Aerodynamic question

[pembquist]

I think prop drag depends largely on the AOA (angle of attack) of the prop. I really don't think the drag or torque would be significanltly different for a spinning vs. frozen prop. Whether or not the prop is spinning torque and drag will still exist (unless the prop is disengaged from the engine). If the prop is spinning all that means is some energy is being converted to heat inside the engine block  (from piston rings rubbing against the engine block). If the prop is not spinning then ur basically converting energy into heat at the prop (and not in the engine). One can think of friction as converting some type of energy into heat, in this case that would be the forward momentum of an airplane.

Don't forget about the compression of the engine.

[drgondog]

In either case, the area of the props represent pretty close to flat plate drag from stagnation pressure on the blades themselves.  That is why multi engine SOP was to feather the prop immediately.

For a single engine a/c (like a Mustang) the flat plate drag of that big Hamilton Standard prop is purty near as much as the Total Drag on the airframe.

[hitech]

smoe, you are missing the increased air flow over the prop do to it's rotation. This is causing most of the drag on the prop as it spins, not the engine.

HiTech

[Zeagle]

And that drag is caused by aoa of the blades. Faster spining prop has more of the blade area presented to the wind than feathered. But  if pitch is the same for both stationary and stopped, the stopped prop would have more drag because the blades would be stalled.

You dont get something for nothing. The only thing driving that prop is airflow.

[earl1937]

A frozen prop(unfeathgered) does not create as much drag as a spinning one.

You sir, are correct! A wind milling prop presents a drag coefienct equal to the diameter of the prop. A prop which is not wind milling only presents the phyiscal width and length of the blade for drag. Guess there is not much use in trying to explain "beta" range in turbo-prop driven aircraft, who have to make a emergency decent. (like the Beech Kingair).

[hitech]

And that drag is caused by aoa of the blades. Faster spining prop has more of the blade area presented to the wind than feathered. But  if pitch is the same for both stationary and stopped, the stopped prop would have more drag because the blades would be stalled.

You dont get something for nothing. The only thing driving that prop is airflow.

This is NOT correct Zeagle.

HiTech

[Zeagle]

Yeah i think you are correct ht. ... The lift from the moving blades makes the difference.

I stand corrected 

[Hajo]

When the engine quits I just set RPMS down to 0.

[icepac]

Try gliding the typhoon with a windmilling prop. and with it stopped.

That said, it's pretty hard to get some props stopped in game with some windmilling down to 30mph.

[R 105]

 I have fond in the P-51D by hitting the minus key 3 times once you are at about 400+ mph in a dive that the pony picks up speed and stays fast for a long way. Even if you are being chased by another 51 with wep on you will still out pace it and have all your wep if you need it later. Does that count as feathering the prop ?

[MK-84]

I have fond in the P-51D by hitting the minus key 3 times once you are at about 400+ mph in a dive that the pony picks up speed and stays fast for a long way. Even if you are being chased by another 51 with wep on you will still out pace it and have all your wep if you need it later. Does that count as feathering the prop ?

No that counts as making no logical sense.  And engine running at less than full power is not going to to provide as great an acceleration as one that is.

[icepac]

Makes total sense.

The prop speed and angle are not condusive to propelling the plane over a speed of 500mph but a feathered prop. will allow a plane to exceed that speed in a dive.

[Slade]

Wow what a cool post.  My brain hurts though a bit.

Just to clarify for my small brain, is this true or false: Leaving engines on and at idle produces more drag than an idle prop so the plane will slow down faster than having the engine off.

[colmbo]

Makes total sense.

The prop speed and angle are not condusive to propelling the plane over a speed of 500mph but a feathered prop. will allow a plane to exceed that speed in a dive.

You'll need power to reach 500 mph even in a dive so feathering the prop would slow you down -- real world.

[100Coogn]

Ever see one of these fall out of a tree?
If it doesn't spin, it falls fast. (no drag)  When it spins if falls slowly. (drag)

Coogan