearabout your son's promotion. Has he been home for R&R leave yet?

[joe nelson]

He's scheduled for January 30th. and we're in the count down mode. 69 days and a wake up!

I've ran into an unusual problem with my project. I was adjusting the cg to see what range I had when I discovered that the aft section would get heavier when the cg was at the 50% point to the 25% point. The model would easily lift the front end off the ground at the 50% to 75% point...I'm confused! My thinking was that with a more equal weight distribution the whole model would lift...But I was wrong. I weighted the front to make the aft part very light but when the rotors were turning the aft section was heavy.

[davh12]

Joe,

I'm not an expert in much............helicopters much less gyros. I have a clear understanding of them as well as a cognitive interest. Could the air flow up through the forward rotor disc be affecting the airflow up through the aft rotor disc,,,even in a small amount? I wonder if there is a way to use dry ice or some neutral smoke to watch the air flow through your rotor system?

Good luck

Dave

[joe nelson]

Morning Dave,

I'm sure that the front disc is causing an air flow problem....but what do I do about it is the question. I have found a NACA study from 1954 that I'm trying to wade through about tandem rotor configurations. I hope this will shed some light on my problem. There are two patents for tandem gyro on the net, one addresses this problem by lowering the aft rotor below the front to avoid this problem...I'd tried it but it didn't work as published. The NACA study indicates that the aft rotor has to be .3 to .5% of the radius of the front rotor to avoid the front rotor wake.... I'm working on that now!

The other the considation is a CG problem but I've only worked with that briefly.

[joe nelson]

I have raised the aft pylon to .5 of the front rotor radius as suggested in the 1954 NACA report. There was some improvement in the rrpm of the aft rotor but I think that this can be increased by reducing the diameter of the aft rotor.

My concern now, is that there may be a lack of volume in my fan. At the highest setting of the fan the model dances around as if it was very light on it's wheels.

The CG has been adjusted to just aft of the front leanding gear legs by washers on the black stick in the pictures. The washers are to compensate the motor that has not been fitted.

[joe nelson]

Today, I think that I have cracked the nut. I have increase the aft mast angle to change the rear rotor thrust angle. By doing this, I've moved the center of pressure to coincide with the center of gravity. The model was put in front of my fan and it was jumping lightly on it's gear. I think that there wasn't enough cfm generated by the fan to actually lift off. With enought forward airspeed I, now, think it will fly.

The problem was in the first model (per plans) the masts were set at a fixed angle. When the tinkering began, I made a gimballed head which made the rotor thrust vector change unlike the fixed angle in the original plan. Before the aft mast angle was changed the rear rotor thrust vector ran through the axile of the rear landing gear. Now, it's 1.5 inches aft of the first vector. I found the middle of the front and rear thrust vectors and co-located the center of gravity at that point.

When the model was placed in front of my shop fan it was very light on all wheels. It danced around wanting to fly. I was to reluctant to change anything until I could measure the current setup.

[joe nelson]

The last few days I have been working on the CG of the model. I think, this is an exercise in form and function. With gimballed heads the center of pressure is moving with every control change. This is most likely the reason why tandem rotorcraft use swash plates rather than gimbals. When aft pressure is applied to the controls, the CP goes well forward of the CG and the nose raises but the aft part of the aircraft stays firmly planted on the ground. This has been my problem for the last few months...I get rotation but no flight at a constant airspeed. This where I have to incert a quote from Birdy; "Igorance is bliss until you discover that you are!"...LOL.

This is, I think, what is happening.

[joe nelson]

In the original plans the mast where set at a fixed angle. The designer warned that the tandem gyro would not fly while unpowered and landings were to made with power. My assumption was to put controlable heads on it to solve this design flaw. At this point, only half of my assumption was correct. It, indeed, needs different heads but not gimballed ones. I will have to give some thought to my next course...to buy or build a set of swash plates.

[joe nelson]

Before I move to a swash plate control system I want to try a few new things. I am going to fix the angle of the aft rotor to approx. 12 degrees. The differtial cyclic is going to be disconnected with only lateral (rudder) movement in the aft rotor. The front rotor will have most of the control input for now. I'm hoping that the CP changes are small enough to be flyable.

The CG has been moved around by placement of washers on the airframe with little or no performance change...the nose still lifts off and the aft is stuck on the ground.

[joe nelson]

I made an error in my last post calling the control input "differential cyclic." Since this a gyro not a helio it would have been "collective cyclic." I think this term would most accurately describe what my controls were doing. The front and rear rotors moved up and down together. What I will try now is "differential cyclic." This will make the front rotor move opposite the rear except in yaw. Yaw will set up as in a normal rudder function.

[joe nelson]

A while back, Rotoplane (Ed) made a suggestion for me to build a wind tunnel. I thought that was a good, doable idea. Yesterday, I read an article about how NASA tests models with low reynolds numbers. It was more complex than I would have thought. They can raise or lower the ambient air pressure and adjust the temperature inside the wind tunnel to get a small model to give the same data as a full size aircraft. They can adjust the wind speed to get higher reynolds values...geeeee!

On the TV show Myth Busters, one episode had them making a wind tunnel to test a concrete airplane. They used soda straws to straighten the air inside the tunnel! Chuck B. told me to make a simular device but I used 4" PVC pipe. I put the yarn "tell tails" in front of the one I made and I saw no improvement. I should have thought to reduce the size of the pipe to be more effective....Hey my learning curve is wide,lol!

[joe nelson]

Today, I've been tweeking the controls. I have them all moving in the right direction but there needs some pitch angle changes in both rotors.

I've also made some changes in the CG weights and now I can move it with little or no effort. This will allow me to test the whole CG envelope. This morning, one test was performed at the 25% station on the airframe. The results were the same ...the nose picked up and the aft wheels were firmly on the floor. I'll add a few more degrees to the aft rotor and take out a few degrees on the front rotor and retest...this seems like a balancing act!

[joe nelson]

Today's problem appears to be weak bell cranks. There is too much slop in the control movement and the jack shafts needs to be increased to 4-40 from the 2-56 diameter. The bell cranks need to be 1/8 inch thick plywood instead of the 1/16 inch now on the model.

If this control setup doesn't work well, my next course of action will be making the aft rotor independent of the front rotor. The rear rotor will have a fixed pitch normally and the only other movement will be lateral (rudder) controlled with the pedals. The aft rotor pitch will only be adjusted like a trim control. The front rotor will be fully controllable.

After a web search and reading a 1954 NACA study I now think the problem of no aft lift off is a function of the shop fan volume. The NACA study gave specific distances of the aft rotor above and behind the front rotor to avoid blade votex interaction (BVI). The model now meets all of the NACA requirements. The other information was about the Bell HSL-1 tandem rotor helicopter. Bell engineers had many problems trying to address BVI. BVI caused so much noise and vibrations the pilots could only fly it for short periods of time. The Navy replaced it after only two years in service...Bell made no other tandem helicopters.

[joe nelson]

This morning, there was a major setback. I must have not had the model securely fastened down and it flipped over while in front of the fan. The front rotor blades were cracked along the basswood and balsa joint and the rear pylon was damaged but the aft rotor blades are OK...they just folded up at the drag hinges. The control linkages were damaged but I was planning on replacing them anyway. I think I'll take some time to replace the airframe to since it was looking exceptionally rough.

[All_In]

Bummer!!! 1 step forward 2 steps back.

[joe nelson]

John,

It is a true bummer! I'm going to take this opportunity to look for a larger output shop fan and to improve the airframe somewhat. I've thought of a few things to strengthen the airframe and simplify the controls. My thinking now, it to make the aft rotor fixed in pitch and only be adjustable to add pitch trim. It wiil also have lateral movement to act as a rudder and to coordinate turns.

[All_In]

Good idea Joe.

I saw Myth Busters make a wind tunnel by cutting packages of straws in half and making a block of straws about 2' x 2' and the placed it in front of the model to even the air flow out seems efficient, simple, and cheap to me.

[joe nelson]

I saw that one to, John. It was one of my favorite episodes...concrete gliders. I think I'll use that techique when I'm back to the testing phase. Initially, I used 4" PVC pipe but when I put the yarn tell tales in front of it there was little or no improvement in airflow. How about putting the straws inside the PVC pipe and glueing them in place as a solution to the airflow problem?

I read Barnaby Wainfan's article in Kitplanes Magazine, in the last issue, where he explains how NASA does wind tunnel testing. They can raise or lower temperature and ambient pressure to adjust for the low reynold's numbers of the models they test. Maybe, I should set my goals for my wind tunnel to have these features.

Having a wind tunnel that I could gather data would let me test things like BERPs and various blade profiles for gyros. Now, all I can do is test if the rotors come up to speed and if the will lift the airframe that is attached to with a set volume of airflow.

[joe nelson]

After some reading and looking at other designs I think that the best course is to make the rotors articulated... the one thing that was needed was "differential collective" and that wasn't possible with the use of gimballed heads on the model. Only "differential cyclic" was available. The AS-18 and J-2 used the articulated head successfully for many years. Now, the big problem is how to srink it to fit the model.

[joe nelson]

As I sat looking at my broken model, I thought of discarding it but that would be too many steps back. The objective is to go forward. I'll strip it down to it's basic parts, 3 sticks of balsa and two sets if wheels. Most of the control links and connections have broken off anyway so a refit will be quick.

Most of my articulated heads, that I've built, are too large and heavy for this scale. I don't want to buy a commercially built head because there is no learning in that. I think the way is clear! Build a smaller head.

[joe nelson]

Here's the condition of the model. As you can see the control links took a big hit when it went over on it's back. The rotor blades have been glued back together and hopefully it won't be out of balance too much. Next I'll try to reduce the rotor head by about half and see if my theory about the articulated head is correct. My guess is that a gimbaled head allows the CP to move too far forward to allow the aft rotor to become airborne.

The pictures are not large enough to see clearly the damage to the controls. I'll try to improve on this next time.

In picture #2 this is what need to be reduced in size by half to fit the scale of the model.

[davh12]

Joe
nice pics..................your prototype gets cleaner and cleaner every time you tweak it.

Dave

[joe nelson]

Dave,

I'm going to start calling it patches for all the mods that I've made to it. It needs a new airframe and an articulated head before it will get airborne completely. I've played with the CG but it seems that it's the CP that is the problem. That is why only the front of the model will lift off when the rotors are tilted back...the CP goes so far forward well ahead of the CG only the front of the model lifts off. With articulated heads the CP will be less of a problem, I think. One other discovery is the blades need more tip weight so small momentary variations in airflow to the aft rotor will have a smaller affect on rrpm.

[joe nelson]

Today, I wanted to varify the airflow with my fan and the new setup with the air straightener. After reattaching it I moved my tell tales to various places in front of the fan. I found eddies in places near my workbench and near my machines. Most importantly, was the "sweet spot" about two feet in front of the fan where the air is smooth.

Picture #1 is the new fan configuration and #2 is the eddies near my machines. #3 is the sweet spot about two feet in front of the fan.

[joe nelson]

Today I noticed an unusal problem that I've overlooked. When adjusting the pitch on the aft rotor, it's rrpm slowed while my hand blocked the airflow. This made me think of "airframe interference" while at a high AOA. It would be catastrophic in a quick stop or a rejected landing as the airflow was interrupted causing aft rotor rrpm to decline. The front and aft rotor are well separated but still needs to be coupled not for clearence but rrpm. A series of shafts and gearboxes would be too heavy for a model gyro...heli yes but gyro no.

[davh12]

Joe,

That's ok if you call it patches. Mine is the same way, but it's aluminum. My wife has had a word or two for me when she stepped on the shavings from my lathe on her way to the washer when I first started my "patches". Patches is nothing more than a project or invention that is improving through innovative thinking and changing things around. Goals would never be met if we are afraid of changing. It is necessary to make modifications to polish the concept and buff away the "dirt" of orthodox thinking. So, we give it one more try. If it goes against physics, then and only then we can discard any idea. But if we're not willing to try, what's the point? As I've said before, we can lose our sense of discovery if we stick to the norm. Far too many worry about what it looks like when they start on a project and fail to make needed changes because of the way it will look to others. I always say, "let's get it working and then worry about how it looks after." Take care.

Dave

[joe nelson]

I could'nt agree with you more! Working through each problem has been a wonderful educational tool and with each "fix or patch" we learn the "why and what fors" of each component. Other than that it's just fun...lol. I have read more research papers and studied more designs than any other time in my life. It makes me appreciate the accompliment of people like Frank Piasecki and Ray Proudy, all great innovators.

[joe nelson]

I've reassembled the model to work on the controls. I need to find a solution to the "differential collective" problem or the aft end of the model will stay on the ground. In a gyro to get lift the pitch of the rotor is increased...that's the same as pulling collective in a helicopter. If the front and aft rotors worked opposite to each other would that be equivalent to "differential collective" in a tandem helicopter? There would need to be a "sweet spot" where the rotor angles would need to fly together...up would require pitch increase in the front rotor and decrease in the aft. The opposite would be true to descend. Perhaps, only pitch control on the front rotor with the aft being fixed at a certain angle.:puke::eek:

[joe nelson]

This morning, I think that I've made a bit of progress. Yesterday, I reconfigured my rotor controls with the front and and aft rotors acting opposite to each other. The model was placed in front of my fan where it floated along very lightly on the floor. I didn't get the front lift off as before but a flat attitude. It didn't fly although it was very very light on it's wheels. If the fan had a bit more volume it would have flown for sure.

I tweeked the model's CP to exactly on the CG and adjusted the rotor angles to where they produced the best rrpm (the sweet spot). It has seemed to work.

[joe nelson]

My eariler statements about the gimballed heads not working on a tandem rotor configuration may have been wrong. As long as the rotors work opposite to one another (front rotor tilt up and the aft rotor tilt down ect) the CP stays relatively stationary. I think, that in this configuration it may give me the "differential collective" that I've been looking for...testing to follow!

[davh12]

Joe,

Hope that you're enjoying your time with your son being home for R&R. Well deserved on his part as well. My Patent Application finally got published. One hurdle out of the way. I'm still a week or two away from my next power up....catching up with my wife on the 4 day..........no helicopter stuff....lol. Godspeed.

Best Regards,

Dave

[joe nelson]

Dave,

I think that's great about your patent! You should feel proud because very few get that far in the process.

My son just returned from a visit to Ft. Sam. He went down for three days to see two of his battle buddies who were wounded during their last operation at Kandahar. Both ,unfortunately, will be discharged... what a s#%ty way to go! God bless them!

Clay has packed so much into the last two weeks. He has been deer hunting where he and son-in-law bagged a six pointer. Then he turned my kitch into a meat processing plant to my wife's dismay for several days. He made tons of jerk and sausage with the instructions to send it to him the day after his leave is over. I guess it will arrive in Afghanistan about the same time he does...lol. His platoon will be eating venison for the rest of his tour, I'm sure. The amazing part of this is that he bagged the deer with my old M-1 with open sights and not zeroed....luck?

[joe nelson]

My search for a larger fan hasn't gone well. It would seem that I'll have to buy an electric motor and belt drive a larger fan. Another method would be to build a rig like the one at Cartercopter. They attached a device to the front of their pickup truck drove at a known speed to test their model. I'll, at least, take a look at to see what that would involve!

[joe nelson]

It has been raining here for a couple of days and I haven't been able to check out the the possibility of the Carter-style mount on my truck. I don't think it would take much more than a piece of plywood and a couple of 2X2 for the bracing.

Hopefully, this will give me some insight to my "differential collective" idea and if it is a fix to my center of pressure movement problem. I'll test it at it's present configuration to see if it will actually lift off. If I'm successful, I'll add the rotor pitch servo to test the diffential collective idea.

[davh12]

Joe,

I remember both of my R&Rs. I was more tired when I got back then before I left because I did so much. Glad he's doing well.

Dave

[joe nelson]

Thanks Dave,
Clay brightened up the place when he was home. He was non-stop the whole time he was here. He did the whole gambit of things like dining out, hunting, travelling to Texas, going to the mall and seeing his girlfriend. I got tired just watching.

During one conversation, he informed me that my M-1 Garrand was a "primative weapon". Needless to say, it made me feel real old...lol. He went on to say, that when you run out of ammo you use it as a club. I told him, that was only after the bad guys had jumped over our dead horses...lol.:boom:

Today was the first day that the weather was good enough to measure my truck for the small platform to mount the model for faster testing. I should begin building it tomorrow morning and maybe get to testing by Friday. I post some pictures when I start.

[joe nelson]

Today was a good day working on the platform and truck mount. I found a few things that I need to change before I start testing.

The first tests will be just to see if the model will fly and at what speed. Then I'll measture the rotor angles and attach the controls to see if my theory on differntial collective works. If successful, I'll install the servos to test the full range of motion. This captive testing should give me the needed information to go on to free flight.

[joe nelson]

I've made a modification to the model which might add a bit of stability to my tandem. I've added Guerney flaps to the aft pylon and in front of the fan it has seemed to have stopped tail creep. My theory was to add a small amount of drag to the aft pylon to reduce it's tendency to swap ends. The Chinook uses a SAS system to prevent this characteristic.

[brett s]

The aft pylon was altered to have a blunt edge & strakes were added on the ramp & aft aux fuel tanks after the A model Chinook to help out there - they were still a handful in yaw with the SAS (C & earlier) or AFCS (D & newer) off, if someone was having a bad day you could lose some cabin windows :)

[joe nelson]

Brett,
The Guerney flaps makes the aft pylon flat on the trailing edge so, I guess, it works on this scale to. I don't have anyplace to put strakes on the model yet... unless you have some suggestions. I was surprized to see how well it worked.

I finshed my platform mount on my truck this afternoon and I should be testing at higher speeds very soon...I'll post some pictures as things develop.

One final question, has there been a tandem that has flown without SAS or AFCS?

[brett s]

Sure - the early Piasecki ones for sure.

Wonder if they tried to deal with the negative stick gradient issue as airspeed increases at all though, or just lived with it...

One of my hobbies is messing around with helicopters & such in X-Plane (http://www.x-plane.com), my Chinook model has those bad habits too - horrible yaw stability without artificial stability & a negative stick gradient, guess Austin got a lot of it right :)

[joe nelson]

Brett,

I don't know about the "dog ships" but I've read that the Navy's HUP 1&2 had a very basic auto pilot. I haven't found much information on the H-21 or H-25 so I don't know if the Army invested in that type of equipment back then.

I find that all the "band aids" to these problems are very interesting and how the designers came to use these fixes. I just hope that I can apply the fixes correctly and have a reasonably good flying machine.

[davh12]

Joe,

it's a primative weapon, but test and true.

Dave

[joe nelson]

Dave,

He was just getting a dig in on ole dad, lol. He also said, that I was in the army when we wore blue uniforms. Just wait until he comes home to get his new uniforms! Man, am I going have some fun with him, lol!!!! He is sure getting cocky now he's a speedy-4.

I got my platform finished but it snowed here this morning and I lost my window of opportunity to test in the mall parking lot. However, I did get some tweaking done this morning on my model. I'm not having any success with the center of pressure with the gimballed heads. When I get the COP at the CG the model just moves around the floor like a hovercraft. It has a level attitude but it's very light on all four wheels...I just need a faster speed...I hope!

[joe nelson]

Yesterday, I was able to test the model but with mixed results. The day was absolutely beautiful with winds G15-20 mph. I couldn't get a good fix on the lift off speed because of the wind. The model would lift and roll to the right then come down hard on the gear. The aft pylon has a 5 degree right tilt to control it's tendency to yaw left. I guess this was not a good fix.

I was amazed at the high degree of tilt needed for lift off...20+ on the front rotor and 28 degrees on the aft. There will also need to have a few fixes on the platform as well. My model mounting technique was poor and caused some problems while testing.

One thing that surprized me was the number of spectators at 7AM on a Sunday morning. One of the Cincinnati Police officers was a crew chief on a H-60 before becoming a policeman. We talked alot and he's coming over to see my shop to look at the other stuff that I'm doing....another rotorhead!

[joe nelson]

After Sunday's testing, I have given some thought to making the aft rotor fixed for the next few tests. I'm not going to make this change permanent just to deal with one rotor at a time. The rear rotor will be fixed at 28 degrees in pitch and 5 degrees left tilt to compensate for the right tilt in the aft mast.

Another thing that I found was the fan height was too low. I added 4 inches to the fan base height and the model performed much better.

[joe nelson]

Today, I made the mods to the problems that was found after Sunday's tests. I moved the front landing gear back two inches to improve the rotational moment of the front rotor. The rear gear was moved forward an inch for the same reason. I added a rudder for improved yaw control but with testing today it seems to have not been worth the effort.

During fan tests, today, the model would rotate lifting the front off the floor with the medium setting on the fan. On high, the model would lift off completely but would roll left and crash. The controls were adjusted to prevent the left roll but did the same regardless of where the control were placed.

[joe nelson]

After giving the roll problem some thought, I think, the airframe is flexing at lift off. Doing some additional fan tests should varify the flexing problem...it's an easy fix.

[joe nelson]

I have found one problem that would have never thought would happen on this scale. One of the blades on the aft rotor is experiencing resonnance/ flutter. While sitting at my work bench I looked up at about a 45 degree angle and saw the blade just vibrating almost fluttering. After several crashes, I don't know if this is the cause or an affect of the roll overs.

The repositioning of the landing gear seems to have improved the model's take off but the verdict is still out on the landings. I'm still trying to make a landing where the blade don't hit the floor first, lol.

[joe nelson]

With the ressonance problem fixed (weak hub bar) I continued testing. One thing that I found is that the model acts more like a cannard winged airplane than a chinook helicopter. I've moved the CG to the 25% station ahead of the center of pressure. I had thought that it should be co-located at the 50% station between the two rotors but that appears to be wrong.

The model is now doing normal take offs routinely but no landings yet. An increase in the coning angle might help here for a bit of stability.

[joe nelson]

Today's testing shows that the left roll is still present but not at the same fast roll rate as before. My fix was to add shims to each of the rear rotor blades increasing the coning angle. With the roll rate slowing, I'll add shims to the front rotor and retest. If problem is still present on the next test, I may reduce the height of the aft pylon from .5% to .3% of the rotor radius (6.5" to 3.9") above the front rotor to reduce the model's roll moment.

[joe nelson]

I started off this morning by adding shims to both sets of blades. The first test was the beginning of a bad day. The model was very light on all four wheels, then, over onto it's back much like a snap roll. This departure was unlike the ones before where it just laid over on it's side. This time, it came down completely inverted breaking it in two. After glueing the model back together the next test I checked the CG and the angles of the rotors...all was in the correct place. Back in front of the fan with medium setting the model was again light on all fours. I felt safe to move to a high setting. The model was stable on it's gear for about ten seconds when it started to depart(crash). I quickly grabbed the control string which went into the fan being caught by the fan blade. The string was reeled into the fan guard and the model was broken for the second time today. It was time for a beer so turned the lights off in my shop and headed to the kitchen.

[joe nelson]

I'm at it again this morning! Picture #1 is the three wheel stance before lift off. Number two is the initial nose high attitude before the aft section picks up.

[joe nelson]

This the next group of shots taken this round of testing. The first shot is from a different angle of the initial lift off. #2 in the set-up for the test. I have 20 pounds of lead to insure no roll-overs, today. This set-up allows me to adjust the head angle without moving the model. The angles for today's test is 40 degrees and 45 aft. The model has about 2-3 inches of movement to avoid a replay of yesterday's performance!

[joe nelson]

Here's a few more shots...it's difficult managing the model and camera at the same time...multi-tasking, lol. Number 1&3 picture shows the little dance the model does when the fan is set on medium... I call this the hovercraft mode. It is just floating around with the wheel barely off the floor. Picture #2 caught the second before it started the rollover and the aft left wheel touches the floor.

[joe nelson]

This morning, the front rotor was removed and the model was placed in front of the fan. The first thing that I noticed was the rollover tendency was still present. The direction depends on the direction that the aft pylon moved while the fan was on. This problem may be the height of the aft pylon (roll moment) or the size of the pylon (pylon area) or a combination of both of these.

[joe nelson]

As a wild guess, I added more shims to the aft rotor to increase the conining angle. I can't get an accturate measurement of the angle, maybe 6 to 8 degrees. I put it in fron t of the fan and it behaves better... just dumb luck!

If the weather holds off, I'll head to the Hobby Lobby parking lot tomorrow morning and test it in some smooth air.

[joe nelson]

The coning angle of the aft rotor what bugging me so I took a length of string pulled it from tip to tip and measured to the tettering hinge. Then plotted it on graph paper and measured it with a protractor. It was 4 degrees! Sorry, I'm trig. impaired, lol.

[joe nelson]

Today, on the "Hobby Lobby test range", lol.

Picture #1 is the start of testing and the wind was calm. #2&3 is the aftermath of gust that came out of nowhere. #4 is the damage caused in the rollover.

I was testing at 15mph and the model was behaving nicely. I had made two circuits and had just turned upwind when the rollover started.

Another observation was, the rpm was so high that it was audible in the cab of my truck. Then the gust happaned. I think we were experiencing a frontal passage because the wind remained steady after that.

[joe nelson]

This morning, I've been working on the servo controls for the model. It has been going slowly due to the size of the UHMW plastic bushings that I'm using to keep the linkages working smoothly. It is a three servo control system...for now! The first two are connected to the front rotor head. One connects to the roll axis of the head and the aileron slot on the computer. The second servo attachs to the pitch axis and the elevator slot on the computer. The second servo is connected to the aft rotor head but it functions opposite of the front rotor pitch. This setup is an experiment to test my theory on "differential collective". The third servo is connected to the lateral axis of the aft rotor head and is plugged into the rudder computer slot. The battery slides fore and aft to adjust the CG location.

PS Take the family to see the move "HOP" they'll love it. Have a great Easter!

[joe nelson]

After installation of the servos, I've discovered the bell cranks are too weak to move without flexing. I'll need to fix the problem by Sunday ...my next opportunity to go to the Hobby Lobby test range. Hopefully, there will be no rain like the last three weeks to stop testing.

The model has been in front of the fan both yesterday and today with the servos attached. Having added weight it making it move slowly and does not lift off as before. I guess that I need a fan with more volume or just reduce some weight.

[joe nelson]

In this mornings testing the model rotates as it has in the past but the servos will not hold the rotors in pitch. The servos are allowing the rotors to pushed all the way aft to their stops. To correct this I'll shorten the arms of the bell cranks to the rotors and lengthen the arms to the servos.

[joe nelson]

Just taking time to tinker with the model today, I installed a three bladed rotor on the aft pylon. I didn't put any hinges on the the head just to see why they were not included in the orginal plans. The blades rotated clockwise. When it was placed in front of the fan with no front rotor it rose up on three of it's four wheels. It then rolled over breaking the blades.

The blades had an aspect ratio of 10/1 instead of the standard 16/1 on normal full size aircraft. I'll add some flapping hinges with the same aspect ratio and retest.

[davh12]

Great pics, Joe. Keep working at it.

Dave

[joe nelson]

Dave,

I've been rained out this Sunday on the Hobby Lobby test range. The model has become too heavy to test in front of the fan so I have to wait until I can test in the parking lot to see if any of my tweeks have worked or not.

My latest tweek is to use a length of heavy-duty wire tie to act as a flapping hinge. It seems to work on the bench but, as you know, that's not good enough.

Good news! My young 11B will be home in two weeks...Man, it's been a long year! HOOAH!

[davh12]

Joe,

Glad to hear your son is coming home. He should get some good leave time and a chain of long 3 and 4 day week-ends. Tell him not to drop his guard for the last 2 weeks.

Dave