February 2001

I've been continuing with the tailplane this month. The first job was to fix the hinges onto the trim tabs. This went pretty smoothly although it's a bit scary when those pop rivets go bang! Why aren't they called bang rivets? Once the flox under the hinges had cured, I fixed them to the tailplane and set about sanding back the flanges to allow free movement. Make sure that you do the sanding at an angle or you will end up cutting back too much. Once this was done, the tabs moved very nicely. When you are fitting the hinges at this stage, I would recommend using ordinary M5 nuts and bolts to avoid damaging the stiffnuts.

With perfect timing the new trim tab drive pins arrived from the factory just as I was ready to fit them - you will have seen that the old ones developed a crack on a particular aircraft and so were replaced. So I set about drilling out the lightening holes. I would recommend that you get some good quality drill bits for this sort of thing as the cheap ones do not last; one or two holes before they needed sharpening. Also, I later bought some metal cutting compound for drilling the pip pin holes which would have been a good idea for the drive pin plates as well.

I made up the fitting template from 8mm MDF. To get a good fit into the trim tab root, I had to sand into the corners a little and trim back the root flange. I floxed the plate and fixed it into position with the template and left it overnight. The next morning when I came to take the template off, the s#!?8*g thing did not line up with the hinge line at all. Either it moved whilst curing or I did not set it correctly to start with. So I decided to take it off and do it again. If you have ever doubted the strength of a flox bond, try breaking it! It took a good deal of grinding with the Dremel and bit of hacksawing to get it off. This time I set the trim tab vertically in the workmate with the hinges perfectly vertical as verified with a spirit level. Then I floxed the plate into place and ensured that the pin was also perfectly vertical and left it to cure. The following day I checked it and it looked good, so I glassed it in. This was a fiddly little lay-up and took a while. I set the middle ply at 45% to the top and bottom plies so that the fibres went over the edge of the plate at an angle for extra strength. Make sure that you flox the edge of the plate and the corners of the root flange so that you do not get any air bubbles.

Drilling the hinges Drive Pin Template 1 Drive Pin Template 2

Having let the fist pin cured, I moved to the second trim tab. I trial fitted the pin on the tab, but try as I might I could not get the thing to line up with the first pin. I bought some aluminium tube and drilled it out to ¼" at each end to fit the pins. The idea is to use the tube to line up the pins, but it would not go. So after a good deal of thought and even more swearing, I decided to redo the first pin, again. This time, I did both pins at once whilst connected with the tube. Also, I clamped a mixing stick to the tabs to make sure that they were correctly aligned and weighted down the tailplanes with sandbags so that they were at the same angle. I double checked the alignment by positioning the hinges on the edge of the bench and moving the trim tabs to make sure I had full and free movement. I did not need to use the template for the aligment as I had left a step of flox at the back of the plate from the previous fixing to act as a guide. I then floxed behind both plates and pushed the tailplanes together so that the tube connected the two drive pins. You can see this in the pictures below:

Connecting the drive pins Pins during curing

This approach was successful and I ended up with perfectly aligned drive pins. I then glassed in the plates as before and left them to cure.

January 2001        March 2001