Dynamic prop balance, calculating weight required using DynaVibe

[petersb]

Expensive dynamic balancers give IPS, angle AND required weight to balance. Therefore there must be a formula they use to calculate the weight. What is that formula ?

I wish to apply it to balance results using the DynaVibe balancer, which only gives angle and IPS. Even if it is only approximate it will at least give a starting point.

My latest balance run gives .17 IPS at 154 degrees.

I did Google a formula (( engine horsepower/10)+30)xIPS. Don't know what horsepower has to do with anything.

Peter

[Walt]

The reason the expensive machines can give weight is because they "learn" the effect from each weight change. The response of each engine/prop combination will be different based on the weight of the rotor system (rotating components), this learning process is how the computor can acurately determine the amount and location(s) of the required weight.

However the formula for "estimating" the amount of weight required is:

Test Weight = ((Engine Horsepower/10)+30) x IPS



You can see (if you can make it out) what happened on this balance (360 w/CS prop)

First weight change (test weight) was 17.6g @ 90 deg which caused a IPS level change from .182 to .114. However you can see it went to far and a bit in the wrong direction (from 1 oclock to 7 oclock postion).

The point of the test weight is to see how the rotor reacted to the change. I told the computer exactly how much weight I added and at precisely what location, so based on that response we now can remove the test weight and add the newly calculated weights/angles.

Next weight change was to remove the 17.2@90 and put 7.8@60 and 9@150
Splitting the weight allows you to adjust the angle precisely where you need it.

Hopefully this gives you an idea of how much weight it takes to make an IPS move on a 360 w/CS prop (which I know is what you are trying to do).

Using the formula above it would call for 8.7g which is probably pretty close for the average spinner radius, if you could add it at precisely the right radial. If you are using the lycoming flywheel its a little farther back than the spinner so it takes a bit more weight to have the same effect.

I feel for ya, using the DV is like taking a math test without a calculator !

[petersb]

Thanks Walt

Peter

[Geico266]

Dynavibe GX2 is now avsilable. It is new and calculates the weigh and much more. They will take your old unit in on trade up for the new unit. Pretty sweet deal.

[petersb]

Originally Posted by Geico266

Dynavibe GX2 is now avsilable. It is new and calculates the weigh and much more. They will take your old unit in on trade up for the new unit. Pretty sweet deal.

Sounds interesting, I will follow up with our club president

Peter