Kitfox Series 7 Super Sport - Show Me Fox

[Jason Murphy]

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.

Polish radius blocks. They were much more of a challenge because they have such a small surface area. My coworker unknowingly supplied the photo for this entry.

Thanks Carrie

[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.

[PapuaPilot]

Blade weights can vary and don't mean a lot until they are assembled into the hub. I'm guessing the blades were assembled in the hub at some point at the factory and the unit was static balanced. Does the hub have any static weights installed on it? If not you could assemble the prop and check the static balance if you can find a mandrel and balance stand.

[jrevens]

Blade weights can vary and don't mean a lot until they are assembled into the hub. I'm guessing the blades were assembled in the hub at some point at the factory and the unit was static balanced...

If that be the case, Phil, it would seem that Whirlwind would clearly inform the customer that it is very important to install specific blades in specific locations on the hub. I don't believe that they do that, as far as I know. They definitely didn't inform me of anything like that with my prop.

[PapuaPilot]

I didn't know that John. Typically props come assembled and have been static balanced, sometime the blades are removed for shipping, but they have specific locations in the hub.

I'm curious to hear how this turns out and what the pre-balancing "IPS number" is. I kinda understand the "moment arm" statement, but a 3.5 ounce (~11%) weight difference between blades is a lot. The only way I can see this working is if they adjust the moment arm using weight as far inboard as possible.

[Jason Murphy]

When I spoke with Whirlwind on the phone they said the blades can go on in any order.

I requested they email me and explain how this works so I am better able to understand. I will post a screenshot on here when they return the email.


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[Jason Murphy]

Installed No. 1 rib on Right Wing. Used yard sticks on the leading edge, trailing edge, top and bottom cap strips to ensure No. 1 rib is parallel to No. 3 rib. Allowed Hysol to cure for 1 hour after mixing and removed excess Hysol and dressed the fillets.

Sanded edge of wing tanks to ensure there is an even gap with the adjacent rib. Placed wing tank fully forward against the front spar. Used a square to mark equal distance from the adjacent rib. Sanded the minimum necessary to ensure the edge of the tank is straight and the gap between the rib and tank is even.

Placed masking tape on ribs and measured equal distances down the rib and made a line. Using a yardstick drawn a straight line on the front and rear of the tank. Will sand to the line to true the leading edge and trailing edge of the wing tanks.

I was advised that a minimum of 9/16” flange is required on the wing tanks and after I sand the edges I need to check for leaks.

I was also advised by Brandon at the factory that I need to leave at least 3/8” gap between the rib and the wing tank for rib stitching. I should also omit the step in the manual that instructs the builder to fill the gap between the wing tank and the rib with Hysol once again for rib stitching.

Rough cut the rear spar for the carry through spar when the wings are folded. This will require additional fitting in the future.

Took creepy selfie to identify myself as the builder in builders log.










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