Back to the beginning: Project Tiger Cub Story part 5

Getting under the skin and having some ideas

Having satisfied myself with the filling and glue work to the wings they now hang them back on the wall and await Gary’s verdict. Then  will be another new experience, that of working with Ceconite. this will be possible without further mods as Jim Romain had already done this for SP with one of his mods changing from the original Tigertex.

Stripping the aileron: Now I have to cut the old fabric from the lower ailerons to see what lurks beneath. On SP these are extended to the full span on the lower wings and linked to an aileron fitted to the upper wing.

As the standard Tiger Cub had the shorter lower ones only, I really look forward to flying this little beast with the extended aileron area and the fin and rudder instead of the all flying rudder and no fixed surface. I have a copy of the test flight report and it sounds fun

As I clear away the old fabric I can see a large alloy plate bonded to both sides of the blue foam that forms the infill between the ply ribs and bolted though to hold the bracket for the rod that connects the two ailerons. The bonding of the foam to the ply ribs and the trailing edge strip is in good shape, there is a bit of damage to the edges of the foam but less than I have already sorted on the wings.

Of course this will take time but considering the length of time the poor little thing spent in its dismantled state being moved around the odd corners of the hangars at North Coates with bits being borrowed for other jobs it is really not too bad.

Then a minor success with my control column assembly. My elevator push rod is sorted. After many hours of rolling a emery tipped dowel between my hands and a final lapping in with an abrasive polish she ran sweetly. I temporarily rig the control column just to feel the whole assembly gliding smoothly though its bearings, great.

Satisfied at last with the state of the lower ailerons I hang them on the wall to await Gary’s verdict and turn my attention to the short wide cord upper ones. After removing the Ceconite the underlying foam was in fair nick with only limited damage and most importantly the glue joints were all in good shape. I couldn’t ask for much better than that. As these where parts designed and made only for the Romain modifications I made sketches in my note book to show the construction and dimensions. These could be useful later as when I rebuild KM as I plan to build her as a Romain modified aircraft as well.

As I am just finishing the last of the crack testing it is time to assess what I actually need to replace rejected components. This will be a few lengths of alloy tube and some channel for making brackets. I also better check with Gary that my understanding of the grades required is right

Also it’s time I get ready to submit to mods that I feel will improve this great little aircraft into an even better one. First I want to revert to a tailwheel undercarriage. There are several reasons for this. Firstly it is stronger, both the tubes that carried to nose wheel where no longer straight and I need to replace both of them. I was far from happy with the way that they were mounted on to those tubes. So I was unsure that they would stand up to farm strip usage. Secondly the drag from such a large pertrubance added to the not inconsiderable drag of a biplane, that  I felt that I could do without. Next was the old enemy of all microlighters, weight. A rough estimate the nose wheel gave me about 2kg right up front. This with its counterbalancing lead on the rear bulkhead. I would be happy to lose both of these. Trouble was that I was far from delighted with the main undercarriage of the original tailwheel design. This was a simple tube extending vertically down from the bottom of the front cockpit sub frame each side. This carried the axle with cross bracing wires and was also wire braced fore and aft. While this was certainly light, I did not feel that it was convincingly strong. The Romain mod for the main wheels was tube braced from both front and rear cockpit sub frames looked good but of course was too far aft for my purposes. So I  thought, a combination of the two. I’ll retain the original vertical tube with axle and cross bracing wires. Then along the lines of the Romain mod use tube bracing to the rear sub frame. That would act in both expansion and compression, using a wire brace to the front would provide good triangulation. Strong and light, I’ll draw it up and see what Tec Office thinks.

The second mod that I would like in place early was to the fuel tank and its mounting. As I had two aeroplanes and only one Tiger Cub fuel tank. I wanted to use the 25ltr Thruster tank that I had bought. This was a nicely made alloy tank but one of the best features for me was that it had a sump in the bottom unlike the original. As a guy who owned boats for a long while I get a bit sensitive about water in fuel. To put this together I will need load calculations to prove to tank mounting up to 6G. Not being very clever, my maths will not handle that.  I’ll have to reassemble the rear cockpit sub frame. then the mounting will need to be made and loaded with weight equivalent to a 6G load on a full tank. Then I will need weigh all the bits and calculate the effect on the weight and balance.

All good stuff, but  I’ll be flying it at least the object is to keep me alive, I’ll drink to that.

 The other mods that I have in mind involve the seat harness and streamlining the struts. The first one to avoid compressing the spine in the event of a crack up. The second because I can’t believe the amount of round struts in the design but I can imagine the drag that they cause. I believe that if I can pull it off this will be a fantastic little aeroplane, maybe the kind of thing that Tom Watson hoped for when he did the first design sketches all those years ago.

Everything so far had  been going well, slowly but well. Then I had a clever idea. It was a fiddly job cleaning and going though all the stages of spraying the unpleasant chemicals needed for the crack testing process. This was made worse by the large number of little brackets that hold the tube work together. So I made up a board where that they could all be suspended so that they could cleaned sprayed and developed with minimal handling. Not a bad idea, not put into practice well though. I forgot just how well penitrant  dye spreads. Most of my careful little labels were now illegible, bugger. It was a good job that I’d been methodical. Some time spent checking the workbook and using diagrams and drawings of bracket profiles in the Kit Build Instructions that I’d got from the Newark Museum recovered the situation. I might feel a bit of a clot, but there was no harm done and I’d learned a bit more.

Then I receive a message from Gary telling me the properties of the types of tubing that I had inquired about and saying the type used in her construction should be as in the Kit Build Instructions. So I read those with great care, nope, not there. Next I went though the Maintenance Manual and the Pilot and Operators Handbook, no luck. I then resorted to reading all the mod forms that used tubing, not there. The only thing left was the bulletins and letters from MBA to the builders of the various aircraft that I had acquired parts of, not there either, Damn. It is beginning to look as if I’ll be pestering Guy and the Tec Office. I know that they are always busy so I’ll try Gary with what I have. That is just a description, high tensile thin walled corrosion resistant alloy tube. O yes, says Gary brightly, that is HT30TF and the Plates will be HE30TF. Great, at last, but hang about, I’ve never heard mention of this stuff before. Not in any of the stuff that I’ve read up or, more worryingly, in any of the suppliers catalogues. I tell Gary this and tentatively suggest that it seems most builds seem to use 6061T6. That’ll do the job he says, the old HT30TF was good stuff in it’s day, but things have moved on since then. Talk about going round the houses to arrive back at the obvious. Still never mind it’s now sorted.

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