Wing structure starts to go together

Tuesday 26th August 2008. 2 hr

Riveted both aft spar assemblies. Riveted #6 inspection platenuts on right wing main spar.

The shop where I bought the compressor (Halfords); a chain of motor parts, accessories and tools suppliers) replaced the regulator for me under guarantee. In fact, after a call through to the manufacturer's help desk, they were willing to swap the entire compressor, but I felt (stupidly, perhaps) that that was too much trouble and it would have involved a trip home to get the current unit. I was just happy to be able to get straight back to work.

With the new regulator installed, I quickly put it to work and began the final assembly of some wing parts for the first time. Platenuts aside, this was the first time I had permanently fixed wing parts to each other and it felt good. It was an easy job for the air squeezer. Having taped up the holes to be left open last night, there was no chance of a boo-boo and that made the work quicker.

I was not happy with the AN470AD4-5 rivets called out for the W907-D and E doublers. They looked too long. I often make my own calculation of the right rivet size rather than take Vans word for it and it is surprising how often they call out really long rivets for the thickness of material involved. I can use my cheap digital calipers to measure the total thickness of the materials but, more often, I look up the thickness of each part in section 4 of the manual and add them up before adding 150% of the rivet shank thickness. Another method is to use the little blue gauge supplied by Isham in their kit. The cut out in the corner for each size of rivet has one side set to 150% of rivet diameter and the other side set to 200%. On this occassion, I decided to use AN470AD4-4s instead and the shop heads still more than filled the shop head gauge.

The missing platenuts from the spars arrived by post today from Vans so I was able to install the final #6 platenuts for the inspection plates on the right wing.

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.

Picking up the pieces

Sunday 27th July (8hr 10min)

Match-drilled reinforcing plates W-907B, C, D and E to the W-907A left and right aft spars. Deburred and edge-prepped all parts. Cut aileron push rod openings in W907D left and right. Countersunk W907C per plans. Dimpled W-907A top flange in way of W907D doubler fork.

I spent Friday in bed with a very heavy cold - no temperature, just feeling sick and very drowsy. By Saturday afternoon, I was definitely on the mend and I felt pretty good this morning with only a little congestion to suggest that I was ever sick. I think I got off lightly. I made the Michael Bublé gig by the way - really enjoyable.

Despite the good news from Vans regarding replacements, it was a sad business to put away the underbent spars. It would have been an interesting challenge to make the repair that Vans suggested but very hard to go right through the process of building the main wing structure with the fear that the stresses of re-bending would emerge as a result of riveting on the top skins and leave me with 'wrinkly wings' through no fault of my own.

I quickly got back into the swing of things by working on the aft spars. I am continuing my plan of carrying out each process on the parts for both wings at the same time. There were no particular problems here but there are a few things to watch out for. All the builders' sites refer to the need for care in deciding which holes on the W-907C doubler plate to countersink and which holes on all the doubler plates to leave open until later. With the help of the plans and these sites, I did not find those issues difficult.

However, what did make me scratch my head was that I seemed to be missing several pre-punched holes on the spar. These holes are for rivets to attach the lower edge of the flap and aileron gap fairings, where they join the W907-D (mid-span) and E (outboard) doubler plates (not the W-907C - its holes are all present and correct). The plans show all six of these holes but they do not exist on the spars and therefore can't be match-drilled through the doubler plates along with the rest. The holes are all pre-punched on the gap fairings themselves so the only option appears to be to match-drill them in assembly with the doubler plates and aft spar using the fairing holes as a guide. I could have done this on the spot but I thought it might be better if the fairings could be clecoed to the skins at their top edge as well as to the spars at their lower edge. In this way, I can be certain that these tabs are hitting the doubler plates at precisely the right point. I better put it on a 'to-do' list so that I don't forget it while the top skins are on for match-drilling.

The other point that wasn't easy to spot, was the fact that the last three outboard rivets through the aft spar and outboard doubler plate (W-907E) need to be flush on the aft side. they will later be covered by an angle associated with the aileron hinge, which is riveted through the neighbouring row of holes. The plans make clear reference to this (if you are careful about reading ALL the notes) but they do not specify whether dimpling or countersinking is appropriate. Some builders have countersunk the doubler plate (leaving the spar untouched) but I think this material is too thin. I need to research this. Somewhere there must be a table giving minimum plate thicknesses for various sizes of countersink. The top flange of the spar was dimpled for the skins so dimpling should not be a problem as the W-907E is made of the same .040 material UPDATE! Section 5 of the manual specifies .050 as the minimum thickness for #30 countersinks, unless the plate to be countersunk is sandwiched between two others, so I have decided to dimple the doubler and countersink the spar, which will be sandwiched between the doubler and the rib on the opposite side