Warbirds in my Workshop

David Glen BSc (Hons) MSc, Model Maker, Journalist and Author

Formerly Spitfire in my Workshop

Forgotten flaps – a remeidial task

Monday, 22nd August, 2016

Those who have seen my Mk 1 Spitfire will know that its flaps are extended. I believe the refinement adds hugely to the model, but it took months to achieve, and so I decided that this time, in the interests of my advancing years, the flaps of my Mk IX would be retracted. 


Having made that decision at an early stage, I went full steam ahead and built the wooden wings back in 2014, giving barely a thought to the flaps, an oversight that came abruptly and rather shocking to mind this summer:


Firstly, the retracted flaps are not, as I guess I had unthinkingly assumed, flush and all-concealing. Instead their leading edges curve upwards and inwards around their tubular spars; Secondly, through the resulting linear gap and other small adjacent apertures in the under wing skin, a significant amount of interior structural detail is visible. In short, I awoke to the fact that without remedial surgery to open space for these features and to give the impression of a void within the wing, I was in trouble!


I am pleased to say that after some thought I arrived at a solution that I hope will serve, but the moral here is how the slightest oversight at any stage of a scratch build project can severely compromise its success.


The first step was to mark accurately onto the wings the position of the flap leading edge, then, using a thin bladed slitting saw in my Proxxon rotary power tool, I was able to make two relatively neat and parallel cuts along the pencil lines, each penetrating down through the balsa and ply rib sections to the sturdy plywood web over which the bottom half of the wing is built. It was then relatively easy to cut and scrape away unwanted material with a sharp chisel, leaving a neat, clean trench within which to reconstruct the wing locally. 


For this I envisaged two hardwood mouldings, one rectangular to demarcate the wing trailing edge and the other in the form of a quadrant over which to form the leading edge of the flap. Serendipity came to my aid here since I was able to find at my local DIY supplier some hard wood quadrant almost exactly equivalent to the scale diameter of the flap spar.


I should add that before gluing the rectangular section in place I clad its rearward visible face with litho plate; the adjacent quadrant will, of course be totally hidden when comes the time to skin the flap with litho plate.


Once any gaps or irregularities in the modification had been plugged with filler and the entire job sanded flush and clean, the result was perhaps rather neater than I deserved.  I plan to engineer in metal those visible portions of the hinges, spars and flap actuating mechanism in due course and to graft them into the model, at which point further routing away of ly and balsa will be necessary. However, for the present, I am at least part reassured that an embarrassing oversight has been corrected.

Back to Spitfire Mk IX Diary

The underside of the wing. But with a lamentable lack of foresight, I had completed the woodwork without any provision whatsoever for the retracted flap.
The shallow saw cuts along the two pencil lines can just be discerned in this picture.
The intervening balsa and plywood has been removed, and a pair of lathes, one rectangular and one quadrant shaped, has been cut to fill the gap.
The work is made good with filler...
..and sanded clean and flush with the underside of the wing. Further small cavities will require routing out of the wood to accommodate the flap hinges, etc., but for the moment an embarasing oversight has been addressed.
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