I’ve been deburring and dimpling flap components as time allowed over the holidays. Finished ’em today.
Now the fun part…over the last week I started deburring all those flap components, as well as those for the new aileron. If you have a Dremel tool, buy a 500 finishing wheel – it’s essentially a 1″ diameter Scotchbrite 7A Medium wheel for Dremel tools, and it’s freakin’ fabulous for deburring in tight spaces!
I repeated the Dec 7 process on the right spar, with the exception of one minor oops…when back-drilling the angle-spar-rib holes I managed to egg out a couple of them in the spar and rib. Per Van’s, the spar holes aren’t a big deal because the spar is sandwiched between the rib tab and the angle. But the rib holes were not so great either, so I took one of the spare non-prepunched holes (see this entry) for the details) and match-drilled it to replace the old rib. Problem solved.
With flap brace parts fabricated, bent and predrilled as necessary I started fitting them to the flap skeletons. The aft-most hole on the rear brace lines up with a prepunched hole on the inboard rib, so positioning the brace is relatively easy. With a cleco in that hole I match-drilled and clecoed the forward end of the brace, then drilled the rest of the holes through the rib. After making sure that the angle was snugly in place and still clamped securely, I match-drilled the angle to the spar…at least the holes I could reach.
The upper flap skin must be removed to finish match-drilling the angle to both the spar and the inboard rib’s forward tab – in fact, the spar is sandwiched between the angle and the rib tab. I know, clear as mud. If you’re to the point of building your RV-7 or -8 flaps, you’ll understand. Some holes can be drilled from the front, but the three holes closest to the angle – the ones that go through the angle, spar and rib – have to be drilled from behind with a 12″ flexible #30 bit.
The end result looks like this…
One last detail – that reference hole at the rear end of the brace gets enlarged to accept the rod end that attaches the flap actuator arm. Once that hole is drilled, two others are drilled for the nutplate that holds the rod end. A nutplate threaded on an AN3 bolt made a good drill jig. The forward nutplate hole is countersunk to accept an AN426 rivet, and according to Vans’ plans the rear hole should be too…but the rib really isn’t thick enough to countersink. I have some AN470-3 universal head rivets, so I decided not to countersink the hole.
With the flap skins fitting properly, it was time to start fabricating and fitting the flap braces. The aft part of the brace is precut and prepunched by Vans, but the forward angle is fabricated from 1″x2″x0.125″ 6061 angle stock. Nothing particularly difficult here, just exercise due dilligence in laying out rivet holes to maintain edge distance on the angle – repeat for the other flap and we’re done.
The aft brace also gets a slight bend just behind the area where it joins the angle. The bend allows it to set flush against the inside rib. Here are the two parts clamped together and ready for fitting to the left flap. The angle is predrilled. Sorry, no pictures of the right flap brace…
The replacement unpunched flap ribs arrived from Van’s; the lower flange of each rib is not punched. I was anxious to try them and get going on the flaps. Long story short – the flap skins were mis-bent and no amount of tweaking with the ribs would fix the problem. I spoke to Joe Blank at Van’s and asked for new skins. To his great credit, he shipped them right away at no charge and with no complaint. Thanks Joe!
Work has been busy; getting the flap braces tweaked took several days with little time spent each day. After match-drilling, the braces are countersunk to accept dimples in the skins. This leaves the upper surface of the brace flush to mate with the flap hinge. Taking a cue from Brad Oliver, I drilled a piece of wood to each brace to guide the countersink pilot and then countersunk the holes. Easy!
Vans’ response on my flap skin problem wasn’t exactly what I was hoping for. They’re aware of this issue, but don’t ship replacement skins any more. They suggested using replacement inboard and outboard ribs with no prepunched holes; according to Joe Blank at Van’s, match-drilling those ribs to the skins will fix this problem. I agreed to try their solution, since the replacement ribs are free. We’ll see if they work.
Meanwhile, I did some cleanup work on the flap braces on both wings. One thing I had neglected to do in the past was match-drill them to the lower wing skins. Before I could do that, I had to tweak the braces a bit with a hand seamer to make them line up smoothly with the skins. The braces are left with a bit of a twist due to the way they’re riveted to the rear spar and doublers. With a little adjustment, the braces and skins line up nicely for match-drilling.
With all those shims in place, it was time to drill the flap hinge and lower skins to the skeleton. With the spars and shims drilled, match-drilling the lower skins was easy. Drilling the flap hinge took a little more work, since it’s one, long floppy piece of AN piano hinge. There’s also very little room for error when drilling it with the proper edge distance as specified by the plans.
The first step was marking a centerline on one leaf of the hinge. I fabbed up a homemade edge marker block similar to the one sold by Avery Tools and marked the leaves of both flap hinges. I then clamped the hinge in place on each flap spar, making sure to align the centerline and spar holes. One minor trick…I used small pieces of thin plywood between the clamps and hinge leaf to avoid squeezing and deforming any hinge eyes. A few minutes with the Sioux and a #41 drill bit, and the hinges were match-drilled to the spar. I then match-drilled the entire structure to #40.
Things were going great, I was on a roll…so I decided to finish up by match-drilling the upper flap skins to the lower skins, spars and flaps I had done over the last two days. I grabbed those flap skins, clecoed them in place…and then found a problem. Remember that picture from October 6?
If you noticed before that the trailing edge bend didn’t look right, you’re very observant. Other builders have had the same problem with flap skins delivered in late 2005 and received replacement skins at no charge. I called Vans and reported the problem, we’ll see what they propose.