Question for the pro's

[Leo]

Re: Question for the pro's

FYI an engine that rotates around a stationary crankshaft is a rotary, not a radial...
The P-38 propellers rotated away from the center nacelle for two reasons as I understand it. The first was turbulence and down force on the tail, the second was to use the inherent torque to help pull against a dead engine on the opposite wing, reducing the tendency to roll in an engine out situation, especially at lower speeds.
Len Morgan said in his Mustang book that it had extreme torque issues at low speed power applications. When training he was told to go to altitude, put the plane in landing config. and speed, then pour on 60". He said one lesson was enough.

Leo

[Unregistered]

Re: Question for the pro's

Leo is right the Len Morgan book is a good read, if you can find it. I sat listening to Pete Law talk ing one night at a party, he was talking about a conversation he had with Kelly Johnson. Kelly told him originally the rotation of the engines on the P-38 was opposite what they were in production, it seems the first time they tried to fly it it couldn't generate enough lift to fly the rotation was interfering with the necessary lift by masking the wing. As an interesting aside the P-82 guys had a similar experience and found the opposite mixing of rotation side to side to their benefit. Their used to be some great Crab boils in SoCal. Hey we should ask Darryl about the RB-51 tail surface, I remember he was the one instrumental in the final configuration.
John Slack

[First time Juke]

Re: Question for the pro's

On Griffon engined airplanes their counter rotating propellers eliminate torque. But if you look the Red Barron, Precious Metal, and Miss Ashley II with the torque eliminated why do they have such tall vertical tails? I heard they have a tendency to fly sideways. Is this true?
Jarrod

I think the slipstream created by Red Baron is so turbulent that a small rudder just wouldn't be effective...the one prop stream is a "clean tornado" around the fuselage.

I don't think a Precious Metal would go quite sideways, but just a few degree changes could make one feel pretty uncomfortable I bet.

JT

[First time Juke]

Re: Question for the pro's

I don't mean to hi-jack the thread, but wasn't there a radial engine built during WWI where the ENGINE rotated? I seem to remember it had trouble turning because of the huge gyroscopic effect of all that rotating mass. Anyone know more about this?

The engines had no throttle either..they cut the engine to get the rpms down. Here is a caption from the movie about Swedens first female pilot..Elsa Andersson.

[Leo]

Re: Question for the pro's

Another great book is Caidin's "Fork Tailed Devil", a lot of good info on the P-38 development.
Did Dreadnaught reguire a taller rudder to increase stability? I know she has one, why?
Also Darryl increased the size of conquest's after his record attempts. A
Is the need for increased area based on speed or power? Is it for more sticking in the wind or better rudder authority?
Inquiring minds....

Leo

[Peashooter]

Re: Question for the pro's

Another great book is Caidin's "Fork Tailed Devil", a lot of good info on the P-38 development.
Did Dreadnaught reguire a taller rudder to increase stability? I know she has one, why?
Also Darryl increased the size of conquest's after his record attempts. A
Is the need for increased area based on speed or power? Is it for more sticking in the wind or better rudder authority?
Inquiring minds....

Leo

This article reveals the answer. It'll raise the hair on the back of your neck! http://www.warbirdaeropress.com/arti...readnought.htm

[stuntflyr]

Re: Question for the pro's

Hi,
I did make a mistake and write counterclockwise from the cockpit, I meant clockwise of course.

Also, Steve gives a good summary of torque himself, and is quite correct about the rigging of racers especially.

Fast Flyin Female engineer, the adverse yaw term is for an aerodynamic effect caused by the drag of down aileron yawing the airplane in the opposite direction of roll. The rudder is used to correct this. The torque effects are the only forces that will be felt in the airplane by any longitudinal rotating masses in the engine. They are probably there, but minimally effective.
P-factor is a term used to describe the effect of the descending blade having more thrust than the ascending blade with a positive AOA. P is for pitch of the prop, at least back when I was taught to fly. You seem to have a lot going on, just some terms in the wrong places.

This is a good thread, John I didn't ever hear or read the P-38 prop rotation/lift problem story. Very interesting. I did hear that the center mounted mass balance was unnecessary. I'm still jealous that you got to ride with Lefty when we were kids.

Hope to see you all at the race.

Chris...

[stuntflyr]

Re: Question for the pro's

I just confered with an old race pilot about the terminology of propeller forces. His take is that the term P-Factor, refers to ALL of the forces acting upon the airplane caused by the propeller.

In other words, it would mean torque, descending blade thrust assymetry, slipstream effect, and more. Even drag on the left tire will be more than the right, so this would be lumped into P-Factor. Effects of the propeller.

In that an airplane has other effects from the prop, like gyroscopic procession, acting upon it could also be P-Factor.

The increase in dynamic mass from adding a larger propeller, especially in the case of Precious Metal or Red Baron, can also be termed P-Factor. This is the case where area aft of the cg needs increased because of the increase in effective keel area ahead of the cg caused by the larger prop mass.

Chris...

[AAFO_WSagar]

Re: Question for the pro's

I just confered with an old race pilot about the terminology of propeller forces. His take is that the term P-Factor, refers to ALL of the forces acting upon the airplane caused by the propeller.

In other words, it would mean torque, descending blade thrust assymetry, slipstream effect, and more. Even drag on the left tire will be more than the right, so this would be lumped into P-Factor. Effects of the propeller.

In that an airplane has other effects from the prop, like gyroscopic procession, acting upon it could also be P-Factor.

The increase in dynamic mass from adding a larger propeller, especially in the case of Precious Metal or Red Baron, can also be termed P-Factor. This is the case where area aft of the cg needs increased because of the increase in effective keel area ahead of the cg caused by the larger prop mass.

Chris...

Chris, it's not rocket science (prop art) but I'm not sure rocket science might be a bit easier to master... ya think??

Wayne

[FlyinLo]

Re: Question for the pro's

Chris, it's not rocket science (prop art) but I'm not sure rocket science might be a bit easier to master... ya think??

Wayne

You're right, props aren't rocket science, they're BLACK MAGIC. When was the last time you saw a racer that was able to accurately predict the performance of a new prop? I sure can't, and I've got a stack of props in the hangar to prove it! And that's not even counting the one the prop guy figured was so bad he couldn't charge me so he kept it and mounted it over his fireplace

[stuntflyr]

Re: Question for the pro's

It is all a bit of art and magic, isn't it? The fixed pitch stuff is definitely hard to predict. I might have a racing prop made for the Pitts, I hope it is a good guess!
Chris...

[jarrodeu]

Re: Question for the pro's

Art Magic and Luck

[Unregistered]

Re: Question for the pro's

Prop guys that accurately reflected a props performance. Carl Friend in regards to the Rare Bears Three blade. Which was designed for use in level flight. Now we will see if Bruce boland was right about the four blade and it's effectiveness.
John Slack