Propellor balance

[learaviator]

I have a balancer that we use for helicopters track and balance mostly, but I have been doing airplane props for awhile with it. I set it up on my 180hp 170 and balanced the prop on it. Attached are the screens from the balancer. You can see the 1st, 2nd, and 3rd moves, it started out at .471 inches per second and ended up at .006 I.P.S. I generally am happy with anything less than .05. I added 37.5 grams of weight the first time, at 340 degrees, and 13.8 grams at 120 degrees the second run. If anyone would like, I will balance their prop on their 170 for free, catch is you have to come to Lake Havasu City, Az. to have it done. But I do sale the cheapest gas around, .20 off for club members, which today would make your price 2.89 for 100LL.

[GAHorn]

That's a fantastic offer!

And some of the added benefits of dynamic balancing is: Reduced cowl-cracking and spinner-cracks, and vibration-induced failures (like gen/alt failures, exhaust-pipes, windshields, etc.) ...and.... one can detect other failures such as cam-lobe failure, etc..

Dynamic Balancing balances the entire engine-rotatables...not just the prop.

[Bruce Fenstermacher]

Well lets see about 45 hours round trip to get there and back, a few nights of hotel and food expenses for the "FREE" prop balance. Hmmmm I'll think about it. The cheap gas might win me over

Seriously that is very nice of you to offer to do this. Where did you put the weight? One thing you must keep in mind though is most 170s don't have a Lycoming and no starter gear ring if that is what you used. Nor do they have a big spinner found on the constant speed props of the Lycomings, though I forget if you have a constant speed prop.

In fact lots of 170s have an very small skull cap with no backing plate though some have the later 172 style spinner. The good news is there are eight prop bolts to put a washer under. The bad news is that if the proper prop bolts are used they are already on the short side and probably shouldn't have any extra washers under them.

[Jr.CubBuilder]

Thanks,I'll take you up on that if I can get down there. I was planning a trip to the south west last spring but it fell through due to various factors. But if this VFR only pilot makes it down there it's a deal. My plane has the 180hp CS conversion also.

[learaviator]

Hey Bruce, that is a good point on the 145 in the 170. It would be tough to find a way to put weight on it, I guess the only way would be to install a longer bolt with added washers for weight. I will do some looking at some planes close by and see what it would take. My airplane does have the c/s prop, I put the weight on the bolts that hold the spinner on the starter ring gear, which of course took a longer bolt so that helped with the weight. I used AN960-4 washers, and AN970-4 large area washers, but since the bolt is so close to the edge of the spinner bulkhead, I did have to cut about the AN970's down on one side to make them fit up against the spinner. And I am happy to do it for anyone that makes it here.

[ron74887]

learaviator and Bruce, I had mine balanced a few years back and they used the stick on wgts which we place on the lip of the back spinner plate. So if they have a normal spinner or the 172 type spinner which has the same lip they work well. you are right about the skull cap. Ron

[Bruce Fenstermacher]

That would be a way to do it Ron. It's obviously held up for you. If the weight happened to come off besides the weight becoming a projectile it would only leave the prop in the original unbalanced condition it started.

[Indopilot]

On my 171 before the 180 conversion, the weight was added by drilling a screw hole thru the backing plate of the spinner and then adding the An970 washers to there. Also something to consider is the age of your engine shock mounts. You can get much better results with fresh mounts as opposed to trying to balance with old ones. As I recall the conversation went something like this. " You say your mounts are over 20 years old? What do you think I am a magician?" Brian

[learaviator]

Stick on mounts are something to consider, I will have to keep that in mind. Maybe replace the sticky tape with the industrial 3M stuff. On my spinner bulhead, you would have to drill through the side of it because it does not stick out past the flywheel. I definetely replaced the engine mounts AND bolts before balancing my prop, raised the front of the engine up 3/8's of an inch.