How is pulling a prop through safe?

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rookie1255

Pre-takeoff checklist
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rookie1255
I've heard of pulling a prop through a few times before hand propping or if it's cold before starting. How is this operation done safely? I get with the magnetos switch off there should be no spark. However, a broken p-lead could mean instant death. Even if the prop is pulled slowly it would still be a strong spark with the impulse coupling on the magneto.

Do you jump back each time you pull the prop through, or is there safety from assuming the magneto p-lead is not broken and that there is no fuel in cylinders since the mixture was pulled to shut off the engine?
 
^^ the above says it all, there is not much to add.
Find someone who is knowledgeable about this to give you a demonstration.
A pilot who owns an airplane with no electrics for example. Most mechanics, too.
 
rookie1255 said:
I've heard of pulling a prop through a few times before hand propping or if it's cold before starting. How is this operation done safely? I get with the magnetos switch off there should be no spark. However, a broken p-lead could mean instant death. Even if the prop is pulled slowly it would still be a strong spark with the impulse coupling on the magneto.

Do you jump back each time you pull the prop through, or is there safety from assuming the magneto p-lead is not broken and that there is no fuel in cylinders since the mixture was pulled to shut off the engine?
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It's best to know your aircraft, know that the mags were tested prior to shutdown and know the fuel was dispelled from the induction system on shut down.
You do this by doing the mag check at idle by going to OFF momentarily then back to both see if both mags quit firing.
then shut down by the mixture and watch for the momentary RPM rise prior to stopping.
when the fuel is gone, and the mags have been proven you are pretty safe.
 
Why you pulling the prop through?

Unless you've got a radial engine you're inviting a problem...
 
I just did the cylinder differential pressure test for my annual, and even with the top plugs pulled, high tension leads disconnected, key out of the ignition and visible on the glare shield, and P-leads visually inspected, it's still spooky moving that prop around.

Nice to physically see that the piston's at TDC through the spark plug hole before pressurizing to 80 psi.
 
SoCal RV Flyer said:
I just did the cylinder differential pressure test for my annual, and even with the top plugs pulled, high tension leads disconnected, key out of the ignition and visible on the glare shield, and P-leads visually inspected, it's still spooky moving that prop around.

Nice to physically see that the piston's at TDC through the spark plug hole before pressurizing to 80 psi.
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How do you know it is at TDC balanced position with out pressure on the cylinder?
 
How do you think pilots without starters start their planes without getting killed each time?
No, it doesn't mean instant death.
No, you do not jump back when you do it.
No, it's not just for radial engines.
I usually pull about 3-4 blades through after priming, then it's mags on, crack the throttle and it starts on the first pull.
 
champ driver said:
How do you think pilots without starters start their planes without getting killed each time?
No, it doesn't mean instant death.
No, you do not jump back when you do it.
No, it's not just for radial engines.
I usually pull about 3-4 blades through after priming, then it's mags on, crack the throttle and it starts on the first pull.
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But Tom has informed us you can't prime unless the prop is turning, so if you don't have a starter, does someone have to push the primer in while you prop?
 
Tom-D said:
How do you know it is at TDC balanced position with out pressure on the cylinder?
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I put a stick in the spark plug hole. It's not hard.

Just how "spooky" it is to move the prop depends on your engine / ignition - on my ride there is no impulse and you have to give it a pretty good spin to make a spark (the "experts" will tell you it is impossible to hand prop a Rotax 912 - but like most internet experts, they are feeding you manure).

In any case, you don't "jump out of the way". For a Pipessna type aircraft, just move it like you plan to prop it, but with less effort. For something bigger...
 
No electrical system in the Luscombe. Every start is by hand. Chock the wheels and secure the tail. Plenty of boobtube videos on how to do it. I will say there is somewhat greater risk with nose gear planes because of the prop angle.
 
Have propped lots of planes. Have even propped some 152s and 172s although as mentioned above the prop angle is awkward. Good procedure (test the brakes) and good communication if there are two people is critical.

When I am by myself I always tie the tail to my truck hitch and set the parking brake. I double and often triple check everything. I like to stand behind the prop when by myself or if starting it without an experienced person in the cockpit. I grab the door frame with my left hand and throw the prop with my right. Depending on the plane and the length of your arms this may or may not work for you.

It is all about respect and knowing that prop can bite, as mentioned it is like a gun you treat it the same whether it is loaded or unloaded.
 
A word of guidance to the unknowing. Hand propping an engine that's ready to start is not a strength exercise. A slow pull through a compression strke can and does start the engine. All the leg kicking and grunting is unwarranted drama. Preparing the engine to be ready to start is a process and not doing it is a small measure of protection but you should always treat the prop as if it's going to start with one compression stroke.
 
My 182Q POH states that in cold wx operations you should hand pull the prop a few times to limber the oil.

I think pulling the prop through slowly is a much different proposition than hand propping.
 
DFH65 said:
I like to stand behind the prop when by myself or if starting it without an experienced person in the cockpit.
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I've taught a lot of people to prop planes and I always tell them to never do this. I watched a guy try to prop his plane for several minutes, exhausting himself. He then did what most of us would do, he pushed the throttle full forward and turned the prop backward quite a few times because it was flooded. He forgot to pull the throttle back and proceeded to prop the plane from behind the prop, but in front of the strut. I seriously thought I was going to see a man get decapitated when the plane surged forward, jumped his small chock, and the strut pushed him toward the prop. Luckily he dropped down and got his foot under the tire which stopped it while someone else turned it off.

To each his own, but the only time I'll prop a plane from behind is a Cub, where I can reach the throttle and the strut is far enough back from the prop.

My method if a pilot is in the plane: I tell them "ignition off" and "fuel on" then I pulle the prop through 4 to 8 blades. I tell them "brakes on", then I pull on the strut to make sure. I then tell them "ignition on". I swing the prop, swinging my leg backwards (I don't think it's drama!). I quickly move to my left if it starts and never walk in front of the prop. If it doesn't start and the prop doesn't stop in a good place (10:00-4:00) for another try, I tell them "ignition off" and I pull the prop into that position and go through the process again.

If it's just me, I have big, heavy rubber chocks like they use on trucks and I tie the tail if possible. I double and triple check that the throttle is barely cracked. I turn on the fuel, pull the prop through, then turn off the fuel. If anything goes wrong and you can hold the plane, it will seem like hours, but the engine will run out of fuel in a fairly short amount of time.
 
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Behind the strut of a Cub? You're making this up, right? It's easy to prop Cubs from behind because you can easily reach the throttle and mixture from the right side through a Cub's door. Side-by-side airplanes and planes with swinging doors make that more difficult. But even as a tall guy with long arms there's no way I could prop my Cub from behind the struts.
 
J5 Cub with a swing door. You have to be in front of the strut to prop it from behind. The tail is always tied with very little slack just enough to unclip it from my hitch. Given the choice I would rather be hit by the strut than the prop just sayin'.
 
There are instances where the Rotax must be pulled through until you hear a thunk. My Rotax will not start with a pull-through. So, the rules I learned with my Cessna's don't count for the new plane.
 
Typo! I meant the only plane I would prop from behind the prop, not behind the strut! The strut is far enough back and as you mention the throttle is right there.
Stewartb said:
Behind the strut of a Cub? You're making this up, right? It's easy to prop Cubs from behind because you can easily reach the throttle and mixture from the right side through a Cub's door. Side-by-side airplanes and planes with swinging doors make that more difficult. But even as a tall guy with long arms there's no way I could prop my Cub from behind the struts.
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DFH65 said:
J5 Cub with a swing door. You have to be in front of the strut to prop it from behind. The tail is always tied with very little slack just enough to unclip it from my hitch. Given the choice I would rather be hit by the strut than the prop just sayin'.
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If the strut is far enough back, I agree. On a Luscombe or a Cessna 140, the strut is pretty close to the prop. I'm not worried about the strut hitting me, I'm worried about it pushing me into the prop.
 
Handpropping a cup from the front or back is easy!

Unless it's on floats...I almost fell in the water a few times.......
 
Now that I see some drift into hand propping techniques, a small thing recommended to me when I purchased my first "no electrical/starter or impulse coupler" plane is to also remove anything that my be lost off your person while propping so that you won't try to automatically reach for them if they fall towards the spinning prop.

I.E. no hat, sunglasses, empty your shirt pocket( fuel sampler, cell phone or pens, etc.) etc.

Lack of an impulse coupler with a wooden prop meant the flip needed a bit of authority to get a spark and enough forward momentum to not kick back.
 
ifly4fun said:
But Tom has informed us you can't prime unless the prop is turning, so if you don't have a starter, does someone have to push the primer in while you prop?
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Many of the aircraft that require you to hand prop, are primed by pulling the prop thru. so it's not a matter of "CAN"T" as you imply. or are you trying to be a smart ass on a serous subject.
 
I prime, then pull four to six blades, then switch on the mags, crack the throttle and pull again. Usually starts on the first blade with mags hot. Flooded start is a whole 'nother animal.
 
IF turning the prop is just to move it to operate the tow bar or remove the cowl.. simply rotate it backwards. it is an impossibility for a mag to fire when being rotated backwards.
 
Capt. Geoffrey Thorpe said:
I put a stick in the spark plug hole. It's not hard.
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With a stick, there is no way to tell when the crank pin and rod are at the perfect TDC.

In that Video when they were pulling the prop thru, how many revolutions did the crank turn?
 
Propping a Cub. Prime and prep for starting. Stand behind prop on right side with throttle set to idle and mixture at cutoff. Hook leg on gear, left hand on door frame, and pull prop down with right hand. Upon starting push mixture to rich and adjust throttle as necessary. If you fail to get to the mixture in a couple of seconds the engine won't run and you do it again. I have friends who fly no-electric Supercubs in and out of crazy hunting strips and hand prop solo with no tiedowns many times every day. The more you do it the better you get. I prefer electric start but I know how to start them without. Like when I've walked away and left the master on!
 
Tom-D said:
With a stick, there is no way to tell when the crank pin and rod are at the perfect TDC.

In that Video when they were pulling the prop thru, how many revolutions did the crank turn?
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If I'm at the point I can wiggle the prop and not see the stick move, I seem to be close enough to ease in the pressure.

W.R.T your question, I suspect that you are confusing me with my father - he was the B-29 mechanic. But, a couple blades gets about one crank rev. (in round numbers). How many blades did they pull?
 
Capt. Geoffrey Thorpe said:
If I'm at the point I can wiggle the prop and not see the stick move, I seem to be close enough to ease in the pressure.

W.R.T your question, I suspect that you are confusing me with my father - he was the B-29 mechanic. But, a couple blades gets about one crank rev. (in round numbers). How many blades did they pull?
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I order to know that all pistons have reached their TDC on compression stroke it requires 2 revolutions of the crank, on a 4 bladed prop that's 12 blades. Most times on a used engine they will just crank it on the starter prior to turning the mags on and start priming.
 
Tom-D said:
I order to know that all pistons have reached their TDC on compression stroke it requires 2 revolutions of the crank, on a 4 bladed prop that's 12 blades. Most times on a used engine they will just crank it on the starter prior to turning the mags on and start priming.
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what if the prop has 3 blades?.....:confused:
 
In the case of the B29, they are pulling it thru to avoid hydraulic lock caused by engine oil draining into the bottom cylinders which can cause major damage. They are not pulling it thru to prime it. Same with any radial engine. I did the same with my stearman and 195.
 
Jimmy cooper said:
In the case of the B29, they are pulling it thru to avoid hydraulic lock caused by engine oil draining into the bottom cylinders which can cause major damage. They are not pulling it thru to prime it. Same with any radial engine. I did the same with my stearman and 195.
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Which is why you need 2 complete revolutions of the crank shaft.
 
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