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rocketman2tm
04-19-2021, 05:56 PM
Tried balancing the prop today with a Dynavibe. At cruise rpm, I was getting 0.99 IPS which seams like a lot. I wonder if part of that is due to some lack of rigidity of the mounting bracket, but it is still definitely out of balance. My question is where and how do you add weight to balance this out. I have a whirlwind ground adjustable propeller and a rotax 912is.

jrevens
04-19-2021, 10:13 PM
Hi John,
I have used lead wheel weights with high strength 3M foam mounting tape for many years with complete success. I’ve done hundreds of balance jobs on experimental aircraft. The traditional approved way is to drill holes in the spinner backing plate and add screws or bolts, washers & nuts. There are multiple reasons why the lead weights are better. They can be easily & accurately trimmed to an exact weight and accurately located exactly where they need to be. I hate drilling holes in an expensive spinner part, and then if something changes you are possibly faced with having to drill another hole (or holes) to correct the imbalance. The lead weights can be easily removed and/or moved/changed with no damage to the spinner. The weights are placed on the inside surface of the outer flange where centrifugal force works to help keep them in place. Nothing has to be disassembled to install them. If the exact location needed for weight ends up where there is a nut plate, the weight can be split and located in two places. My balancer calculates the amount of weight and the locations if that’s necessary. I’m not aware of any of the weights I installed ever coming loose. As a further precaution I smear a small fillet of silicone sealant around the perimeter of weights to help stabilize and seal the mounting tape from moisture. The mounting surface of the spinner is lightly roughened with fine sandpaper or Scotchbrite pad and cleaned very thoroughly with alcohol or some kind of no-residue cleaner/degreaser. Consider that this type of weight is reliably used on auto wheels, and are basically exposed to all kinds of moisture, dirt, road salts, etc. The inside of that flange on a spinner plate is pretty well protected from all of that, as well a being an ideal location for other reasons. I repeat though - proper installation is necessary.

Shadowrider
04-20-2021, 06:35 AM
The dynavibe should tell you the weight you need to add? Yes you want the mount rigid so it will give an accurate reading. Are you using a dynavibe classic? Many on here can help with that. Yes .99 is way out of balance

PapuaPilot
04-20-2021, 08:23 AM
That is way out of balance and you really need to get that taken care of ASAP.

If the Dynavibe is telling you to put the weights in line with one of the prop blades you may want to have a static balance done first. If Whirlwind has the data on how to do this you may be able to do it yourself, other wise have a prop shop or someone who has done this help you.

Just so it's clear. A static balance is done to the prop by itself and a dynamic balance does the prop with the engine, spinner, spinner bulkhead, etc.

efwd
04-20-2021, 08:54 AM
I believe I recall that Whirlwind static balance their props before shipping. I just called them and they confirm that. Be certain that the tips are tracking one another and that the pitch on each blade is as close as possible to the others.

jrevens
04-20-2021, 10:23 AM
John,

Is the lack of rigidity you’re talking about in the accelerometer mount? That needs to definitely be rigid. Ideally you want to measure somewhere around 0.05 ips. So, as others have also said, 0.99 is not good. Do you have the Whirlwind carbon fiber spinner? Your specific question was how & where to add weight, but I just want to add that a prop can be very well balanced statically and the rest of the spinning assembly, i.e. the spinner, can be badly out of balance. It’s unlikely but not impossible that you might have gotten an un-matched set of blades. Since we’ve met and talked before, I know you’re probably very aware of what I’ve said, so please forgive me for drifting a little.

PapuaPilot
04-20-2021, 10:42 AM
John,

Is the lack of rigidity you’re talking about in the accelerometer mount? That needs to definitely be rigid. Ideally you want to measure somewhere around 0.05 ips. So, as others have also said, 0.99 is not good. Do you have the Whirlwind carbon fiber spinner? Your specific question was how & where to add weight, but I just want to add that a prop can be very well balanced statically and the rest of the spinning assembly, i.e. the spinner, can be badly out of balance. It’s unlikely but not impossible that you might have gotten an un-matched set of blades. Since we’ve met and talked before, I know you’re probably very aware of what I’ve said, so please forgive me for drifting a little.

Those are all good points John.

The only other thing that I would add would be to see if the spinner is perfectly centered and not wobbling while it is running. This could cause a very high IPS reading. Where I work we mark the spinner and bulkhead so the spinner can always be installed in the same position.

rocketman2tm
04-20-2021, 11:19 AM
I checked out the mount this morning and it felt more rigid than I was giving it credit for. I also triple checked the blade angle and tracking, which were both within spec. I do have the whirlwind carbon fiber spinner. From what I can tell, the spinner does not look like it's wobbling. I'll mark it so I can ensure it will always go on in the same orientation. I bought a box of the .5 ounce weights from NAPA and I already have the double sided foam tape and silicone. I'll try that tonight. Looking forward to a smooth airplane.

Thanks guys for all of the input. I appreciate having this forum to get good insightful advice from those that have been down this road before.