Mustering Blades-Paul B.

[darrellwittke]

Say Paul, I see you are browsing... I was wondering if we could have a discussion on those mustering blades you mentioned to birdy.

As I recall, those blades were the Chuck B. design with 8H12? inboard section tapering to VR7 outboard airfoil. Am I correct?

I also remember you stating they did not have speed stability in that whatever speed setting you put them at is where they stayed.

And you also mentioned they have incredible climbing power, ie. "tons of lift."

I have no interest arguing with you over negative or positive twist, I do hope we can have a civilised discussion to come up with some wild guesses as to why the lack of speed stability.

My thoughts are: 1) These blades are very efficient to be able to provide extra lifting power. 2) With your composites man, Allen?, if you produced these blades (which require composites because of tapering shape) you could have a good share of the two place market. 3) The lack of speed stability (to my admittedly simplistic thinking) has to be related to offset and trim spring used on the rotorhead.

Did you also say those blades have more shake?

I also wonder about the increased shake of dragon wings (of which I have a pair), I wonder if the positive upturn on the ends increases H-force on both dragon wings and mustering blades?

Perhaps Chuck B. or Raghu will comment, ( I see I digressed on the core question.) So if you would be so kind, Mr. Bruty, would you share your thoughts as to what is going on aerodynamically with your mustering blades?

With greatest respect, Darrell

[Aussie_Paul]

Say Paul, I see you are browsing... I was wondering if we could have a discussion on those mustering blades you mentioned to birdy.

As I recall, those blades were the Chuck B. design with 8H12? inboard section tapering to VR7 outboard airfoil. Am I correct?

I also remember you stating they did not have speed stability in that whatever speed setting you put them at is where they stayed.

And you also mentioned they have incredible climbing power, ie. "tons of lift."
These blades have nothing at all to do with Chuck B. other than discussions on the forums. I had asked Chuck what he thought could happen if we built this blade design.

These blades are being developed by Rob Patroney in Queensland, with help from myself. Rob had never produced rotors for the 1200 lb gross weight machines until I came along, and asked him to help develop rotor blades for my Firebird project. 26' were the largest Rob had made. We went to a longer hub bar to get me 29' and then Rob produced a longer mould, and we have been experimenting ever since.

They did not have pitch stability. The major design component for pitch stability is the amount of reflex of the airfoil. The VR7 has no reflex.

Experts please yell if I am getting it wrong!!!!


I will report what I found.

The original Rob blades were the 8H12, and are all composite blades with an alloy hub. I flew these (29') on Hybrid at a gross testing weight of almost 1100 lbs. I think that the engine rpm for a certain speed was 4800. I have a drum of concrete that I use to keep my testing gross weight the same for all tests.

The next blades were 30', tapering from root to tip and thinning from root to tip. The airfoil was 8H12 from the root to the last 3' here the airfoil changed to the VR7. These blades had a negative twist. Blade tip twisted leading edge down.

There blades were not pitch stable. When stick free every bump would change the attitude of the aircraft, and it would stay at that new attitude and the speed would adjust to that attitude. There was very little trim spring change from roughly 30 to 70 kts. They cruised at the same speed using 400 engine rpm less. The extra foot diameter would have helped this a little. These blades would almost fly with no airspeed on the clock in ground effect. I loved them to show off with (mustering with them would be great), but they would not be good for a trainer or long cross countries due to the lack of pitch stability. With the CLT airframe there is no PPO tendency, but you do have to fly them a little all the time. Just like driving a car.

I sent them back to Rob and he heated them up a little and lifted the trailing edge a little to introduce some reflex. There was a small improvement in pitch stability. I then fitted a trim tab on each blade 2' from the tip. The exposed tab was 8" X 1 and a 1/2". I bent them up 5 degrees and that improved the pitch stability about the same amount as Rob had done lifting the trailing edge. I have these blades FOR SALE!!!

The set that I am currently flying is 30', tapering from root to tip and thinning from root to tip. The airfoil is 8H12. These blades also have the same negative twist. They are the same blades except for the change in airfoil.

These blades are stable enough to train with and are the blades that I flew to Alice Springs and back last Easter. During the testing flights these are operating using 200 engine rpm more than the previous set with the VR7 tips, and do not hang in as long behind the power curve. I believe that they would pass the proposed Sport Aircraft pitch stability tests.

I am now waiting for a true Firebird before I conduct any more testing. I will need to match the blades and the offset to the new machine/enclosure. The last fine tuning of all the testing that I have conducted will need to be with the final shape.

All of Robs blades are extremely smooth.

I hope Darrell and all that this has been of interest.

Aussie Paul. ;) :D

[Doug Riley]

Paul: A couple things may be going on here that you haven't mentioned here. I flew McCutchen Skywheels composite blades for a number of years, and base my thoughts partly on that experience.

Fiberglass (or fibreglass) composites are quite strong in tensile strength for their weight. They are not very stiff for their weight, however. This makes them ideal for sporting goods that we want to flex without breaking (fishing poles, tennis rackets and such). Aircraft parts, OTOH, are better off being stiff than limber. In order to get the stiffness we need in something like a rotor blade, we end up adding a lot of weight (unless perhaps we use sophisticated structures such as honeycomb).

The extra weight, in turn, makes chordwise balancing a challenge. Did you you check the chordwise balance of your blades? Use weights to move it forward of its natural point (which is apt to be 40% or more of chord)? An absence of chordwise balance at the aerodynamic center of the blade will make the blade (or wing, or tail feather) unstable. McCutchens tend to "balloon" in updrafts as a result of tail-heavy balance.

Because of the weight problem, composite blades may end up more limber than metal ones. This adds to the blades' tendency to twist the wrong way when their angle of attack changes.

These issues may have been beaten to death in past go-arounds. If so, forgive my repeating them here.

[quadrirotor]

As you know, Doug:
"the whole art of pedagogy rests in repetition..."

[Aussie_Paul]

Doug, the blades are balanced at the 25% mark. Robs standard blades, with the 8H12, are balanced on the 25% point and leave the McCuchens well behind for stability. Very stable and very smooth.

I understand what you say about the balance point of the blade, and the unstable ballooning of the McCuchens. I trained with both 25' (200 hours) and 27' (1300 hours) McCuchens. Rob greatly improved them with the balance point and the manufacture accuracy.

What we are trying to do, of course, is to pick up some efficiency, meet a minimum pitch stability standard and to keep the blades extremely smooth. It is a tough call, but you don't know if you don't have a go. :) Rob is busy building a house at the moment. Hopefully it won't be too long before we get on to the next stage.


Aussie Paul.

[Doug Riley]

Paul: Good on the balance issue. Selection of airfoil and determining how much you can cheat on the requirement of zero pitching moment (assuming you use a cambered foil, not a symmetrical one) is the other basic stability task. Sounds as if that's what you were doing by adding small amounts of reflex post-construction.

Pitching moments of specific airfoils (with and without various amounts of reflex) can be calculated using computer programs. Reflex, of course, adds trim drag and adds no lift, so it's undesirable from the efficiency standpoint. How much you can cheat without hitting RPM instability will depend on the blade's torsional stiffness. I suppose you know all this.

Interestingly, it's common in designing sailplanes to employ high-moment airfoils (drooped trailing edges) and NOT to balance out the moment with tail down-load. (In a conventional airplane, tail down-load is the equivalent of reflex on a tailless wing such as a rotor blade). Instead, to balance the nose-down pitching moment, a very aft CG location is used. One little sailplane I know uses a CG location that's more than 40% of the chord. The results are (i) less drag, but (ii) an aircraft that's statically unstable in pitch with respect to airspeed. That's because the pitching moment of the wing varies by the square of the airspeed, while the balancing moment created by the aft CG doesn't vary at all. There's only one airspeed where they cancel each other out, and any departure from this one airspeed will get larger and larger unless the pilot corrects. This is not at all what we want in a rotor blade, since we have no way to "correct."

So I'd be careful about shaving off reflex to improve performance.

[darrellwittke]

I've been busy the last two days and just got back. Your post is very informative and well-spoken.

Too bad about the VR-7 pitch instability as I would sure love that high lift-slow flight capability. I have a feeling you will have a very good market for your 8H12 blades and kudo's to your composites man, Rob Patroney, for evidently doing an excellent job on what must be a very demanding and difficult task.

Thanks again for the info. Darrell Wittke

[Aussie_Paul]

Darrell, the stability is only an issue for inexperienced gyro pilots. Anyone who has gone solo in a gyroplane would not even think about the fact that they were not as stable.
It is exciting stuff that we are doing. I don't seem to get much support from my own country though.


Aussie Paul.

[Aussie_Paul]

Thanks Doug.

Aussie Paul.

[Chopper Reid]

Paul, the mustering blades that you are talking about, are they the ones you were flying on at Avlon ??

[Aussie_Paul]

No Brian, at Avalon I was flying a Raf with an effective stab. better than a stabdard Raf but not a patch on Hybrid.

Aussie Paul.:)