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It is quite common to find that the inboard lower surface of RV-8 flaps do not match up well to the fuselage. This view is looking aft, at the inboard lower surface of the left flap, with the hinge line near the top of the picture. The forward part of the lower skin, not yet trimmed, sticks down quite a bit below the fuselage. The aft end of the trailing edge is sticking down below the fuselage fairing. The whole thing looks quite untidy.

I wasn't sure what I was going to do about this until I found Randy Lervold's description. Randy trimmed the inboard edge of the skin to match up against a seam in the fuselage skins, and he bent the inboard edge so it matched the fuselage. I was a bit troubled by the fact that Randy's solution had a small portion of the flap trailing edge sticking down perhaps a quarter inch below the flap to fuselage fairing. That would cost at least a hundredth of a knot, and looked less tidy than I wanted. So, I decided to "improve" upon his concept by trimming the upper surface skin a bit more, to allow the bend in the lower surface to start further outboard.


Once I trimmed the upper skin, and trimmed and bent the lower skin, I was very happy to see that it fit very nicely. But I was quite dismayed to find that the inboard portion of the lower surface skin was much less stiff than I had expected, due to the loss of support from the upper surface skin. Now I saw why Randy had trimmed his flaps the way he did. Drat. I should have simply copied Randy's idea, without trying to "improve" upon it.


I did some serious head scratching, and finally fabricated reinforcements from 0.040 aluminum. The reinforcements attach to the inboard flap rib at the upper and lower rivets, and then extend inboard to support the lower surface skin. They appear to add more than enough stiffness.


I need to add one more rivet to connect the two portions of the lower flap skin, as the two layers are spread slightly apart at the inboard end. I didn't get the right reinforcement installed today, as it turned out that one of the holes was in a slightly less accessible location, and I would need my pop-rivet dimple tool to dimple the flap skin, and it was sitting home in the basement. I also need to bring a different bucking bar so I can get the most outboard rivet on the lower surface of the reinforcements. Next work session.


After spending many extra hours work because of my distaste for having part of the flap sticking down a quarter inch below the fuselage, I wondered how the flap to fuselage interface is done on other aircraft. There are two Mooney M20s in the hangar, so I peered under an M20F. I was amazed to see a huge hole between the inboard edge of the flap and the fuselage - the hole is about 8 x 4 inches, and must create a lot of extra turbulence.


The hole between the flap and fuselage looks like it would act as a huge scoop, catching the air. Ugh.


After installing the left flap reinforcement, I bolted the flap pushrod to the actuator, for hopefully the last time. Then I installed the left wing intersection fairing.

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