Trimming a Super Chief

[Paul Kobe]

I have some trimming questions on a BMJR Super chief I just finished building.  I got the plane in the air this past Saturday.  I flew it 3x but I was a bit disappointed.  The outside (OS) wing was low on normal flight and when inverted it was high.  Quite a bit- enough to see both tips.
From what I read, it has a warped wing (?) or maybe flaps.  The wing looks okay as far as I can tell but the inside (IS) flap has a bow in it.  I tried to build it flat - weighting it down as suggested but it bowed anyhow.  I put the flaps on anyhow thinking the flap hinges might keep it level with the TE but that did not work.  The hinge near the wing tip did not hold.  The bow on the IS flap is as follows (from wing tip to the fuselage) the flap tip is about ¼” below the TE center, the middle of the flap is up about 1/8” from the TE and the hinges and control horn keep the rest of the flap centered on the TE. 

The OS flap had some distortion, but the flap hinges seem to be keeping it true.  While it is not perfect the flap stays centered on the TE.

Could the shape/ position of the IS flap be causing the OS wing to be low on normal flight?  Then cause the OS wing to ride high when it is inverted?  Is this causing the wing to be unlevel?  I thought about removing the IS flap then fly it – if the plane flies level maybe it's the flap.  Then I'll need to build a new flat flap.  Or should I try trim tabs?

Thank you
Paul

[Dan McEntee]

    Hi Paul;
   You have a pretty good description, but without having the model right in front of me, it's hard to be really precise in determining what it needs. The flap issue is definitely causing you some problems and needs to be addressed first. Sounds like it may have been made form some softer, punkish wood. The flaps and elevators need to be very stiff, and might not be the best place to try and save weight with really light wood, which can be soft. If the outboard flap is OK, I would concentrate on repairing the inboard flap. This can be done sevral ways. One is to make a completely new flap using stiffer wood. Another would be to steam the old flap and get it to lay flat. Once you achieve that, you can take a piece of hard, stiff wood and inlay a sort of spar in the middle of the flap running span wise. The spar can be 3/22 or 1'8" wood, cutting it as straight as you can possibly make it, and sand one edge flat.. Cut it wider than what you would need by about 1/32"  Cut the slot on the flap as nicely as you can. Take your time and make several cuts.  start and stop the slot about an inch from each end. Sand the slot to accept the spar and make it just snug, where you don't have to force it in. When you are satisfied with the fit, pin the flap to a plat board laying on some wax paper. Next apply some Elmers glue to the spar and work it into place. Push it all the way down and pin it into place. Let the glue dry thoroughly. If you can, trim the spar while the flap is still pinned down, carefully, then block sand it flush with the surface. When satisfied, pull it off the board and sand the other side. It should still be flat and be ready to refinish. That may sound like a whole lot of work, but if you don't have wood for a new flap and want to get at it right away, it's what you can do right now, and really won't take much longer than building a new flap.  While you have the flap off, you can sight the wing to see if it's straight. You do this by looking at it from the back of the airplane. Raise and lower the tail and put the trailing edge in the middle of the top and bottom of the wing surfaces. If there is a twist in it, you will see it. This takes a bit of practice. Sometimes just sighting down the trailing edge from the tip will do oit also. If it's twisted, twisting it the opposite way and heating the wing gently with a monokote irona to shrink the covering will help hold the adjustment. Just tweak it until you see some wrinkles, and then apply the heat, relax, and then let it sit a few minutes. This can work with iron on coverings and with dope finishes. Steaming it can work also. Again, it helps to have the patient right here on the table, but this all should get you started. GHood luck with it.
  Type at you later,
   Dan McEntee

[Paul Kobe]

Thanks for the suggestions.  I will go and build a new flap and work on keeping in flat and level. Thanks for tip on looking for a twist in the wing.  It will take a while to fix.  Thanks again,

Paul