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Prop balance hardware

RV7A Flyer

Well Known Member
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Quick question...we're planning a prop balancing session with a group of RVs here on the field this coming weekend, and need to make sure we have sufficient hardware for about 6 planes. Anybody have the bolt size needed for Hartzell CS props handy right quick-like? I can pull the top cowling and look, but if someone has it it would save me a trip and I can get them (and the nuts and washers) ordered from ACS today...

TIA!
 
If you want to use the holes around the rim of the standard Lycoming flywheel, you want a box of various lengths of AN4 bolts - the minimum length will be -7 because of the thickness of the flywheel. You can go up in length from there, but only a couple of dash numbers or you can start interfering with the cowl. Then get some different styles of AN4 all-metal lock nuts, so that you have different weights available, as well as a handful of washers - standard, thin, and larger fender washers, all AN4. That’s basically what I have in my balancing box.

I also have some drilled out AN4-7A bolts for if I need to go just a touch lighter - you can see a Kneeboard Note I wrote last week on the Kitplanes website for more details. (BTW - someone took me to task for reducing the strength of the bolts by drilling the shanks, so I did some twist-off testing, and I stripped the threads off the bolt and out of the nuts before I broke the bolt.....)

Paul
 
If you want to use the holes around the rim of the standard Lycoming flywheel, you want a box of various lengths of AN4 bolts - the minimum length will be -7 because of the thickness of the flywheel. You can go up in length from there, but only a couple of dash numbers or you can start interfering with the cowl. Then get some different styles of AN4 all-metal lock nuts, so that you have different weights available, as well as a handful of washers - standard, thin, and larger fender washers, all AN4. That’s basically what I have in my balancing box.

I also have some drilled out AN4-7A bolts for if I need to go just a touch lighter - you can see a Kneeboard Note I wrote last week on the Kitplanes website for more details. (BTW - someone took me to task for reducing the strength of the bolts by drilling the shanks, so I did some twist-off testing, and I stripped the threads off the bolt and out of the nuts before I broke the bolt.....)

Paul

That's exactly what I needed to know! Thanks, Paul! You tha man!
 
If you want to use the holes around the rim of the standard Lycoming flywheel, you want a box of various lengths of AN4 bolts - the minimum length will be -7 because of the thickness of the flywheel. You can go up in length from there, but only a couple of dash numbers or you can start interfering with the cowl. Then get some different styles of AN4 all-metal lock nuts, so that you have different weights available, as well as a handful of washers - standard, thin, and larger fender washers, all AN4. That’s basically what I have in my balancing box.

I also have some drilled out AN4-7A bolts for if I need to go just a touch lighter - you can see a Kneeboard Note I wrote last week on the Kitplanes website for more details. (BTW - someone took me to task for reducing the strength of the bolts by drilling the shanks, so I did some twist-off testing, and I stripped the threads off the bolt and out of the nuts before I broke the bolt.....)

Paul

You are going to a lot of work drilling metal out of bolt when you can just split weights.
 
I prefer to have as few bolts on the flywheel as possible - just personal preference.

What do you do when the desired drilled weight bolt does not fall on the 30 degree bolt pattern? You have to split weights. Why not do that in the first place. It's only about 12 grams or you could just forget about it because it wont make that much difference anyway. Ive balanced .11 IPS and they can never tell the difference and that's about the out of balance for a drilled weight bolt.
 
What do you do when the desired drilled weight bolt does not fall on the 30 degree bolt pattern? You have to split weights. Why not do that in the first place. It's only about 12 grams or you could just forget about it because it wont make that much difference anyway. Ive balanced .11 IPS and they can never tell the difference and that's about the out of balance for a drilled weight bolt.

Completely your choice what you’d like to do! Now folks know they have a choice.
 
Prop balancing works for most people I’ve worked with, but YMMV. Paul has some good advice about using drilled bolts to lighten the moment. We have used some titanium hardware (nuts and washers) to do the same thing, because we have gotten them for free. They are kind of expensive. Adding weights every 30* is a limitation, but with flexibility in weight, it is definitely doable to a fine degree. We are going to be balancing a couple RV12’s and going to experiment with automotive wheel balance weights. The easy benefit is, with a gram scale and a tin snip, you can come up with any weight you desire. Not sure how robust the installation will be, but we have some ideas that may work out.
 
Stickon weight caveat

IF you put the adhesive weights on the ID of the flywheel so centrifugal force is not an adversary, AND the ignition uses a crank sensor, there could be a conflict.
 
I've done hundreds of balances both experimental and certified using professional grade equipment (DSS) and even had 'formal' training.
The standard approved procedure is a split weight solution which I use 98% of the time, there's that rare case where a single location happens to work but that's the exception.
 
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