[Steve Ashby]

I just finished riveting my left flap and took it out of the V-jig. I then put it down on a (relatively) flat surface and it appears as though there might be as much as a 1/8" to 1/4" twist in the flap. Am I toast? Although this comes in the category of the horse already out of the barn, I am not real happy with Van's plans regarding the 8 flaps. They say to build it straight, but they give you no clue how to keep it straight. I tried to keep it as straight as I could in the V-jig (by sighting down the trailing edge), but I have no clue how to make it any straighter. In the aileron plans, it said to place it on a flat surface while riveting the spar. No corresponding instructions for the flaps, however. What should I do?

 

[sprucemoose]

Now you know why RVs all park with their flaps down. It is not, contrary to popular opinion, to make getting in and out easier. It is so that no one can see that your flaps and ailerons don't line up because one or both are warped.

Mine each had 1/4 inch or so of twist. I built them both on the same bench, which I thought was flat, but they both have the same twist. Maybe the bench was twisted. Oh well. You said that you put them on a "relatively flat" bench. How do you know that the flap is perfect and the bench ain't warped?

Unless you're going for a Gold Lindy, fugetaboutit and move on.

 

[pierre smith]

Hi Steve

Hi Steve,
Your bench may/may not be warped but try this technique:

Hold your flap by the ends with the trailing edge facing you. (maybe back away by three or four feet with it propped up). Tilt it forwards and/or backwards while looking at the trailing edge and try to align your view so you can see that thickest part (spar area) above and below the trailing edge line at the same time. A warp will definitiely show if there is one. As the other poster mentioned, 1/4" is not much but I'd ask Van's,
Regards,

 

[sf3543]

Removing a twist in aileron or flap

It is probably possible to remove much of the twist, if you want to. This method works for ailerons and I'm sure it will work for flaps as well.
Just drill out all the rivets along the hinge line on the bottom of the flap. Weight the flap down on a flat surface. Run a drill bit or reamer through each of the rivet holes, in the new position and rivet things back together. (The drill may not even be needed, but may identify that one hole or so that is off a bit.)
It's amazing how much slop there really is in a long row of rivets, prior to riveting and it is easy to create a twist during the riveting process.

 

[RatMan]

The very first line about flap construction "Flaps are the easiest control surface on an RV to build."

Love it!

Yep, I did it too. Drilled out the long row on the bottom and the twist went away.

 

[Steve Ashby]

You guys are the greatest. I will employ the prescribed fix and, for the next flap, I will weight it down on a flat surface (just like the aileron) before riveting that last row on the bottom of the spar. Onward and upward.

 

[vmirv8bldr]

Timing is everything!

Talk about timing! I've got Flap #1 in the jig cleco'd now, plan to start riveting tonight! Excellent advice, and very timely. You guys rock! (This forum too!)

 

[Steve Ashby]

Bad news. I drilled out all of the rivets in the bottom of the spar (a real pain), weighted the flap down on a flat surface, tried to re-ream the holes (a waste of time since they were pretty well wallowed out from drilling out the rivets) and then re-riveted the whole row (I had to use -4 rivets instead of the -3.5 because all of the holes were slightly enlarged). When I took the weights off of the flap, you guessed it, the twist reappeared! Now, however, it is only 3/16" of a twist instead of 1/4". C'est la vie. All in all, it was hardly worth it to remove only 1/16" of the twist.

I started the right flap tonight and I am trying a different tack. After drilling the ribs to the spar and the bottom flap skin, the plans call for you to drill the spar and the bottom skin to the flap hinge. Before doing that, I will locate or fabricate a dead flat surface and then turn the flap assembly over and clamp it to the flat surface (top end down, without the top skin). Only then will I drill out the bottom of the spar, the bottom skin and the flap hinge. Hopefully, that will minimize any twist along that rivet line. I'll report back once I finish my right flap.