adjusting wing wash for rebuilt wings

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kayakalex

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I just got my 7ECA flying again after rebuilding the wings. In level, coordinated flight the right aileron is up about 1/4" at the trailing edge. It's like I'm applying a little bit of right aileron, though it flies like this hands-off. If I move the stick left to even up the ailerons, it starts a slow roll to the left. In stalls-- power on or off-- both wings seem to stall at the same time, but I think the right aileron is up a little throughout the stall.

Is this a wing wash issue? I'm considering unscrewing the clevis on the rear strut of the right wing to reduce a little lift. Bad idea? Is this a really fine adjustment or should I start with several turns and see what happens?

FWIW, I rebuilt the wings with the Milman aluminum spar kit and their replacement leading edge kit. I spent a lot of time getting everything trammed and levelled before attaching the leading edge metal, which wraps around and screws to the rear face of the spar at top and bottom. The wings were rigid even before covering. I'm going to have to round up a couple of big friends to adjust the wash.

Thanks in advance for any advice. -Alex
 
Alex-

As I understand your post it flies straight and level, ball centered, hands off, with one aileron deflected 1/4" from streamlined with the wing???????????? If that is the case I would probably not touch anything.

You say one aileron is deflected 1/4", is that at both inboard and outboard ends? It is extremely difficult to get both the wings and ailerons perfectly square after covering, 1/4" in quite good, excellent.

Tom-
 
I'd add to Tom's comments:
Don't change the wing incidence unless you know the starting point - get some simple rigging boards to measure the washout/washin.
 
This is almost always the case whenever a wing is removed from the aircraft, and it is quite easy to fix. I've done the aluminum spar STC too, and the adjustment is the same.

Unless you have disassembled the wing struts during recover process, you can assume that they are close to factory settings. So all you have to do is wash out the high wing to get it to fly level. This will take a couple of flights to accomplish unless you've done it many times, as I have. (I can usually get it straight with one adjustment)

You will need: A hand held mirror, appropriate wrenches and a couple of cotter pins, an extra set of hands to press upwards on the wing.

Using the mirror in flight, look through the green house window at the rudder and press on the rudder pedals to make it fair with the fin. Once you know that the rudder is straight and a mis-bent rudder trim tab is not the issue, notice which way the airplane rolls.

Once on the ground, the "high" wing is the one you want to adjust. You will want to make it lift less, so remove the cotter pin on the bolt holding the rear lift strut, and loosen the jamb-nut on the attach clevis. Now comes the helper. Have him or her press upwards on the wing using a flat palm at the corner forming the outboard aileron cut out, but not the trailing edge, just enough to allow you to slip the bolt out. This is a relativly hard point.

Turn the attach clevis two or three turns out, reattach and safety. Go fly and repeat until all rolling tendancy is removed. You should be able to get it to fly straight for prolonged periods in smooth air.

If your ailerons tend to "stick", unzip your headliner and make sure the aileron cross link cable is not rubbing on a steel tube, indicating it was not assembled properly. Also look down the wing from the root rib with a mirror and light to make sure you didn't twist the aileron cables during assembly.

I have seen aircraft come from the factory with these defects, so it is easy to do.

If you do all this and you notice the rudder wants to sit at an angle to the fin, adjust the rudder trim tab to remove any residual rolling moment.

If you enjoy spins, and your aircraft is not spinning well, you might have washed out the wings a little too much. You can go back and wash-in both wings (SHORTEN the rear struts several turns) and you can check your ailerons in flight. If BOTH ailerons are a bit higher than faired with the wing, you can use the cable turnbuckles to adjust them down. This will lower stall speeds and make the aircraft spin a bit better. Always make your adjustments based upon the assumption BOTH ailerons are equally up, down or faired. Not one faired and the other up a quarter of an inch.

These are not critical adjustments you will be doing. There is a wide margin for error, so unless you make more than 8 or 10 turns on the attach clevis, you can't get in much trouble. Do have an A/P help you as this is not owner/operator legal work.
 
Steve-

No doubt your method works fine, BUT since many of these planes have had the rigging adjusted by those less experienced than you I strongly suggest rigging to zero/flat after assembly so that you have a known starting point rather than whatever position someone arrived at the last time. Using the mirror to check rudder position is interesting but since many planes fly with the rudder less than streamlined it is better to center the ball with the pedals while holding the wings level with the ailerons. After the wings are rigged properly it is a simple matter to adjust the rudder tab as required.

While it is refreshing to you use wash out, rather than simply using wash in, to adjust rig it is better to apply an equal amount of each to opposing wings to prevent a significant disparity between wings.

Tom-
 
Dave, Steve and Tom,

I rigged up an incidence gage with a straight board, a level, some wedges, and duct tape (of course). I put the tailwheel on some milk crates to get the plane almost level. Then I checked the incidence at the root and compared it to the incidence at the aileron bay, as shown in the service manual. Within the limits of my measuring technique, the wings are flat. And looking from tip to root along the undersides, I see no twist. I realize these aren't super precise measurements, but there's nothing obviously out of whack.

Unfortunately, I do not have a skylight-- project for another day-- so I'll have to do something else to fair the rudder. The main impediment at this point is our fog and low wintertime ceilings.

Thanks for your thoughtful replies. I'll try some of your suggestions... soon, I hope.

Alex
 
Alex-

These are rather simple flying machines, you need to be accurate NOT precise, I'm certain your results are fine. I wouldn't be concerned about the rudder, the important thing is that the ball is centered while you are holding the wings level with the ailerons. After you get the wash in/out adjusted correctly then adjust the rudder tab as required to hold the ball centered. You would be surprised at the number of aircraft that fly perfect with the rudder slightly out of streamline.

An incidence board is unecessary if you use a Prop Protractor or the modern digital equivelent.

Tom-
 
Interesting discussion. I've noticed the right aileron on my 7GCAA is about a 1/4"-1/2" displaced when flying straight and level (hands off) with the ball centered. From Tom's post, it sounds like this isn't completely abnormal.
 
:D

We just completed the Milman wing kit without using the leading edge kit. Our recoverer had difficulty mounting the kit (finding ribs for screwing in the #4's) and we returned it to Milman.

Milman, by the way, was very helpful and took the leading edge kit back. I am very impressed with Milman and their products. As I mentioned in another post, we completed the job, including a full Decathelon sunburst 3-color scheme in aerothane, on the whole plane, for about 60% of the new factory wing cost.

The airplane flies great but after trimming we noticed that the plane banks ever so slightly, hands off, to the left, most of the time. After gently moving the ailerons around some it might bank slightly to the right, but usually goes left. The pressure to correct this is so small it seems not worth fooling with but we can't figure out why it's not consistent in one direction or the other.
 
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