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Appendix A - Spar sizes

Modern F1A spars are greatly over engineered for other model types. Bear in mind that nobody uses less than a 5.8 mm high-tensile steel joiner in a modern wing and that the spar is engineered to match! The spar can be made a lot lighter for other classes. Carbon D-box structures should be sized along the following lines:

Class	D-box	Spar
F1A	2 x 83gsm cloth, 1 x 120gsm unidirectional cloth	1mm flanges, 8 mm -> 1 mm wide, 8 -> 1.5 balsa end-grain web, 15mm diameter (4.5 g/m) carbon sock SC1045

F1B/F1J	1 x 83 gsm cloth	0.2 mm flanges, 3 mm -> 1.5 mm wide, 3.0 -> 1.5mm med. balsa web (spanwise grain), 10 mm diameter (3.2 g/m) carbon sock SC1032

Stab/fin	1 x 83 gsm cloth	0.2 mm flanges, 1.5 mm wide, 1.5 mm medium balsa web (spanwise grain), 1 layer 83gsm cloth (set at 45 degrees) on the rear of the web as a D-box closure

The assumptions made in constructing this table are:

the spar is full depth
the D-box has enough ribs inside to prevent the shell deforming under torsion
the wing behind the spar is carbon TE + carbon capped straight ribs.

NOTE: these estimates do not apply to LDA models designed for 100m+ launches, which need much stronger wings. I had retired from the F1A game, become a glider pilot, and bought a Standard Libelle sailplane by the time LDA models arrived on the scene.

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