Is the propeller a loaded gun?

[rubberprune]

Here is a video about taking precautions while hand-starting a prop engine:
Prop swinging - YouTube

In this video Bob Tait recommends treating a prop at all times as a 'loaded gun' regardless of magneto and master switch positions: faulty wiring, undetectable by the operator of the aircraft, could cause a magneto send a spark to the plugs if the prop is turned. :ouch:. Sound advice.

My question is, when it's required to hand-rotate a prop a small amount, for the purpose of attaching a tow-bar, dressing the prop, for close parking another aircraft's wing in a small shared hangar, or inspecting an alternator belt, how should this be done safely if the prop is potentially 'loaded'?

[Radix]

............

[rubberprune]

Thanks Radix.
It it any safer to rotate the prop counter to the normal operating direction?

[stevef]

Turn it backwards. It doesn't damage the vacuum pump vanes, no matter what you might be told.
That's from Parker Hannefin, who make them. :cool:

[dubbleyew eight]

the answer to the question is yes and no.

if the engine is stopped with an idle cutoff which starves the carburettor, induction manifold and engine cylinders of fuel air mix, bringing it to a stop, then the propellor is as safe as houses and can be moved about as much as you like especially with the magnetos switched off and the mixture still in the idle cutoff position. there is simply nothing in the cylinders to ignite. the Continental O-200 with a Marvel Schebler Carby is just such an engine.

however if you look look at older engines such as the Gypsy Major which is not stopped by idle cutoff, but is stopped by switching off the magnetos, these engines MUST NOT HAVE THE PROP MOVED since the cylinders possibly have a combustible mixture in them and any stray spark from the magneto will ignite the mixture and probably start the engine.

Clear enough? That is what it is all about.

[zondaracer]

Before shutting down the engine, do a magneto dead cut check. Shut down the engine by starving it of fuel. Make sure the mag is off, key out. Turn the prop, if necessary, with extreme caution.

Basically, take as many precautions as possible.

[dubbleyew eight]

SteveF I pull my dry vac pumps apart about every 5 years, check them, clean them and reassemble them with a dry graphite powder lube.
doing this has its little challenges but I am yet to see any wear in the vanes in 15 years.

the inner of a dry vac pump is a hard carbon block with angled slots in it.
in each of these angled slots is a hard carbon blade about 5mm thick.
as they wear the dust is a lubricating carbon (graphite?) dust.

what will bring them undone is an oil leak into them gumming up the dry low drag environment they usually experience.

if moving a prop actually does break the vac pump blades I wouldn't crucify the miscreant because in reality the blades would have been so worn that they were about to break anyway.

one reason why YOU dont service these is because some of the parts are quite delicate and and are very easily ruined.

[lasseb]

if the engine is stopped with an idle cutoff which starves the carburettor, induction manifold and engine cylinders of fuel air mix, bringing it to a stop, then the propellor is as safe as houses [....] there is simply nothing in the cylinders to ignite.

If you stop an engine that has direct injection - like most constant speed engines - using mixture idle-cut off, you will most certainly be able to start the engine with mags-on and mixture still in the idle-cutoff position. In fact, this is the preferred start-procedure for warm engines.

It can be quite difficult to see from the outside if the engine has a carb or not, so don't count on the idle-cutoff theory unless you are 100% certain what the engine is, and how the previous user stopped it...

[B2N2]

Without getting into endless amounts of theory and equally endless discussions about difference between engines.......

When you move the propeller always make sure you stand outside of its arc and move the prop with a flat hand against the blade instead of gripping it with your fingers.

http://b.vimeocdn.com/ts/189/828/189828220_640.jpg

This stuff is not a joke kids, one mistake can cost you a career.

http://avstop.com/news_january_2012/img6D.jpg

[rubberprune]

Excellent observations and suggestions people. Thanks for all your input! : )

Is the act of counter-rotating the prop by hand (that is, turning it opposite to direction of normal operation) any less likely to trigger the magnetos?

[dubbleyew eight]

the secret to being a good pilot is to let all the other schmucks make the mistakes and learn from their expensive experiences.
it also pays to have a very good understanding of basic principles, standard operating methods and the reasons why they have become standard methods of operation.

when our airfield was experiencing some acceleration in the numbers of hangars being built I used to drive home via a different taxiway each night to have a look at the new developments.
one night I came across a hangar with a very neat circular hole in the hangar door. (I have a photo of it). obviously to a pilot it was the exact diameter and height of a typical aircraft propeller, but what had caused the hole?

a few nights later I drove down the same taxiway and the hole was gone. repaired as though it had never occurred. ...hmmm interesting.

it took just over a year to find out what had happened. for over six months there not a sign of the hangar owner on the airfield.

the story goes like this...
the guy built a Vans RV, a six I think it was.
since he had built it he decided how he operated it.
this idle cutoff nonsense was a crock. he found turning the magnetos off, just as he did with his car, just as easy. so that is how he decided to operate his RV. all went well for months. he had forgotten his magneto key on one occasion so he left a key in the switch most times. the hangar was securely locked so it wasnt a problem.

on the day in question he had been out flying and enjoying the RV. taxyied back and switched off in front of the hangar.
he rolled open the hangar and pushed the aeroplane back into the hangar.
closed the doors and was getting ready to leave.
without much thought about, as he walked past the aeroplane to the side door he pulled the prop straight to make it look neat.
unknown to our hero, as he hopped out of the aircraft, his trouser leg had snagged the magneto key and rotated it from "off" to "left".
as luck would have it his tweaking of the prop clicked the impulse coupling on the left maggie and the engine started and roared back into life.
in the moment before the thrust overcame the machine's inertia and moved it forward he managed to leap clear of the prop.
the aircraft moved forward smartly across the hangar floor and came to bear on the inside of the door. the spinner gave way almost immediately and then the prop started grinding through the sheet metal of the door.
by about this time the hero had picked himself up off the floor and managed to get to the cockpit from aft the wing and shut off the magnetos.

you can work out for yourself all the things he did wrong.
I've got to go and wipe this grin off my face.:D

[zondaracer]

FAA Hand-Propping Accident Video - YouTube

[rubberprune]

Thank you dubbleyew eight, you have made my day in a most entertaining way.
: )

[rubberprune]

Thanks Zondracer. Unbelievable situation. What could the pilot hanging on to the strut do? Useless holding on, but in extreme danger of being struck by the prop if he let go. Not to mention the dizziness!
And the combi. I'm not sure what his intentions were. Stop the plane dead, or 'herd' it somewhere else? Oh boy!

Point taken.