Kitfox Series 7 Super Sport - Show Me Fox

[jrevens]

Called Whirlwind regarding the prop. They advised they do not balance the blades by weights they balance using moment arm. I shouldn’t have any problems with the prop. Call if I have a vibration after the prop is mounted.

Hi Jason,
I sure don’t want to give you any unnecessary concern, but I’m confused by Whirlwind’s reply. That seems to be a pretty considerable difference in weight, and I can’t understand how the blade set could possibly be in static balance based on moment arm unless there was a substantial variance in the density of the blade material throughout the length of the blades at corresponding distances, or a big variance in cross sectional shape (volume) between the blades at any particular station or distance from the hub. I wouldn’t think that would be the case. I’m just trying to understand… perhaps someone with a better understanding of this than I can penetrate my ignorance.

[Shadowrider]

My guess is prop builders don’t want to tell customers that their props are out of balance. So many variables that effect prop balance that in my opinion it’s mandatory to balance your prop. Get your prop and spinner installed and then get a dynavibe and balance the prop. Your exhaust, and aircraft will thank you in a couple hundred hours.

[jrevens]

My guess is prop builders don’t want to tell customers that their props are out of balance. So many variables that effect prop balance that in my opinion it’s mandatory to balance your prop. Get your prop and spinner installed and then get a dynavibe and balance the prop. Your exhaust, and aircraft will thank you in a couple hundred hours.

I love my Whirlwind prop, but the point is that their reply to that kind of imbalance seems pretty bogus. I’ve dynamically balanced hundreds of props over about 40 years, and it’s always advisable to correct static imbalance first, IMO. I’ve personally known several prop builders. The ones I knew checked & corrected static balance, at least to a certain degree before the propeller left their shops. That amount of blade weight difference (over 3 ounces) may prevent a really good dynamic balance job. I wonder if the heavy blade was not an original in the set?

[alexM]

I wonder if the heavy blade was not an original in the set?

I had the same question for Jason. The blades are serialized and WW was going to furnish him with the serial numbers for the blades sold to original owner.

[jiott]

I have never added microballoons to SuperFill. It is already so light that it seems pointless for weight savings. Someone correct me if I'm wrong, but I believe SuperFill already has microballoons as it comes in the can.
MB will help reduce sag, but SuperFill is not very runny, especially if you let it set for a bit.
Most of my MB that came in the kit were used in the Hysol as instructed in the build manual (for instance in mounting lift strut brackets).