Aerodynamic question

[MK-84]

What produces more drag?

A single engine prop with the prop windmilling or stopped (not feathered)

and why?

[DanielTS]

Windmilling i would guess, as you are making the wind rotate the propeller and essentially power the engine as well, as the spinning prop will set the engine in motion. On the other hand, if the propeller is stopped, it only causes drag based on its surface are, not based on setting a heavy motor in motion. In game this is supported by your plane decelerating faster if you turn the engine off but keep rpms high than if you turn the engine off and lower the rpms.

[icepac]

I've noticed that some props won't stop windmilling even when you're straight up and your airspeed is 11mph.

[hitech]

Windmilling produces a significant amount of drag. The reason is that since the blade is turning,the air it is traveling faster over it's surface. And drag is related to the square of the air velocity. Also as the prop speeds up it produces lift, when it is driven by the engine the lift is due to the AOA is pulling the plane along. When the engine is not producing positive torque, the air is now driving the prop from the other side and producing a negative AOA on the prop blades, and hence it is producing lift opposing the direction of travel.

It is easiest just to think of in terms of total energy. It obviously takes energy to turn a prop, that energy comes from the air/momentum of the aircraft.

HiTech

[Shuffler]

Windmilling produces a significant amount of drag. The reason is that since the blade is turning,the air it is traveling faster over it's surface. And drag is related to the square of the air velocity. Also as the prop speeds up it produces lift, when it is driven by the engine the lift is due to the AOA is pulling the plane along. When the engine is not producing positive torque, the air is now driving the prop from the other side and producing a negative AOA on the prop blades, and hence it is producing lift opposing the direction of travel.

It is easiest just to think of in terms of total energy. It obviously takes energy to turn a prop, that energy comes from the air/momentum of the aircraft.

HiTech

The lack of misspellings in this post is worrisome. I'm concerned something has happened to HiTech. Tonight I will play AH backwards to see if I can find out.

SOMEONE SAVE THE WALRUS!!!!!!!

[jollyFE]

someone needs to check under hitechs bed for a seed pod

[GScholz]

Windmilling produces a significant amount of drag. The reason is that since the blade is turning,the air it is traveling faster over it's surface. And drag is related to the square of the air velocity. Also as the prop speeds up it produces lift, when it is driven by the engine the lift is due to the AOA is pulling the plane along. When the engine is not producing positive torque, the air is now driving the prop from the other side and producing a negative AOA on the prop blades, and hence it is producing lift opposing the direction of travel.
It is easiest just to think of in terms of total energy. It obviously takes energy to turn a prop, that energy comes from the air/momentum of the aircraft.
HiTech

If the engine has seized with the prop unfeathered wouldn't the prop just try to turn the whole plane and expend just as much energy generating torque?

[gyrene81]

If the engine has seized with the prop unfeathered wouldn't the prop just try to turn the whole plane and expend just as much energy generating torque?

   

[Hazard69]

If the engine has seized with the prop unfeathered wouldn't the prop just try to turn the whole plane and expend just as much energy generating torque?

Actually it does. Of course with absolutely no success (you'll never see the plane rotate, too much lateral stability to overcome for such a small force). It ends up expending energy as drag.
After an engine seizure, with prop unfeathered though, you are pretty much out of options and are just going to have to live with the added drag (which will be significant). In the event of a oil/radiator hit, monitor affected parameter closely and feather then shutdown the engine before it seizes.

[icepac]

A frozen prop. won't try to roll the plane because it is stalled.

It would probably impart more roll when fully feathered than at fine pitch.

[pembquist]

 Do the props on the multiengines in game feather? Wait, what is the damage that lets your prop windmill other than running out of gas?

[GScholz]

A frozen prop. won't try to roll the plane because it is stalled.
It would probably impart more roll when fully feathered than at fine pitch.

Makes sense. Thanks 

[hitech]

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

[Hazard69]

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

True, I was just saying that a frozen unfeathered prop will create more drag than a frozen feathered one.

[smoe]

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

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.