Fauvel AV36 - Optional Ballast

With an all up weight under 7lb and a wing loading of just 8.4oz/sq ft, this model was never going to be a racing machine. However, since I'm flying it off the slope, a certain amount of penetration is necessary to enable the model to be flown in windier conditions than were perhaps envisaged when Gordon Waite designed it as a thermal soarer. So I decided that the option of adding a bit of lead might come in handy.

Clearly, the ballast needs to go as close to the cg as possible. Similar logic was of course applied to the design of the full size machine to ensure that variability in the weight of the pilot doesn't upset the handling so the best place for the ballast is in the area of the pilot's seat.

Had I thought about this earlier, I might have made the seat a more substantial (and easily removable) structure so that ballast could be attached directly to it. However, that's not practicable with the current seat and, rather than re-make it, I decided to try to work out a method of fitting ballast under the seat, from behind the wing mounting bulkhead.

First off, a couple of mounting bars were made up from 3mm ply and fitted with 6mm T-nuts.

Next, a strip of lead was rolled around the bars, then covered in heat shrink sleeving. The weights were determined by how much lead the bars could sensibly accommodate.

This last picture shows the ballast bars fitted just behind and below the pilot's seat. Although they fit quite neatly once in place, the bars have to be manoeuvred into position through the aperture in the bulkhead, then held in place while the nylon bolts are fitted. This is a bit fiddly, hence the central screws and plastic sleeves which serve as handles during the fitting process.

I've now had the opportunity to fly the model with one bar of ballast in place. There was no adverse effect on the cg and it coped pretty well with a wind of 20 - 25mph. Penetration was still a bit of a struggle at times though so next time I'll try fitting both bars.