Top 20 (oz8724)

About this Plan

Top 20. Lively aerobatic model. Wingspan 42in, for 4 function radio.

Quote: "TOP TWENTY was designed at the outset as a Club-20 aerobatic model, which caused a lot of head scratching as to wing areas and weights - and, of course, motors. In this case, I based the design on the capabilities of the Veco 19 which I had been using previously in an R/C car, and which was therefore nicely run in.

The all-up weight that I had to aim at had to be under 3 lb, giving the model a wing area of 300 sq in or thereabouts for a reasonable loading. To avoid a sensitive beast, and to achieve a good smooth performance, a medium to long moment arm was used, with a 20% tailplane area.

With a small low-wing model, tip-stalling is always a possibility, so the tip section is 17% symmetrical compared with the root section of 14% symmetrical, and to further help in this direction the ailerons are kept short of the tips, and of the strip variety rather than inset.

The final all-up weight came out at 2-3/4 lb, giving a wing loading of 21 oz / sq ft which seemed about right to me and has, in fact, produced a model that is nicely responsive and capable of the schedule - and can be flown in windy conditions without suffering too much.

CONSTRUCTION: Wings. Cut the root and tip templates from 1/16 ply to the rib outline, with only the spar slots cut. Drill these for 6BA bolts where shown and clamp five blanks of 1/16 and two blanks of 3/32 in between them. Carve and sand to shape, cut W1 and W9 to the templates. Having two sets of ribs, make additional cut-outs for the undercarriage beam and dihedral braces, and then add the 1/16 doublers to W1, W2 and W3, and the torque block to W1.

Assemble the wing panels over the lower spar, pinned to the building board, packing the trailing edges up with some 1/4 in sq and carefully checking the alignment. Next add the top spar, leading edge, and trail-ing edge, followed by the leading edge sheeting and trailing edge capping..."

Top 20, Radio Modeller, December 1977.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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