You will have heard the addage about measuring twice and cutting once. Well, in a momentary lapse of concentration I forgot this fundemental rule whilst measuring out the cuts for the trim tabs. Instead of being 184mm at one end and 155mm at the other, I cut it 184mm all the way along. It was only when I was trying to work out where the hinges are supposed to attach that I realised that I had no flange to attach them to. PANIC! All that work ruined. However, a call to the factory gave me some relief - this cock-up could be repaired, we have the technology. But I thought I would complete the starboard closeout before I tackled the more difficult repair.
First of all, be warned that this a fiddly and time-consuming layout. It pays to be well prepared with everything you need carefully laid out and readily to hand. The manual is pretty good for this lay-up and if you follow the instructions carefully, it is not too bad. One learning point, though, be sure that you put your hinge reinforcements on the correct side - I almost got it wrong, but at this point I was double-checking everything. All of the glass was laid-up on cling film and squeegeed out before putting into place. If you don't do that, it is almost impossible to get rid of the excess epoxy from such a confined space. At the end of a long afternoon, it all looked pretty good.
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| The completed closeout |
And now, on to the repair. I was advised by the factory to glue a flat piece of plastic - I used a sheeet of perspex - on to the top skin with a straight edge along the line of where the flange ought to be. I then used some sheets of acetete glued together along the trailing edge to match the thickness of the skin. The closeout was then performed pretty much normally with the perspex making up for the lack of a top skin.
Once the close-out had cured, the perspex sheet and acetate were removed to leave the close-out skin along the line of the flange. The next step was to sand back the top skin about 8-10cm back from the trailing edge with a very shallow angle so that the foam was only just exposed along the edge. The foam tends to rip when sanding it after it has been exposed to epoxy, so you need to go carefully and some filling will be needed. I then layed in a new top skin using two layers of uni along the same alignments as the original skin and peel-plyed around the edges.
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| Perspex Sheet glued to top skin | Close-out in progress | Replacement top skin |
After the new skin had cured I sanded it flat so that the original profile was maintained. The result was pretty good, I think, although the flange near the root of the tailplane had sagged by a small amount, about 1mm or so. I'm hoping that this will not be a problem when attaching the hinges, but we will see.
On to the trim tabs. These were pretty straight-forward, although they were extremely fiddly. Don't believe what the manual says, they took a good four hours. I would recommend fixing a straight-edge along the flange edge to ensure straightness - I used a piece of aluminium angle stuck on with double-sided tape. Once everything had cured, I feathered in the top surfaces and cut the groove for the flox corner. I found a small bubble on the leading edge which was easily filled using a syringe. Finally, I laid-up the bid on the tips. Again all the lay-ups were done on cling film first.
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| Trim tab close-out |
February 2001