Prop drag

[Lister Noble]

This question has cropped up from a motoring/engineering forum regarding an experimental vehicle travelling faster directly downwind than the wind speed.
With a fixed pitch prop,whilst gliding,would there be more drag "freewheeling" or prop stopped.
I know that the prop is directlyattached to the crankshaft on most aircraft and most will not freewheel,but if it was disconnected from the drive,and could freewheel?:)

[DERG]

same in both ..same drag..I thought Jane DoH already asked this question?

[Checkboard]

There is less drag with a fixed pitch rotating prop - whether "free-wheeling" or connected to an engine (obviously more drag when connected to an engine) - than with a stopped propeller.

[3 Point]

Is the engine running or not? ie is the engine burning fuel and turning the prop at a low, non thrust producing RPM or is the engine not burning fuel but being driven round by the wind flowing through the prop?

In the latter case then the energy to rotate the engine is coming from somewhere; specifically some of the potential energy released by the aircraft's descent is being used to drive the engine round. This will show up as steeper glide angle ie a worse L/D ratio; the extra drag because the energy has to come from somewhere!

I agree with Checkboard; engine driving a non running engine produces more drag then a stationary prop.

Happy landings

[Rogal]

On Piper Cub and C150, 152, 172 (turned off) engine can by driven by air flow - in that case drag is much more higher. During my basic trainning instructor was turning off the engine when he could. In order to get better L/D in an emergency I was teached to slow the plane and stop the propeller. My last proficiency check was performed with another FI - he didn't turn off the engine, only idle the throttle. I didn't make it to the runway...by a bit. I'm almost sure that with stopped propeller it was possible.

Sorry for my poor English, lot of work have to be done on it ;)

[Lister Noble]

YouTube - Prop Drag Test Movie (http://www.youtube.com/watch?v=jI-UG9RSlJo)

I think this video answers the question over static or freewheeling prop.:)

It doesn't matter if it's in water or air,effectwill be exactly the same