Es wird zwar immer gemacht, und ich mache es auch manchmal wenn ich keinen Tug habe, aber tatsächlich steht in vielen POH, dass es nicht zulässig ist.
Eine diesbezügliche Nachfrage bei McCauley brachte diese Antwort:
Why SHOULDN’T I Tow My Airplane By The Propeller??
A person absolutely, positively can cause serious damage to the actuation parts inside their McCauley propeller if towing the airplane by pulling on a propeller blade. This may at first seem very odd since the aircraft is “pulled” by the propeller whenever it flies; what’s the difference? This is a very common misconception.
There are two things many people overlook - the absence of both centrifugal load, and natural Centrifugal Twisting Moment (CTM) on the blades. On typical single engine application, the blades see approximately 15-20,000 lbs. of force trying to “throw” them from hub while in flight. This force also strengthens the blades by “straightening” them. Thirdly, the blades are
also trying VERY hard to go “flat” or to low pitch when the propeller is spinning due to the “CTM” within the blades. Keeping this in mind, the blade actuation system includes a composite phenolic link that is designed to be used solely in compression; tension will snap it. This link translates linear piston motion into an arc motion thru an actuating pin installed on the outer perimeter of the blade base. The blade rides on a ball bearing assembly and rotates when “pushed” by this link. This is how the blades change pitch in flight.
During normal flight, the blades are actuated thru this link under compression ONLY. The link is compressed because the piston (moving under oil pressure from the governor) is pushing it from one direction, while the blade CTM (see above) is pushing it from the opposite direction. The link compression at cruise of a typical propeller application such as a new Cessna 182 is approximately 1000 psi. A rough representation of the link can be seen in the graphic below joining the piston and the blade actuating pin (sticking up from the blade). The actual link is much shorter - about 2" long. While the graphic is very
crude, it does correctly illustrate the relatively tiny amount of phenolic material on the ends of the link vs. the large amount of material normally under compression in the middle. This end material is there simply to keep the link attached to its neighboring parts; it is NOT designed to be pulled upon.
If an aircraft is regularly towed by pulling on the blades, it is very possible that eventually the blade will be twisted the “wrong” way byhand, putting the link under tension, snapping off one of these ends.
This is not hypothetical stuff; it’s proven fact and we’ve witnessed MANY cases of it over the years at McCauley.
If you must pull a single engine aircraft by its McCauley propeller, hold the blade as close to the base as possible, and the blade by its TRAIL EDGE. This will put the link under compression, much reducing the chance of links being snapped.
Regarding pulling on a fixed pitch propeller: Obviously the risk of damaging actuation parts does not exist, so most of the above does not
apply. However, let’s not forget the lack of centrifugal load again even f/p props are designed to pull the airplane when this load is present in normal operation. Centrifugal load GREATLY improves the blades’ resistance to bending; they are naturally held stiff and straight while spinning. As this strength is missing when stationary, there is a good possibility of bending a f/p propeller blade if it’s pulled too hard by hand on the ground.
If you must do this (and most of us have), hold the f/p propeller as close to the base of the blade as possible. The reasons for this: 1) The blade is fatter and much less likely to bend, 2) the “bending” force you are applying to the blade is much less at the base than the tip since the “moment arm” is shorter.