Category Archives: Flaps

I’ve kept the straight edge I match drilled the right flap leading edge into clamped to the edge of one of the workbenches, to remind me to finish the flap. Today was the day to do that. Same process I’ve described previously – bind the trailing edge with double sided construction tape, then keep drilling 13mm holes out of the straight edge, using a squeezer through the holes to set rivets. Once again it worked a treat, and the right flap trailing edge is perfectly straight. This is also the last trailing edge I have to do – that’s all seven now done and they’re all dead straight. That leaves bottom skins, wiring and fairings for the wings – which I’m putting off for a while so I can make progress on the fuselage.

The right flap is now done, except for riveting the trailing edge. This is the last control surface assembly, and it seemed a bit odd to realize after I’d countersunk the trailing edge wedge that I wouldn’t need the drill jig any more. Assembly was straightforward, except for some reason about half a dozen holes on one end of the trailing edge were offset slightly, just enough for cleco’s to not fit. Match drilling through these holes worked fine without any enlargement so they weren’t that far off.

A long time ago on the empennage I messed up a VA-140 trailing edge wedge, and stole one from the wing kit. That left me one short. An RV-7 builder in Melbourne kindly obtained one for me along with his empennage kit. I finally unpacked it last week and used it for this flap – so thanks Joe!

Still plenty left to do on the wings, but I have some primer expiring towards the end of the year and a few months of mild weather coming up so I’m going to make a start on the fuselage in the coming weeks.

I’ve had yet another break from building, but this time it was for a good reason – a flying trip! We went on Aussie Flyaway’s latest air safari “across the top”. This is the second time we’ve gone on one of Tony and Angela’s organised air safaris. This time there were just five aircraft, shared by a group of thirteen. It was a fantastic trip, covering a bit over 4,500 nm in two weeks. We were originally going to rent a 182 out of Redcliffe, but then changed over to going in a friend’s Cessna Corvalis. Apart from a diversion to Birdsville (where we got stuck for two days) due to thunderstorms while enroute to Alice Springs, the weather was fantastic and the trip went off without a hitch. More incentive to get on with the build!

The last major assembly yet to do for the wings is the right flap. I started this over the past few days, and have it up to the point where all the ribs, spar and flap brackets are de-burred and assembled into the right flap skeleton. Next step is to match drill and de-burr the skins.

To rivet the left flap trailing edge, I used the same method that worked so well on the rudder and elevators. It was a bit tedious because there are a lot more rivets on the flap – but the trailing edge turned out straight as an arrow.

I temporarily fitted the flap to the left wing, and it looks awesome. To do this, I made up a couple of temporary bushings. Normally, a 3/8″ bronze bushing is pressed into the flap brackets. This interferes with bottom skin placement/removal while still under construction, apart from which if the bushing is fitted now it has to be masked off for painting. I made some temporary bushings, using 3/8″ soft aluminium fuel line. Take off some of the outside diameter with an abrasive wheel in a die grinder, until it will just easily fit into the flap bracket hole. Then use a band saw to slice small sections off, about 1/4″ long, and de-burr. These temporary bushings go in place so the flap can be trial fitted to the wing.

I’ve spent the past few days riveting the left flap together. Turned out to be more work than I expected – glad I’m not building both flaps at the same time. I had my second bucking bar accident for the project. While riveting the very thin (0.016″) top skins to the main spar, just when I was thinking about taking a break, I clumsily allowed the rivet gun to walk off the spar and onto the aft skin, smashing the skin into the edge of the bucking bar. This caused the skin to be stretched and raised where the hit took place, so I had to deal with the problem before closing up the flap.

I used a flat metal surface (the side of a tungsten bucking bar) and a 1/2″ flush die, set up in the DRDT-2 frame, to gently push the stretched area of skin back into place. This turned an outward stretch into a slight inward bulge, which is what I wanted (so it can be filled before painting). Although it would probably be OK as is, I decided to de-stress the area I had worked so I drilled a #40 hole right through the middle of it, and dimpled the hole. I fitted a flush rivet and after doing so the skin was almost dead straight again – just a slight inward bulge which will come up fine with a tiny bit of filler. I hate making mistakes like this, once it is filled and painted no-one will know it is there, but I will…

I bought a cheap USB camera for $5 on EBay, and found it useful while riveting on the bottom skin with the special RV-10 long empennage bucking bar. You get this thing lined up by sighting a line drawn on the centre of the bar through the rivet hole, before placing the rivet in and hitting it with the gun, all while not moving the bucking bar. The camera was great for inspecting the rivets, and any that are under-driven and need a few more whacks, the camera made it easy to line the bar up where it needed to be. On the empennage control surfaces, I had to do all this by feel, the $5 camera made life a lot easier. A few sample views are included in the slides.

I have a few pulled rivets around the flap hinges that I can’t do yet, I either need to buy a long #33 drill or a tiny drill chuck for the angle drill. I also need to grind the top off a rivet puller to get close enough to set them.

For the trailing edge, I’m going to use the same method (double sided tape) that I successfully used for the rudder and elevators. I scuffed the primer up on the wedge, and inside the skins, cleaned all the surfaces with Acetone, and applied the 3M F9460PC VHB double sided tape to each side of the wedge. The most important part is to let this set up for 15 minutes, so that the paper can be easily removed. I slid the wedges in place, and with a helper pulled the remaining paper from both the top and bottom side of the wedge, while quickly getting the wedge in place and cleco’ing it down to the straight edge that I had previously match drilled to the trailing edge. I left it to bond overnight, so apart from the few pulled rivets I need some tooling for, the flap is complete except for riveting the trailing edge.

Building came to a halt through most of May while I travelled overseas. This wasn’t all downside, since the trip was to the USA. Needless to say, I came back with a couple of suitcases bursting at the seams with aircraft parts!

Looking around the workshop while still jet-lagged, I decided to go ahead and tear down the left flap assembly, because it was in the way. I want to do a bit of priming around a few areas of the fuel tanks, and adding all the parts from one flap to the tank bits makes up a reasonable amount of material for a priming job. There’s actually a lot of work in disassembling and de-burring a flap, because there are a lot of small parts. The hours added up on this job and I was glad to not be doing both flaps at the one time.

Since I had great success with the trailing edge method I used for the empennage control surfaces, I’m going to use the same technique for the flaps and ailerons. I bought a piece of angle aluminium, 50mm x 50mm x 6mm thick, 3 metres in length, and match drilled the trailing edge wedges in place, right through into this section of aluminium angle. This provides a straight edge to cleco the flap to during assembly, and I’ll enlarge the holes in sequence and use a pneumatic squeezer to set the rivets, as described previously for the rudder.

Dimpling the skins was easy, as was countersinking the trailing edge wedges using the jig I previously built for the rudder and elevator trailing edge parts. After all this work I no longer had a flap lying on the floor, but instead had a spray booth full of parts for the left flap. I’ve got a few things left to do with the left fuel tank and left outer leading edge auxiliary tank, then I’ll get set up to prime the whole lot.

In-between left wing top skin riveting sessions, I’ve started on the flaps. Left flap parts are de-burred and cleco’d together, except for the trailing edge, ready for match drilling. There’s quite a bit of de-burring / preparation time for all of the parts in each flap.