Pulling by the Prop

[PTK]

Quote: Emmet

"I hope we can agree that a static force on the prop perpendicular to its direction of rotation, such as applied when attempting to move the airplane on the ground, is very different than the dynamic loads parallel to its direction of rotation, such as when the engine and prop are rotating in flight"

 

"As being an engineer for over 20 years... all that comes to my mind is - what a complete bullshit ..."

Engineering is a science of facts and numbers - not opinions !

Just my 5 cents

[maniago]

Quote: allsmiles

I don't think so. I respectfully disagree. You know, what is really disturbing is that we have these engineers on here who should, in theory at least, have a different perspective on things. 

You, an engineer, can't understand the real physical issues introduced when a localized force is applied on a small area of the blade of a prop at rest? You don't see how this can potentialy "bend" the blade and at the very least throw it out of track? You don't understand that that the prop relies on centrifugal force to stay rigid? Which only happens when it is spinning and not present when not spinning?

You as an engineer don't undestand  that the phenolic links are not very strong in tension such as when you push on a static prop but extremely strong in compression such as when spinning? You don't see that applying a localized force on a static prop can cause misalignment of the actuating pin mechanism and upset the blades in the hub?

Really??!!

Let me attempt to enlighten you. A spinning prop is indeed very different than a static one. It relies on centrifugal force and draws its strength from the compression forces of this force. To make the argument that the prop withstands much greater loads in flight than can ever be applied to it by pushing on it is ludicrous. Unless ofcourse you try to push on it in flight and compare the forces. 

I never handle my airplane by the prop nor will I allow anyone else to do it. But each to his own.

And these are my two cents.

 

[Cris]

Ok enough already. I am not an engineer but I will say that we all have opionions and I work at being respecful. Allsmiles generously bought our Mooney Group Lunch yesterday & I as well as the others say THANKS. I tried to get him to come over but he had family pressures. Had he been there he would have been treated to a good laugh & I'll bet he would have even lauged at himself as we were all prepared to push & pull pn my poor Mooney hoping that the prop would not disintegrate. What we need here is the ability to get to know one another on a personal basis which allows a great deal of fun. Any takers? And these are my two cents .   

[maniago]

But isn't that what we are doing?  Trying to dispell wives-tails and rumors?  Not long ago, this would have been a heated discussion on "to lean or not to lean", having forgotten what our round motor breathren knew long long ago...

But, I don't see personal attacks or name calling.  That is clearly beneath us.

[PTK]

Quote: maniago

I don't think so. I respectfully disagree. You know, what is really disturbing is that we have these engineers on here who should, in theory at least, have a different perspective on things. 

You, an engineer, can't understand the real physical issues introduced when a localized force is applied on a small area of the blade of a prop at rest? You don't see how this can potentialy "bend" the blade and at the very least throw it out of track? You don't understand that that the prop relies on centrifugal force to stay rigid? Which only happens when it is spinning and not present when not spinning?

You as an engineer don't undestand  that the phenolic links are not very strong in tension such as when you push on a static prop but extremely strong in compression such as when spinning? You don't see that applying a localized force on a static prop can cause misalignment of the actuating pin mechanism and upset the blades in the hub?

Really??!!

Let me attempt to enlighten you. A spinning prop is indeed very different than a static one. It relies on centrifugal force and draws its strength from the compression forces of this force. To make the argument that the prop withstands much greater loads in flight than can ever be applied to it by pushing on it is ludicrous. Unless ofcourse you try to push on it in flight and compare the forces. 

I never handle my airplane by the prop nor will I allow anyone else to do it. But each to his own.

And these are my two cents.

 

[Cris]

Quote: maniago

But, I don't see personal attacks or name calling.  That is clearly beneath us.

[maniago]

PK,

They are not totally different.  They are totally related.  Static tests and stressors are related to dynamic tests and stressors.  When we torque the bearing cap bolts on the crank, the crank is static.  But we know that those torque settings will provide the correct amount of "holding power" when the crank is flinging around dynamically. So is the same with the bolts that hold your prop to the flange.

A really good slide rule engineer would probably model that moving prop as just a prop that is stationary for a micro second, then is in a new stationary position a micro second later.  And the two positions and stressors in those positions are interrelated and can be recreated in a much more static modulus test.  Harmonic stresses are much harder to test for, and tend to be empirical (tho a nod to computers must be made these days).

That said, pulling on your prop is far more akin to the static testing, for which the entire assembly (ie the whole airplane) has been modeled and tested.

But I understand what you are trying to say, and it is important to approach the subject cautiously and "safety-wise", as you are.  Some people use caution where its not necessary, but that's a whole lot better than throwing caution to the wind instead.

Similarly,  I hope you change your oil more often than 50hrs and fly every two weeks to keep the water off your cylinder walls.  But its not required! haha

M.

[Emmet]

Wow.  Dr Smiles (dentist I believe - wonderful profession BTW) you totally crack me up!  You have got to be writting this stuff just to egg us engineers on, because I can't stop laughing.  That said, I have to take the bait - silly me.

Please, please go back to your Stress and Strain books from freshman year.  Bending (or perhaps flexing is a better word really) is absolutely necessary of metal structures or they would fail imminently.  Ever seen a helicopter blade moving? They flap like a birds wing when moving.  Your AL prop also flexes as it moves through the turbulent air too.  Take a stobe light to it.  Ever seen an engine crank flex while in motion?  They vibrate like a sonic toothbrush.  Its down right scary, but thank God they do.  As long as the modulus of bending is NOT exceeded, all is well (though in truth, AL has a fatigue life based on number of flexes as well as its modulus; wood and iron compounds, modulus only).  But you and your body just can't do the damage you are insinuating.  Well, unless you are really Clark Kent, and youre just toying with us mear humans.  And oh by the way, there is no such thing as centrifugal force, only centripetal, but that's another entirely different arguement. 

Please please, stop with this.  Youre killing me.

[PTK]

OK Maniago, can I have all those x-rays and strobe light image studies of my prop! I'm going for a second opinion! 

On a second thought what's the use. They'll probably happily give me a third one as well telling me I dress my prop funny too!! 

[maniago]

PK, You can usually find anything on You Tube, but I struck out on crankshaft flex, which is odd since its totally cool to see.  Probably have to dig into a drag racing forum.

However, I then looked for camshaft flex as they do the same thing and got this:

Personally I had to stop it as I began to hurl!  Your mileage may vary haha 

[John Pleisse]

Quote: DonMuncy

To those who erroneously state that Mooney advocates against pushing/pulling on the prop; My K model POH says;

"When no towbar is available, or when assistance in moving the aircraft is required, push by hand: (1) on the wing leading edges, and (2) on the inboard portion of propeller blades adjacent to the propeller hub." 

[rob]

I don't think they are. The instruction also includes when assistance is required; so basically it's saying "no big deal" as I read it.

[John Pleisse]

Quote: rob

I don't think they are. The instruction also includes when assistance is required; so basically it's saying "no big deal" as I read it.

[jetdriven]

So can anyone produce one accident or one SDR blaming pulling on the prop to park the plane anywhere? Is there ANY proof?   Because so far all I hear is "yellow ticket" theorists spouting theories masked as fact while the ATPs pull their airplanes out of the hangar as they have done for 80 years.  FAA examiners watch applicants do it on check rides.  I did too. 

 

Anyone? Anyone?   

[takair]

Some good reading on the care of propellers and some failure modes to be aware of:

http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgAdvisoryCircular.nsf/list/AC%2020-37E/$FILE/AC%2020-37e.pdf

[John Pleisse]

Quote: jetdriven

So can anyone produce one accident or one SDR blaming pulling on the prop to park the plane anywhere? Is there ANY proof?   Because so far all I hear is "yellow ticket" theorists spouting theories masked as fact while the ATPs pull their airplanes out of the hangar as they have done for 80 years.  FAA examiners watch applicants do it on check rides.  I did too. 

 

Anyone? Anyone?   

[201er]

Quote: N4352H

 

Kind of like choking cylinders and valve guides trying to run a 4bLyc LOP at 8,000 msl. You might not feel the damage until well after 300 hours of doing it. However, eventually..........you will.

[jetdriven]

Mike, didn't you get the message? LOP burns valves and cylinders.  That's why there is a pile of cylinders at our shop full of carbon and didnt pass the annual and our engine blew mid 70s with 1500 hours.  

[PTK]

Quote: N4352H

Like many things, it is the overall cummulative affect of repeating a varied action. Of course pulling and pushing a plane by the blades isn't going hurt anything, probably the first 100 times. A little loose shim this time......a little blade imbalance next time......a little crank detuning the following time...... x 200. Cummulatively, over many cycles it will cause problems. Not actually by doing it, but on start up after you do it. Another thread of absolute mathematical fact required to sway total common sense.

Kind of like choking cylinders and valve guides trying to run a 4bLyc LOP at 8,000 msl. You might not feel the damage until well after 300 hours of doing it. However, eventually..........you will.

I guess you could say pushing and pulling by the blades would be almost like not having to purchase 5 power tugs which.......would pay for a tear down. Great logic, eh?

[jetdriven]

That's a straw man argument, PK!  How about some data, because all I can smell from here is manure.  

[PTK]

Hey Byron, could it be that stale camguard you're sniffing?

 

 

In all seriousness it really is different strokes for different folks. We all have our ways of doing things. What a boring world this would be if we were all thinking alike! Round but boring!

On a second thought maybe it wouldn't be so bad, everybody would fly Mooneys!

Did you put in the fire extinguisher?

[jetdriven]

This thread remInds me of virgins debating the merits of various whorehouses.  I haven't done hbe fire extinguisher mod. We just slammed out the annual in ten days, all redone interior plastic, rerigged gear,bunch of other stuff. 

 

[jetdriven]

Disregard 

[PTK]

Quote: jetdriven

This thread remInds me of virgins debating the merits of various whorehouses.  I haven't done hbe fire extinguisher mod. We just slammed out the annual in ten days, all redone interior plastic, rerigged gear,bunch of other stuff. 

 

[orangemtl]

Hey, can someone out there help me?

See, I was pushing my plane into the hangar, and accidentally reached up and pushed on the prop.  Bent it right over the cowling like a coffee stirrer.  

So, here's the question: do I just reach up and bend it back into shape, or should I leave it to a qualified A&P mechanic? I think it has something to do with the elastic modulus of the alloy, divided by the angle of deflection, or something.  But I'm no engineer, so your guess is as good as mine.