Dimple Dimple Dimple

Wednesday 20th August 2008 2hrs 50min

Deburred and dimpled remaining left wing main ribs. Dimpled both aft spars. Dimpled J stringers for both wings. Began to install tank attach platenuts on spars.

Still tired (it's the diet and the gym sessions you know), I wanted relatively undemanding work this evening - and there was lots of it. You have to have a certain tolerance for tedium in this game as well as the ability to pace the work over a long project in which the finishing line is so far in the future that it can barely be imagined. This evening was one of those evenings that tested these attributes. I didn't count them but there are a lot of holes in a set of wing main ribs and another bunch of them in the stringers and aft spars. In fact they would be fairly easy to count as there are 15 ribs and the stringers and aft spars involve 6 times the number of rivets across the entire length of the wing. I must do that count in some future idle moment.

The air squeezer is a blessing for this task as it is really fast and provides a consistent pressure on each stroke. You do have to make sure from time to time that the adjustable rivet set (don't even think of getting the non-adjustable kind that relies on shimming out the die with washers) is adjusted to the point where the two dies meet firmly when you close the squeezer with no material between them. I find that this loosens slightly during a long dimpling session and needs fairly constant checking (every 30 strokes or so).

One thing to watch out for is getting so embedded in a rythm that you follow that rythm regardless of whether the work is properly positioned for the stroke or not. This is when you add new holes to your ribs, stiffeners or, worse again, your skins. You need to retain enough concentration to ensure that the guide pin is firmly through the hole EVERY TIME before you pull that trigger.

The Orndorff videos show George using his hand squeezer for this job and it looks as if it would not be much slower than the air squeezer. He holds the saqueezer near vertically with the tip of one handle down on the bench and uses his right hand to move the other handle while his left hand moves the work through the jaws.

I love my DRDT2 dimpler but it is no use on any hole near a flange so it is restricted mainly to sheet material. I am certain that I would hate the usual red hammer-driven C-frame dimpler as much as other builders say they do. Smitty hates it so much that he will use a pop-rivet dimple die to dimple an entire wing skin. As he says, time is what he has most of.

Towards the end of the evening I moved on to one of the last jobs on the spars, which is the riveting of three platenuts near the inboard end that take the tank attachment bolts through the inboard-most attach bracket. These are close to the reinforcement plate and for that reason, the top and bottom one are angled at 45 degrees. However, that does not leave a lot of space to get a bucking bar in between the plate and the barrel of the platenut. The other (forward) side of the spar gets countersunk as the rivets called out here are AD4263-4s and you need a flat surface against which to mount the tank attach brackets. Again the spar structure intereferes here and there is not enough space to get a countersink cage onto the top and bottom-most rivet holes. I used the deburring cutter in my electric screwdriver to countersink these holes, checking regularly with a rivet until I got the right depth.

Whether I am so out of practice in bucking rivets or whether the placing is so awkward, I messed up a few of these rivets and had to drill them out either because they were not properly seated in the countersink on the forward side or because of a faulty shop head. When the same problem started to occur on the second spar I decided to call it a night. It is very important to know when it is better to take a break or persist in the face of a problem.

More Stringers

Monday 18th August 2008. 2hr 40min

Match-drilled J stringers to to skins. Removed top skins and fitted bottom skins.

I had the top skins off when I realised that I had forgotten the J stringers, so back on they had to go. I lost about 30 minutes to this mistake.

By the way, I find my (very masculine) workshop apron excellent for this work as it has a large belly pouch. I take a full storage box containing about 150 clecos and just tip them into the pouch before starting to cleco on something big like a wing skin. The pouch also takes the cleco pliers and keeps them to hand. There is another pliers in the toolbox for when I absent-mindedly hide the first one from myself. The pouch also works in reverse to collect clecos when dissassembling.

Match-drilling the J stringers and fitting the bottom skins went exactly like the righthand side but quicker.

Stringing it together

Friday 15th August 2008. 6hr 35min



Completed match-drilling of top right wing skins. Cut and edge-prepped J channel stringers for both wings. Match-drilled J-channels to right wing skins. Installed bottom skins and match-drilled. Dissassembled right wing. Deburred right wing ribs.



You get 4 lengths of J channel stock in the kit, each long enough to produce the longer outboard stringer. If they made them just a little longer, you could get two of the shorter inboard stingers out of the same length and then they would only have to supply three; unusual for Vans not to have spotted that possible economy.


Fitting is quite simple, though in my small workshop, I had to lift one end of the wing off the stand and move it so that it was pointing towards the open door and then, with the other hand, slide the longer stringer into its place, beginning with one end out through the door. Even with lots of clecos on board, the wing is light enough that this did not count towards my quota of exercise for the day.


The outboard end of the outboard stringer is clamped flush with the edge of the outboard W-903 skin but it is not clear from the instructions wheter the inboard end of the inboard stringer is similarly set flush with the edge of the W-902 inboard skin or with the inboard W-910 rib. The manual says "Clamp the W-926A inboard stringer in place at the W-910 inboard rib, locate it and drill to the skin" which seems ambiguous to me. I went with flush to the edge of the skin on the basis that I can cut it back. However, this leaves me with less overlap. If I am wrong, I could put some extra rivets through both stringers (but not the skin) along the overlap to strengthen the join or I could use some scrap to make a third layer to extend the overlap. Most likely, I will just leave it, even if I have to cut the stringer back to the inboard rib.

I used a small clamp on the stringers at the overlap to make sure they were lying tight together before I began to drill. I pulled out a new drill bit for this operation as I wanted to cut the holes with the minimum of feed pressure on the drill. The line was visible in the centre of all holes as soon as the two end holes were lined up. This required the stringer to be placed tight against the aft edge of the slots in the ribs, but the 'curl' of the J section seems to be perfectly centred in the cut-outs at that position. I would have preferred to work from the centre out but, this being impossible, I worked from both sides inward,, using a line of 6-8 clecos in the holes immediately preceding the one I was drilling and moving them along as I worked. I left a cleco in place at each rib as I passed.

The bottom skins went on without drama. I had to take off the top skins so that I had enough clecos Both leading edges are still clecoed at this point. These two, together with one set of skins, use my full stock of 300 3/32 clecos. In fact, I could do with another dozen so that the bottom skins could be clecoed in every 4th hole all over.

After match-drilling, I took the wing apart and deburred the ribs. If I had followed the Vans sequence, the wing skeleton would be primed and riveted at this point and I would have had to debur and dimple the ribs while assembled. My way is definitely easier and I believe (hope) that the assembly with clecos is firm enough to properly match-drill the skins.