View Full Version : design tip for tractor designer/builders
08-30-2004, 10:41 AM
I came across some info this weekend I though I should share here on the conference. I donít remember seeing it here before, but I couldíve missed it.
Basically, with a tractor design it is good to check the % of fuselage before and aft of the rotor. To do this, put the fuselage in flight attitude (level), drop a vertical line from the rotor head (Iím really not sure if it should be the teter bolt or the pitch pivot), then measure in front of the line to the prop, and behind the line to the front edge of the rudder. The ratio should be about 60/40, with 60% behind the vertical line from the rotorhead. The further away from 50/50 the better.
I was told that a few tractors have gotten into flat spins while in a power climb at low airspeeds; the p factor will start to yaw the fuselage and if you donít have enough moment arm for the tail it will turn into a flat spin. At least one of the tractors that it occurred to had been flying for several years without incident, and I believe the front to back ratio on them was close to 50/50.
These were not any tractors designs that are currently flying as far as I know: definitely not a LittleWing.
Just a heads-up for anyone tinkering with tractor designs, I wasnít aware of it when I was building mine. Turns out mine is very close to 60/40, but itís still good to know and watch out for it. :cool:
08-30-2004, 11:03 AM
lots of thanks for this precious info , i thought in a tractive design
now i m aware of that and should re-consider rudders potition and tail size, thanks
08-30-2004, 11:51 AM
Hi Victor, I like how well you could see, but the drive and cooling seem a little complicated. I was wondering what is the angle you need to rotate and what your thinking was on that? Thank You, Vance
08-30-2004, 12:14 PM
firstly i thought we could mount a car fan onthe engine shaft , then always ducting an airflow exhausted behind the engine where an intercooler could be located.
about drives, i agree it is not the simpliest way.
whitch angle do you mean, i may misunderstand your question... :( tell me more please..
08-30-2004, 12:27 PM
Hi Victor, The angle that it sits on the ground compared to the angle it flys. My friends refer to rotating in order to fly. This usualy happens before the main gear leaves the ground. There is some controversy about how much is desirable. I am sorry that I did not express my self more clearly. Thank You, Vance
08-30-2004, 12:41 PM
okay vance !!
in the drawing you can see quite the fight attitude , the on-ground angle is about 20 degrees in this drawing, i thought it for a 1m60 propeller and tried to keep some ground clearance for it .... i see what you try to point.... a such take off posture could be bad ?? you wonder if the gyro willget enough ground speed to rise the tail ... depends on the rotor rpm, prerotated ? not ? dont really have satisfying answers..
consider my drawing as a general layout, i just wanted it to look a little "sexy" ... it certainly could (will) be refined if i would plan to seriously build it.. i only try to plant a seed in some brains .... and let some one grow it up.. why not?
i am actually on helicopter data.... ;)
08-30-2004, 01:13 PM
Michael Guard said:
"I was told that a few tractors have gotten into flat spins while in a power climb at low airspeeds; the p factor will start to yaw the fuselage and if you donít have enough moment arm for the tail it will turn into a flat spin. At least one of the tractors that it occurred to had been flying for several years without incident, and I believe the front to back ratio on them was close to 50/50."
That was a Jim Eich JE-2, Michael.
Floyd Brown, using a metal prop, got one in a flat spin from which he couldn't recover. Spun all the way to the ground. Floyd walked away with a few bruises and scratches but the gyro didn't survive.
I once flew a gyro in California that belonged to a person by the name of Royce Tanner (I think) that had a long nose pod on a Bensen airframe and standard Bensen tail. I put it down at the end of the runway without going around because it felt like it would rather fly backward than frontward.
08-30-2004, 01:31 PM
I guess in a flat spin it would descend at the same rate as a regular vertical descent? Maybe the rotating motion of the fuselage would actually help lessen the impact when it hits the ground?
08-30-2004, 02:23 PM
Here's a pic of the JE-2; if you hold your little ruler up to the screen to measure, you can see it is pretty close to 50/50.
08-30-2004, 04:32 PM
Jim Eich was a good friend of mine, Michael so I hate to be critical with him no longer around, but his JE-2 could have greatly benefited from a longer tail cone.
Jim was somewhat of a disciple of Arless Riggs; you may have seen his name mentioned in older issues of "Pop Flying."
Arless was an old desert rat who used to build tractor gyros from Taiwan door skins and carve rotor blades from planks with a stick of rebar embedded in the nose for chordwise balance. Everything tied together with a layer or two of fiberglass and polyester resin.
Arless was actually quite a clever gyro designer. His machines were always 2-place and he and his wife flew all over the California desert country in them, never with a serious crash. He probably couldn't have flown any better had he been legal.
08-30-2004, 05:37 PM
I seem to remember Helicopter Ed getting into trouble with his tractor design. It had a Rotorway body on it. It got into spin that almost ate his lunch.
08-30-2004, 05:45 PM
The bottom line is to remove the rotor, tie a rope to the teeter bolt and hang it from an oak tree limb.
If it doesn't weathercock the right way, you're likely to be in serious trouble.
The gyro does not fly better when it is legal, on the contrary.
09-01-2004, 03:24 PM
:) :) It was nice of you to post an informative note on how to check the percentage of airframe before and aft of the rotor mast. I am along with my associates building three littlewing two place units, and I might add, having a great time at it. May I ask what you are building ? I hope it is a tractor type unit. Thanks Rich.
Good afternoo;n all,
My name is Tony Stiles and I have been a gyro enthusiast for some time,(PRA#17081) and have enjoyed the organization and it's expertise plus the invaluable helpand assistance from a multitude of it's msmbers.
My interest in gyros came about as a result of seeing a number of gyros at early EAA conventions, which led me to join the PRA. I have had the privilege and honor pf knowing and talking with some of the greatest and most knowledgeable people in the present gyro comunity and some who are sadly no l;onger with us.
Whaat I know toda;y is totally attributable to the help and advice which recieved from them. Having attended over 19 EAA co;nventions in a row and eventually deciding that I would never own a P-51 Mustang or a $100,000 kit plane or for that matter a high dollar antique airplane, I eventually confined my activities to alternate engine forums and the gyros in the ultralight area.
Over the past 15 or so years I have even narrowed my interest in the gyros down to the tractor design only. In this time pleriod I have "crashed"probably at least a dozenor more gyros, I used the term"crashed" loosely to mean as in crashed in the waste basket ,or as in an unfinished scale model or in a few cased an unfinished prototype. All off the so called "crashes"were the result of the help andexpertise and advisefrom the wonderful and caring efforts of the people to whom I went for there input and I am proud to say everyone of them was a membera of the PRA. It is because of this advice and help that I am praobably alive and well today because my ignorance and sometimes stupidity was very large then. I would say that I got a whole lot more than just my membership m;oneys worth. I never went to a Bensen Day gathering or a Regional fly-in or definitely the National(where ever it was ) that I did not come away with somuch advice and information that I was still working on it in December, especially regarding the tractor design.
This brings me to the point of why I have chosen to join this forum, I amstill seeking all the desigh information on tractors that I can find. I will be looking foward to Andy Keech's talk at Mentone and his Forum on Tuesday ( the second day a Oshkosh )and as always, talking with Ron Herron (the man with the Plan) and any oth;er individuals who have interest in the tractor design.
Great strides have recently been made in the pusher design leading to safer flying and I think there needs to be a extended effort, to be as vigilant and cautious in the experimenting with the tractor design lest it produce some of t;he same results as the early pusher designs. ddDI feel there is just as much to learn regardign the tractor design as there was waith the pusher, there will definitely be a lot or "do ,do this and don't do that " in the new tractor designs.
Hope to see many of you at Mentone this year and will also be at the PRA tent at Oshkosh.
I am courious as to what you folks think of this machine.
is it safe.... will it fly , etc.etc.
it was at one time a Bumble Bee... but sense the bee was so unstable on the ground I modified it...
the best idea I could come up with was a tail dragger design to stop the thing from wanting to flop over on the front right or front left ... the extreamily fast steering of the tricycle landing gear was mostly to blame no doubt... and the entire craft was of the Loosie-goosie feel to it.
Now its rock solid on the ground, i have even done 18 to 20 mph brod-slides on the pavement ( due to an unwanted sharp left hand turn that i think i have solved now )
it is a Pusher, not a tractor( obviously ) Yes its ugly...
but personally i could care less what it looks like as long as it flys SAFELY!
that theory obviously holds true in my workmenship, it may be ugly but its strong as heck ! <grin>
so I was hopeing for your critisum , to point out flaws i may have over looked.
your help is greatly appreachated.
thank ya !
06-15-2005, 06:05 AM
could you post some larger, detailed photos from different angles and zoom in on details like connection points, linkages, etc? I think that would help those here in answering some of your questions.
I'll see what i can do ... thanks !
06-15-2005, 11:50 PM
G'day Bob. In my opinion the gyro would be extremely unstable as soon as the tail wheel gets light. The C of G is so far behind the mainwheels that it would try to swap ends at the first excuse. I am not suprised that it has done broadsides with you on the pavement. With this undercarriage setup it would only have to get a few degrees off line and you would be along for a hairy ride and couldn't do anything about it. This is the reason why most modern aircraft are tricycle undercarriage.
Most tail draggers try to get the main wheels back as close as practicable to the C of G as possible.
If you could keep the tailwheel planted as firmly as possible you may get away with a take-off, but an aborted take-off will definately see you sitting in a tangled wreck. Not trying to discourage you but rather trying to save you from big expense and possible injury.
Your origonal Bumblebee must have had a something badly wrong to behave like it did.
Ah ! thats interesting Tim ! and it makes sense !
it would explane the problem i have been having indeed !
if i can get this site to let me up load a few pics I'll show some more pics....
Your right about the mains on most tail draggers i have seen their just behind the engine , where i expect the cog is ! ... hummm , not a darn thing i can do about that eather.... my design is flawed ! bummer!
... that is something i had over looked.... as close as i can tell the cog is about 16" up the mast inside the gastank .... that puts it way behind the mains like you say !
as far as the Original bumble bee goes , I checked the plans over and over again and everything was fine , the only thing that could have been some of the problem was the decoupleing springs on the front wheel being too small and me takeing it on a dirt feild instead of a paved landing strip... the rear suspension bungie cords were replaced by heavier springs, and they may not have been strong enough in looking back ...
add it all up and ya get a loosie goosie craft....
well, heck ! ..... i was hopeing someone would have a REASON it does what it does.... i think you nailed it Tim I thank you ! very much
even if it isn't what i wanted to hear , it probly saved me alot of repair again ! because i would'a kept trying to get it off the ground and sooner or later i'ed have gotten that dredded sharp left turn again !
heres a pic if i can up load it
THANK YOU !
06-16-2005, 05:42 AM
Any chance you could move the mains back a bit?
I ran into the same problem and I relocated mine further back; it helped a lot.
06-16-2005, 07:34 AM
Couple of quick questions, so forgive my ignorance of the BumbleBee design. First, the cable going from the rotorhead to the instrument pod, is there a rigid structure going from inside the pod to the keel? From the photo I was envisioning mast flexing playing havoc with the pod.
Secondly, have you done a hang test on your machine? I imagine with the weight of the gear so far forward, and pilot weight moved forward to accommodate the fuel tank that the CG is well forward as well. Again, I'm unfamiliar with the original design, so that's why I'm asking.
if mine were a tractor it could be done i am sure but its a pusher ! and the center of gravity is behind the pilot by an inch or two so i would have to move the front wheels back to at least the seat.... maybe more. so I would loose alot of the advantage that i originally had in mind with the wide stance way out front.... its best to put her back to a trike i think !
there is a 2x2 alum post inside the insterment pod however I just kind'a took a shortcut and ran the cable over the nose of the pod then to the turn buckel.... i don't realy need the cable on there .... I just thought it might help support the mast if it needed it , couldn't hurt i don't think ! <grin>
Yes i have done a serries of haing tests recently, it was originally hainging at neg 4 degrees nose down in a laden haing test .... Sonny J convienced me to get the nose down to a neg 10 degrees , I did that by tilting the mast back , adding cheekplates and moving the head a bit foward ... and 9.5 degrees was obtained on the final haing test .
actually the seat is moved back almost 6" believe it or not ! it was a long way foward ... that was one of the first things i did , got it and the tank as close to the mast as I could . infact i had to add blocks to get the foot pedals back so i could reach them thats how much i moved the seat hehehehehehe ! ....
I have tried real hard to compact everything as close as possable to the mast and keep the weight low for maximum pingulim effect, however i have sense learned i should have worried about center of gravity not so much the pingulim effect !.... live and learn i guess !
I guess the whole question is Mute now guys as I am in the proccess of changeing it back to a tricycle landing gear arangement at the moment
when Mceagle mentioned the wheels being so far infront of the center of gravity the lights finally came on ! .... but of corse thats the problem ! how stupid of me ! ..... I over looked one thing in the design and it came back and bit me good ! ....hehehehe I could see no way of saveing it and make it a stable , docile machine so its back to the trike !
.... oddly enough about 3 months ago I had already contemplated going back to the tricycle LG ... and had desided how i would do it ...
I am about 3/8 done already tonight by tomarrow I should have the mains on and be working on the nose wheel !
Thanks for the help guys ! ... and Mcegle where were you 3 years ago ! HAHAHAHHA ! you saved my bottom for sure ! thank you !
catch ya later !
here's what I got so far ! whatcha think ? think it'll fly ?
Notice the height diferance between the rear mains and the front wheel , do you think that will hurt anything ? besides give more room to rotate ?
thanks guys !
06-17-2005, 05:18 PM
here's what I got so far ! whatcha think ? think it'll fly ?
Notice the height diferance between the rear mains and the front wheel , do you think that will hurt anything ? besides give more room to rotate ?
thanks guys !
That was fast! Hard to tell from the photo but could you post some zoomed-in closeup pix of the cluster plate area and the gear connection points? Also a closeup of the joint where you extended the front keel. That would help to better see what's going on there.
Get an inspector to check it out, which you'll need to do anyway if it's over 254 lbs., and from appearances it may be.
if it is more than 254lbs I'll lighten it up ! easy to do with all the steel I have on it !
when i get the keel tube extension done I'll probly post a pic, but all the holding power will be inside the tubes and just a 1/8" plate on the outside, I'm not worried about the joints brakeing I've gone with over-kill in mind on the striength of all the joints it would supprise me to no end should anything fail.
there are techinally 2 cluster plates at the base where the mast connects to the frame rails , one for the main gear , other for the mast. the one on the mast is 1/2" plate steel with a 1/8" steel bar welded edgwise down the length of the plate. I used steel because I didn't have 1/4" Alum plate, the attachment point for the rear wheels is the same one that held the wheels to the front, I just took the entire unit off ,turned it 180 degrees and slipped her back under the gyro just behind the mast. its a 1/4" steel plate arrangement with a tower pointing down to hold the tie-bar that holds the wheels togather, eventually I plan on makeing strut shocks from motorcycle shocks I have for the rear wheels so I have suspension on all 3 wheels . and that tower thing will be cut off and ground smothe. I'll probly lighten it up by 10 pounds easy when I get the steel off the thing (grin)
I was more concerned with the front wheel being higher ( aprox 6" ) than the back wheels .... I can't think of a good reason that it would be bad to have the nose wheel a bit high.... but I have made mistakes in that sort'a thing before ! hehehehehe
I'll update photos at a later date ...
Good evening to all
Have been watching the tractor design thread and glad to see the advice and information on design and handling. I have also noticed on some other threads,some questions about electric pre-rotors, and find this is a subject that is expecially noteworthy to a tractor design . If you do not have a 2x2 or a 2x4 mast rising directly in front of you in your design then you are going to have a bit of a problem in routing your pre-rotor drive system up to your rotor. this will usually limit you to either a manual method, a hydraulic system or a electric system . The electric system is to me probably the least expensive and the easiest to make, but has a sever torque problem on engagement.
Normally this could be handled with a soft start motor controller or a PWM(pulse width modulator) but there is a technical problem here and it comes from the starter motor getting it's negative connection by being bolted directly to the frame, rather than through a cable .
Almost all of the controllers made today use MosFet transistors for control and there are two types of these transistors, one is known as N-channel and the other is known; a P-channel. For reasons I cannot explain the P-channel type do not have the power capaacity that the N-channel type do and the ones of the P-channel that even come close are unreal in cost.
The commercially available units are usually the N-type which MUST ago in the negative side and this of course is bolted directly to the frame and it is not practical to isolate the starter from the frame, and even building a P-channel type unita is ipractical and cost prohibitive.
However there is a reasonable and inexpensive way to handle this problem, I must first make a very clear statement IF YOU WANT POWER OUT YOU HAVE TO PUT POWER IN,so don't even think about getting a real significant result with a electric pre-rotor if you are going to try to use a small motorcycle battery or a garden tractor battery, You must use a serious outomotive battery with say 900 to 1000 amp cranking capacity , so this obviously is not a good choice for a ultralite.
The best cost effective and simple way to handle this problem is to insert a starter solenoid switch in the positive cable (this should be at least a
# 4 welding cable of good quality) going to the starter. the starter solenoid switch sh;ould have bridged across it's main terminals a piece of stainless steel welding rod either 1/8 dia. or 3/16 die. depending on the sixe of the starter andthe current draw, a second switch on the panel mounted beside the regular pre-rotor switch is all that is needed to give the desired action.
When thepre-rotor switch is operated first and the second switch is open the initial spike current will be forced to go through the stainless steel bridge ( this maybe from 4 to 8 ilnches in length and may or may not be in the form of a coil) and the nickel and chrome content in the stainless steel bridge will choke down the voltage to a desirable level of around 8 volts, to achieve this will likely require some experimenting with the length of the stainless steel rod. WARNING THESE SPIKE CURRENTS CAN REACH ABOVE 200 AMPS FOR UP TO ONE SECOND OR MORE, I'LL BET YOU DIDN'T REALIZE YOU WERE DEALING WITH THAT KIND OF POWER. ALSO THIS SOLENOID SWITCH AND STAINLESS STEEL BRIDGE MUST BE MOUNTED WHERE IS WILL NOT BE SUBJECT TO FUEL SPILAGE OR NEAR PAINT OR IN A CONFINED SPACE BECAUSE THE STAINLESS STEEL BRIDGE MAY GET RED HOT DURING THE 3 TO 5 SECONDS THAT IT IS USE BECAUSE IT IS DISSIPATING A GREAT DEAL OF POWER FOR THIS 3 TO 5 SECONDS.
After the pre-rotor switch is operated,wait for about 1/2 of a revolution of the rotorblade (3 to 5)seconds and operate the second switch that closed the starter solenoid contactor switch that will now bypasses the stainless steel bridge and puts full current and woltage to the starter on th;e pre-rotor . When the rotor has reached it's potential rpm then turn off both control switches on the panel.
For some great information on Toyota starters go to Google and type in Toyota starters and go down to about the 5th Entry and click on Toyota starting systems , this site is a PDF down load and has a lot ofgreat information on Toyota starters, there history and power ratings and testing procedures.
Hope to be using this method on my tractor if I ever get it finished
Great Idea Tony !
any yes you'll need a big battery to put up with that kind of "resistance" in the system , but it should work great , especially if you use heavy automotive starter sylinoids... deninately ground strap everything !
don't plan on having the alum returning that heavy amprage , at least I wouldn't,..... use copper web ground straps they flex well for the starter to move with the rotor head and all... but go big ! remember you are asking the equivelant of cranking a 500c.I. V-8 engine for a long time ! things will get real hot real fast ! unless you use big cables ! (and ground straps).... as you probly know the smallest cable used in the system will determan the resistance of that system.... so head it off at the pass and go biger than ya need !
Just my 2 coppers !
good luck to ya !
06-18-2005, 01:22 AM
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06-18-2005, 08:26 AM
I just re-read what I wrote last night and I'm sorry for sounding so rude in my post. I hope you understand though that I was speaking only out of concern for your well being. Nobody likes to dis' others' work because its obvious you've put a lot of work into your ship. But red flags go up when critical errors are obvious even in tiny photos.
And when you mentioned 1/2" thick steel cluster plates... are you aware how weight distribution affects VCG? There's a reason why engineers spend years designing aircraft the way they do, and even small changes can have dramatic consequences that might not be obvious.
If we here didn't speak up when we see something wrong, we would be doing you a great disservice, and would have failed in our mission to improve the safety of our sport, and ensure the safety of those involved in it.
06-18-2005, 08:14 PM
Fast rebuilding Bob. The only problems I can see with the different heights of the undercarriage is to do with the rotor angles of attack while on the ground. If the nose is sitting low then every degree that it is low, it is taking angle of attack from the rotors, making them much slower to come up.
At the opposite end, every degree that the nose is low is a degree too far forward past horizontal that the rotors will move, making it harder to find the neutral angle of attack of the blades for slowing them down with safety.
Hope this helps.
Not a problem Brian ... I asked ! hehehehe !
yah the weight has been taken into account so not a wory there .
and thanks McEagle ... already thought about that so thats been considered....
on the other hand it gives ya the ability to slow the blades down by pointing into the wind and tieing the stick foward, as is my practice .... they should slow down faster ....
sense there is no rotor brake on the craft that is a good thing !
its scary then some body drives up on a quad and hops off .... i get up and walk over to meet them if they were to walk towards that rotor they'ed be tackeled ! ..... all it takes is one gust and you could be missing a head ! ....
06-19-2005, 06:03 AM
Thanks for understanding, Bob. I know you've got your mind made up already about training yourself, but will you at least have your ship inspected by a DAR? Or at the very least an experienced gyro builder/pilot before doing any taxi tests?
When you said: "yah the weight has been taken into account so not a wory there", how did you account for it? By what method? Do you know where the CG is currently located or how far it's offset from the thrust line? I can't help it, but my gut is telling me that all that 1/2" & 1/4" steel on the undercarriage may have the effect of creating an extremely HTL configuration, which is dangerous.
Anyway, let us know when you can. Not meaning to rag on anybody... this is all just part of the building process and very necessary. Though I disagree with the criteria for your decission to self-train, we'd all like to see you succeed, and safely.
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