The next task was to set up ready to drill the holes for the locating lugs and pip-pins. The manual suggests using wooden blocks to support the torque-tube and gluing them to the table using "bondo". I have read elsewhere that some people decided to put the tailplanes back in the foam jigs, but I felt that you could get better adjustment using the wooden supports. So I bonded the blocks to the table and once the bondo had cured, set the tube in position using hot-melt glue to hold it in place. However, as I tried to manoeuvre the tailplane into place, the glue bond gave way, so I had to start again. This happened twice before I decided that the glue gun was not a good idea. To overcome the problem, I made a second block that could be screwed to the top of the first to clamp the tube in position. This worked much better until I was moving the tailplanes around on the tube and the bondo gave way. So I decided to screw the blocks to the bench to ensure that they would not move. With the blocks now set properly, I could get on with the levelling. I had made a levelling blocks from pieces of 18mm MDF - actually part of my original bench top - waste not, want not. The block is placed on the pins of the drive plates and the tube moved until the block is level. Once level, I screwed down my clamping blocks to ensure that the tube would not move subsequently.
|
|
| Torque-tube clamping arrangement | Levelling the torque tube |
Once the torque tube was levelled correctly, I slid the tailplanes into position and levelled them as per the manual. I used old bits of foam as shims to support the trailing edge in the correct position. I then marked the position of the drive plate locating pins on the root of the tailplane and drilled them out. The first set of holes were not marked well and needed to be enlarged to get the sleeves to sit in them properly with the tailplane in the correct position. The second pair of holes were better, but still needed a little enlargement and both sets of holes needed multiple dry runs before I was happy with them. I then floxed the sleeves into the holes. To ensure correct alignment of pins and sleeves, you have to slide the tailplanes into position and ensure that they are level whilst the flox around the sleeves is curing. I slapped plenty of Vaseline on the drive pins to make sure that they did not get bonded to the sleeves during the process. I double checked the levels and left the whole thing to cure for a day or two. After everything had cured, I slid the tailplanes off and then on again and everything lined up perfectly - huge sighs of relief all round. I then just put a little flox around the collars of the inserts to make sure that they were fully supported.
Now on to the pip pin holes. I have to admit to being extremely nervous about this section, it looked a little daunting. However, it turned out to be relatively straight forward. First of all, I had decided to build in a cover for the pip-pin hole. The idea of a hole did not seem terribly aerodynamic to me and offended my sense of aesthetics. Some builders have suggested leaving it as a hole, but taping it over for each flight. However, I wanted something a little more permanent. I found the perfect cover in the shape of a plumbing fitting from a Great Mills DIY store - see the picture below. I had to trim it a little so that it wasn't too deep, but otherwise it was unaltered. I cut the appropriate sized holes in the top skin of the tailplane using the Dremel fitted with a small router bit to the depth of the fittings. Then, I made a conical hole down to the torque tube. It's easier to see on the diagram below:
I made a flox corner around the top skin and put a little flox around the bottom of the hole to ensure that I did not get any bubbles. I then lined the hole with two plies of bid and floxed the insert into place on top of it. This is a tricky operation and I later found that I had rucked up the cloth as I pushed the insert into place, so a slightly looser fit is better. I then coated the cap with some Vaseline to prevent it being bonded into the insert and screwed it into place to make sure that the insert did not distort during curing. I found later that the epoxy fumes affected the washer and it lost its shape somewhat, so it's probably best to leave it out during curing. At the knife trim stage, I trimmed the bid so that it was flush with the top skin and also used a narrow-bladed screwdriver to push the bid away from the cap to help prevent sticking.
The following day I removed the caps with little effort - the Vaseline did the job perfectly. Unfortunately, as mentioned above, the bid had rucked up in a couple of places and I ended up grinding it away and replacing it with a new piece.
 |
 |
 |
| The plumbing fitting - a waste pipe end stop |
The hole for the cover | The pip pin cover in place - sorry, slightly out of focus |
Now, onto drilling the hole for the pip pin. I bought some new drill bits for this including a long ¼" bit that cost me £15 - outrageous! I also bought some cutting compound to prevent overheating. I fitted a special spirit-level attachment to the drill to ensure that I kept it vertical. And then, I just drilled and it all went smoothly. I enlarged the hole in the bottom skin to 10mm and floxed in a short length of plastic tube as a drain hole. And that was it - nothing to worry about, really. The following day I tidied up the edges of the hole and cleaned up the bench and the rest of the workshop and that was the tailplane more or less complete. I did not add the fletner strips at this stage as I was having difficulty finding some balsa wood, so I decided to get going on the flaps.
The flap jigs have to be set out quite carefully to ensure that they are level and have the correct washout. I needed to shim the outboard jig with some cork tiles and a strip of card to get everything correctly aligned. I layed-up the rib and once it had cured, cut it to shape with a fretsaw. It needed a bit of sanding to get it to the correct shape and I decided to make it sit just below the level of the core so that I did not get any proud spots - the hollow would be filled with flox later. Once the jig blocks were set correctly, I laid in the cores and whilst checking for straightness, I noticed that the step in the trailing edge was noticeably bowed, probably because of wire drag during cutting. A call to the factory reassured me that this was not a problem.
The top skin lay-up was pretty straight forward although it is difficult handling the long pieces of uni. The best solution that I found was to have my wife hold the cloth on a large piece of card and gradually move along the length of the core whilst I manoeuvre the cloth into position.
 |
 |
| The bow in the trailing edge | Bottom skin lay-up |
April 2001