Reason for Rotating Propeller to Vertical When Done

Jim Logajan said:
I think maybe PoA needs a "Useless Aviation Minutiae" subforum.
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I wouldn't classify the danger of rotating the prop forward as Useless Minutiae. A guy can end up with useless appendages that way.

I recently watched a guy teach a woman--probably a student--how to rotate a propeller so she could hear the click of the impulse. She was leaning over the prop blade while she pushed it down. And he let her do it. I couldn't believe it. Who is teaching instructors these days?
 
Dan Thomas said:
I wouldn't classify the danger of rotating the prop forward as Useless Minutiae. A guy can end up with useless appendages that way.

I recently watched a guy teach a woman--probably a student--how to rotate a propeller so she could hear the click of the impulse. She was leaning over the prop blade while she pushed it down. And he let her do it. I couldn't believe it. Who is teaching instructors these days?
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I would love to start a plane that would fire on a 1/4 revolution of the prop by hand.

When I learned, we were taught to hand pull the prop thru 3 or 4 blades to "bring the oil up into the cylinders".

Logic tells me that the first 3 or 4 blades on the starter would do the same.
 
I've had several taildraggers with wooden props. Years ago it was taught to always leave a wooden prop in the horizontal as if left vertical, moisture might collect in the lower blade upsetting the balance. I was also taught to always treat any prop as hot and not move them in a casual way. This has proved to be good advise over the years as accident reports have verified. ( mags not wired properly, etc.)
 
We watched a thirty minute hand prop demonstration at OSH that was very informative.

The main point from it was treat every prop like a loaded gun.

If the p lead connection to the mags is compromised, it will fire. More correctly it fires every time you hear the impulse spring click. The only thing that keeps the spark from finding the plugs are the p leads that ground it.
 
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JoseCuervo said:
I would love to start a plane that would fire on a 1/4 revolution of the prop by hand.
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All you need is some fuel and some spark. You can easily get that with very little rotation on many aircraft engines.

Plenty of folks have faced a nasty surprise from not using enough caution.

I've met many A&P's that have been bit by the prop before.
 
Especially given that the discussion is about moving the prop right after shutting the engine down. It's more ready to run at that moment than when cold starting.
 
Jimmy cooper said:
I've had several taildraggers with wooden props. Years ago it was taught to always leave a wooden prop in the horizontal as if left vertical, moisture might collect in the lower blade upsetting the balance. I was also taught to always treat any prop as hot and not move them in a casual way. This has proved to be good advise over the years as accident reports have verified. ( mags not wired properly, etc.)
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Old Wives tale.

Wooden props really don't give a hoot where they are positioned. The first two minutes of running will spin out any moisture. That is what the holes in the tip are for.
 
Stewartb said:
Especially given that the discussion is about moving the prop right after shutting the engine down. It's more ready to run at that moment than when cold starting.
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There is absolutely no way of making the mag. produce a spark while being turned backwards.
 
Tom-D said:
Old Wives tale.

Wooden props really don't give a hoot where they are positioned. The first two minutes of running will spin out any moisture. That is what the holes in the tip are for.
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Yes of course TOM would have a different take but that's the reasoning behind leaving a wooden prop in the horizontal position according to the manufacturers at that time. ( they apparently did not check with Tom. )
 
gms5002 said:
I turn my horizontal so it doesn't get in the way of the tow bar.
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Yep. My prop stops vertical on shutdown every time - no exceptions ever that I can remember. It has to be moved in order to connect and use the tow bar.

txflyer said:
If the p lead connection to the mags is compromised, it will fire.
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I had a bad P-lead once, so now I'm like a bomb defuser every time I have to move the prop.
 
Jimmy cooper said:
Yes of course TOM would have a different take but that's the reasoning behind leaving a wooden prop in the horizontal position according to the manufacturers at that time. ( they apparently did not check with Tom. )
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Do you realize that wooden props have a varnish coat, and the holes in the end of the prop is the only way to get moisture in.

Show me the reference you think the wooden prop manufacturers adhered to back in the day?

Guess who's been flying wooden props most of his life?

The only way you can get enough water in a wooden prop to make a difference is to soak one blade in a water barrel for about a week.
 
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jesse said:
All you need is some fuel and some spark. You can easily get that with very little rotation on many aircraft engines.
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Nope not quite, when you shut down by pulling the mixture, where are you going to get fuel?

When you turn the engine backwards how are you going to get spark?

Shutting down by mixture and turning the prop backwards is as safe as it gets.
 
Tom-D said:
Nope not quite, when you shut down by pulling the mixture, where are you going to get fuel?

When you turn the engine backwards how are you going to get spark?

Shutting down by mixture and turning the prop backwards is as safe as it gets.
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:idea:Light goes on in head as to WHY we shut down by pulling mixture to idle cutoff. Thanks!
 
Tom-D said:
Nope not quite, when you shut down by pulling the mixture, where are you going to get fuel?
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I see what you're saying. But then why does my plane (Lance w/IO-540) hot start just fine without ever enrichening the mixture?
 
Tom-D said:
When you turn the engine backwards how are you going to get spark?

Shutting down by mixture and turning the prop backwards is as safe as it gets.
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We're not disagreeing Tom.

My statement below remains true:
All you need is some fuel and some spark. You can easily get that with very little rotation on many aircraft engines.
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jesse said:
We're not disagreeing Tom.

My statement below remains true:
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And, my statement remains true, I would love to fly an airplane that started on the first cylinder compressing by a 1/4 turn of a prop.

I have just never started a plane that fired instantly.
 
JoseCuervo said:
And, my statement remains true, I would love to fly an airplane that started on the first cylinder compressing by a 1/4 turn of a prop.

I have just never started a plane that fired instantly.
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A 1/4 turn of the prop on a 4 cylinder is going to run one cylinder through its entire compression stroke including the mag firing the plug. If the conditions are right it will indeed start...the only thing missing is whether or not the fuel/air ratio will make a boom that'll ruin your day. Plenty of mechanics have found it can indeed happen.
 
JoseCuervo said:
And, my statement remains true, I would love to fly an airplane that started on the first cylinder compressing by a 1/4 turn of a prop.

I have just never started a plane that fired instantly.
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99.99% of the time it won't start.
 
A nice Stearman flew in the other day with a huge wooden prop and no spinner just the bolts and the prop.

I thought it looked way cooler than anything. :yesnod:
 
Stewartb said:
Especially given that the discussion is about moving the prop right after shutting the engine down. It's more ready to run at that moment than when cold starting.
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Which is why I do my mag ground check right before shutdown.

All this talk about not touching props is great....until you have one that you had to pull through before starting.
 
timwinters said:
He's likely referring to:



Turn it forward, there's a chance of ithe engine firing. Turn it backwards there's a chance (at least in some people's opinions) of damaging a dry vacuum pump.



My pump is wet, so I'm not concerned about it. It turn the prop backwards as needed. It's horizontal when I'm moving the plane and relatively vertical after it's parked to keep it out of the way as much as possible when I'm walking around in the hangar.
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I turn mine backward anyway and we have a dry pump. Reason? I got to see a cutaway of how the dry pump works and frankly, if the carbon vanes are short enough to snap off they're already too short to be flying behind them, IMC. Finding the vacuum pump dead at next start up would be an exercise in realizing you let the pump go WAY too long on an IFR certified aircraft anyway. Break em. Fine by me. And they're not going to break if they're long enough. No way, no how. Find a mechanic with a cutaway version to look at and tell me how you'd damage one that wasn't a) ready to break anyway, or b) had a manufacturing defect or other internal problem.

Jim Logajan said:
I think maybe PoA needs a "Useless Aviation Minutiae" subforum.
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It's called "the whole site". ;)

jesse said:
A 1/4 turn of the prop on a 4 cylinder is going to run one cylinder through its entire compression stroke including the mag firing the plug. If the conditions are right it will indeed start...the only thing missing is whether or not the fuel/air ratio will make a boom that'll ruin your day. Plenty of mechanics have found it can indeed happen.
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Another reason to buy big sixes! ;)

As far as the P-lead check goes, I know someone who had one break right at shutdown from the engine stopping vibrations and shudders right after he tested it, and he got a nice scare when he turned his prop forward (no I don't know how he got fuel in there if he shut it down properly with mixture either, but it happened...)

I treat the prop like it WILL fire when I move it, not like it MIGHT fire. Never in the arc when moving it and ready to move myself backward at least and hopefully off to a side. But I don't put any value on a p-lead check that happened a minute before the prop stopped and the vibration stopped. All that tells you is that it was connected when you did the test. Still might have fallen off after that, or been chewed off by a critter, who knows. Almost a useless test.

The prop is always hot. And always gets turned backward. And I'm still ready to get out of the way. That's it for me.

The other rule is, "nothing is attached to the nose wheel if you're hand is not attached to whatever it is". I only break this rule in one location and it's very ritualistic.

The tug stays on long enough for me to walk to the door and set the brake in front of our hangar because it's not perfectly level there. Leaving the tug in "gear" (really it's belt driven) makes sure the airplane won't go anywhere until its brakes on or chocked so I can put the tug away.

But nothing and I mean nothing interrupts that walk to the door to set the brakes and then right back to the nose wheel and the tug or towbar comes off. Other than that, my hand is always attached to whichever one I'm using. If I leave the front of the airplane, the nose wheel device leaves with me. Nothing stays attached to the nose wheel unattended. Ever.
 
I've got three blades...which one would you like vertical?
 
Sam D said:
I see what you're saying. But then why does my plane (Lance w/IO-540) hot start just fine without ever enrichening the mixture?
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Because it is fuel injected, It won't run long with out moving the mixture to rich.

But yes, if you have fuel injected engine and a hot mag, you can get a cylinder to fire with the mags off and the mixture at idle cut off. (full lean) It's all because the fuel injection lines will still have fuel in them which bleeds out after shut down.
 
jesse said:
A 1/4 turn of the prop on a 4 cylinder is going to run one cylinder through its entire compression stroke
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Nope. You may get "lucky" but there's no guarantee. A quarter turn will bring one cylinder to the top of its stroke, but it may be the exhaust stroke rather than the compression stroke (it takes two revolutions to fire all the cylinders).
 
Huh. When I used to prop my Cub and had the prime correct I could pull the prop 12-15" through one compression stroke and it'd fire right up. That's a lot less than a quarter turn.
 
Captain said:
Why is picking one to be vertical on a three blade different than picking one on a two blade?
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In a two blade, making one vertical makes the other vertical.

In a three blade, there's no way to make them all vertical. WHat do you wnat to accomplish? Put one blade at 12 oclock? At 6 Oclcok? What about the other two?
 
Warners and Rangers typical set up right tend to "burst" into life more so than any other engines I've seen.

I tend to place my props at a 45° angle in the hangar. Greatly reduces the running into them.


Jim R
Collierville, TN

N7155H--1946 Piper J-3 Cub
N3368K--1946 Globe GC-1B Swift
N4WJ--1994 Van's RV-4
 
I have a 3 blade and if parked outside, try to have it vertical below the spinner, so that bird **** doesn't get all over the spinner.
 
I grew up in aviation, mostly flying old taildraggers. I was always told your prop should stop at the 10/4 position. So far all of my planes have done this. I'm not sure if that's just how they're set on old taildraggers, but it does leave the prop right where it needs to be for hand-propping.

When I look at photos I've taken of my friend's planes, they all stop in the same position and we tend to leave them that way. Now there's always that one genius who want to rotate your prop so he can get the photo he wants. I like to have nice, pleasant conversations with that guy!

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Pilawt said:
Yep. My prop stops vertical on shutdown every time - no exceptions ever that I can remember. It has to be moved in order to connect and use the tow bar.
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JoseCuervo said:
And, my statement remains true, I would love to fly an airplane that started on the first cylinder compressing by a 1/4 turn of a prop.

I have just never started a plane that fired instantly.
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The A65 on my taildragger will usually start when warm if you rotate the prop fairly slowly (CCW from the front) just far enough to trip the impulse couplers. Of course the fact that it has no mixture control and must be shut down with the mag switches makes this more likely but in many engines it's quite possible to end up with a combustible mixture after shutting down with the mixture control.
 
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