I finished the left aileron. Uneventfully. Did a trial fit to the left wing, it lined up perfectly with the flap! It’s good to complete all the external surfaces for the left wing, the end is still a fair way off for the wings but it is at least now in sight…
Left aileron ready for final assembly steps
Previously installed platenuts for static wicks
Ready to match drill trailing edge wedge
Match drilling trailing edge wedge into large angle aluminium straight edge
Match drilling trailing edge wedge into large angle aluminium straight edge
Overdone clecos, match drilling finished
VHB tape on trailing edge wedge, ready for installation
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.
Set up to squeeze every 7th rivet in left flap trailing edge
Set up to squeeze every 7th rivet in left flap trailing edge
After squeezing with flush die, to partially set rivet
After squeezing with angled die, to set double flush rivet
Set up to squeeze every second rivet
Set up to squeeze every second rivet
Set up to squeeze every second rivet
Filling in more rivets
Set up to squeeze remaining rivets, only two cleco's left
Scrap aluminium (after other flat used for right flap)
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.
Riveting flap ribs to spar
Flap skeleton riveted
Flap skeleton riveted, ready for nose skins
Left flap nose skins, top skin cleco'd in place
Left flap nose skins, top skin cleco'd in place
Top skins to main spar riveting, with bucking accident evident
Bucking bar accident on top skin ... oops
After flattening out stretched skin, stress relieving with a #40 hole, and dimpling for a rivet
Left flap - riveting bottom skins to main spar
Empennage bucking bar used for riveting bottom skins to main spar
Riveting bottom skin to main ribs, using MS319-BS pulled rivets
$5 USB camera shot to check riveting of skins to lower spar using empennage bucking bar
Picture from $5 USB camera to check setting of awkward corner rivet, bottom skins to rear spar and aft rib flange
Left flap trailing edge wedges after scuffing and cleaning with acetone
Trailing edge wedges with 3M F9460PC VHB tape applied
Trailing edge wedge in place, ready to pull paper from tape and cleco to straight edge
Trailing edge, cleco'd to straight edge while wedge bonds to skins
Riveting the wing outboard leading edge was straightforward, really happy with the result. With that done and all the tank zee bolts torqued, I reconfigured the workshop to prime the left flap components. I prepared the aileron pushrods, and remaining four wing inspection covers, just to fill out the amount of material for the priming job.
Left wing leading edge riveted on
Left wing leading edge riveted on
End of aileron pushrod drilled #40
Rod ends match drilled #30 to pushrod ends
Aileron pushrods, rod ends, wing inspection covers ready for priming
Over the past week or so I’ve done a lot of work on the left wing leading edge assemblies – the main fuel tank, and the outboard leading edge assembly which incorporates an auxiliary fuel tank. Although I outsourced the construction of these, there were a lot of problems which I’ve had to address – leaks, mis-alignments, riveting etc. I finally got to the point where I was happy with each assembly and it was time to combine them with the left wing box section.
I did a trial fit of the two assemblies, to make some adjustments and ensure they fitted with each other OK (I had already done a trial fit of each assembly to the main spar). I then primed all of the overlapping surfaces, and the open bays. They were supposed to be primed during (outsourced) construction, but that didn’t happen either. I was a bit late shooting the primer on during a winter’s afternoon here, and the temperature dropped rapidly, so I set the tanks up with a heater to keep them warm. The primer cured OK. The biggest problem with priming occurred the day before, when I drained the rusty water out of the compressor. There was quite a bit in there, so I got impatient and unscrewed the drain valve a bit too far – it flew off and with pressure in the compressor, water went everywhere and cost me an hour of cleanup time. I won’t be repeating this mistake anytime soon.
After priming, I installed the stall warning vane, microswitch and wiring. I also installed the auxiliary transfer pump. During normal operation, the main tanks are vented through the auxiliary tanks, so fuel in the auxiliary tank will syphon through into the main tank. The transfer pump is only there as a backup in the event that an air leak into the main tank (leaky fuel cap for example) prevents the auxiliary tank fuel from being drawn into the main tank. Rather than land with fuel in the auxiliary tanks, the transfer pumps can be used as a backup to empty the auxiliary tanks into the mains. The fuel lines are accessible through the stall warning inspection cover.
With the two leading edge assemblies bolted together, and the fuel lines in place and properly torqued, I pressure tested the entire assembly – both tanks and fuel lines. After fixing a minor leak due to a bit of proseal interfering with a fuel drain O-ring, the entire assembly held pressure with no leaks!
Then came the acid test. Will the two leading edge assemblies and the wing box section fit together properly? I set them all up on the work benches, they came together with surprising ease, and fitted to perfection. I modified the wing stand, fitting it with a section of carpet now there is a leading edge on the left wing, hefted the wing into the wing stand, fitted all the tank bolts and screws, and cleco’d the outboard skin in place. Now it looks more like a wing!
Next step is to rivet the outboard assembly in place.
Left wing main and aux tanks, ready for trial fitting
First bay of outside leading edge assembly, mated to main tank
Trial fit, viewed from outside end
Cut out for stall warning vane
Trial fit of left wing leading edge assemblies
Here's what happens when you unscrew the drain valve too far
Outside leading edge assembly after priming, main tank in background
Tank overlap strip after priming
Left main tank, upside down, after priming
Left main tank after priming
Heater to help cure primer, very cold ambient in winter afternoon
Tank overlap strip, stall warning vane slot
Stall warning, backup transfer pump, fuel lines installed, ready for assembly
Stall warning, backup transfer pump, fuel lines installed, ready for assembly
Pressure testing *both* assembled leading edge tanks, including fuel lines
Pressure testing *both* assembled leading edge tanks, including fuel lines
Stall warning micro-switch and wiring
Ready to mate leading edge assembly with wing box section (both upside down)
Leading edge assembly and wing box section bolted and cleco'd together
Assembled left wing back in modified wing cart, top side
Assembled left wing back in modified wing cart, bottom side
A few other notes on the auxiliary tanks:
I fitted a few #8 platenuts to the flange of each rib adjacent to the tank bays in the auxiliary tanks. NAS1801 screws secure these through the main spar.
The auxiliary tank is not easily removed, since it is riveted in place. This is obviously a compromise, and is one of the reasons I did a lot of pressure testing of the system. If a fuel leak occurs in the aux tank rear baffles, the options for repair are limited – drill everything out or cut an access panel in the bottom. The fall-back is to remove the fuel lines and convert the wing back to a standard arrangement with an empty, unused auxiliary tank. To this end, the vent fitting has been included in the main tanks even though it is not used (blocked off) at present.
Each auxiliary tank holds approx. 65 litres. A float type sender is included, there is a drain valve and of course a separate fuel cap.
