Video - hand prop close call

[alpha1]

http://www.flightsafetyaustralia.com/20 ... -the-prop/

[Redneck_pilot86]

Very close call, a simple error almost cost him his life. Note - he was preflighting the aircraft, not attempting to hand prop it. As stated in the article, he had left the mag switch on at shutdown the previous night.

[alpha1]

My bad Redneck, and thanks for the clarification...as you correctly point out, he was NOT trying to hand prop it.

[springlocked]

Inspecting prop - turn it backwards - it fired as soon as the impulse mag kicked in -- good procedure since you can never tell when you might have a live mag even if the switches are off. How do you treat a gun when you first pick it up??

[DonutHole]

Some accessories can be damaged if you counter-rotate the prop on some ac.

Why was he spinning the prop as part of his pre flight?

[Redneck_pilot86]

Some accessories can be damaged if you counter-rotate the prop on some ac.

Why was he spinning the prop as part of his pre flight?

Common practice when operating off gravel, to check for prop damage.

[Maynard]

And with a little effort in your back and hip, there's no need to hand turn the prop to check the blades.

[DonutHole]

Some accessories can be damaged if you counter-rotate the prop on some ac.

Why was he spinning the prop as part of his pre flight?

Common practice when operating off gravel, to check for prop damage.

Eyes maybe?

[shimmydampner]

Pretty common to run a hand along the leading edge to feel for nicks.

[AirFrame]

Also common to check for hydraulic locking in the lower cylinders on radials?

[DonutHole]

Pretty common to run a hand along the leading edge to feel for nicks.

I don't get this fascination with touching things. It's not an annual inspection it's preflight. Use your eyes. What is a private pilot going to do if he feels a nick anyways? Hope he isn't going to pull out the file.

To check for hydraulic lock on radials you pull blades through with the starter and mags off.

[Broken Slinky]

Pretty common to run a hand along the leading edge to feel for nicks.

I don't get this fascination with touching things. It's not an annual inspection it's preflight. Use your eyes. What is a private pilot going to do if he feels a nick anyways? Hope he isn't going to pull out the file.

I can pick up a nick in the prop a lot easier by running my fingers across it than by eye. If it's bad enough I can walk over to my AME and see if it should be dressed or...
I touch just about every nut and bolt on control surfaces too. Much rather find out its loose in my warm hangar than at 9500' in -20C temps.

[Redneck_pilot86]

Pretty common to run a hand along the leading edge to feel for nicks.

I don't get this fascination with touching things. It's not an annual inspection it's preflight. Use your eyes. What is a private pilot going to do if he feels a nick anyways? Hope he isn't going to pull out the file.

To check for hydraulic lock on radials you pull blades through with the starter and mags off.

I don't get this fear of touching things. If you rely on your annual inspection to find problems with your aircraft, you shouldn't be flying. I know lots of private pilots who are quite capable of filing out a prop nick, and it if they aren't capable, they can do as others posted and contact an engineer to see if it needs to be addressed. Ignoring it is not a suitable option. I find 90% of the prop damage I discover by feel, every time I go near a prop I run a hand along it.

[pelmet]

Ok then, you have decided to move the blades in the normal direction of rotation. How about, first putting in some chocks if available, park brake set, throttle closed, mixture idle cutoff, mags off, and fuel selector off. Of course most of these things are to prevent the runaway aircraft.

[tbaylx]

Inspecting prop - turn it backwards - it fired as soon as the impulse mag kicked in -- good procedure since you can never tell when you might have a live mag even if the switches are off. How do you treat a gun when you first pick it up??

Don't turn props backwards, the alternator/generator brushes wear in with the rotation of the prop, if you turn it backwards it will lead to chips in the leading edge of the brushes and accelerated wear and or failure. That goes for turbines as well with starter/generators.

As mentioned, no need to turn a prop to inspect it for damage.

If you need to turn it, ensure mags are off and turn it in the normal direction of rotation.

[5x5]

I don't know why the old pilot's tale of accessory damage from hand turning a prop backwards persists.

I think it's partially due to an idea that seems to be common sense - they're made to spin one direction so if they turn in the other direction they can be damaged. But I challenge anyone to provide any reference from an actual part manufacturer that includes any such warning.

If you've ever taken an alternator apart, there certainly are "brushes" in them. Small carbon blocks that are pushed against a shaft by light springs. And they do wear in the direction of the rotation. However, they are not pushed hard against the shaft as the springs behind them are very small. And the shaft they are against is very smooth. Turning at extremely low speed in hand-powered movement there is no way that any edge will "catch" or chip.

I suppose that in a situation where the alternator was very high-time and the brushes were almost worn out and extremely thin there might be a very remote chance of damage of some sort but it would likely fail soon in use anyway at that point.

The other more commonly stated concern is that of damage to the vacuum pump. This seems a bit more likely from the "common sense" view as vac pumps work with relatively fine graphite vanes touching and rotating against a shaft. Closer tolerances and not pushed by springs so no forgiveness. Once again though, in the manufacturer published installation and maintenance guides you will find no warning against turning it backwards, at low speed by hand. Checking directly with the supplier tech support contact confirmed there is no risk of damage.

So if you are going to turn a prop by hand for purposes other than starting, please, please, please turn it backwards and avoid the risk of injury.

[tbaylx]

I don't know why the old pilot's tale of accessory damage from hand turning a prop backwards persists.

I think it's partially due to an idea that seems to be common sense - they're made to spin one direction so if they turn in the other direction they can be damaged. But I challenge anyone to provide any reference from an actual part manufacturer that includes any such warning.

If you've ever taken an alternator apart, there certainly are "brushes" in them. Small carbon blocks that are pushed against a shaft by light springs. And they do wear in the direction of the rotation. However, they are not pushed hard against the shaft as the springs behind them are very small. And the shaft they are against is very smooth. Turning at extremely low speed in hand-powered movement there is no way that any edge will "catch" or chip.

I suppose that in a situation where the alternator was very high-time and the brushes were almost worn out and extremely thin there might be a very remote chance of damage of some sort but it would likely fail soon in use anyway at that point.

The other more commonly stated concern is that of damage to the vacuum pump. This seems a bit more likely from the "common sense" view as vac pumps work with relatively fine graphite vanes touching and rotating against a shaft. Closer tolerances and not pushed by springs so no forgiveness. Once again though, in the manufacturer published installation and maintenance guides you will find no warning against turning it backwards, at low speed by hand. Checking directly with the supplier tech support contact confirmed there is no risk of damage.

So if you are going to turn a prop by hand for purposes other than starting, please, please, please turn it backwards and avoid the risk of injury.

Its actually a maintenance practice not to turn the prop backwards, Even a relatively new alternator brush will wear and develop an edge, and the armatures have grooves in them that catch the edge and most certainly do chip. If its your aircraft, do as you please, if its owned by someone else and you're hired to fly it, dont' take internet advice, ask your maintenance department what they want you to do and operate accordingly.

[5x5]

Its actually a maintenance practice not to turn the prop backwards

Who's practice and where is it written/published. I certainly can't find any such reference or recommendation using Google.

Search some of the automotive forums and people there routinely run alternators backwards in modifications, engine swaps and what have you. That's at much higher a speed than you can turn a prop backwards. The only problem they encounter is cooling due to the messed up airflow spinning backwards.

The tiny grooves you mention on the shaft where the brushes touch are so small they couldn't possibly catch a brush edge.

[GyvAir]

I agree with 5x5 on this. You will never hurt an alternator by turning the engine backwards by hand. There are no grooves in the for the brushes to catch on. The entire circumference of the alternator slip ring is a continuous smooth machined surface.

Photos of commutator vs slip rings, for those unfamiliar:
http://www.aeroelectric.com/articles/Al ... ors_1.html

While not non-existent, there aren’t very many generators still in use on GA aircraft. I’ve barely dealt with them, so can’t speak to the susceptibility of say an old Delco Remy to being turned backwards. Turning some generators backwards definitely does have potential to chip or even break a brush. If you’ve ever seen/heard someone try to turn a single shaft turboprop such as the Garrett TPE331 backwards, you don’t need to be told this.

Modern dry air pumps seem to be unaffected by turning backwards. I have neither heard nor seen evidence, anecdotal or otherwise, that a pump failed due to that in decades.
Hydraulic pump won't care. Mags won't be hurt. Tach generator or mechanical tach drive? Fuel pump? Oil pump??
I'm not thinking of anything that should be adversely affected.

As far as not turning an engine backwards during maintenance, I don’t know too many people that don’t turn the prop back and forth at least a little while checking mag timing, or performing a compression test.

[beaverpuq]

If memory serves the 0-540 in Comache 250 says not to turn backwards because of the vacuum pump vanes. Something like the impeller on outboards. They are curved one way.

[CarbHeat]

And if memory serves me, I recall the IO-520 with a newer style starter adapter also prohibiting turning the engine in reverse because of the spring on the starter drive catching and causing damage or even itself breaking.

[Spandau]

I don't like to turn props unnecessarily but turning some backwards can cause damage. When I have to turn a prop I double check that everything is switched off and then turn the prop forward like I'm expecting it to fire. That guy was very, very lucky, but who had a camera trained on him like that? I'm sure it wasn't but it looked a little staged.

[PZL 1000]

I had one kick on me once hand-proppin' a Cessna 180 on wheel skies. The pilot had a live mag but had not been testing for it on shut-down. I've still got all 10 fingers so I was lucky. It's common practice to turn a prop through before any kind of start in very cold weather. Radial engines get pulled through even before a first start on a warm day to eliminate the chance of hydraulic lock. It is very important to check for a live mag during shutdown. It only takes a second.

[DonutHole]

Most of the radial guys I know use the starter and count blades before flipping the mags

[TeePeeCreeper]

Most of the radial guys I know use the starter and count blades before flipping the mags

No counting blades... (5-7 blades) two blade or three bladed prop? That kind of shit gets confusing!

Book says "3-6" primer "strokes"... Some of the birds at work like 8 full primes on a cold morning... Others prefer 6 with 10 "accelerator" throttle pumps (mags off of course)

Know your machine, every radial engine has its own quirks and quarks...

All the best
TPC

PS; There is no reason to turn a blade by hand on a horizontally opposed engine. None. (Unless you are flying a "Champ" or "J3"... Then again doing so if it's your only way out of the bush and your in a jam is handy to know how to do.

The guy in the video was lucky, fortunately for him!