WW2 propeller question

[skooterN2767K]

I have noted that several WW2 fighters including some Spitfires, Seafires and the Fw190D used wooden propellers. I heard Kermit Weeks state that the Spit had some tourque issues and the lighter wood prop helps reduce torque due to the effects of a lighter flywheel. Is this correct? It seems to make sense. I know the Germans were short on metal also, but were they also reducing torque effects as well? I know Mauser was using glass reinforced plastic stocks on the Gewer K43 rifle , so the tecnology was available for them to make composite blades. I believe the German prop blades were covered with fabric and or fiberglass. Did the JU88 also have wood blades?? Any other allied fighters?? Also interesting is the shape of the FW 190 prop blades. It seems maybe they had it right and the MT, Whirlwind and Hartzell claw props seem to be close in shape. Thanks! BTW, my ww2 german airplane hating friend just bought a Bucker Jungman !!

[bdk]

The higher the mass in the blades, the farther out towards the tip the mass is concentrated and the faster the blades rotate, the higher the polar moment of inertia. The higher the polar moment of inertia, the greater the forces of gyroscopic precession. With a tractor configuration the forces are destabilizing, requiring larger tail surfaces. Also, with higher forces the engine mount needs to be stronger. Those are the primary dynamic concerns. Naturally you have weight and balance to think about as well. Lighter is always better as long as you can achieve the required strength. Look at a wooden Stearman prop vs. a metal one though, and you can guess which one is more aerodynamically efficient due to the blade thickness. Once you balance all these tradeoffs and optimize the design, you'll be all set!

[Matt Gunsch]

a further advantage of the wood props is in the event of a prop strike, the damage is usually confined to the prop and does not require a engine teardown.

[bdk]

I heard Kermit Weeks state that the Spit had some tourque issues and the lighter wood prop helps reduce torque due to the effects of a lighter flywheel. Is this correct?

No. Torque is reacted by the "bite" the prop has on the air (the prop's resistance to rotation). The weight of the prop has no effect on torque. The weight of the prop does have an effect on how quickly the engine can change RPM though.

[skydaddy61]

I heard Kermit Weeks state that the Spit had some tourque issues and the lighter wood prop helps reduce torque due to the effects of a lighter flywheel. Is this correct?

No. Torque is reacted by the "bite" the prop has on the air (the prop's resistance to rotation). The weight of the prop has no effect on torque. The weight of the prop does have an effect on how quickly the engine can change RPM though.

Well, yes and no. A lighter prop *will* have a lower moment of intertia, resulting in lower gyroscopic forces (which are usually lumped in with "actual" torque as "those forces which requires a bootful of rudder to correct on takeoff or in slow flicght")

[muddyboots]

what is this? Teach muddy to fly week?

[retroaviation]

I don't know about you, muddy, but there are just too many words in this thread for me to understand.

When talking about "torque," this is a picture that always pops into my head. It was taken by my good friend (and fellow WIXer) Neal Nurmi, moments before the Rare Bear blew the engine in 1992. Check out the wrinkles in the fuselage and the paint lines where the cowling and fuselage meet. Now THAT is torque!




Gary

[bdk]

I don't know about you, muddy, but there are just too many words in this thread for me to understand.

When talking about "torque," this is a picture that always pops into my head. It was taken by my good friend (and fellow WIXer) Neal Nurmi, moments before the Rare Bear blew the engine in 1992. Check out the wrinkles in the fuselage and the paint lines where the cowling and fuselage meet. Now THAT is torque!

Gary

OK, more words for Gary...

The engine cowling is clearly displaying torque (from the deflection in the engine mount isolators I'd guess). That torque is easily reacted by an ever so slight aileron deflection at speed. The wrinkling of the fuselage, if sustained, is buckling of the skin from the download on the horizontal stabilizer which puts those skins into compression and causes them to buckle. When the skins buckle like that the load gets transferred to the adjacent longerons.

[skooterN2767K]

Thanks for the input guys! I've been arguing with a guy that "doesnt believe there are any ww2 german engines left in runnable condition" He foolishly believes every DBenz powered ME 109 flying has a Allison or RR Merlin modified to mount inverted!! He certainly doesnt think the engine in the FW190D13 "Yellow 10" is an original engine. Does anyone know how many Jumo 213 engines are currently runnable? I know there is at least the one in Yellow 10, and a D9 that Claus Colling (FLUG WERKE) restored (not being confused with the new built d9 with the allison) and that there are 2 or 3 Ju88s currently being restored to flyable condition.

[skydaddy61]

When I was with Pond's outfit in MN in the 90's, one point of the speil about our Mk XIV Spit was that the wooden blades were ironically only available from a German manufacturer.

[The Inspector]

Another thing to take into account was the AXIS' critical shortages of strategic materials from the middle of the war until the end, hence BUNA rubber for tires, synthetic oils, lubricants, and fuel derived from coal. If I, as a strategic planner can utilize the aluminum consumed in making a propeller into manufacturing thinner sheet for wings and fuselages, I'll get by with wooden propeller blades which have the added benefit of usually breaking off or failing in an easier manner in a nose over, gear collapse, etc without damaging the engine block or crankshaft.