RV-12 Wing Wobble Revisited

Since posting my original "wing wobble" message a week or two ago, I now have a much better understanding of the problem.

Originally I thought the fore/aft play could be solved by increasing the thickness of the W-1207B doublers with shims. Ken Scott set me straight on that issue: Play is actually caused by the 1207B's being too short, a situation that arises from over trimming the inboard ends. And it doesn't take much - maybe .010" or so.

The solution, according to an information sheet Ken sent me, is to "Tape a dial caliper to the wing skin and adjust it so it just touches the side of the fuselage. (Use a spacer between the caliper and the wing skin, if necessary, to clear the rubber wingroot seal.)One person can rock the wingtip foward and aft while the other checks the indicator, and measures the total play."
After measuring, if the play is .010" or greater, the old doubler has to be drilled out and replaced with a longer one, which Van's stocks.

When I measured the play in my wings, I got .012" on the right wing and
.029" on the left one.

Since both wings had more than the mimimum accetpable play, I ordered two replacement doublers from Vans. These oversize doublers are
available in four over sizes, ascending in length from .010 over size to .045.
As I recall they cost $11.50/ea.

Ken said they have become aware of a few RV-12 with excessive play, but I'm wondering if there aren't more out there than a "few."

Walt Shipley

That sounds like a pretty tight tolerance. A maximum of 0.010" play (0.25mm in our terminology) doesn't seem like much over a 4' wide wing. Having nicely rounded the ends of those doublers, I can see myself having to order new ones - and I haven't even trial fitted the wings yet! No wonder some people have reported difficulty getting the wing pins in.

Wing wobble

I'm not near my plans nor the wings, but won't it be necessary to remove the skin to replace the doubler?

Scott

Easy to replace, no skin removal required. I did my right wing in about an hour.

rgmwa said:

That sounds like a pretty tight tolerance. A maximum of 0.010" play (0.25mm in our terminology) doesn't seem like much over a 4' wide wing. Having nicely rounded the ends of those doublers, I can see myself having to order new ones - and I haven't even trial fitted the wings yet! No wonder some people have reported difficulty getting the wing pins in.

Click to expand...

Robert, The freeplay is measured at the wingroot against the side of the Fuselage as someone else moves the wing fore and aft at the tip. Because the wing is about 12 feet long and about 4 feet between the doubler plates (3:1), a movement of .010" at the wing root will be equal to about .030" fore/aft movement at the tip. Yes...I agree..not much!! Somewhere there was a warning about how much material you remove from the rounded nose of the 1207B and 1208B spar stubs while you deburr....for the very reason that it can cause too much wing fore/aft movement. A friend here in Aus was too careful, and didn't remove enough....and we couldn't get the wing pins in!...although that is probably the better way to have it. You can easily file more off later!!!

Thanks Marcus,

Yes, less than a millimetre total fore and aft movement at the tip doesn't seem like a lot. I was aware to be careful to remove very little material from the stub spars so it may work out OK when I do a test fit. Still, it would have been helpful if the plans actually stated what the movement tolerances were (unless I missed it), and also the fact that Van's have longer stub spars available if you get it wrong. Perhaps an area where the plans could be improved? I wonder how many other builders knew about these wing movement limits before Walt posted this thread?
R.

It would be easier just to put a little shim in the opening. Any thoughts about that?

Gagarin737 said:

It would be easier just to put a little shim in the opening. Any thoughts about that?

Click to expand...

Hmm, you would first have to figure out how thick to make the shim, then decide how to affix the shim to the inboard end of the receptacle.

I considered doing something like that, but discounted the idea because if the shim is too thick and you can't get the spar pins in, getting the shim back out might prove difficult. Also, Ken Scott didn't see shimming as a solution.

Walt

I had a little bit of wing play as described. Thought I might try shimming. BUT! I had not yet installed the wing root seals, for a variety of reasons. (Primarily time-related for prepping the plane for an April still-pretty-cool-temperature inspection. I reached the 25 hour flying mark and took off the cowl and did all the engine checks - all is well! So a friend and I took off the wings today and put on the Van's wing seals.

NO PLAY AT ALL now!!! Putting the wings back on was not difficult, but it did take two of us pushing in at the wing tip while a 3rd guy slid in the pins. See you at OSH!

Bill H.

Wobble ...wobble

My kit is 120003 and my wings were assembled in 2008. The wings were finally mated to the fuselage in 2010 and I called Vans and reported the wobble. At the time I was told not to concern about the free play and that they were all like that, no measurement of the wobble required... Since the wings were removable an exact fit would be impossible. I flew the plane for a year ... No problem ... Now my plane is at the FBO for it's first yearly annual and they have to fix it. I am told they have to upgrade the fuel tank too, even though I didn't want a new tank I ordered one for $755 because the repair would be more than a new one.

Anyone know where it STATES that the Service Bulletins for an ELSA are not mandatory by law ... Where in FAR's ... Where oh where. Too late too help me this year ... But maybe in years to come. Obviously, I decided not to be a builder for life ... Thought I could just be a pilot ... Oh the expense in that decision! My first annual will be about $3500.00.

JerryG150 said:

Anyone know where it STATES that the Service Bulletins for an ELSA are not mandatory by law ... Where in FAR's ... Where oh where.

Click to expand...

The FARs do not state what is NOT mandatory. Just like they don't state that a neighbor's recommendations are not mandatory.

The key is that they do state what IS mandatory and Service Bulletins are not listed, even for certified aircraft operating under part 91.

Only Airworthiness Directives are mandatory.

Has anybody considered drilling through the mount and stub spar to install a 1/4" bolt to lock the stub spar in place? Not a good option if you routinely remove wings, but for those of us who don't take them off except for annuals it seems a good option to correct minor wobble.

BTW my wobble is about 1/32 inch up and down on the leading edge. Has anybody seen that? I'm doing the annual now so I definitely want to address this now.