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Vibration balancing question

ljpgrif

Member
After replacing the lycoming crankshaft oil seal, the prop was reinstalled and dynamic balanced from 0.41 to 0.03 ips at cruise rpm.....question....should it be 0.03 ips throughout the rpm range?

Thanks
Larry Griffin
 
After replacing the lycoming crankshaft oil seal, the prop was reinstalled and dynamic balanced from 0.41 to 0.03 ips at cruise rpm.....question....should it be 0.03 ips throughout the rpm range?

Thanks
Larry Griffin

I balance mine at 2400rpm, which is my long-range cruise rpm. Last time I did it I didn't test at various settings. I suspect you'd be changing balancing weight and position constantly if you tried that, eventually having to choose a particular RPM.
 
Abuura question ?

I have wondered how folks balance for cruise when static is only 2150 on my FP prop. Will a CS turn 2400 static ?

I have imagined mounting the sensor and taking readings in flight . That would require a removable window in the cowl and and I am not there emotionally yet.
 
Having balanced hundreds of props and observing vibration levels at various RPM's, I can tell you that the change in IPS is negligible
from about 2200 up to 2500.

No problem doing it at 2400 with a CS but depending on prop pitch/available power a FP typically maxes out around 2200 ish.
 
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I have wondered how folks balance for cruise when static is only 2150 on my FP prop. Will a CS turn 2400 static ?

I have imagined mounting the sensor and taking readings in flight . That would require a removable window in the cowl and and I am not there emotionally yet.

I've done this on my Zlín. No way I can get 2400RPM on the ground.
Mounted the tach sensor on the alternator pad at the left side of the engine. Put the reflective tape on the back of the flywheel. Worked out well, but it takes much more time to do it. Done it on my RV-10 once too.
I'm using the Smart Avionics PB-4 balancer. Not sure how the sensors from other balancers fit under the cowling.

Lenny
 
I have wondered how folks balance for cruise when static is only 2150 on my FP prop. Will a CS turn 2400 static ?

I have imagined mounting the sensor and taking readings in flight . That would require a removable window in the cowl and and I am not there emotionally yet.

Last balance was 2018, notes specify 2400rpm. The prop for sure will spin up to that on the ground; I attach the tailwheel to my car, chock, and apply parking brake.
My setup would not work in the air.
Picture1.webp
 
Vibration variation

After I put 17g on the starter gear and got it to 0.03 ips at 2400, I called it good.

But, when I reverified I noticed variations on rpms changes....950 rpm 0.01.....1200 to 1600 rpm 0.21 and continues down to 0.03.

This was my first balancing job with a new Dynavibe. It was a easy task and just wondering about it.

Thanks everyone for the info.....

Larry Griffin
Arkansas
 
I'm always in a state of "cringe" when I balance a prop. It just seems like I'm abusing the prop/engine running it hard on the ground like that. Since I own the equipment, I decided I'd do it airborne on my latest prop/engine combo.

I found it darned near impossible to get consistent results while airborne and ended up going the traditional route of multiple ground runs with minor tweaks each time. I wound up with a great result (0.03ips @ 2400rpm) and the smooth is noticeable. I've got a basic Aces balancer... similar to the basic DynaVibe--Ford vs. Chevy near as I can tell.

For anyone embarking on the prop balancing path for the first time, I advise caution. It's easy to get out of your routine and break something. I was helping a friend balance the prop on his beautiful Giles G200 and he forgot to latch his rear-hinged canopy. I stood at the wingtip with the balancer in hand as the canopy violently departed the aircraft and scattered itself in little tiny pieces over a 100 foot debris field. I've also heard of prop strikes when the tail floats up. It seems like a straightforward process, but it's fraught with peril.

I've helped a few friends balance their props and I've done a few of my planes since the G200 incident, but I brief the process thoroughly each time and have a deep respect for the potential pitfalls.
 
I'm always in a state of "cringe" when I balance a prop. It just seems like I'm abusing the prop/engine running it hard on the ground like that. Since I own the equipment, I decided I'd do it airborne on my latest prop/engine combo.

I found it darned near impossible to get consistent results while airborne and ended up going the traditional route of multiple ground runs with minor tweaks each time. I wound up with a great result (0.03ips @ 2400rpm) and the smooth is noticeable. I've got a basic Aces balancer... similar to the basic DynaVibe--Ford vs. Chevy near as I can tell.

For anyone embarking on the prop balancing path for the first time, I advise caution. It's easy to get out of your routine and break something. I was helping a friend balance the prop on his beautiful Giles G200 and he forgot to latch his rear-hinged canopy. I stood at the wingtip with the balancer in hand as the canopy violently departed the aircraft and scattered itself in little tiny pieces over a 100 foot debris field. I've also heard of prop strikes when the tail floats up. It seems like a straightforward process, but it's fraught with peril.

I've helped a few friends balance their props and I've done a few of my planes since the G200 incident, but I brief the process thoroughly each time and have a deep respect for the potential pitfalls.

Good tips. Does the balancing need to be done at that high of an RPM? What happens if you balance at 1700 and fly at 2500 RPM? Is it an improvement, but not as much as if you balanced at 2500?
 
The added weights create a centrifugal force which then creates an imbalance that is set up to oppose the original imbalance of the prop. The higher the angular velocity (RPM) the higher the centrifugal force, and at higher than balancing RPM you are now creating an imbalance in the opposite direction from the original.

I tried balancing at 1800 rpm instead of 2500 and it wasn't working out very well. A tailwheel airplane on titanium gear and 300hp just makes way too much thrust at 2400-2500rpm, not something I want to deal with on the ground.

Came up with a good trick recently. I have a pretty steep hill going up to my hangar. Annoying, but it turns out to be a great feature now. I taxi up on it halfway and then I can get to 2300rpm without it pulling me off the brakes or even picking the tail up, and that's close enough for balancing.

It's also important that you balance in the vertical plane. If you do it on the horizontal you are also balancing the engine. Not a good idea. I tried :)

Lenny

Good tips. Does the balancing need to be done at that high of an RPM? What happens if you balance at 1700 and fly at 2500 RPM? Is it an improvement, but not as much as if you balanced at 2500?
 
Good tips. Does the balancing need to be done at that high of an RPM? What happens if you balance at 1700 and fly at 2500 RPM? Is it an improvement, but not as much as if you balanced at 2500?

I’ll let other, more knowledgeable folks comment on the whys and wherefores of balancing as close to cruise RPM as possible. All I know is that I’ve tried it both ways and it seems to me that closer to cruise nets me a smoother feel in the air.

I can’t seem to get a good grasp on the physics of balancing a spinning disc. My brainpower peters out at the teeter-totter level.
 
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