Ed Franz asks:
Yes. The DLG experiments Joe and I were working on before we discontinued our composite models for business (NOT engineering) reasons verified this.So Don,How light is light in a R-E discus launch H/L? My XP3 weighs in at 9.25 oz, too heavy?
If the planes aerodynamics are properly matched to its weight, there is no launch height penalty or penetration penalty to being lighter. In other words, if a very lightweight DLG doesn't launch well, it's not because the weight is too low, it's because the aerodynamics are wrong. There is no great advantage on launch height either, overall it's pretty much a wash IF the designer did their homework properly.
However, at any flight condition (including cruise and penetration) where a significant amount of lift is being made, and especially at best L/D speed and below, the lighter airplane has a significant advantage in induced drag. The rules limit the span to 1.5 meters, so the only way to make a significant reduction in induced drag is to reduce weight. The lighter airplane will have an induced drag advantage linearly proportional to the weight difference, assuming the planforms, twists and airfoils are equally well designed.
The structural issues in particular become more critical for the lighter designs, Reynolds numbers are more of an issue, and in general the designer's job is significantly more difficult. Be prepared to do your homework, or buy your model from someone who did.
Don Stackhouse @ DJ Aerotech
[EMAIL PROTECTED]
http://www.djaerotech.com
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