Warbird Information Exchange

I wonder if Paul Sr. of American Chopper will jump in as another way to use his extensive machine shop on cable television.

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"Take care of the little things and the big things will take care of themselves."

Interesting question. In most cases wooden or composite props are lighter than metal ones. In some aircraft it only means a difference in the weight and balance envelope. If they want to avoid any problems in that area I would think they could add weight, probably lead, to the blades. Most controllable pitch blades whether aluminum or wood/composite have a pocket milled into the base to which weight can be added anyway in order to bring all the blades to the same weight. So if the new composite blades have that feature it shouldn't be too hard to make it large enough to add enough weight to duplicate the original weight of the metal bades.

I would think harmonics and vibration would be another challenge as well but given the experimental category the P-82s will be operating under I would think that there would only be a basic examination of that parameter. They would probably mount the propeller in a fixture and induce vibrations for some period of time and at different orders to see what happens. There is a video of a metal fixed pitch prop being tested and it is amazing to see how much it flexes during a third order vibration test.

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"I can't understand it, I cut it twice and it's still too short!" Robert F. Dupre' 1923-2010 Go With God.

Don't forget also that the right engine on the P-82 rotates in the opposite direction.

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The more I learn about aircraft, the more I realize I still have to learn.

Are they Wood or Composite?

I have an old Composite blade here in my living room, so I understand the idea of it being a steel shank and a wood blade.
But, MT builds composite propellers for aerobatic airplanes and the like that are new composite materials.

Remember the Cheyenne 400LS with the huge plastic blades, Chuck Yeager set a time to climb record in one.
They have a spar that runs out to about 11 inches from the tip of the blade, apparently you can tear that much off and not have
to do any type of engine work, from what i heard. The blades were getting very scarce for a while, dont know if that has changed.
A customer of ours sold his spare blades just before catching a taxi light with his own. The hunt for new ones took a while.

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Good question, but probably not. Wood props have much better harmonics than metal props, and are much more fatigue resistant. I would think if you were going from an installation where the wood prop is standard and trying to switch to metal, you'd be much more likely to have a problem than a metal -> wood conversion.

The only exception is the flywheel issue. A metal prop acts like a big 'ol flywheel. On some engines, that might be important. Dunno about the Allison.

Speaking of which, I can't think of any "stock" Allison installations that would have used a wooden prop. Anyone want to throw one out there?

Don't forget that the British and Germans used variations on "composite" blades during WWII. Rotol "Jablo" blades were made of compressed wood and they also used Douglas fir and spruce. VDM used wooden blades also, and they all seem to have worked just fine. I'd guess that the new composite blades should pose less of a problem in the areas of vibration and harmonics than metal.

Scott

The polar moment of inertia is less with a wood or composite prop, so the gyroscopic forces are less. This is a primary factor in the structural analysis of engine mounts. Should result in better handling too, although how much it would be noticed is the question. Composite blades are also much stiffer than aluminum which raises the resonant frequency significantly. Composite materials are very fatigue resistant- more so than metal if designed properly.

I just can't wait to see the Bob Hoover Shrike act done in a P-82 with both props feathered!

Can anybody in the Hollister area confirm that the G-6 engine from the Minn. P-82 is actually in Polar Bear? I hope that all the testing goes well for Reno 2011. If the testing goes well, maybe the Minn. P-82 could be ready for Reno by 2012?
Jaybo

The MT propeller blades are beechwood cores which are overlaid with composite. MT commonly makes left hand rotation propellers, for the right engine of a number of C/R aircraft (Navajo comes to mind) and also the M-14.

However, I _seriously_ doubt that Polar Bear had any engine modifications whatsoever for this test. I'm not exactly sure what would be proven by installing an ultrarare version of the V-1710, if even that was possible. If harmonics are a problem, one would need to test the entire system, which includes the airframe. I expect that the use of Polar Bear is simply an expedient way to flight test standard parts (the governor and prop hub) that will not change from one installation to another.

"Speaking of which, I can't think of any "stock" Allison installations that would have used a wooden prop. Anyone want to throw one out there?"

Some test clubs were wood.

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The engine in Polar Bear is the engine that is always in her. It is not a G-6 from the P-82. Besides everyone knows the only good part of a G-6 is already used at Reno. In Merlin engines........

We replaced the dowty rotol props on our cheyennne 400LS with certified props from MT. They are 5 blade schimitar shape.
We gained about 6 or 7 knots TAS. It seems to climb a bit better also.
The cabin is quieter inside and out.
Lost 50 lbs. over the dowty props. No rubber boots to replace, the dowtys are fairly high maintenance.
The cheyenne 400 also has props that turn opposite directions.
The only cons we have are that the aircraft does not slow down quite as good in beta.
The old dowtys are now hangar display.
We also gained about 5 inches of ground clearance.

A few people wanted to know what is happening with the P-82 in Minnesota. They are getting close to mating the fuselages back to the center section. The wiring is about 95% complete as is the hydraulics. The gear can be retracted and the flaps can be extended. The fuel controls for the Allison Engines are working very well with all of the new parts that Pat Harker has had made. As you now know the new MT propeller were put on Polar Bear the P-51A, and it worked very well.
As far as a timeline is concerned it will probably be a few more years yet before the P-82 returns to the air. Pat Harker has every intention that when the airplane flies it will be at Oskosh, and it will fly.
On a personal note back on July 4th, 1987 I had the privlege and honor of flying in Polar Bear when it was owned by Moon Spillers. I then wrote a short article on Moon and the P-51 which went into Warbirds Magazine of EAA.
There probably will be a photo essay on the Twin Mustang before long thru a guy whose first name is Max out of Minnesota.

Thanks for the info, Ed! So, I take it that with the new MT props, that there will be no modifications done to the stock P-82? Can you confirm?

There probably will be a photo essay on the Twin Mustang before long thru a guy whose first name is Max out of Minnesota.

There already is one

http://maxair2air.com/09AIR/P-82Progress2/01.html

This one b4 the other one:

http://maxair2air.com/09AIR/P-82/02.html