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Saturday, January 12, 2008

Chuck glider from one 1/16" balsa sheet: Part 1, Aims

There is an interesting thread on the Small Flying Arts forum, started by Allan Wright (the designer of the Gambler AG radio control discus launched glider DLG). It is all about designing and making a chuck glider out of one balsa sheet of dimensions 3 x 36 x 1/16". You are allowed to use glue and clay for ballast, but nothing else. The glider is to be flown indoors on various tasks. E.g. longest glide, duration, spot landings, etc.

Very interesting challenge. I thought it would be fun to go through the design process and share it on this blog.

DESIGN OBJECTIVES

I decided that the main aims are:

1. A good glide. So this means maximum span and minimum weight (which is the same as min wing loading and max AR - see earlier blogs on L/D)

2. Stability

3. Trimmable for straight flight AND a turn. This is different to the usual HLG objective, which is a thermalling circle (usually a left turn for a right handed thrower))

4. Reasonably robust (for the spot landing) but not a "tank". This means that the extremely light weight Indoor HLG designs are out of the question

5. Simple design and easy to build - suitable for a beginner

MATERIALS

There is a huge variation in balsa. My 1/16" sheets vary from 9g (very light and flexible) to about 20g (hard and stiff). I'm going to make the first prototype from mid weight stuff. After playing with my sheets and waving them around (which I must admit was fun) , I decided to go for a 17 x 3 inch wing.

PLANFORMS

I did the sketch above on the train while commuting. Squared paper allows you to estimate wing area.
  • Planform A is the whole rectangular sheet: big area, 51 in^2 and AR of 5.7
  • Planform G is sort of elliptical: area is 43 in^2 and AR of 6.7
  • The others are somewhere in between
Planform A would have the most lift and drag, G the least. The shape also affects the strength of the wing, especially at the tips. I have probably decided that the design will be a 3 panel polyhedral (two breaks). This allows easy gluing to the fuselage and since each panel is small, more stiffness and strength. Lighter tips are better.

At the moment, my favourites are D, E, F and K. Hmm....need to think about this....

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