|Antique Model Aircraft||
Ad Astra (Cont.)
The last operation before cutting is to mark the notches at each corner of formers except No. I, into which, fit the longerons during assembly.
Using a veneer saw for preference, cut round all outside edges of formers where possible, and with plane clean down to pencil
Sections of Fuselage Formers
lines, not forgetting to make bevels where required. Drill a small hole on the inside edge of each former, through which passes the fretsaw when cutting out. For those who may not have done fretsawing before, the method of procedure is as follows: -If you have no proper platform, obtain a piece of wood roughly 8 in. by 4 in. by 1 in., and at one end cut a V 2 in, deep by 1 in. wide. Screw or 'clamp this to bench, allowing 5 in. overhang; with the V pointing towards you. Select a saw, and insert one end into the bottom jaws of the saw frame, with the teeth pointing down, and screw up tight. Then thread the former with the pencil lines uppermost on to the saw, through the little hole
already drilled, and insert loose end of saw into top jaws of frame, and screw that up tight. Screw up thumb screw at top until saw is tensioned. Place the piece to be cut over the V and hold it down firmly with forefinger and thumb. Work saw up and down gently, applying a slight forward pressure, meanwhile keeping saw vertical. Don't twist it suddenly sideways in the cut, or a broken saw will be the result. Watch progress of saw, and alter its direction when required by a slight turn of the wrist, either to left or right. After going round the inside to the lines on the former the centre piece will fall out. When formers are completed mark prominently, say, in the left hand top corner, the number of the former counting from front of fuselage. This prevents mistakes likely to occur when assembling. Rear fuselage plates, items II and 12, can now be made up. Keep slots at rear to take stern post a fraction undersize. Lay longerons each in turn on the layout and mark position of
formers. Cut to length at rear ends, but not front ends until after assembly. Mark number of former to be fitted at each point. The next operation is to fit the longerons to formers. Various methods may suggest themselves, but the writer has found the following method best: -Screw or clamp a piece of wood about 1 in. square on to the bench, and allow an overhang of 24 in. Make a 1 in. radius on one edge. Now thread formers number 3, 4, 5 and 6 in order on the bar, keeping the numbered corners the same side, and either facing front or rear. Pierce longerons at centre of points marked on them, and drive a 1/4 in. pin just through, Take each former in turn, and glue and nail longerons in slots, using the I in, square bar as the anvil, supported with left hand. Glue and nail all four lorngerons in position at one "sitting," and when completed, before glue is set, lay fuselage upside down on flat board, with three small weights distributed'. along its length, over the formers. When dry No. 2 former and rear plates, items 1 I and 12, can be fixed. Finally, when glue is set, cut off longerons flush with No. 2 former, glue and nail former No. I, rear struts and stern post in position, also at this stage fix in packing blocks. Check fuselage for being true, clean up, and round off sharp corners of longerons, etc. Make up undercarriage fittings, item No.3, and fix, after which glue in compression struts, item No. 5.
Wing or Main Plane
Carefully study drawing and wing schedule, and set out wing in plan on the board full size. Cut leading and trailing edges, also main spar, half way through at points indicated in items Nos. 26, 27 and. 32.. Steam bend, and hold in position between nails
until dry; then fix packing blacks on to main spar. Mark, and cut out, ribs from I/I6 in. hickory or birch, making first a master template from the rib profile giving ordinates, item No. 39. This particular section was evolved after much wind tunnel experiment, and, though it looks very deep, gives a high lift/drag ratio, which is what we want. When making up ribs it has been found best to first fretsaw to outside shape, clean up, then cut lightening and spar holes out. Item No. 3I illustrates how the hooks for elastic bands to attach wing to fuselage are
·mad·e and fixed. They may be made up and attached to centre
section ribs before assembly. Mark out positions of all ribs on spar, leading and trailing edges.