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Pushing and pulling via the prop.

WingnutWick

Well Known Member
Hello all,

Just getting an idea on if it's bad or not to gently push/pull the airplane by the root of the prop close to the spinner to move it around. Airplane in question is an RV-6A with O-320 H2AD fixed catto prop.

Thank you!

Cheers
 
I push and pull my RV-6A by the prop and was told to do so by my mechanic. Think about it, the prop is pulling the plane through the air so there is much more load on it when flying than you could put on it on the ground. Now I do like you said and push/pull near the hub not way out at the tip, even though I doubt even that would cause any issues.
 
I push and pull my RV-6A by the prop and was told to do so by my mechanic. Think about it, the prop is pulling the plane through the air so there is much more load on it when flying than you could put on it on the ground. Now I do like you said and push/pull near the hub not way out at the tip, even though I doubt even that would cause any issues.

For a Hartzell CS prop, Hartzell recommends against this. The reason given is that supposedly without the centrifugal force of the prop rotation pulling the blades into their bearings, the bearings can be damaged from pulling on the blades.

Frankly, I find it hard to believe that gentle pull or push at the blade root could be any harder on the bearings than some of the occasional "violence" of engine start-up and shut-down when the prop doesn't have much rotation velocity...

Skylor
 
Ah, I guess I left out a bit of info. I have a fp prop on my plane. I could see where it might be slightly different with a cs prop but with how light our planes are I still don't see how that could cause a problem.
 
For a Hartzell CS prop, Hartzell recommends against this. The reason given is that supposedly without the centrifugal force of the prop rotation pulling the blades into their bearings, the bearings can be damaged from pulling on the blades.

Frankly, I find it hard to believe that gentle pull or push at the blade root could be any harder on the bearings than some of the occasional "violence" of engine start-up and shut-down when the prop doesn't have much rotation velocity...

Skylor

Approximate percent of people who use prop to pull their Hartzell (and others) equipped RV's is 100%
 
why do it?

There is a thrust bearing in the engine but on the ground it has no oil pressure.
If you can push or pull without turning the prop it's probably ok but if it turns as you are pulling it could damage the bearing. So why not just push on the cowl and pull with a tow bar?
 
sorry, i gotta disagree. it is just totally illogical that my little 5 fingers pulling at the hub of the prop on that bearing is gonna damage it while it lugs around that airframe at 200 mph being pulled by 200 hp. oil pressure or no oil pressure. i would be way more cautious of damaging my cowling.
.
 
Post 5 +1 This issue is that if the prop mfg.s OK pushing and pulling on the prop then people will push and pull on the tips and asymmetrically. If you push and pull at the hub and do it evenly on both sides, you are fine.
 
Wife and I have owned 20+ personal use airplanes over the past 47 years. We have pulled or pushed on the props, near the hub, on all of them.

I have had many of the engines on our planes apart (I'm an A&P/IA), and the engines on other's planes apart also,and have so far, never witnessed damage caused by this practice.
 
sorry, i gotta disagree. it is just totally illogical that my little 5 fingers pulling at the hub of the prop on that bearing is gonna damage it while it lugs around that airframe at 200 mph being pulled by 200 hp. oil pressure or no oil pressure. i would be way more cautious of damaging my cowling.
.

Spot on given that heat is what degrades bearings and their lubrication. Turning the prop by hand will never heat to even close their continuous design run temperature.
 
Just ordered a ground adjustable Sensenich Prop and the instruction say, "Do not use the propeller as a tow-bar to move your aircraft." Started designing a tow bar for the tail wheel today. But it does seem that if the prop can pull the plane through the air I should be able to push/pull on it near the root. However, I will follow the instructions.
 
Yeah...as long as you're at the root, you're not going to come anywhere near the load produced by a Lycoming spinning at 2700RPM's.

Disclaimer, I fly a Catto 3-blade FP prop.
 
There is a thrust bearing in the engine but on the ground it has no oil pressure.
If you can push or pull without turning the prop it's probably ok but if it turns as you are pulling it could damage the bearing. So why not just push on the cowl and pull with a tow bar?

Following that logic, you would never be able to start your engine. Your crank, cam and rod bearings are dry (not technically dry, they have only the coating of oil from the last run) for several seconds after each start up(probably at least 25 revolutions with a relatively tight pump), until the oil gets flowing by the pump. And those crank and rod bearings are getting WAY more force on them than you pulling on the prop while you turn it.

Larry
 
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So why not just push on the cowl and pull with a tow bar?

Push on the cowl? Kinda tough given the orientation of its surfaces relative to the direction the push needed to move the plane. Also, the cowl doesn?t seem well enough supported structurally to be suitable for pushing.

The bogie bar is what a lot of use for a tow bar. It is definitely not made for pushing and pulling, only for steering. It?s a given it will brake before too long if use for pushing n pulling.

Erich
 
Had this discussion during RECIPS II class in A&P school. General consensus from several instructors was that, as has been mentioned, crankshaft/prop-hub combo is the strongest engineered components of an AC. But a consensus point against, aside from any manufacturers warnings against doing so, was the possibility of a hot mag situation and/or broken p-lead. An inadvertent turn of the prop might end badly. Just something to keep in mind.
 
I do it

I have no towbar, always use prop at hub (Sterba woody). Can't hurt the thrust bearing doing it, but you will hear some people realize there is a slight "click"or "bump"they feel when pushing/pulling, which is because the thrust bearing and all the crank bearings, have clearances FWD and AFT to allow for expansion during heat up and dynamic movement that would cause seizure if it were tight. The crank bearings are really more of a bushing (no balls or rollers) as one would speculate, but just a simple plain bearing made from a relatively soft material, requiring continuous lubrication. On another note, I too have an O320H2AD..great engine for less $$ than most others. I have built several, and like the simplicity.
 
I have no towbar, always use prop at hub (Sterba woody). Can't hurt the thrust bearing doing it, but you will hear some people realize there is a slight "click"or "bump"they feel when pushing/pulling, which is because the thrust bearing and all the crank bearings, have clearances FWD and AFT to allow for expansion during heat up and dynamic movement that would cause seizure if it were tight. The crank bearings are really more of a bushing (no balls or rollers) as one would speculate, but just a simple plain bearing made from a relatively soft material, requiring continuous lubrication. On another note, I too have an O320H2AD..great engine for less $$ than most others. I have built several, and like the simplicity.

Just to clarify for the curious, the Lycoming does not have a thrust bearing/bushing. The crankshaft has about a 3/16" ring (it is integral to the crank, just machined) on it just forward of the nose bearing area. That ring sits inside a cavity machined directly into the case with for and aft thrust surfaces, just forward of the nose bearing reatiner area. It does not get a direct, pressurized oil feed either. THough it receives a great deal of oil flowing out of the nose bearing interface, due to its proximity to that bearing

Older auto engine typically used the side flange of the forward bearing shell for thrust. The Lyc nose bearing is not designed that way.

I push both my RVs via the spinner while using a tow bar for sterring; only because it is easier than using the prop. Easily fixable if I cause any damage. I pull via the tow bar. I find pushing with the tow bar to make it impossible to get precise steering. When needing a lot of force, like when stuck in grass, I do push on the prop root area.


Larry
 
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Larry is correct

You are correct Larry, just the thrust flange on the LYCO, but the layman's explanation was about the crankshaft for-aft free play that some folks get nervous over. My last overhaul was a little CONTI which does have a true thrust bearing.
 
Oil Slinger

Larry
“Just to clarify for the curious, the Lycoming does not have a thrust bearing/bushing. The crankshaft has about a 3/16" ring (it is integral to the crank, just machined) on it just forward of the nose bearing area. That ring sits inside a cavity machined directly into the case with for and aft thrust surfaces, just forward of the nose bearing reatiner area. It does not get a direct, pressurized oil feed either. THough it receives a great deal of oil flowing out of the nose bearing interface, due to its proximity to that bearing”

The feature Larry mentions is the oil slinger which is integral to the crankshaft in a Lycoming engine. It’s purpose is to remove the oil from the nose bearing and sling it to a drain port and return it to the crankcase and is never even in contact with the case in a tractor configuration. The thrust face is on the crankshaft at the front of #1 rod to the crankcase. In a pusher configuration it (oil slinger) would serve as the thrust surface which seems to work even though a casual observation would cause you to question whether it was up to the task. Either way It’s stronger than the force you can put on it by pushing pulling on the nose of the crank.

Now back to the OP question I’ve always used wood props and push and pull the heck out of them near the hub and have no issues with the practice.
 
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Larry
“Just to clarify for the curious, the Lycoming does not have a thrust bearing/bushing. The crankshaft has about a 3/16" ring (it is integral to the crank, just machined) on it just forward of the nose bearing area. That ring sits inside a cavity machined directly into the case with for and aft thrust surfaces, just forward of the nose bearing reatiner area. It does not get a direct, pressurized oil feed either. THough it receives a great deal of oil flowing out of the nose bearing interface, due to its proximity to that bearing”

The feature Larry mentions is the oil slinger which is integral to the crankshaft in a Lycoming engine. It’s purpose is to remove the oil from the nose bearing and sling it to a drain port and return it to the crankcase and is never even in contact with the case in a tractor configuration. The thrust face is on the crankshaft at the front of #1 rod to the crankcase. In a pusher configuration it (oil slinger) would serve as the thrust surface which seems to work even though a casual observation would cause you to question whether it was up to the task. Either way It’s stronger than the force you can put on it by pushing pulling on the nose of the crank.

Now back to the OP question I’ve always used wood props and push and pull the heck out of them near the hub and have no issues with the practice.

Always appreciate being schooled by the experts. I never really noticed exactly where the thrust interface was and assumed it was the "slinger," but never really noticed that it only hit the case in only one direction. I always took measurements externally via crank movement, as opposed to a feeler gauge in the interface.

Larry
 
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The warning to not push/pull on a Hartzell CS prop has to do with the prop?s steel ball bearings not always in their proper position (when not rotating with rat Atis all force) in the aluminum prop and hub races, potentially causing little surface imperfections/stresses in the races. This is what I was told by a prop overhaul tech during Q&A at a prop shop tour. This wouldn?t apply to fixed pitch props.

Bevan
 
Just getting an idea on if it's bad or not to gently push/pull the airplane by the root of the prop close to the spinner to move it around. Airplane in question is an RV-6A with O-320 H2AD fixed catto prop.
The airplane pushes and pulls on the prop in flight, and the loads are a lot higher than you will apply on the ground. Put your hands near the spinner, and push or pull all you like, you'll never hurt the fixed-pitch prop or your engine.
 
Just to clarify for the curious, the Lycoming does not have a thrust bearing/bushing. The crankshaft has about a 3/16" ring (it is integral to the crank, just machined) on it just forward of the nose bearing area. That ring sits inside a cavity machined directly into the case with for and aft thrust surfaces, just forward of the nose bearing reatiner area.
That *is* a thrust bearing. It's not a separate, replaceable part, but it is a thrust bearing.
 
That *is* a thrust bearing. It's not a separate, replaceable part, but it is a thrust bearing.
Lycomings production run skipped this step on my 0-360 engine........

Bearing;
a part of a machine that bears friction, especially between a rotating part and its housing

Best
J.

~
 
That *is* a thrust bearing. It's not a separate, replaceable part, but it is a thrust bearing.

so, if that is a bearing, what do you call the specially designed inserts that go between the machined case and the crankshaft. A bearing, or technically a bushing in these applications (it is the constant flooding of oil that gives it bearing like properties), by definition is a separate component that goes between the assembly and rotating shaft for a a variety of purposes. What you describe could be called a load bearing surface or interface, but certainly not a bearing, as defined and used in the machinery business.

Not saying that bearings are required (lyc cams are a good example of a bearingless interface - again flooded oil supply provides bearing like qualities), only the semantics of a common language.
 
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Oil Slinger NOT a thrust face

Snowflake
?That *is* a thrust bearing. It's not a separate, replaceable part, but it is a thrust bearing.?
The feature of the crankshaft mentioned is NOT a thrust face in a tractor configuration. As a matter of fact the Lyc. overhaul manual specifies a clearance of .002?-.006? between the forward surface of the oil slinger and the crankcase. If this clearance is not maintained the crank can weld itself to the case as the forward face is largely dry from oil. On the dyno when they rub it makes a horrible sound, a high pitched squeal. The overhaul manual cautions you to check this clearance when swapping cranks into different cases that weren?t manufactured together as the factory sets these clearances as a set during assembly.
Sorry for rant and now back to the OP regularly scheduled question.
 
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