Thread: Discussion Scratcho
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Old Jan 09, 2013, 12:27 AM
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AvB
Wind, hill, ... I'm keen ...
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Australia, QLD, Woody Point
Joined Nov 2006
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I think it's a combination of things that simply thru good luck have worked well together!

In priority I'd say the biggest things that made the Scratcho so much different and better to the SC 1, 2 and 3 are:

1) HN1038 foil. So much faster and slipperier than the old RG15. And it can still "thermal" and responds excellently to camber. Excellent frontside, excellent in DS.

2) Planform ... yes, I have no proof but I do think the planform of the wing and the overall airframe shape works really well for some reason. I looked at several planes that I thought were simple designs but tracked really nicely in DS (Vector, Flying Fish, etc) and compared them to the things I liked about the SC2, and sketched out shapes on the shed floor till I thought it looked good! Definitely a "TLAR" approach but I think it worked.

3) Tips ... I know they are squarish in shape but they are cut off at the 8 degrees angle, and undercut at the ends (as per Helmut Quabeck's concept from the 80's) , and from that the tip shape of the plug was sanded to a very teardrop smooth rounded shape, which I think helped to reduce drag at the tips.

4) Tail .. again I have no proof but I think that the stab position somehow struck it lucky. It's done as a simple glued-on X-tail, stuck straight onto the boom. Compared to T-Tail you'd think it might be adversely affected by being right in the wing wash but it seems to be perfect. Really great tracking and elevator feel.

5) Toughness! All the SC planes were made with the primary aim of being light enough to be really fun, but very tough to survive hard knocks. Or be crashed into a tree DSing like Asto did at Cass, and with 45 mins fixing a snapped boom and wing crunch, it's back doing 152mph the next day! I know that's nothing to do with planforms etc but tough planes are just so valuable to your all-round sloping experience. It means more stick time and better flying skills and less frustration in the shed.
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