I posted a reply to an article on May 1st and an interesting point was brought up that left me with a question that hopefully someone can explain.
Is there an airspeed at which a rotating prop produces less drag than a stationary prop?
Explain the relationship if you would between airspeed and drag. I know a prop is a rotating wing. I know that as airspeed increase the drag increases by a larger factor. But I do not understand the relationship between a rotating wing, airspeed, and drag. So someone with a PhD. in astro, quantum, Micro, or any other prefix you can apply to the word aeronautics, help a mechanical based engineer understand. (Use small words if you feel it necessary).
This question does not apply to Multi-engine configs…only to SRxx’s or the alike.
FWIW Mr. Woor brought up a good point with the diesel engine configuration. Just how big is the battery going to have to be to start this thing?
I think you answered your own question. No the component of drag for a prop at any given pitch is the same whether the prop is spinning or not.
The only difference is a stationary prop produces no thrust to compensate for the component of drag. So now we come to what I think is the heart of your question–does a windmilling prop produce more or less energy than a locked prop at the same pitch? No–it takes energy for the relative wind to rotate the prop (albiet prop drag remains constant). However, once the prop has momentum the component forces tend to counteract or equalize. But, as the prop windmills we have to add the energy required to rotate the prop and its connected components, thus, we may derive the following simplified expression:
E = T - (do + dp + dr),
where E is available energy, T is thrust, do is other drag, dp is prop drag, and dr the energy required to rotate the prop. Therefore, where T is 0 then E will always be negative, and where dr is 0 then E will be less. Of course this is something of an over simplification.