The shock of the Big!

Sunday 20th July 2008. 5 hrs 30 min

Completed inventory and storage of wing kit. Countersunk left wing for tank attach and inspection plates

Just before putting the emp away, I wanted to check that the rudder hinges were set up okay. Unlike the elevator hinges, access to insert bolts is very restricted, particularly for the top two rod-end bearings. Not having any suitable nails, I used some allen keys, one of which had to be cut to fit - no biggie as it was a cheap freebie that had come with some self-assembly furniture. The hinges lined up fine and I had 'full and free' movement of the rudder.

I finally finished the inventory by going through the long narrow pieces such as tubes, angles, spars, fairings and so on. - Every piece of the kit was present and correct. It is quite a juggling act now to get everything properly stored above the rafters of the shop. When the wings are completed, I am going to have to put in a second 'deck' up there. The design of the shop included enough head-room below the rafters to allow the wings to be slung there if necessary. However, they would restrict access to the area above and I would need to re-locate the light fixtures to the walls so I would rather not avail of that facility.

Eventually, I got going on the wings! The spars are beautiful, as many builders have mentioned. They are also the biggest pieces to be handled so far. The first instruction; "To begin wing construction, rivet the tank skin attach platenuts to the spar as shown in DWG 11" looks very sparse and is a signal that you better be more self-sufficient from now on. However, it is followed by another paragraph that fleshes out how it should be done so don't forget to read on.

The platenut rivet countersinks went without a hitch. However, the countersinks for the #8 screws were a bit of a shock. They are far bigger than any countersink I have done so far. Also, they greatly expand the size of the existing pre-punched hole and they totally disregard the idea of leaving a cylindrical portion of the hole, which I had thought was important. These countersinks go all the way through the material - and then some! The justification lies in the fact that we are talking about screws here rather than rivets and the load is more than adequately spread by the platenut. If we were dealing with a big rivet in these holes then countersinking to this depth would not be acceptable. However, it comes as something of a shock to be putting such big countersinks into this beautiful spar, but you just have to get on with it.

To check that the countersink was the right size, I used the dimpled test piece method rather than the sawn off #8 screw head as mentioned in the manual. I set the countersink cage depth using trial holes in a piece of waste before touching the spar itself. However, if you are doing the same, just make sure that your test piece is not 'dished' around the dimple and that it is otherwise flat in all directions. Otherwise, your tester will 'rock' from side to side even when the dimple is fully seated in the countersink, fooling you into thinking that you need to cut deeper. I think this was what got me into trouble on the equivalent dimples on the HS spar. No problem this time, however and I was very happy with the countersinks I produced.

Another considered departure from the manual was in respect of the countersink cutter used. The manual says to use a #30. For my money, the problems that builders have had in producing perfectly formed countersinks here all relate to the fact that the guidepin of the cutter is smaller than the hole that is being countersunk. Yes, the hole itself will centre the funnel-shaped cutter to some extent but it still moves around as it works. The solution recommended by some is to clamp a piece of aluminium behind the hole with a #30 hole in it to hold the cutter steady. Okay, but how do you centre this #30 hole on the pre-punched spar flange hole, which is already larger than #30, so that you can clamp this guide piece in the right place?. I think the instruction to use a #30 cutter is based on the assumption that builders will not have the correct size cutter. Fair enough. However, Isham (planetools) include a #21 cutter in their RV kit, along with a #21 drill bit and this is the perfect combo for the job.

My method was to:

1. drill out the screw holes in the flange (not the rivet holes!) to #21,
2. prepare a guide piece with a #21 hole in it (actually the offcut from the angle used for the HS attach brackets),
3. use the drill bit shank to centre the guide piece on the spar flange hole and clamp the guide piece to the flange with the drill bit still in place.
4. Now I was able to go ahead and countersink to the required depth knowing that my countersink would be centred on the hole, perfectly formed and to the correct depth - result!

Beware that the platenuts for the inspection plates on the bottom flange are smaller than those for the tank skin attach platenuts. The screws along here (4 platenuts at each of 3 locations) are #6, for which #30 is the correct cutter. I don't understand why they call out #40) I still used a guidepiece with a #30 hole as I didn't want to change a winning formula. Having some guide material left with a hole the exact same as the cutter guide pin is essential, otherwise the cutter will wallow around once it breaks out the other side of the flange and starts to enlarge the hole.

I used an artists' brush to spot-prime all the countersinks. I intended to just wipe off the excess but it dried so fast that I couldn't . However, a stanley knife blade worked perfectly with no effect on the anodised flange surface- just like scraping paint off glass after painting a window.

Work was slow today. I expected to get both spars done and the platenuts actually riveted on. The slowness was partly because I had been on a long lay-off from building. I spent longer than I should have foostering around with setting and re-setting the countersink cage. I have two of them, specifically to cut down on re-setting, but three would have been better because I want to keep one permanently set for #40 countersinks at all times and the other was being changed between #30 and #21. If I get another, I can leave it permanently set for #30 and use the third for all other sizes.