10 February, 2006

Sophisticated Dude

After pranging my Sophisticated Lady a month back, I decided that the fuse was unsalvagable, but the wing was undamaged. Naturally, I put everything else on hold and just built a new fuse. I finished it today, and I have dubbed it the Sophisticated Dude, because it has none of the elegant charm of the Lady.

I kept the band-on wing but used a laminated bulkhead (0.25 balsa with 0.0625 ply facings) to retain the dowels more securely than the original design. I also added a little more space up front for the battery, so that I could use a bigger pack if I wanted.

The biggest change was the use of a CFRP shaft for the tailboom. While folks have been doing this for years, Midwest now makes a very good line so you don't have to go and get an arrow shaft. They were kind enough to also provide stiffness test data to me upon request. For those of you that are interested, all of the hollow tubes can be approximated (in bending) as a material with a modulus of 1.125 Msi, and then a standard MOI calculation for the tube size.

I made every attempt to salvage the tail feathers from the original; I wanted some sense of continuity. Unfortunately, the stab required a conplete rebuild with new spar and new ribs, but I was able to use the original form. The fin was not so cooperative, and it came apart when I was removing it from the fuse. I built a new fin and rudder assembly, getting rid of that T-tail contraption that always made me a little nervous. You can see the size difference next to my Talon fuse.

After radio installation, but prior to balancing, the fuse weighed in at 16 oz, and the wing at 11 oz. With the 4.625 square feet of wing area on the Dude, it has an unballasted wing loading of 5.8 oz/sqft, not bad for a 2 meter bird. I think that I'll be able to get it in trim with less than 6 oz of lead, which would leave me about 7 oz/sqft. Might even be to light to fly down here this time of year.

Turns out I was able to balance it with 4 oz of lead in the nose. Embarrasingly enough, I also read the scale wrong the first time. The weights should have been 15.5 oz for the fuse and 10.5 oz for the wing. This gives a total loading of 6.5 oz/sqft, not too shabby. I think that the CFRP tailboom really helped, leading to less weight in the fuse, but also less weight needed to balance the plane.

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