Well, for this discussion, lets assume that the device that makes the propeller go round real fast is broke. Heaven forbid that the nut behind the stick did not bring along enough fuel for that device.
Even if all you are doing is to pull the engine back to full idle, what you have is about about a 6’ diameter expanded steel plate in front of the airplane. Put an outboard propeller on a rope and drag it behind the boat. It will cause a tremendous amount of drag even if it is on s swivel. Same thing applies to an propeller on an aircraft. the flatter the pitch and the faster through the air you are moving, the more drag you have. So an adjustable pitch propeller that can be put into a high pitch condition so it rotates slower will cause lest drag than a fixed pitch propeller.
Also, on worn out training planes quite often the compression is rather low in comparison to higher powered engines and getting the plane slow enough that the compression will actually stop the prop is sometimes difficult unless you really work at it. An larger engine with higher compression like in an Lycoming IO-540 can be shut down with the prop in high pitch and a gentle stall with full flaps will allow the compression to stop the prop quite nicely. also, an increase in airspeed is less likely to start it windmilling again.
I heard a story one time about an Cessna-180 that was working at 10,000 feet above ground level and need just about all the fuel to get the job done. As it was well within gliding distance, they stayed up to finish the job. As soon as it was over, the prop control; was pulled to low RPM = high pitch position, the mixture was cut , full flaps applied and the aircraft gently stalled to stop the prop and then they played glider for a while and circled well into the traffic pattern at the airport of choice. On final the prop was moved to high RPM or flattest pitch position and the starter bumped to get it to spin enough for the air to keep it moving, mixture in and the mags hot and so there was enough fuel to taxi tot he fuel pumps.
The feds get cranky if you run out of fuel before you get to the pumps. Just a story I heard.
The prop going around dragging the engine along is really just a little below the RPM of a normal full idle position with the engine actually running. ( depends somewhat on the airplane and engine combination and a few other factors) but the propeller acts almost like a solid disk when spinning as far as the air is concerned. It is constantly deflecting the air passing through it all the way around the rotation area of the area the prop covers as it was a solid plate.
There was a “Beta” prop made that could be put into a truly flat position in flight and revers when on the ground. when it was in the ‘beta’ position and the engine RPM kept up to normal cruise RPM, like say 2400 RPM. it produced so much drag that in something like a Cessna-206, the airplane would have to be kept in a near vertical dive if any flaps were also extended to keep the airspeed high enough to actually control the aircraft.
It took a lot of training to make pilots able to use this feature, it was expensive, and for the size of planes it was designed for, it was not a really good fit ofr a lot of reasons.
Watch a C-130 being put through it paces and you will see what flat props and reversing props can do with a good, well trained pilot at the controls.
The P&W turboprop engines automatically go to a totally feathered position with engine shut down. (Think Beech KingAir) This is both the blessing and the curse of that engine design, great for in flight glides with a total power failure but not so good for getting into small places with the engine out.
Interesting stuff to mess with when learning what all a particular aircraft can do. It is a shame that more advanced training still does not teach a lot of the things that can make or break your life.
