Doubloon (oz2559)

About this Plan

Doubloon by EB Jones. 1/2A power competion design.

Quote: "At the 1974 Nationals, the engine run for the A power event was to be restricted to seven seconds' duration, instead of the normal ten permitted, while the flight maximum was reduced to two minutes, and so this model was designed with these factors in mind.

The restrictions seemed to dictate a fairly small model, but my findings with previous small-area 1/2A class models suggested experimentation in other directions, as the result had been inconsistent glide performance. Using a variable incidence tailplane plus auto-rudder would probably be the ideal, but a simple, easy-to-build model was required, so an attempt was made to build VIT characteristics into a straightforward design.

The idea was to have a reasonably sized model, climbing fairly straight, with a good pull-out at the cut-off stage. The thin, flat section, low pylon and large fin appeared to give the required climb characteristics, while the auto-rudder meets the good pull-out requirements.

American experts have decided that moderate areas, combined with low aspect ratio wings with thin sections, give a good glide, coupled with a reasonably quick, viceless climb. Also, the three-piece wing system is quick to build, light and fairly rigid - considering the section.

It is possible to fly this design with a forward centre of gravity, which improves stability and glide, and practise has shown that a 70 per cent position seems to be about right. Fortunately, the prototype seemed to have all the right characteristics, and with the usual adjustments to auto-rudder and tailplane packing it consistently turned in over two minutes on a 6-1/2 second engine run, increasing to 3:30 - 3:50 minutes with 9-5 seconds of power.

Construction is best commenced with the wing and tailplane, as it gives these components time to 'age' somewhat while the fuselage is being assembled, which all helps prevent the bogey of warps appearing. Also, the fuel proofer has a chance to fully harden - important if high nitro content fuels are to be used..."

Update 05/01/2017: added article, thanks to RFJ.

Supplementary file notes

Article.

Corrections?

Did we get something wrong with these details about this plan (especially the datafile)? That happens sometimes. You can help us fix it.
Add a correction