Reason for Rotating Propeller to Vertical When Done

eetrojan

eetrojan

Pattern Altitude
Joined
Jan 19, 2012
Messages
1,531
Location
Orange County, CA
Display Name
Display name:
eetrojan
Under "Securing Airplane," in addition to items like tie-downs, chocks, control lock, etc., my flight school's Cessna 172 checklist says "Prop... VERTICAL".

Why does this matter? Is there some substantive reason for proactively doing this?

I'm not super excited about hand turning the prop without a good reason.
 
Hmm... maybe so you don't bonk your forehead or eyes into the thing by accident (as weak as that may be)? There's a guy here who says he puts his prop vertically so birds don't sit on the blades.
 
Some places want the prop rotated to tell the fuel guys that the plane needs to be refueled. Some others want it left in a position where water (rain, snow, sleet) will drain out instead of freezing in place inside the spinner.
 
I've heard the fuel thing too, personally I don't want line guys messing with my fuel because of how my prop came to rest, that's what fuel tickets are for.


From my experience I leave my prop horizontal, or with the third blade on top, or for a 4 blade in a X, reason is the plane can be towed that way as needed, without someone having to touch your prop.
 
James331 said:
I've heard the fuel thing too, personally I don't want line guys messing with my fuel because of how my prop came to rest, that's what fuel tickets are for.


From my experience I leave my prop horizontal, or with the third blade on top, or for a 4 blade in a X, reason is the plane can be towed that way as needed, without someone having to touch your prop.
Click to expand...

Me too....:yes:
 
We do it on our club plane for two reasons. Less chance to walk into it, and less room for birds to poop on.
 
The only time I move a prop is in preparation to start, never after shutdown. My prop stops where it stops and stays there until next time.

Guys I see who do move their props move them to horizontal to assure a passing wingtip won't catch their prop.
 
Stewartb said:
The only time I move a prop is in preparation to start, never after shutdown. My prop stops where it stops and stays there until next time.

Guys I see who do move their props move them to horizontal to assure a passing wingtip won't catch their prop.
Click to expand...


That is my experience too.........
 
i turn mine horizontal after shut down because it gets polished after every flight.

bob
 
If I pull through to park, it's staying however it falls, which is usually vertical. If I have to break the tow bar out, it goes horizontal. If there's freezing weather forecasted, I'll assure it's vertical.
 
gms5002 said:
I turn my horizontal so it doesn't get in the way of the tow bar.
Click to expand...

Makes a great push point also. ;)

I need horizonal for taking the cowel off. :yes:

I have heard wood props need horizontal for balance. Not sure why, but that is what I heard from the old timers.
 
Last edited:
Spinners collect water, except when they are vertical.
 
A prop must be placed vertically so the birds can poop on your spinner!
 
I set mine vertical in the hanger so no one walks into it.. hard to see in the dark and not much room between nose and door. Lots of good reasons to do it and not to do it.....depends on the situation more than the plane and prop.

Frank
 
Mine is horizontal to make room for the tow bar. I only move it if it happened to stop almost vertically.

I am not good enough yet to watch the prop and pull the mixture at exactly the right moment to always stop horizontally. ;)
 
Geico266 said:
I have heard wood props need horizontal for balance. Not sure why, but that is what I heard from the old timers.
Click to expand...

Wood props can absorb water when they get wet. That water tends tocollect in the lowest blade and throws the balance off a bit. Leaving the prop horizontal tends to even that out.

Better to keep the finish in good, tight condition so the rain runs off, but seme older prop designs with the riveted-on brass leading edges are hard to seal. I made a vinyl cover for mine that has a velcro closure all along the bottom edge. Keeps the sun and rain off it.
 
I think I heard you want horizontal to save your prop seal. :dunno:

It depends on the situation.

I'll leave mine vertical sometimes when I'm working around it but most the time it's horizontal when it's perched in the hangar. I can see leaving it vertical outside in freezing or nasty weather to keep the spinner drained out and maybe less ice accumulation.
 
Back when I was a lowly student pilot, one of my CFIs suggested dressing the prop horizontal to reduce the chance of a passing wing tip hitting it. Parking was kind of tight back then. The planes at the flight school we're alternated from high wing to low wing in parking so they could be parked closer together (wingtip of low wings were even/under the wingtips of high wings). The rows were tight as well.
 
Heard of a few instances where water got into the turbine through that stacks and froze up, prop was not in a position to tow the plane to warmer positions, so it just had to sit and freeze more.
 
James331 said:
Heard of a few instances where water got into the turbine through that stacks and froze up, prop was not in a position to tow the plane to warmer positions, so it just had to sit and freeze more.
Click to expand...

Had that happen in a helo. Blades will still advance because of the freewheeling unit but they won't go backwards. Definitely don't want to force it either. Pretty much done until it melts.
 
EppyGA said:
I usually put mine horizontal.

Curious about your statement above?
Click to expand...

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.
 
For 25 years I've parked outside in Alaskan weather and have never been concerned with or experienced any water or ice in a spinner.

I was taught long ago that engine clearances in the minutes following shutdown are the closest they'll ever be as that hot engine stops circulating oil and sits in still air. My reluctance to move my prop is related to that.
 
Stewartb said:
For 25 years I've parked outside in Alaskan weather and have never been concerned with or experienced any water or ice in a spinner.

I was taught long ago that engine clearances in the minutes following shutdown are the closest they'll ever be as that hot engine stops circulating oil and sits in still air. My reluctance to move my prop is related to that.
Click to expand...

If that's a factor, the engine won't turn. Air cooled engines have loose tolerances precisely because of that.

I doubt it's as hot as it will ever be after a landing. You've been idling the engine. CHT is a lot higher after an extended Vx climb.

Remember, the engine is not producing heat after shutdown. It's just equalizing what it already has, and temperature probes aren't always at the hottest part.
 
Last edited:
register@teamandras.com said:
I'm not super excited about hand turning the prop without a good reason.
Click to expand...


EppyGA said:
I usually put mine horizontal.

Curious about your statement above?
Click to expand...

I'm referring to some potentially ignorant notions that I have from earlier training:

1. Risk of Starting by Hand Turning Prop – As background, I trained in a plane with a Rotax 912 engine. Part of the pre-flight procedure was to measure the oil level after rotating the propeller to pump oil into the dry sump located outside of the engine casing. I was taught that it was safe to rotate the Rotax 912, that it would not start on prop rotation if the key is out of the ignition and hanging.

I’m probably being overcautious, but I was also taught that the Cessna 172 may start if the magnetos are not properly grounded, even when the ignition switch is in the off position. The Cessna’s checklist includes a momentary-off “ground check” after each flight, so I assume this is a real difference. On the other hand, maybe the Rotax has the same risk of starting due to a faulty ground connection while "off" and I'm just an idiot.

2. Risk of Damage from Rotating Prop Backward – I was taught that I could damage the Rotax 912 engine if I rotated the propeller backwards – supposedly it could damage the vacuum pump, or draw air into the hydraulic tappets, or something like that. I am not sure if there's a risk of damage with the Lycoming engines.

Feedback welcome!




Edit - Evidently it is relatively safe to rotate the propeller in a plane with a Rotax engine because “the ignition system is only able to generate enough power to power itself once the engine is turned over to a minimum of 300RPM in the case of Rotax 2-Stroke engines and 220RPM in the case of the Rotax 912 / Rotax 914 series.”
 
Last edited:
register@teamandras.com said:
I'm referring to some potentially ignorant notions that I have from earlier training:

1. Risk of Starting by Hand Turning Prop – As background, I trained in a plane with a Rotax 912 engine. Part of the pre-flight procedure was to measure the oil level after rotating the propeller to pump oil into the dry sump located outside of the engine casing. I was taught that it was safe to rotate the Rotax 912, that it would not start on prop rotation if the key is out of the ignition and hanging.

I’m probably being overcautious, but I was also taught that the Cessna 172 may start if the magnetos are not properly grounded, even when the ignition switch is in the off position. The Cessna’s checklist includes a momentary-off “ground check” after each flight, so I assume this is a real difference. On the other hand, maybe the Rotax has the same risk of starting due to a faulty ground connection while "off" and I'm just an idiot.

2. Risk of Damage from Rotating Prop Backward – I was taught that I could damage the Rotax 912 engine if I rotated the propeller backwards – supposedly it could damage the vacuum pump, or draw air into the hydraulic tappets, or something like that. I am not sure if there's a risk of damage with the Lycoming engines.

Feedback welcome!




Edit - Evidently it is relatively safe to rotate the propeller in a plane with a Rotax engine because “the ignition system is only able to generate enough power to power itself once the engine is turned over to a minimum of 300RPM in the case of Rotax 2-Stroke engines and 220RPM in the case of the Rotax 912 / Rotax 914 series.”
Click to expand...

I was taught that the Rotax is not to be rotated backward due to the gearing. But, yeah, I was taught to rotate all direct drives backward to avoid a possible hand amputation.
 
Tom-D said:
Spinners collect water, except when they are vertical.
Click to expand...

I disagree. It can be a PITA to get a fuel tank access panel on a wet wing fuel tank to stop leaking. Sealant isn't applied to spinners they will leak even faster.
 
I believe it has already been mentioned but the only valid reason I can think of for positioning the prop vertically would be to lessen the chance of anyone walking into it or banging their head on it. When I am working on an airplane this is what I do for that reason.
 
register@teamandras.com said:
I'm referring to some potentially ignorant notions that I have from earlier training:

1. Risk of Starting by Hand Turning Prop – As background, I trained in a plane with a Rotax 912 engine. Part of the pre-flight procedure was to measure the oil level after rotating the propeller to pump oil into the dry sump located outside of the engine casing. I was taught that it was safe to rotate the Rotax 912, that it would not start on prop rotation if the key is out of the ignition and hanging.

I’m probably being overcautious, but I was also taught that the Cessna 172 may start if the magnetos are not properly grounded, even when the ignition switch is in the off position. The Cessna’s checklist includes a momentary-off “ground check” after each flight, so I assume this is a real difference. On the other hand, maybe the Rotax has the same risk of starting due to a faulty ground connection while "off" and I'm just an idiot.

2. Risk of Damage from Rotating Prop Backward – I was taught that I could damage the Rotax 912 engine if I rotated the propeller backwards – supposedly it could damage the vacuum pump, or draw air into the hydraulic tappets, or something like that. I am not sure if there's a risk of damage with the Lycoming engines.

Feedback welcome!




Edit - Evidently it is relatively safe to rotate the propeller in a plane with a Rotax engine because “the ignition system is only able to generate enough power to power itself once the engine is turned over to a minimum of 300RPM in the case of Rotax 2-Stroke engines and 220RPM in the case of the Rotax 912 / Rotax 914 series.”
Click to expand...

Rotating the Rotax 912/914 backwards can get air in the lifters - apparently there have been some failures. Lycoming / Conti do not claim to have this issue. (The whole oil system on the Rotax 912/914 is quirky...)

The Rotax does not have any sort of impulse on the magneto so you have to spin it reasonably quickly to get a spark (as you note). But the 912 can be hand propped, contrary to what some "experts" would like to tell you.

Many other piston aircraft engines have an impulse coupling to cause a magneto to fire the spark plug even when turning slowly (you can hear it click when you turn the prop). Turning it backwards is a safer option since it won't trip the impulse.

So, yes, there is a difference.

Note: The risk to vacuum pumps is small and many have suggested that if it breaks because you turned the prop backwards, it was ready to break anyhow.

The impulse connection is a spring connection between the magneto and the engine that allows the magneto to be held in position while the engine rotates (at low speeds only) until the spring winds up, the system trips, and the magneto spins fast enough to make a good spark.
 
Capt. Geoffrey Thorpe said:
Rotating the Rotax 912/914 backwards can get air in the lifters - apparently there have been some failures. Lycoming / Conti do not claim to have this issue. (The whole oil system on the Rotax 912/914 is quirky...)

The Rotax does not have any sort of impulse on the magneto so you have to spin it reasonably quickly to get a spark (as you note). But the 912 can be hand propped, contrary to what some "experts" would like to tell you.

Many other piston aircraft engines have an impulse coupling to cause a magneto to fire the spark plug even when turning slowly (you can hear it click when you turn the prop). Turning it backwards is a safer option since it won't trip the impulse.

So, yes, there is a difference.

Note: The risk to vacuum pumps is small and many have suggested that if it breaks because you turned the prop backwards, it was ready to break anyhow.

The impulse connection is a spring connection between the magneto and the engine that allows the magneto to be held in position while the engine rotates (at low speeds only) until the spring winds up, the system trips, and the magneto spins fast enough to make a good spark.
Click to expand...

Thanks for this great explanation!

Just to make sure, with the key out and the mags off, is it OK to rotate the prop backwards on all Cessna 172s?
 
I think if I was running a flight school, I wouldn't create any requirements around moving the prop after shutdown. Seems like any small benefit to be had by a horizontal or vertical prop would be significantly outweighed by the one person who forgets to turn the mags off and gets an unpleasant surprise.
 
Capt. Geoffrey Thorpe said:
Many other piston aircraft engines have an impulse coupling to cause a magneto to fire the spark plug even when turning slowly (you can hear it click when you turn the prop).

The impulse connection is a spring connection between the magneto and the engine that allows the magneto to be held in position while the engine rotates (at low speeds only) until the spring winds up, the system trips, and the magneto spins fast enough to make a good spark.
Click to expand...

It also serves the very important function of retarding the spark to at or near TDC. The engine will not start if the spark is occurring at the 25 deg or so advanced setting at starter cranking speed. Engines without an impulse coupler use a retard breaker and shower of sparks module.
 
If you don't do a "mags off" check before shutdown to assure there isn't a hot mag you have no business touching the prop on an airplane. It's fine wherever it is. If you must move the prop, move it backwards. It makes me cringe when I hear the impulse coupling click as folks pull the prop through.
 
I think maybe PoA needs a "Useless Aviation Minutiae" subforum.
 
The school I use rotates props to vertical in the winder to stop water from accumulating in the spinner during winter and freezing.
 
You must log in or register to reply here.
Back
Top