Warbird Information Exchange

Just a few aviation questions I have. Please be patient with the new guy.

What does it mean to have a feathered prop? And a runaway prop?

And why were German WWII fighters painted with the spiral on the spinner? It would seem obvious that it was turning with all the noise and exhaust and wind.

I'm sure I can come up with others, these are the ones that were bothering me today. Thank you in advance.

on constant speed props you can adjust the blade angle so the blades are facing fore and aft. This used primarily after a engine failure to decrease drag. Without doing so is like throwing out an anchor. Runaway prop is a term used to describe loss of control over a contant speed prop.

It's cool and probably scares the cr*p out the the guy your shooting at!
Over to the experts......................

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Correct me if I'm wrong, but don't you feather a prop when the engine stops? Feathering turns the blades perpendicular to their normal position during flight. This turns the narrow side facing the direction of flight so as to reduce drag from a non-working engine.

As for the German aircraft... I could be wrong, but I always heard that it was just kind of a "neat" thing to do. I guess it looked cool while flying? I've also heard it was similar to that of the Flying Tiger's shark teeth.

Here is a C-130 with a feathered prop (I know it is a bad pic, but it was the first one I found)

I believe that explains it well.

Thank you gents...

Popular theory is that the spiral spinners helped to thow bomber gunners off their aim.

Dave

I don't know why the Germans did it, but some of todays airliners have a spiral, known as a helix on the spinner to discourage bird strikes.

I thought it was the make the drunks in the terminal get dizzy and fall over.

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Don't touch my junk!!

on todays jet engines, I thought it was more cautionary.....used to let ground crews know that the engine is running when they see it spinning. I believe this is right cause all your high mounted engines dont have this.

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And then there was Cook Cleland that painted one blade of his air racing Corsair white so it looked like it was turning slower than it was....Threw the others off!

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I am a citizen of the Air

I read somewhere that the spinner "Decorations", were unit identification. Helped other guys in friendly units identify you.

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on todays jet engines, I thought it was more cautionary.....used to let ground crews know that the engine is running when they see it spinning. I believe this is right cause all your high mounted engines dont have this.

I'm going to have to agree--as someone who drives past them every day, we live by that and the anti-collision light

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I agree with Dave.

I think the spiral marking on the spinner was meant to made it harder for the enemy to properly judge the speed of the aircraft to "lead" it in gunnery. Doesn't the spiral make it appear that the aircraft is moving more slowly?

I've also got a Warbird question to piggyback onto this thread.

Please tell me what that boomerang on the tailplane of P-38's does. I've read that it's a "mass balance horn", but a Google search didn't help me. What's it for?

It's the counterweight for the elevator. There are several different types of counterweights. Some are like the P-38 elevator where they hang lead "balls" off the end of a rod, positioning the weight forward of the hinge line. Some may not use an actual weight, but simply use the design of the surface to make the appropriate counter balance...such as on the rudder of a Piper Cub. Many surfaces, such as the ailerons on Mustangs, Mosquitos, B-29's, etc., have a weight arrangement built in to the leading edge of the surface. Every manufacturer has a different way of counteracting control surface high speed flutter. You could start a whole new thread on the "hows and whys" on that subject though.

Hope that helps.

Gary

Thanks, Gary. I get it.

To better answer the second question of the original post, a runaway propeller constitutes an overspeed (rpm) condition. A large majority of WWII mutli engine airplanes sport a Hamilton Standard propeller hub such as a 23E50. Should the cable that connects the propeller control lever break, the RPM should go to approx. 2200 RPM and remain there. Should the speeder spring in the governor ( this unit controls the oil flow used to moves the blades) fail, the propeller should move to high pitch(low RPM - about 1200 RPM).
A runaway propeller is a propeller that due to a combination of either engine oil pressure and centrifugal twisting moment has gone to such a low pitch (highRPM) that the feathering pump (auxillary electric pump to move oil thru some valves to the inside of the propeller hub for blade movement to the feathered position) cannot overcome the low pitch forces to bring the propeller to a higher pitch (low RPM) or feathered position.
I started out thinking I could simply explain this but...
Some later hubs such as the 43E60 had internal cams and valves that moved or opened and whem rpm reached a certain threshold say 3100 RPM, the prop became "fixed pitch" and could be controlled with the throttle.
The only method used to help maintain a runaway propeller rpm is to always reduce the throttle (even though the prop is independent) and to pitch the airplane to a high angle of attack to attempt to place a greater air load on the blades in an effort to maintain RPM or retard it.
I've never had it happen but a friend of mine flying a PB4Y-2 had an overspeed on #4 while on departure one day. He had his hands full nursing the airplane around the pattern to a successful landing, with the propeller still intact. The reason for which this happened is too much to explain here for the small percentage of readers that would understand these types systems.