KGSS28

Hello All I have the following question

Do you need to balance the hub of an APC in the 17 to 18 inch range ? If so where do you add the weight and what do you use for that weight? I can get the tips no problem but have never tried the hub.

Thanks

fancman

My Feedback: (16)

Check out prop balancing video at this site.

http://downonthedeck.com/videos_instruction.htm

Scott Smith

My Feedback: (4)

I don't. But I do mark the heavy side of the hub and install that opposite the keyway on my OS140RX. If it seems to be vibrating excessively, turn it 180 degrees.

Engine/crankshaft is not close to being balanced so why bother balancing the prop? Check them, sure, but don't spend hours trying to get it perfect.

fancman

My Feedback: (16)

May not be totally necessary to balance hub but it only takes a few minutes to eliminate the source of additional vibration from your airplane so why not take the time especially with a heavy prop like the 17 or 18 inch APC.

Jason Arnold

I'm balancing some APC 17" props at the moment and they are the worst I've seen from APC. APC props normally balance up with minimal effort but these 17" versions are shockers. The hole in the hub looks to be drilled off centre on my props. I have run the reamer through them on the drill press so the hole is square to the engine. The 17 x 12N seems to be the worst of the lot. I bought two of them and both hub holes are the same. It's interesting to note that looking at the face that pulls up against the prop hub, the hole looks centred.... It would seem that APC's mould is out of whack.

Cheers
Jason.

Dave Smith

I use APC 17x12 props a lot,and often find the hole is not drilled true. Usually means a waste of money.
Some of their other sizes might have this problem also.

Dave

dreadnaut

My Feedback: (5)

This is pretty much true. The vibration of a single cylinder reciprocating engine is actualy a very complex animal. Inertia of the piston traveling back and forth is the major source of vibration. This is partialy counteracted by counter balancing the crank. It is imposible to counterweight the crank so that it will totaly eliminate vibration. This is from the fact that the counterweight is traveling in a circular path. If you counterweighted the crank so that it completely canceled the inertia of the piston, the counterweight will impose a vibration at a right angle to the path of the piston equal to that of an unbalanced piston.

There is a mathematical formula called Freudensteins equation (No kidding). It allows you to plot the ''shaking force'' of the piston - rod - crank system as a radial vector on a polar graph. The graph actualy looks a little like a guitar body. By playing around with the counterweight mass, you can optimize the shaking force to a roughly equal parralell and perpendicular component.

Not all engine manufacturers use it. I once had a Supertiger that ran more smootly with an unbalanced prop, you just had to be concious of which side was the heavy side. The vibration you get from an unbalaced hub is pretty insignificant.