rickair7777

For/aft crank play is a normal part of engine design and there are thrust bearings in both directions. You can't hurt them with your bare hands. Oil seals are designed to work within that range of play.

rickair7777

Yes, it's common and won't hurt the motor. But a hot mag could still hurt you bad. Low risk, just depends on your personal tolerance.

JohnBurke

Actually, you can, hence manufacturer recommendations to the contrary.

There are many things which are common practice, but not necessarily correct practice. Pushing down on the horizontal stab and vertical stab chine on Cessnas to lower the tail to swing them is one such example.

Pushing on the prop spinner is another improper practice that's often used.

rickair7777

Of course the manufacturer would not authorize something which they haven't evaluated or engineered for.

But you know enough about engines to know that you're not really going to hurt it. With no oil pressure could you cause metal/metal contact and rubbing? Sure. Is the rubbing going to be severe enough to reduce the practical life of the bottom end? Not in my opinion, unless the engine was bone dry with no assembly lube.

If we're talking some highly stressed race engine that's going to live at redline, then sure use the kid gloves. But a stock aircooler? Pretty tolerant.

BoilerUP

I almost feel like this discussion is akin to the "NEVER operate lean of peak - you'll burn up your cylinders!!1!" mentality that some piston pilots and mechanics continue to believe.

Obviously a towbar should be used...but let's be real, if you are using a hand towbar there is almost no way to generate enough force to move the aircraft fore or aft unless you place your hand on the base of the propeller; at least that is my experience with anything heavier than a Warrior or 172 (to include but not limited to Arrow, 182, , Bonanza, Saratoga and SR22).

N9373M

I use a towbar and push using the air intakes built into the cowl, if that makes sense. Works for 172, 182, M20E and P28R.

JohnBurke

That's your experience as a mechanic handling damaged spinners, or the cracks that result to cowlings, or prop flanges, or your experience as a guy that's pushed on the propeller?

I fly lean of peak; I do it all the time, when appropriate (it isn't always). I also judiciously use the propeller, when appropriate.

I've seen cowlings damaged, spinners damaged (and that have failed), and propellers damaged from pushing and pulling on the propeller, and I know two individuals who suffered head injuries when struck by a prop after moving it.

I've seen a lot of people push on the spinner, on the assumption that rather than apply asymmetric forces on the propeller by pushing on one blade, pressure on the spinner is along the thrust line of the engine. The spinner is decorative in many cases, in many others it's important for engine cooling and part of the design for the pressure cowl. Regardless, it's easy to get out of balance, to damage a backing plate, or to misalign the spinner or deform it by pushing, and it's a way to start cracks, too. I've seen each.

When I install a spinner, I use a torque screwdriver and take pains to ensure it's aligned, and check it in operation; imbalance or misalignment can cause failure, which can lead to propeller and aircraft damage. Pushing on it can be part of that.

I don't know any propeller manufacturers that recommend pushing or pulling the aircraft by the propeller, and I'm not aware of any engine manufacturers that make that recommendation, either. I'm aware of a number of warnings and cautions by different manufacturers against moving the aircraft using the propeller.

In small aircraft that are easily maneuvered, it may or may not present a hazard to the prop, crankshaft, prop flange, seals, and bearings, but then again, it may. It's always a good idea to avoid handling the propeller any more than necessary, regardless of the mag status. One needn't be afraid of the prop, but it should be respected.

I've seen more than a few people grab the prop tips to push or pull; definitely a bad idea.

Some have said that one can't apply as much force to a propeller by pushing or pulling as is applied in operation, but that's not an accurate statement. The force applied to a propeller when static is not at all the same as applied to the prop during operation. When pushing or pulling on a static prop, a direct moment is placed on the blade and shank on a specific direction, with no centripetal force acting on the blade. The actions on the propeller, shank, hub, and seals are quite different when the propeller is "pulling" outward as the prop spins. The rigidity of the propeller and the stress it experiences are quite different in operation, than when static. Is it going to break off in your hand? No, but that's irrelevant.

The strength and characteristics of a propeller in a static state are different than when it is in motion, and the lack of centripetal force on each blade when the push/pull is applied by hand does not mirror the force acting on the blade when the prop arc is developing thrust in operation. It's best not to compare or confuse the two.

BoilerUP

The base of the propeller is not the tip, or the spinner, or cowl, or anything other than the base of the propeller.

Not a A&P, just a dumb pilot that has moved a LOT of airplanes by hand and seen fleet airplanes moved by hand with never an ill effect.

But I've been wrong before, so caveat emptor etc etc...

JohnBurke

You don't say? Truly dizzying intellect.

There you have it. Conclusive in-depth research of a scientific nature. Certain far in excess of that provided by the engineers and manufacturers who designed the propellers and powerplants, and wrote the approved data and direction specifying not to move the aircraft using the propeller. But, as long as you never had an ill effect, then it's okay.

It would be helpful if you will go ahead and contact the manufacturers so that they can have their errant direction removed from their publications, to avoid further future confusion.

Grumble

The horror!!!!