Prop balancing

[Brian Miller]

balancing props! me and a good a good friend have different ways of removing material from the blade. I was told many years ago to remove from the back not changing the lift on front edge and my friend says to remove from front is proper. DOES IT MATTER? just curious.

[M Spencer]

Put the engine at T D C and put the heavy blade oppsite the cylinder ( light blade at cylinder ) . 

At the field , If theres a problem , anyway . Or try it if its a shaker .
Getting the props at 90 Deg on a twin , both at T D C , can solve harmonic cr*p .

[pmackenzie]

Removing material from the face can change things (like pitch and under camber) more than the back. Allot of props are thick behind the high point of the back so it's a good place to start. Also, it's usually ok to move the high point farther forward as allot of prop have it at 40-50%. The only time I would consider taking something off ahead of the high point is if the prop sits horizontal in the balancer. Ultimately after you have the optimum airfoil, you have to start reducing the blade thickness all over. Usually it should come in balance before that. Allot depends on the prop and what you have to do to it. On some you have to reshape the whole thing and you can bring it in balance while doing that but the leading edge is usually the last thing you blend in.

Motorman

I think this has come up before, but by your description it sounds like your "back" would be what I call the "front"?
(i.e. you mention "high point of the back", where for me the back is basically flat on most props)
You also throw in the word "face", that to me sounds like you are describing the back?

For me front is the side the pilot can't see, back is the side he can.
Or put another way the front of the prop faces the same direction as the front of the plane.

As I said, I seem to recall a discussion where the other way around was argued for.



Pat MacKenzie

[Alan Resinger]

Airplane propeller terminology seems to baffle people.  Think of things as how the relate to the pilot sitting in the cockpit.  The pilots right side is denotescthe right side of the aircraft and vice versa.  The side of the propeller that faces the pilot is tne face of the prop.  The part of the prop being hit by the airstream is considered the bac, of the propeller. Seems weird but that is the way it is.  For propeller rotaton just sit in the pilots seat and if it rotates toward the right wjnv it is a right hand rotation prop.  If it rotates toward the left wing it is a left hand rotation prop, not a pusher pfop as some incorrectly refer to it as.  A pusher prop is mou ted on tbe rear of the aircraft and alos can be either right or left hand rotation.

[john e. holliday]

Put the engine at T D C and put the heavy blade oppsite the cylinder ( light blade at cylinder ) . 

At the field , If theres a problem , anyway . Or try it if its a shaker .
Getting the props at 90 Deg on a twin , both at T D C , can solve harmonic cr*p .

Thanks Matt, I was told this many years ago on a prop that was close.  Was told many props were ruined because people didn't know what they were doing.

[pmackenzie]

Airplane propeller terminology seems to baffle people.  Think of things as how the relate to the pilot sitting in the cockpit.  The pilots right side is denotescthe right side of the aircraft and vice versa.  The side of the propeller that faces the pilot is tne face of the prop.  The part of the prop being hit by the airstream is considered the bac, of the propeller. Seems weird but that is the way it is.  For propeller rotaton just sit in the pilots seat and if it rotates toward the right wjnv it is a right hand rotation prop.  If it rotates toward the left wing it is a left hand rotation prop, not a pusher pfop as some incorrectly refer to it as.  A pusher prop is mou ted on tbe rear of the aircraft and alos can be either right or left hand rotation.

Odd, because every description I have ever seen of carving a prop you carve the back first to form the pitch. Back/rear that makes perfect sense to me.
Calling the rear part of anything the front makes no sense at all.
And introducing "face" as a term for one of them is really strange. Golf clubs have faces, but not sure propellers do 

Pretty clear that the OP was using front/back the way I do, perhaps the person he was getting advice from was using the other way around?
So in fact they were both saying the same thing.

[pmackenzie]

Just thought of something - a spinner is sometimes called a nose cone.
If my nose is pointing north, then so is my face.

That would then logically mean that the face of the prop should be what I call the front, and you call the back   

[Steven Kientz]

Back to prop balancing. I was shown to use CA or clear fingernail polish instead of removing material. That way you're not changing the front or back of the prop. Works on wood/plastic(MA), not sure about  CF props.

[Chris Cox]

Just thought of something - a spinner is sometimes called a nose cone.
If my nose is pointing north, then so is my face.

That would then logically mean that the face of the prop should be what I call the front, and you call the back   

Hi Pat - Alan is absolutely correct in his description of propeller terminology.  It really is confusing and I suspect something people will never be fully clear on.  Unfortunately, a lot of confusion results when people explain one thing, but the other person has a 180 degree understanding of the terminology being used.

Hopefully my insert works.

http://www.thaitechnics.com/propeller/tg8/cross_section.jpg

[Chris Cox]

The link in my last post may not work.  Maybe this one will.  It has a “very” clear diagram showing the face and the back of a propeller (FYI - if I was in charge, I would have done it the other way, but I wasn’t...)

http://www.thaitechnics.com/propeller/prop_intro.html

If this doesn’t work, just google aviation propeller terminology.

[Bill Ervin]

Since seeing the terms “suck side” and “blow side” a few years ago on Hip Pocket they have become my favorite descriptors.

[Lauri Malila]

So far I have been able to find the measurable differences (blade shape, thickness..)in the in the blades I use to assemble my props from. So the main goal is that props are dimensionally symmetrical around center axis.
If you cannot find differences by measuring (vernier, micrometer, comparator, fingers..) it means that there are variations in material density, and those props should not be used.
But I have the luxury of choosing the wood before joining and also all blades are machined at once, with same machine setting.
I would not take the path of choosing a prop orientation to interact with engine balance, even thoughvit has a theoretical advantage. Not all props are off-balance in a similar way. It’s better to fix balace issues with shaft/spinner only. L

[FLOYD CARTER]

Of course, I balance every prop before use.  Props from major manufacturers are usually very close to balance "off the shelf".  I find that a light sanding of the varnish on the heavy side almost always gives balance.  This does not change the airfoil perceptably.  Alternately, putting an extra coat of varnish on the light side accomplishes the same result.  Any prop requiring sanding down to  the wood  should be discarded as being poorly made.