Originally Posted by
Captain Beaker
that's a red herring, the amount of torque to turn the engine over at say 120rpm could just as easily be applied to an engine that is stuck solid.
Page 149 of naval aviators, figure 2.19 has a good diagram that shows a wind milling propeller can produce substantially less drag than a stationary unfeathered one. Note that this is for a very course prop. The converse applies for a fine pitch prop.
This is perhaps the something 'definitive' the OP requested.
https://www.faa.gov/regulations_poli.../00-80t-80.pdf
You don't understand the text or the diagram very well at all, and apparently didn't read the text.
You don't understand drag or the energy absorbed by using the slipstream to turn a propeller, either, and no, it's nothing like "applying torque" to a frozen engine.
Go back and read Page 148 of your referenced text, Aerodynamics for Naval Aviators. It specifically discusses the necessity for feathering a propeller, and states, among other things:
It states that the parasite drag of a feathered propeller is "a relatively small contribution to the airplane total drag." More importantly, it goes on to state:
"
At smaller blade angles near the flat pitch position, the drag added by the propeller is very large. At these small blade angles, the propeller windmilling at high RPM can create such a tremendous drag that the airplane may be uncontrollable."
It's for this reason that an overspeed propeller in aircraft such as the P-3 and C-130 pitchlock and the reason that the inability to feather an engine is a big problem, and also the reason for negative torque sensing to relieve drag even on an operative engine when in a windmilling state at low power settings. Do you understand this?
ANA, same paragraph, goes on to state "
The propeller windmilling at high speed in the low range of blade angles can produce an increase in parasite drag which may be as great as the parasite drag of the basic airplane." That's
not a red herring. Read it again.
Moreover, the same paragraph continues to state: "
Thus, a propeller windmilling at high speed and small blade angle can produce an effective drag coefficient of the disc area which compares to that of a parachute canopy." Still a red herring?
Regarding aircraft control, the same paragraph states: "The drag and yawing moment caused by loss of power at high engine propeller speed is considerable and the transient yawing displacement of the aircraft may produce critical loads for the vertical tail. For this reason, automatic feathering may be a necessity rather than a luxury."