Hartzell Dynamic Balance

Bob Axsom · #1 09-15-2010, 07:17 PM

I always try to do things as well as I can for my RV-6A and after fretting over dynamic balancing for some time I finally had my prop balanced at Hartzell Field this morning by the company service personnel. They were very polite and accommodating and yesterday they provided hangar space a plant tour and gave us two company hats.

The process involved running up the engine, cycling the prop, increasing the rpm to 2550 then reducing it to 2450, signaling the operator to take a reading. After this the operator added washers to the spinner and the process was repeated. The operator did some more work (I assume weight adjustment) and the process was repeated again. Then the spinner was removed and a hole drilled in the spinner backplate at a location indicated by a computer and a standard weight was added. I was told the the displacement before the balance process was approximately 1/4" and the weights added during the three cycle process was some much smaller number.
I asked don't you want to run it again and I was told no it isn't necessary.

When I started the engine to leave it did seem smoother and I broadcast that to them on 123.0. Later in flight I really could not tell any difference from the operation/vibration/noise/visual observations before the dynamic balance procedure.

The process was cheap $269.50 and it was quick (minutes not hours). From many years of testing in aerospace I cannot accept the fact that it is acceptable to apply weight to determine what is needed in one place then use a computer to mathematically determine where to install a different weight to have the same effect then do that and call it done with no post installation verification. My belief that Hartzell does it better than anyone else is not verified. If you are contemplating this performance mprovement you should be aware of how it is done at this facility and consider whether it is worth making a trip to Piqua, Ohio to have it done.

Bob Axsom

Walt · #2 09-15-2010, 08:12 PM

Bob,
I agree completely with you! I would never consider not doing a final balance run to confirm any weight changes made during the process.

I have also found (and was taught) that better results will usually be achievable using the flywheel "balance" holes that Lycoming provides and using 2 locations instead of just one. Trying to nail a perfect balance with one hole is very difficult (if not impossible) not to mention I'd prefer not to drill holes in backing plates if possible! Also once you drill the hole you are committed so any further "tweaking" is not possible (probably why he didn't want to run it again). When using 2 flywheel holes you can adjust the weights as many times as necessary to get it just right.

Using this process I have been able to routinely achieve balance results in the <.03 in/sec range usually in under 5 runs (3 is normal). I'll assume your guy meant .25 in/sec when he stated a 1/4"

The upper acceptable Limit is .2 in/sec and many prop balance folks will be more than happy to quit anything under that.

I get a personal satisfaction out of getting it in the .03 in/sec range (or less) and find this is usually achievable with a little patience picking the correct weights. The fact that I enjoy working on RV's probably helps and with nobody breathing down my neck to "hurry up and get it done" (been there done that) I can assure you I do a better job than the "average" shop (and probably have better equipment than most).

Not to make you feel bad, but you mention a "bargain" at $269, my regular price for an RV is only $150 and I'm having a special this month for $100

brianwallis · #3 09-15-2010, 08:39 PM

There is an advanced system out there that has a learning mode. It has several profiles... you can bump it... push it.... etc etc... but it learns.... and you enter the profile... you run it... you measure it and you add one set of weights. It learns exactly what you did and what the changes were. It then predicts exactly what you need to get exactly ZERO... It's a pretty swinging system... but realllllllll expensive. I use one of the smaller pieces of equipment and yes... I have to do a few more runs but I'm saving 4 grand. (and yes.... we always do a final run.... even if I had the Super Duper Daddy Warbucks system.. I would still do a final run... because you have to put in the logbook what the final numbers are... not what they were predicted to be.)

Best
Brian

Walt · #4 09-15-2010, 08:50 PM

Brian,
Sounds like you're describing the Dynamic Solution Sytems MicroVib II that I use, as smart as it is, there are still practical limits to it. It can compute the "Perfect" one point solution and predict the results based on it's learning mode but in reality, a one point solution is nearly impossible to achieve in the real world. Even the manufacturer recommends using 2 balance locations for best results.

AX-O · #5 09-15-2010, 10:38 PM

Bob,
what was your final IPS reading?

I also prefer to use the holes on the flywheel. You can do whatever combination you can imagine and get it very close. Once someone start drilling holes that reduces the number of options later (remove prop, file a blade down, etc.) or makes it a little more complicated later on. I have been able to balance 4 RVs down to 0.01 IPS. Most of them are in the 0.02 to 0.03range. At work we call it good when the rotors are below 0.20 IPS. Once you get to approx 0.10 IPS your body won't be able to feel much differences below that.

I enjoy reading your posts, I hope that makes a difference in your quest for speed. But if it does not, It will at least reduce aircrew fatigue and maint cost.