Is a rigid 3-bladed rotor for UL possible? I think yes….ignoring the 254 thing….

Vance

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How much do you feel your 3 blade system will weigh?

Not absolutely sure....but right now, I can see almost 30 lb over the 254 lb limit.

When I began building Mariah Gale I found value in articulating the why of it including the reasons for the build and the goals of the project.

I would love to see a similar mission statement for your aircraft. I suspect I am not alone in this.[/B]

Hello Ed,

Are you indicating that you think your three bladed rigid rotor system with servo flaps will weigh 30 pounds more than a two blade semi rigid rotor system?

Why do you feel it will be heavier?

Are you designing something without performance parameters, goals and without a mission?

Again, why?

Thank you, Vance
 

RotoPlane

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To get an idea about the changes in rotor behaviour when drag is added one might have a look at this analysis of a rotor with tip jets:
http://hdl.handle.net/2060/19930082771
The most interesting part is tables one and two. Note e.g. how collective changes from slightly positive to negative with increasing drag.

I couldn't find Table 2 Juergen….perhaps you meant Table 1, part 1 and 2? I am sure there is a big difference in drag between a tip-jet and a streamlined housing further inboard at the 75% location.

One of the reasons I decided on tapering my blades was to increase the power of the driver section of the blade and help to make up for some of the servo-flap drag. Can't wait to find out how well my eyeball engineering has worked ;).
 

RotoPlane

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Ed,

You state you are a good airplane driver, do you have private pilots license?

.

Yeah….I is a good driver. I forgot to say "Yeah". You know, in the movie "Rain Man", where the Dustin Hoffman the savant says "Yeah, I'm a good driver." It was kind of a joke….kinda ;).

No I never seemed to find the time. What's weirder is I have owned three planes, a Tri-Champ (which I loved), a Cessna 150, and finally a Cessna 172. I have logged about 40 hours but also have "well" over 50 hours more unlogged. I just couldn't seem to find the time with my jobs overtime (lead inspector at Douglas), plus to be honest; I dreaded taking the final check ride. I just was fine with renewing my student ticket several times. I've taken many solo cross-countries, taken off and landed in LA smog with special VFR often, night flights…everything. The only time I wasn't solo was when I was flying with a licensed pilot, usually my brother. Just before I became a father, I sold the 172….which ended my flying career.

A couple years ago, I flew with a CFI friend in his Cessna 210 and after having the controls for a spell, he said it would only take maybe 10 hours of instruction and I could take the check flight. Maybe someday.....
 

Alan_Cheatham

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Given that your ultralight gyro will not be ultralight legal and illegal to fly and given the three bladed rotor precludes flying on a Sport Pilots license, finishing your PPL may be a viable choice. A PPL for fixed wing can legally fly a EAB gyroplane as long as it's a single seater, you will of course have to take training to learn how to fly a gyroplane, but at least it would allow you to drop trying to stay within the impractical UL weight limits.

.
 

RotoPlane

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Hello Ed,

Are you indicating that you think your three bladed rigid rotor system with servo flaps will weigh 30 pounds more than a two blade semi rigid rotor system?

Why do you feel it will be heavier?

Are you designing something without performance parameters, goals and without a mission?

Again, why?

Thank you, Vance

The 2-bladed rotor would have weighed ~70 lb and the 3-bladed rotor will weigh ~90 lb, even though its blades are ~5 lb less each. I was very close to 250 lb total before and now I can see ~270 lb….and I know how a new flying design seems to rob calories from the air and gain weight just sitting there. I want to be totally up front with the FAA and as I understand it, one can usually get a weight waiver for testing a design if one can show them it is strong enough.

Are you designing something without performance parameters, goals and without a mission?

Of course not. My performance parameters are shown in the spreadsheet, my mission and duel goals has been to try to make a safe UL for up to 300 lb pilots (one of the reasons I am using foam and S2 glass) and to take what I've learned and apply that to a larger EAB 3-place machine with a larger wing and much higher cruising speed.

My rotor (if it indeed flies well) will allow direct control of the airframe, control of the rotor pitch plus fly more like a fixed-wing and I consider those worthwhile safety features. If I fail…well at least I can say to myself that I tried.
 

RotoPlane

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Given that your ultralight gyro will not be ultralight legal and illegal to fly and given the three bladed rotor precludes flying on a Sport Pilots license, finishing your PPL may be a viable choice. A PPL for fixed wing can legally fly a EAB gyroplane as long as it's a single seater, you will of course have to take training to learn how to fly a gyroplane, but at least it would allow you to drop trying to stay within the impractical UL weight limits.

.

Oh Alan….you would have to bring up the commonsense stuff huh ;).

Not only that, it has a collective….also a no-no for sport pilots. If I just halfta….I will go PPL.....…or get a new students license again….
 

joe nelson

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Ed,

One thing that you'll need to work out on your project is the reversing mechanism. When you autorotate the controls reverse because of the change in wind direction. I didn't have to worry since my project was a gyro that flew in autorotation all the time unlike your helo.

Another problem that I experienced was balancing the blades to 25% cord with all that hardware on the trailing edge of the blade. A brass rod might do the job if it was built into the leading edge of the blade. This also make the blade heavier than I'd like but makes for a high inertia system.

The next thing to consider will be the control linkages. I tried three different methods of controlling the servo flap when I was experimenting. At first, I only had two strings attached to the flap itself so see what it would do in front of a fan. Both blade and flap were balanced to 25% cord. The main blade airfoil was an 8H12 and the flap was a 0012. The second method was two 1/8" cables attached to a bell crank on the interior of the blade mounted at the blade's 75% station. The last setup was the same bell crank attach with a 1/8" stainless steel rod with HMW plastic as bushings to account for the coning of the blade.

For my experiments, I used the same ratio between blade and flap as on the Kaman HH-43. One note is that the trailing edge of the blade must be coplanar to the leading edge of the flap. With the flap mounted at it's 25% cord station, the flap's leading edge when moved up will be above the blade plane and when moved down it will be below. I discovered that in this configuration the authority was improved. Overall, the flap had good authority even with the low speed fan.

My goal is to incorpate the servo flap with blades attached to a strap pack like on the MD 500 for more testing of this configuration.
 

brett s

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One thing that you'll need to work out on your project is the reversing mechanism. When you autorotate the controls reverse because of the change in wind direction.

I don't see why anything would be different with cyclic control or collective via servo flaps whether in powered flight or not, what am I missing?

In a coaxial or intermeshing system yaw control will reverse in autorotation if they use differential collective for yaw, that's a totally different issue.
 

RotoPlane

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Ed,

One thing that you'll need to work out on your project is the reversing mechanism. When you autorotate the controls reverse because of the change in wind direction. I didn't have to worry since my project was a gyro that flew in autorotation all the time unlike your helo.

Another problem that I experienced was balancing the blades to 25% cord with all that hardware on the trailing edge of the blade. A brass rod might do the job if it was built into the leading edge of the blade. This also make the blade heavier than I'd like but makes for a high inertia system.

The next thing to consider will be the control linkages. I tried three different methods of controlling the servo flap when I was experimenting. At first, I only had two strings attached to the flap itself so see what it would do in front of a fan. Both blade and flap were balanced to 25% cord. The main blade airfoil was an 8H12 and the flap was a 0012. The second method was two 1/8" cables attached to a bell crank on the interior of the blade mounted at the blade's 75% station. The last setup was the same bell crank attach with a 1/8" stainless steel rod with HMW plastic as bushings to account for the coning of the blade.

For my experiments, I used the same ratio between blade and flap as on the Kaman HH-43. One note is that the trailing edge of the blade must be coplanar to the leading edge of the flap. With the flap mounted at it's 25% cord station, the flap's leading edge when moved up will be above the blade plane and when moved down it will be below. I discovered that in this configuration the authority was improved. Overall, the flap had good authority even with the low speed fan.

My goal is to incorpate the servo flap with blades attached to a strap pack like on the MD 500 for more testing of this configuration.

Hi Joe,

This rotor is designed for a gyroplane.

The blade only, will be balanced with full length leading edge weight at 26% of the chord. Then the servo-flap assembly will be installed including the root bellcrank and the two S.S. cables that run inside UHMW polyurethane tubes. The servo-flap housing extends beyond the blade leading edge and that is where the final chordwise balance weight is placed to again balance at 26%.

I'm using two ~3/32" dia. S.S. cables as mentioned above. I don't see how one control rod will work because as the rotor spins up, centrifugal force will try to throw that rod out against the bellcrank travel stop…it must be balanced on each side of the bellcrank….unless you have some kind of mechanical balance thingy.

I'm locating the 0015 flap in the same position as you and is balanced at 26%….the drawing is below
 
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RotoPlane

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Brett is correct, Joe. The only time I will need to reverse the blade pitch with negative collective, is if I gather the intestinal fortitude to do this maneuver…straight and level. Of course the rotor would need to be tipped up toward the nose a bit so it will still maintain autorotative rotor rpm. Vance said he won't try it ;).
 
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joe nelson

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My bad! You are spot on, Brett. Sorry, I was STUCK ON STUPID (SOS), lol.

Ed, look at the Kaman SH-2's system. It uses push rod connections to the flaps. The bellcrank at the rotor blade root is counter-weighted to compensate for CF...I'm not trying anything new here...I don't have the background for it!
 

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I couldn't find Table 2 Juergen….perhaps you meant Table 1, part 1 and 2? I am sure there is a big difference in drag between a tip-jet and a streamlined housing further inboard at the 75% location.
You are right Ed, it's table 1. My idea was that your blade performance would be somewhere between the case cdj=0 and cdj=0.1. Depending on your thrust coefficient you might want to set your angle of attack for zero servo flap deflection such that you cover the whole control range you need.
 

RotoPlane

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Very good point Juergen….thank you! To lift an AUW of 550 lb, the blades AoA must be 2.8° and if the blades started at 0°, part of the servo-flaps <= 20° half travel has already been used….how much depends on the blades final torsional stiffness.

I will need to figure the best way to build-in 2.8° in the grips….or better yet, a way to vary the degree of nominal pitch setting. To still allow low HP, high rpm spin-ups, the servo-flaps can be adjusted by negative collective and they will then twist the driven section of the blades to 0° after enough rotor rpm is obtained….rotate the collective back to nominal 0, the blades return to 2.8° and off we go…..

I need to check if this blade pitch change will affect their ability to hand start.
 

Rotor Rooter

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Ed,

I can't recall if this subject has been discussed before, let alone what the answer might have been. So to briefly go off topic, the following question is asked.


Have you considered the use of Active Blade Twist without the root change?, as is used by IVO on his propeller blades?

The intention is to implement this on the back-pack Electrotor-SloMo project and two (or more) heads are better than one.


Dave
 

RotoPlane

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In a way that is what the servo-flap does Dave. The hub-arms and blade root will twist a little while the flap twists the blade at least twice to three times as much at its location. Note that the blade outboard of the flap housing doesn't twist but just follows the tilt of the housing.

I wonder how stable a blade would be with "Active Blade Twist" because if a blade is flexible enough to twist, then it may be prone to climbing and diving own its own, unless there is a lot of positional torque. I don't see this happening with a servo-flapped blade due to its dual role as a pitch control and a horizontal stabilizer for the blade. Just thinking out loud…..er…in print.
 

Rotor Rooter

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Ed.

Just some thoughts.

In both cases the root of the blade is fixed.
In both cases a twist is imparted to the blade at approximately 75% of span.

I suspect that in both cases the rate of twist (twist per foot of span), that is applied between the root and 75%R will be continued on out to the tip.

With Active Blade Twist using carbon composite construction;

The torque tube, between the root at 75%R, would be produced out of diagonal thread. http://www.cstcomposites.com/Small_Tubes_under_17mm_OD.htm
This is made so that it is flexible in bending but is not flexible in twist.

The skin of the blade would be produced out of carbon cloth with the fibers running span-wise and chord-wise. The skin could also incorporate pultruded tubes or rods with the carbon tow running span-wise. http://www.cstcomposites.com/pultruded_profiles.htm This is made so that the skin is flexible in twist but is not flexible in flap or lead/lag.

One major advantage of carbon composite is that you can control which movements are to be flexable and which are not to be flexable. Plus there is the advantage of lower weight etc.

The control force for the composite blade may be slightly greater then that for the servo-flap but the profile drag and induced drag will be less.

In addition, if some party was to setup to produce these in a reasonable quantity it could go a long way toward the advancement of recreational rotorcraft.

Dave
 
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