Hand Prop 101

[flyguy]

Moved from parts for sale, tie-down release gizmo.

OK, here I go with my school-teacher gene showing itself:

When do hand-propped airplanes run away and hit things?

When they are STARTED without being tied down at a throttle setting other than IDLE. You will notice it requires three conditions.

WHEN STARTING: I have NEVER heard of an airplane running away from a pilot when it was sitting there idling AFTER starting, absolutely never if it is chocked. I suppose you might bang the throttle getting in the door, but you should have a good grip on something by then and not get thrown out of the airplane.

THROTTLE OPEN: If you always turn the engine over backwards (slowly) to clear flooding it is very unlikely to fire, even if the mag switch is on or failed. Turning it backwards WILL clear the problem the same as forward and anybody that tells you otherwise is completely and totally mistaken. When you do this the airplane must absolutely be--

TIED DOWN: This only applies when you START the engine--that is ALWAYS when they run away. AFTER the airplane is started and idling you can safely untie the tail, remove the right chock, walk around the airplane and put the right chock in the airplane, remove the left chock and get in the airplane. If the airplane creeps a little when you remove the left chock, you can restrain it a bit with your body until you get your foot on the step.

I have used this technique for 30 years on 3 Taylorcrafts and never had a problem, EVER, and every runaway incident I know of (4) violated one or more of these rules.

You don't need a remote release. Just be sure it is ALWAYS tied down and chocked when you START IT, especially when you are clearing a flooded condition, and anytime you pull the engine through.

By the way, though I am not positive about this, I suspect anytime you start the engine without someone at the controls your liability insurance is null and void and you will be the one who pays for damages. I base this opinion on the fact that aircraft insurance companies will generally do anything they can to avoid paying a claim.
DC

[Pearson]

Re: Hand Prop 101

Daryll,

All excellent points! For me, the biggest thing I do in the interest of safety while hand propping is to get my mind on what I am doing. This may sound stupid to have to say such a simple thing, but really when do we make mistakes? It is when we are not paying attention to what we are doing. Every single time I begin to prop my plane I make a mental note to slow down and mentally run through a checklist. Even then, before each swing of the blade, I mentally ask myself if I have done everything needed. We all know the throttle has to be set a certain way and the airplane secured. Every pilot who has had an airplane run away also knew it, but they weren't paying attention to what they were doing and forgot an important step. So for me, the greatest safety point of hand propping is to get your mind on what you are doing.

Merry Christmas!

[n6346m]

Re: Hand Prop 101

Turning it backwards WILL clear the problem the same as forward and anybody that tells you otherwise is completely and totally mistaken. .
DC

Flyguy,
I am curious as to the logic you use to support your contention that turning your prop backwards is not better than turning it forward. Usually when I get a flooded engine it is because I have left the fuel valve on too long prior to attempting to start it and my good little Stromberg is dripping fuel out of the bottom. There is too much fuel in the intake system to properly atomize and ignite properly wetting the plugs.

Prior to putting on a primer ( used mainly in the winter) the way I would get fuel into the cylinders is by pulling the prop through several times to "prime the cylinders". The way I understand the physics of a four stroke engine, pulling the prop through in the direction of normal rotation allows the piston to suck in mixture from the manifold during its downward travel during the intake stroke and pushes the burned gasses out during the exhaust stroke.
Correct me if I'm wrong, but if you rotate the engine in the opposite direction wouldn't it suck in fresh air through the open exhaust valve on the downward movement of the piston and subsequently push it out the carburetor when going up with the intake valve open with the throttle butterfly fully open. This not only dry out the plugs quickly, it also clears the intake system of excess fuel. I have always had much less trouble clearing a flooded engine using the backwards rotation technique since I learned to fly in 1964, although I haven't done it much lately since I rarely flood the engine any more. I have finally figured it out.

[flyguy]

Re: Hand Prop 101

Bob,
I think that is what I said. Hummm, yep that is what I said.

"Turning it backwards WILL clear the problem the same as forward.... " (that is they will both get the job done)

What I actually believe is that backwards will clear it better and for exactly the reason you state.

I didn't say that it was better because I have no way to prove that. I do know that it works AS WELL from experience.

I was pussyfooting on that sentence and resulted in it being convoluted or at least confusing.

Actually I was expecting to get jumped on by about 10 guys yelling that it doesn't work to turn it backwards. Chuckle.

DC

[vetdrem]

Re: Hand Prop 101

Fresh air is not "sucked in on the exhaust stroke".

The crank and cam are still connected together, so the exhaust stroke ALWAYS happens when the exhaust valve is open and the piston is moving into the cylinder. The intake stroke ALWAYS happens when the intake valve is open and the piston is moving out of the cylinder. Neither condition gives a hoot which direction the crank is being turned.

I feel that the clearing of the cylinders happens because you have the throttle open, and the venturi effect is less, therefore, less fuel being sucked into the throat of the carb, and inot the cylinders. (I'm probably wrong, but it's the best explaination I can come up with).

I don't think that there is much difference turning it either direction to clear the flooded condition, but I wish there was a diffinitive answer so the raging argument at our airport would come to an end.

Louie

[Marv]

Re: Hand Prop 101

My theory is to clear the engine, full throttle counter clockwise or clockwise with ignition off. I usualy go counter clockwise in case ignition switch fails, it may not start counter clockwise. To prime go counter clockwise with ignition off and throttle closed 3 or 4 revolutions. Marv

[crispy critter]

Re: Hand Prop 101

I'll say something that most of you will disagree with but try this......if you leave the throttle closed and continue to pull the engine threw in a direction to start the engine will continue to flood worse. Try leaving the throttle closed and rotating backwards....it clears the engine the same as if the throttle is open in either direction. IMHO always clear a flooded engine backward with throttle closed and mags off....about ten blades in a backward rotation,leave the throttle closed,go mags hot,then throw the prop. She'll start almost everytime. If you rotate the engine backward it doesn't matter if the throttle is open or closed because you are pushing out the intake and pulling threw the exhaust trading air for gas while pushing/wiping,clearing the excess gas out and pulling air in. Backward with throttle closed and mags off,tripple safe and does the same job.

[vetdrem]

Re: Hand Prop 101

I have been thinking about this since I made a posting.

I think I was wrong... (I hate saying that).

After thinking about it, drawing pictures, tilting my head to the left while rotating my hands in a circle, I have come to the conclusion that from the top of the (normal) exhaust stroke, if you rotate the crank in the oposite direction, the exhaust valve will open and piston will move out of the cylinder. And as you said, fresh air will be drawn into the cylinder through the exhaust. At that point, the exhaust valve will close.

I guess I'm having crow for my Christmas dinner, anyone want a wing?

Louie

[flybikefarm]

Re: Hand Prop 101

Kevin that is exactly how I do it. I hardly ever flood the engine on my cub when I am by myself. Most of the time I turn down offers of help unless I know the person can prop in the proper way. George

[flyguy]

Re: Hand Prop 101

Louie,
You are likely correct about the throttle opening as I understand from one of our CFI's, at least sometime you cannot restart a 0-200, with it windmilling, wide open (climb) throttle. Too much air going through, not enough gas. He had to put a 150 into a field off the end of the runway because of that effect. New CFI, stupid mistake. Never did that again.

Pretty obvious the key question is: Does the air flow in reverse through the engine if you turn it over backwards? Knowing that for sure should point to some logical conclusions about clearing the excess fuel.

Just now I see it as follows--

Air does flow through the engine in reverse when turned backwards.

The problem is the excess gas in the manifold.

It is easier to clear gas, from the intake manifold, downward through carb than upward through engine.

Cylinders will have gas-free air in them as a starting point as opposed to having some possibly still rich mixture from flow in from the manifold.

Having no fuel mixture in the cylinders is a better initial condition for starting if the problem was a flooded condition.

Having the throttle open allows greater air flow. Greater air flow clears excess fuel more efficiently.

On the other hand, from a safety standpoint, as Kevin says, it is SAFER not to turn the engine over with the throttle open.

That is my logical walk through,
Darryl

Edit: Louie, I am sure we all have done that here at times, probably more than once. Chuckle.

[crispy critter]

Re: Hand Prop 101

Louie,Sorry about the crow. Didn't mean to prove anyone wrong,just trying to make it right. Everything works in reverse when rotating the engine backward. The intake on a tcraft is an updraft(like most aircraft),it will not hold enough liquid fuel to keep the engine flooded,if it ain't in the cylinders it will run back into the carb and out the overflow(running/dripping on the ground under the airbox). Safest method is to rotate the engine backward with throttle closed and mags cold. Trust me,it WILL work best and safest doing it this way. If you ask why mags off???? Two reasons...first, it is possible for the mag to generate a spark backward,not likely but possible. Second, if there is enough gas build up in the cylinders it is possible,once again not likely but possible to get a diesel affect and the engine kick back forward and start with a short high RPM burst. Once again,none of this is likely but possible so rotate backward with throttle closed and mags off.

[Hank Jarrett]

Re: Hand Prop 101

Used to be a rumor that you could damage an impulse mag by turning it backwards. Anyone know for sure?
Hank

Not a Mag guy

[crispy critter]

Re: Hand Prop 101

No,it will not hurt it at all.

[Robert Lees]

Re: Hand Prop 101

"There is no horizontally-opposed piston engine that can be harmed by turning it backwards"

There. I've said it.

Discuss.





(to become a separate thread, but comments are welcome here first)

[Mark Julicher]

Re: Hand Prop 101

It might not bee too good to turn a dry-vane vacuum pump backwards, but impulse mag is OK. Last time I checked, very few non-electric BC12s had a vacuum pump