What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Dynamic prop balancing

Chattin35

Well Known Member
Hi all,

At 80 hours on my -7, I had the prop dynamically balanced. Figured I'd share the results...

My engine/prop (YIO-360-M1B / Hartzell BA from Van's) was pretty well balanced from the factory at .09. But, balancing down to .02 made the aircraft noticeably smoother. I can barely feel any vibration now when I hold my hand on the airframe.

Dynamic balancing is definitely recommended.

Here's a pic of me test flying the new config...

gIvTkJxl.jpg
 
I've balanced a number of props for people and they all have a story similar to this.

On my first plane (certified), I got the prop balanced after flying it for about 40 hours. It was a world of difference--I could put my hand on top of the panel and not feel any vibration. I took an acquaintance up for a ride and he called it "turbine smooth."

+1 for dynamic balancing.
 
I just had my LongEz prop dynamically balanced using the Dynavibe instrument. The baseline measurement was .46. After five iterations, we got it down to .1 and called it quits. We certainly could have done better, but felt we were at the point of diminishing return. We spent about 1.5 hrs on the procedure at $95/hr. A flight after the procedure confirmed the engine felt definitely smoother, but it wasn't a day and night difference. Let's face it, an O-320 with a light composite prop is still a reciprocating, power pulsing mass, not a turbine. It was worth the effort, though.
 
How expensive is it to have a prop dynamically balanced?

Check with your local EAA chapter to see if they have the equipment... I know one in the Puget Sound area that offers a deep discount for rental of the equipment and a knowledgeable person to help you with the work.
 
I might need to take you up on that offer. Flying from La Crosse, WI would be a quick trip and it sounds like it could be done in a day.
Thanks,
Pat
 
I lucked out, my son bought a DynaVibe. My Yak-55 does not have a spinner, so it took me 3 days to balance the prop (after a day to build a frame to mount the sensors to the M-14P engine). Balancing a 2 blade without a spinner is done by sanding off or adding paint to the blades.
OK, I'm slow and methodical. I'd be charged $1000 for that kind of service.
Get your prop balanced, it's worth $250 or more!
 
Can anyone attest to repeatability of the dynavibe? Spent several hours with a buddy who has one and kept trying to improve on 0.16 ips. Gave up after we backed up to a previous weight configuration and the readings didn't come remotely close to the first trial. We removed everything and ran once more and had .6 ips when the original run was 0.42.

Sent the unit back to dynavibe and they found nothing wrong with the unit.

I'm sure glad I wasn't filing on my prop
 
For any unit, the accuracy and repeatability will be dependent on the mounting of the accelerometers- if they are not solidly mounted or are otherwise free to vibrate on their own the resultant data will be contaminated. Other factors that can contaminate the data include airframe buffeting from wind and propwash.

My dynavibe has been pretty repeatable - i checked my -6a four months after i originally balanced it and got a reading that was 0.01 ips off; i'd be tempted to attribute this to bug guts etc 😜
 
Can anyone attest to repeatability of the dynavibe? Spent several hours with a buddy who has one and kept trying to improve on 0.16 ips. Gave up after we backed up to a previous weight configuration and the readings didn't come remotely close to the first trial. We removed everything and ran once more and had .6 ips when the original run was 0.42.

Sent the unit back to dynavibe and they found nothing wrong with the unit.

I'm sure glad I wasn't filing on my prop

There must be something else causing the vibration. Only a spectrum analysis can tell you if the vibration is caused by something else, like a plug not firing or something like that.
 
I spent 3 days balancing my V530 propeller on 9 cylinder M-14P engine. The Dynavibe I used was very repeatable, and every change I made was sensibly indicated in the next reading I got.
I did expend considerable effort into making a strong & ridged mount for the sensors and followed the instructions closely for distance and size of reflector tape etc..
Jesse's comment about a plug not firing makes sense as well. Perhaps you have a plug with high resistance, a leaking intake tube, of loose propeller bolts? It could be anything. The Dynavibe may be telling you something that you should know? If that's the case, then you'll get double the value!
The next more expensive DynaVibe can help find those pesky hard to find problems. I would like to try one because I have a gear reduction engine and would like to know the difference between propeller vibration and engine vibration.
Meanwhile, I look forward to balancing my RV-8 w/ Catto 3 blade, and my wife's RV-4 w/ Sensenich carbon fiber ground adjustable 2 blade.
 
Part of what I do when I do a prop balance (I use a DSS Microvib II which is quite expensive) is the spectrum analysis like you see below. It can definitely show abnormal vibrations and help to figure out what is going on.

715abspec.png



Another advantage of the better balancers is I can generally get a balance done in just a few runs. The one below was done is 2 runs, 3 runs is the average.

715ab.jpg
 
Last edited:
More results...

I just flew to Oregon and back over the weekend and noticed my CHTs running about 10 degrees cooler on each cylinder.

This could have been a number of factors like the engine continuing to break in (only ~80 hours on it). But, the OAT was about the same as I've seen lately and I was cruising at the same power settings and altitudes I normally do.

YMMV. But, it was interesting to note the engine running slightly cooler after after balancing the engine/prop.
 
Has anyone tried the ACES 1015 balancer? It's pretty close to the price of the Dynavibe, but I believe it tells you the weight to use, in addition to being able to split weights over two positions.

Rusty
 
Lucky for me, lycomings have a "flywheel" with 12 perimeter holes, 30 degrees apart, where I can mount the optimal bolt/washer/nut counterbalance. An earlier post mentioned that balance was effected by directly modifying (e.g., spot painting) the prop. I guess on engines without a flywheel nor spinner backplate, this is the easiest route toward dynamic balancing....if you happen to be lucky enough that the rotational inbalance is along the length of the prop. Otherwise, I don't see how you can satisfy a polar plot inbalance by just working on the prop.
 
Our chapter recently bought the ACES 1015. I've helped do three planes so far, all Lycoming. It's very easy to use, just follow the instructions on the screen. As was mentioned it allows you to split the weight to two angles. So if it wants weight at 78 degrees, you say you want to split it at 60 and 90 degrees and it gives you the amount of weight at each of angle. Like I said, just follow the instructions.
 
Thanks for the report. I had a 2020 years ago, and it looks like the 1015 works the same for standard dynamic balancing. It lacks a second channel, and doesn't have any vibration spectrum analysis, but I don't recall ever using those anyway. The 2020 was really impressive if you do your part, and by that I mean giving it correct angles and measuring the weight you add precisely.

Cheers,
Rusty
 
Lucky for me, lycomings have a "flywheel" with 12 perimeter holes, 30 degrees apart, where I can mount the optimal bolt/washer/nut counterbalance. An earlier post mentioned that balance was effected by directly modifying (e.g., spot painting) the prop. I guess on engines without a flywheel nor spinner backplate, this is the easiest route toward dynamic balancing....if you happen to be lucky enough that the rotational inbalance is along the length of the prop. Otherwise, I don't see how you can satisfy a polar plot inbalance by just working on the prop.

In general, for metal two-bladed props, isn't the imbalance always along the length of the prop since that is where the longest moment arm is?
 
Stupid balancer questions

I'm planning to balance my prop soon and have some basic questions.
I'd like to use the "flywheel" holes to add weight as needed.
1. Should I use 1/4" hardware? If yes then if the weight needed is less than the weight of a bolt/washer/nut, I would add a similar combo 180 around then fine tune with washers or is it acceptable to use smaller hardware in the 1/4" hole in the flywheel.
2. Is it OK to do full power runups with only the lower cowl on? I've seen photos of runs with just the upper cowl off and some with both halves removed. I've looked at prop balancing videos but haven't found any that go into the, dare I say "nuts and bolts" of the operation ;)
Thanks, Gunther
 
I'm planning to balance my prop soon and have some basic questions.
I'd like to use the "flywheel" holes to add weight as needed.
1. Should I use 1/4" hardware? If yes then if the weight needed is less than the weight of a bolt/washer/nut, I would add a similar combo 180 around then fine tune with washers or is it acceptable to use smaller hardware in the 1/4" hole in the flywheel.
2. Is it OK to do full power runups with only the lower cowl on? I've seen photos of runs with just the upper cowl off and some with both halves removed. I've looked at prop balancing videos but haven't found any that go into the, dare I say "nuts and bolts" of the operation ;)
Thanks, Gunther

I have used 3/16 hardware when the weight of the 1/4" is to much, when doing this I make sure to tighten down the bolt at the edge of the hole so it can't migrate outboard on its own with the centrifugal force. I generally balance at 2400 which is a good cruise RPM but less than full power. I've not had any problem leaving the bottom cowls on an RV.
 
I have used 3/16 hardware when the weight of the 1/4" is to much, when doing this I make sure to tighten down the bolt at the edge of the hole so it can't migrate outboard on its own with the centrifugal force. I generally balance at 2400 which is a good cruise RPM but less than full power. I've not had any problem leaving the bottom cowls on an RV.

My mechanic used 1/4 inch AN4 hardware on my flywheel. Installed identical nuts and bolts at two holes 180 degrees apart.

Final balancing was done by adding either AN960 or AN970 washers to the light side only.
 
My mechanic used 1/4 inch AN4 hardware on my flywheel. Installed identical nuts and bolts at two holes 180 degrees apart.

Final balancing was done by adding either AN960 or AN970 washers to the light side only.

I've tried this as well, and theory says that should work, but the reality is balancing with 3 positions vs 2 (as is normal) does not work very well and most often leads to additional run time to get things tweaked with the end result being no better. The bolts don't carry any load other than their own weight, they just need to stay in the holes.
 
Thanks, guys! I'll be using a dynavibe basic so I believe it will be an iterative process anyway and for me time spent is not a factor. I'm expecting a learning curve too so who knows how many runs it'll take. Nice to know I can use smaller H/W if necessary. Next up will be my hangar neighbor's corvair powered Zenith 650. Then I'm doing my wheels! (The dynavibe site links to a YouTube vid of someone performing "on aircraft" wheel balancing).
Gunther
 
I've tried this as well, and theory says that should work, but the reality is balancing with 3 positions vs 2 (as is normal) does not work very well and most often leads to additional run time to get things tweaked with the end result being no better. The bolts don't carry any load other than their own weight, they just need to stay in the holes.

Actually my point was that the weight of a single bolt and nut might simply be too heavy if the imbalance is small.
 
I have been restoring fabric aircraft and maintaining light aircraft for over 30 years in CYEG area and now have an awesome job (7 years) maintaining a fleet of 737NG's and 767's for a Calgary based airline. I spend all of my time off still working on light aircraft and some Robinson helicopters. I'm also finally building a RV-8. I have a very fancy DSS MicroVib II balancer that will do spectrum analysis. If any of you RV Alberta folks want to use it, let me know? I'm NOT looking for extra work!! I can show you how to use it and get you started. The fee might be to help stock the hangar beer fridge. I live at CEE6, so you could fly in, do your balance and leave an hour or three later. If interested please PM. :)

Cheers,

Phil
 
Last edited:
Dynamic Propeller Balancing in NW

For those of you in need, I am performing Dynamic propeller balancing out of KAWO. I am an A&P and use some of the newest equipment on the market. Flat fee, no by the hour charge. :D Additionally, I can perform an aircraft spectral analysis to help identify airframe vibrations that are not associated with a prop out of balance.

A vibration issue isn?t always detectable by feel, because often owners and pilots have lived with vibration for a long time and have simply gotten used to it. There are always symptoms, however, such as: a panel that shakes, random instrument failure, fatigue cracks that appear or grow, cracked baffling, a compass that won?t ?settle?, a rough RPM range and even tingling or numbness in pilot extremities. These symptoms, such as the fatigue crack should not be ignored. The cheapest insurance you can get to ensure aircraft health.

Contact me for time sand details. [email protected]
 
Dynamic balancing is not "once in a lifetime" type of thing to do either.....every couple of years is recommended or after doing maintenance like cylinder changes, reclocking a prop, etc. I'm also able to do dynamic balancing....located near Fayetteville NC. I recently performed one on my friend's RV8a and made a significant, noticeable improvement...interestingly, he had had is prop balanced by someone else years ago...and when I checked it, the vibration levels were better with no balance weights than they were with the former balance weights installed. Either the previous person didn't know what they were doing or the engine / prop combination changed over time.

Ellis... A&P/IA, building an RV7a, 2017 contributions made.
 
Back
Top