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Searching for Trim Problem, HELP!

Dougrv6

I'm New Here
Hi, I hope someone can help, I built my rv6 in 96, she flew hands off,flat out at 216 mph @ 2600 rpm (i know 6 over vne) for 6 years. on one beautiful night flight i left her flaps down 1st notch to 160 mph (hard to admit but you need to know). slowed to 90 and returned to the airport, upon inspection i found i had bent both flap hinges 1/4 in. down. the next day i removed the flaps, reset the hinges, pulled all inspection panels and checked for any other damage. everything looked great. topped tanks and went for a test flight. well, she now banks slowly to the left and will not quite make 200 mph @ 2600 rpm. in the last 5 years i have tried to repair my mistake, i have leveled the canopy rails and measured everything using a laser level and a steel rule, checked all control surfaces with the original template, removed wingtips, installed tufts of yarn all over to look at airflow, and many many other checks. the only thing that in visible is the alerons are: left 1/4 in.up, right 1/4 in. down in level flight if i align them with the flaps and wingtips in flight she banks slowly to the right. she still flies great and i fly quite often. if anyone is interested i really need some help with this. i am in lansing mi. thank you, Doug and Tammy Aves
 
Flap flap

I'm sure you have tried this, but try raising your right flap a couple of turns or lowering your left flap a couple of turns, or both. Don't have a clue where the speed went, but I'm sure that the engine isn't putting out what it did when it was new.

RT
 
I had a similar situation after repairing one flap leading edge. I tried everything to get in back in trim. I thought adjusting the flap rods was changing the angle but one of the flaps was bottoming out because the slot in the fuse was not large enough to allow the flap to come up. I couldn't see this because this slot is covered with the flaps up. Making the slot slightly larger solved my problem.

Ken
 
Well, I guess you bent your wing

I started building my RV-6A in 1996 but they are different because you have manual flaps and mine are electric. First question, You say you bent your flap hinges down 1/4" but you provide no details on exactly how they were bent. That may provide a clue as to how the forces were applied, etc. and maybe that can be analyzed to determine the most likely effect on the wings. The earlier performance figures seem extremely outstanding and the current figures sound like Van's book values. The best case is that in the reinstallation of the flaps you have some roll in their relative position to each other which can be corrected by adjusting the linkage to the actuator weldment. The fuselage is not perfect so if you rerigged relative to the fuselage after leveling the canopy deck instead of relative to the wing airfoil you could be putting in some roll with great precision. I would take the roll out by changing the flap linkage rigging regardless of what caused it but that's me on my airplane not advice to you on yours. As far as speed difference is concerned I can think of two things that could effect that difference. One is the drag caused by something trying to roll the plane one way and the ailerons offset to fight that roll force with an opposite roll force. An other is a lower position of your flaps up in the cruise position which changes the airfoil to a higher lift shape with greater drag. My guess is you will never see 216 mph in level flight again.

Bob Axsom
 
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I bent the lower skin just aft of the rear spar brace, I built a tool to bend it back and it did not even break the paint. I reset the control surfaces with the original airfoil template, I also have adjusted the flaps independantly up to 1/2 in. with little result. I have raised them both and lowered both, i loose speed when lowered, no change when raised. Doug
 
OK That sure helps

It sounds like when you pulled your flap lever driving the actuator linkage down the air load on the flaps was so high that they were no longer the weakest opposition to the downward force. As you pulled with your mechanical advantage the downward force was accommodated by the trailing edge of the wing where the flaps are attached bending downward. There was probably some yielding of the weldment but most of the force was applied to deforming the wing and of course it doesn't spring back like the steel. There may have been some yielding of the rear stub spar interface with the fuselage fittings, etc. and distortion of the fuselage and twisting of the wings. The wing would see this high speed activation as a downward pulling force on the lower wing skin with a lot of tension on the rivets attaching the lower skin to the rear spar. The rear spar would tend to roll forward with respect to the upper and lower wing skins. Any twisting of the wing itself would increase the incidence angle of the wing and that would induce more drag and cause the plane to fly slower. The fact that there is a new roll force that has to be offset with the ailerons is an indication that the wing was twisted unevenly on the left and right side. You can use Van's incidence rigging procedure to try to detect the twist/incidence condition. I don't know what you can safely do to correct a problem if you find it. From your description I would expect to see something like a higher angle of incidence, maybe wash-in of the left wing relative to the right wing.

Bob Axsom
 
Two possibilities:

1. The bent wing skin and flap hinge was not put back in the same place as before. Find another short wing RV, and look very carefully at the contour of the wing lower surface with the flaps up and compare it to yours. Use a long straight edge and make some measurements to get a good idea of what the contour is.

Look at the upper wing surface where the trailing edge of the upper wing skin meets up with the flap upper surface. Check the contour here too.

2. Maybe the flaps are now twisted a bit. The outboard flap trailing edge could be twisted a bit up. Take a very, very close look at the flaps, checking for twist. You might have to remove the flaps and place the lower surface on a flat table to see the problem.
 
I moved the flap hinge up so the flap was just touching the top skin as before, the lower wing was slightly concave just ahead of the rear spar when i built it but i don't remember how much, so i put masking tape on it and leveled it with body filler. it did not change a thing. when the flaps were off for repair i checked them on a flat surface and layed them top to top they were flat. i will try to locate another rv this week and put them side by side and study them carefully. i had not thought of that, i have been a mechanic for about 35 years and sometimes it ts the simple things that get cha! Thanks for all of your input, we might find the answer this time around, i have been trying many different things for about 6 years so far. at least i have learned a lot. keep em coming! Doug
 
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