Over the past month I've made new nacelles in GRP for a radio controlled twin engined model aeroplane I built a few years ago, and am now building a new wing for it. The previous wing had nacelles made of balsa and ply and were now a bit tatty.
Making the nacelles, which are about 300mm long, 100 mm wide and 80mm deep, necessitated making a balsa wood plug to the exact shape that I needed the nacelles to be, then using the plug to make GRP moulds. I then made the two nacelles, each one in upper and lower halves, in the moulds with a layer of gelcoat and two layers of glass cloth and epoxy resin. They take a few days to harden sufficiently to retain their shape.
Fitting them is difficult as they need to be cut and shaped to fit to the wing cross sectional shape, and accomodate the engine and the propeller driver boss at the front. There are lots of lines and angles to get right. Anyway, shaped and fitted three of the four halves over a period of a week or so, taking my time to avoid mistakes. Then marked up the fourth and final half ready to cut.
As usual, I measured several times, from various baselines, marked the line of the cut with 25mm wide masking tape and cut (once) the part along the edge of the tape with a cutting disc in my Dremel.
Along the wrong side of the tape.
I've just finished laminating up a new nacelle half.
Rats.
Bet TheLurker OTP wouldn't have made the same mistake.....