Wooden Helicopter blades?

[wierdscience]

Intresting strobe effect in this video-

http://youtu.be/OYqE6EqU84Q?t=3m30s

[wierdscience]

Still "guv'mint" interference...... it it was viable, it would stand on its own with no university nonsense.....

Slave labor Jerry

[Thruthefence]

Lazlo; I'm not aware of any aircraft propellers made for certificated aircraft, manufactured of carbon fiber. Doesn't mean they aren't in the pipeline, just that the certification rules, continuing airworthiness programs, and cost competitiveness in the marketplace haven't come together.

Regarding the venerable Bell ne Scott 47, I understand there is a composite blade coming to market for it.

I got a chance to look at an ex Soviet bloc Mi-24 "Hind" at the heli-Expo this spring, up close, hands on. I was amazed at the combination of crude bodge & watchmaker-like workmanship, in the same package.

I also noted, the Horizontal stabilizer, which appeared to be trimmable, was of "dope & fabric" construction. Like a damn Piper Cub! A very formidable Gunship.

And to think Rambo shot one down with a Bow & Arrow!!

[Evan]

If those blades are built the same as the Huey they have a high alloy full height steel spar at the 1/3 chord point. It is very springy and also acts as a bullet firewall to help prevent catastrophic damage from firearms and trees. There is a cockpit video online of a military pilot flying some type of military helicopter and he hits a tree. It vibrates like crazy but still stays together until he manages to land.

[philbur]

A bit more here though:



Phil

Doesnt seem to be much bending stress here!

[Evan]

But isn't carbon fiber superior in almost all categories, except for fatigue life?

Carbon fibre composite is wonderful, until it isn't. It has a nasty tendency of failing catastrophically with no detectable or inspectable warning. That is why the FAA requires a 2 times design safety margin for carbon composite and only 1.5 for wood and aluminum. That negates most of the weight advantage of carbon composite.

If anybody can come up with a reasonable way to reliably inspect carbon composites on site and in situ they will make a billion dollars.

[dalesvp]

New Blades

Nice! $13,500 for a rebuild sounds like a bargin for what parts cost now.Are they still making new blades?

I do not believe anyone is making new blades. A rebuilt blade is certified to be "as new" and they do last for years of normal use. The big enemy of wood rotor blades is not use, rain or age; it's trees!

[lazlo]

There's not a better material out there then wood, for building airplanes. The latest-greatest "high tech" props are wood.

http://www.steenaero.com/Products/propellers.cfm

I'll preface this by saying I don't know d!ck about aeronautical design, but that doesn't seem to matter here

That link compares wood versus aluminum props, and the comparison table makes perfect sense to me: wood having superior moment of inertia and vibration damping. But isn't carbon fiber superior in almost all categories, except for fatigue life? All the ultralight human-powered aircraft are carbon fiber, and my model aircraft friends use carbon fiber props.

I'm pretty sure all modern military helicopters use carbon fiber/composite rotor blades -- I know the Apache does, and the rotors are rated to survive a direct hit from a 20mm shell and continue flying...
The Hind uses aluminum honeycomb, but that's a Vietnam-era design.

[A.K. Boomer]

Doesnt seem to be much bending stress here!

Right -- now try stopping the blades and supporting the entire copter by the stagnant blades ----- depends on the material - take your pick - snap - or bend...

remember -- the outer parts of the blade are where the majority of the lift work is being done (due to higher tip speeds) so you don't get to grab the props close to the hub and call it good -- u actually have to grab it more out at outer parameters and a little inboard as well - snap - crackle - pop

[J Tiers]

Nope,paid for by industry,staffed by university,establishes data points for products already in developement.

None of that slopping tax money to companies who don't have a worthwhile product like is all the rage these days.

Still "guv'mint" interference...... it it was viable, it would stand on its own with no university nonsense.....

[Evan]

Same with trying to suck the last little bit of lift to avoid a hard landing on an autorotation.

[Thruthefence]

Raising collective pitch before the rotor is below operational rpm induces extreme bending loads in the blades, (eg, "coning"), leading to failure of the blades. The centrifugal force adds considerably to the ability of the rotor disc to lift the aircraft.

And if you look at a bell 47 rotor head in profile, you will see that there is a bit of "pre coning" built into the assembly. On a bell 206, it's a little more obvious. It's analogous to dihedral in a fixed wing aircraft.

[The Artful Bodger]

Doesnt seem to be much bending stress here!

[philbur]

On reflection I think you may be correct in that the stress due to the angular velocity has a tendency to reduce the bending stress due to the weight, but nevertheless the two stresses are additive and the sum is always greater that each individually on the lower side of the blade and always less than the sum on the upper side of the blade.

Phil

Im not so sure your correct on that

[wierdscience]

Years ago I worked on '47 and Hiller blades, they are wood with a metal spline down the middle, metal leading edge, laminated spruce spar, trailing foil made of balsa. The older blades were finished with varnish which was recently (1990s) upgraded to West Systems marine finish. Here is the company still in business:

http://www.tulsarotorblades.com/

Photos of the blade repair processes and tooling:
http://www.tulsarotorblades.com/pics/pics.html

Nice! $13,500 for a rebuild sounds like a bargin for what parts cost now.Are they still making new blades?