Using the starter to move the prop

J

JordanD

Here so I don’t get fined
Does it cause any harm to click the starter for a second or two to move the prop out of the way of where you need to hook up the towbar on a Warrior or 172? I'm not crazy about moving the thing by hand, but I don't want to burn up a starter or worse.
 
Check mags off, move it by hand. There's no reason not to. You're talking 1/4 turn at most, and likely you're just at or past the compression stroke in one direction, so turn it away from the compression stroke.
 
Turn it by hand, backwards, so you don't fire the magneto impulse coupling. Even if you do it's a non-issue if the mags are off (and the ground wire isn't shot), but I've never heard of an engine being accidentally hand-propped backwards. As long as you're turning the prop slowly, forwards is also fine if backward requires too much force from engine compression.
 
Counterclockwise from the pilot's point of view? I was under the impression that was bad for it.
 
JordanD said:
Counterclockwise from the pilot's point of view? I was under the impression that was bad for it.
Click to expand...

Some people say it can damage the vacuum pump(s). It won't hurt the engine itself.

I'm with everyone else though. Move it slowly and don't force it past a compression stroke and you'll be perfectly safe.
 
Why would it be bad? When you're dealing with an engine that's basically 1940s-60s technology, what component would you actually be hurting?

I found this thread from 2003:

http://forums.jetcareers.com/threads/which-way-to-turn-a-prop.5858/

The only issue brought up there is the potential for premature wear on dry-vacuum pumps... but to be honest dry vacuum pumps are such pieces anyway that I think that's a bogus argument (and that's essentially what the old thread concluded as well - the attachment that gears the pump into the engine is purposely made of plastic, so that when the pump inevitably seizes up the plastic attachment rod just shears off to prevent engine damage/stoppage). In other words - it's attached to the engine with plastic... it has bigger problems than turning backwards. :)

However, this guy articulated exactly why I turn the prop backwards:

ananoman said:
The only problem with that method is that the distance you move the prop has nothing to do with the likelyhood of the engine starting. If you move it in the direction of normal rotation, you increase the risk that it will start. In the left magneto there is an impulse coupling that engages at low rpm. The impulse coupling is spring loaded and 'catches' as the engine rotates. It then springs forward, accelerating the magneto. By doing this it retards the timing and generates a hotter spark than would otherwise be possible at low rpm, increasing the chances of a start. If you turn the engine you will hear the impulse coupling 'click' as it releases. At higher rpm when the engine is running it disengages.

If you turn the engine the wrong way, the impulse coupling will not engage, making an accidental start unlikely.
Click to expand...

In the event that my magneto ground/P-leads are eff'ed, I don't like the idea of increasing the likelihood of an inadvertent engine start by allowing the impulse coupling to wind up and spring the prop forward.

Also if you ever get a chance to go into your local mx shop while they're compression testing an engine (the "leak down" way where they fill the cylinder with compressed air), ask them what happens if they let go of the prop. Better yet, see if they'll show you. It's dramatic. So while I like to avoid firing the impulse coupling, I'd rather turn the prop forwards if it builds up too much compression resistance going the other way, because if you lose your grip the prop jump out of your hand and cut you while it relieves the pressure in the cylinder. (Again, this was more of an issue as an AMT apprentice doing compression tests.)
 
inigo88 said:
Why would it be bad? When you're dealing with an engine that's basically 1940s-60s technology, what component would you actually be hurting?

I found this thread from 2003:

http://forums.jetcareers.com/threads/which-way-to-turn-a-prop.5858/

The only issue brought up there is the potential for premature wear on dry-vacuum pumps... but to be honest dry vacuum pumps are such pieces anyway that I think that's a bogus argument (and that's essentially what the old thread concluded as well - the attachment that gears the pump into the engine is purposely made of plastic, so that when the pump inevitably seizes up the plastic attachment rod just shears off to prevent engine damage/stoppage). In other words - it's attached to the engine with plastic... it has bigger problems than turning backwards. :)

However, this guy articulated exactly why I turn the prop backwards:



In the event that my magneto ground/P-leads are eff'ed, I don't like the idea of increasing the likelihood of an inadvertent engine start by allowing the impulse coupling to wind up and spring the prop forward.
Click to expand...
It could only do that if there is fuel as well. And since we don't shut our engines down by cutting the ignition........ there shouldn't be enough.
 
Right. So basically unless you left the mixture rich and the magnetos on both and primed the engine and cracked the throttle just right... do whatever you want. :)

To me it's just a "feel good" thing - knowing I'm taking every precaution, if possible.
 
No, it's not bad, but why put the extra ware on the starter?
I'm sure if you were paying the mx bills, you'd see it from my position, too.
 
JordanD said:
Does it cause any harm to click the starter for a second or two to move the prop out of the way of where you need to hook up the towbar on a Warrior or 172? I'm not crazy about moving the thing by hand, but I don't want to burn up a starter or worse.
Click to expand...
I would be more comfortable turning the prop by hand.
msmspilot said:
Some people say it can damage the vacuum pump(s). It won't hurt the engine itself.

I'm with everyone else though. Move it slowly and don't force it past a compression stroke and you'll be perfectly safe.
Click to expand...
Certain vacuum pumps have the vanes angled in the pump body, theoretically turning one of those backward could jam it up and break a vane.
Erik1010 said:
No, it's not bad, but why put the extra ware on the starter?
I'm sure if you were paying the mx bills, you'd see it from my position, too.
Click to expand...
My objection to bumping the motor with the starter is much more of a safety one than a wear one. A little bump to put the blades where you want them is not an appreciable amount of wear on the starter. However...
z987k said:
It could only do that if there is fuel as well. And since we don't shut our engines down by cutting the ignition........ there shouldn't be enough.
Click to expand...
You'd think so, but in the engines I have the most experience with, if you, say, replace a starter and then crank it in the shop even with the mixture ICO, after shutting off the engine with the mixture, the engine will try to fire every time unless you have a setup that allows you to shut off the mags while cranking the engine (I.e, separate magneto and starter switches). And that is the main reason I suggest not bumping the starter. Also, if you turn the prop slowly by hand, you'll be much more aware of what is in the prop arc and less likely to clonk the tug or another airplane with the blade. Obviously standard precautions apply, make sure the mags are off, do a mag ground check before you shut down, leave the airplane chocked until you're actually ready to tug it, etc.
 
I never said it was excessive, but like anything that moves, there is wear.
Why not check to make sure the mags are off and move it by hand? I don't see the harm in that.
 
z987k said:
It could only do that if there is fuel as well. And since we don't shut our engines down by cutting the ignition........ there shouldn't be enough.
Click to expand...

Roger Roger is correct on this...theoretically by pulling mixture on shutdown there isn't any fuel left, but that's not true. Try it yourself: shutdown your engine normally, then 5 minutes later with mixture in ICO, try starting it. At least on the TSIO-520 we fly, it will fire for several revolutions every time, certainly enough to kill someone.

In our ops, it is SOP to pull the cylinder through backwards to feel for compression on all six cylinders every pre-flight. This is done every day and has been SOP for years, and I've never heard of a problem with a vacuum pump because of this. It is worth the theoretical risk of breaking a vane in the vacuum pump (again, at least in our pumps this has never been a problem) over the risk of having a hot mag and killing yourself, especially if you do this right after shutdown.
 
Go find a grass strip and hand prop a cub.

It will do a few things for you. It will show you what is necessary for combustion such as a spark and fuel. It will show you that you would likely need to turn the prop through a few times to prime the cylinders. Lastly, it will show you that it is relatively difficult to hand prop an airplane.

Make sure the mags are off and grab the prop and put it where you need it.
 
USMC-SSGT said:
Go find a grass strip and hand prop a cub.

It will do a few things for you. It will show you what is necessary for combustion such as a spark and fuel. It will show you that you would likely need to turn the prop through a few times to prime the cylinders. Lastly, it will show you that it is relatively difficult to hand prop an airplane.

Make sure the mags are off and grab the prop and put it where you need it.
Click to expand...
I gave my student that same schpiel when I taught him to hand prop our TriPacer. Darn thing fired on the first pull. Though, we have a primer system so you don't have to pull the prop through to prime.
 
Moving it by hand backwards is typically safe. Washing airplanes at my school I have towed them around often and have had to move the prop. I have also had to move the prop when accessing the front of the cowling to get all the bugs off.

With our fuel injected IO-360s on the Skyhawks typically are not prone to catching on the first spark unless there is fuel in the cylinder after a prime or a hot start. So with the cold engines, I am careful, but generally not too worried. Keeping myself out of the prop arc, I will typically with my hand move it intentionally and move my hand out of the prop arc with purpose. When the plane has just flown and the engine is hot, I will be even more cautious. I ALWAYS check to make sure the mags are off before even touching the prop. As a dispatcher at a flight school, when I close at night, I inspect each plane for a proper postflight you would be amazed what students forget... One of the most fundamental things to be taught. Music, Mixture, Mags, Master, Motion. I know it's taught and engrained in every student here, and I have never found the mags left on, but I won't leave that to chance...
 
You must log in or register to reply here.
Back
Top