Just use a distant pivot point and a hand-hold, with just a single template, on the near end. This works superbly well, at the cost of having to do a couple of back-of-fag-packet-sums. It was in Francis Reynolds’ column and he describes it as“ pivot point cutting” One end of the hot wire is attached to a fixed pivot point some distance away, and your hand at the other end provides the tension( which can be varied at will) and follows the one template.. It resembles a cheese-cutter, and does work very well, and is easy to set up.
The method can be used to cut wing and fuselage cores of any taper. Obviously it can’ t cut rectangular wings, but that’ s not too much of a problem. Tapered wings look better, can be built lighter and are a little more efficient.
Very low taper wings can be a problem as the fixed pivot might have to be in your neighbors back lawn. Fig 1 shows the quick bit of maths you have to do.
Key: R is root length, T is tip length, S is the span of the foam section to be cut, and PD is distance to the pivot from the tip.
So, in the case of the Mustang, the main wing has a root dimension of 225mm and the tip 150mm. The foam span is 422 mm. So the distance from the tip to the pivot point is 844 mm.
Picture 6 shows the setup and the result is in picture 7.
Pivot Distance, PD =( S) divided by( R / T – 1)
This method also works well with a fuselage, calculate the taper and distances as above, place one template at the“ fat” end and cut away.