Saturday, January 12, 2008

Chuck Glider from one 1/16" balsa sheet: Part 2, PLAN

As I said, I could not decide on the wing planform. So, I asked my wife to choose one out of D, E, F and K. She went for E. Why? Because it looked the best. Good enough reason for me! I suppose E requires the least amount of work too, which is in keeping with the Design Objectives.


I sketched out a quick plan for the prototype (left). PLEASE NOTE: this is for the prototype - the final plan is in Part 5 of this series of blogs (in Feb 08). You can download by right clicking and then saving. Each square represents an inch.


1. All dimensions are inches except for the close-up of the fuselage cut lines, which is in mm.

2. Longish nose for less overall weight. Some indoor gliders have really long noses.

3. Nose skid for hard landings.

4. Wing aerofoil: flat underneath, sand the LE to an elliptical profile, top and bottom parallel for about 33% and then sand a taper on top to as sharp as I dare at the TE. (Most lift force from a wing comes from its angle of attack, not its aerofoil shape. Here, I'm just trying to improve on the "flat plate". Perhaps Prototype 2 will have undercamber...)

5. The TE of wing tips, stab and fin should be really thin so that trim can be "breathed and bent" into the balsa. (This is the typical HLG way to warp flying surfaces for trimming).

6. Build it straight (no stab tilt, wing offset, skew, etc). It should fly straight and level! Turn can be induced with blue-tack on one wingtip, a bit of rudder and wing warping.

7. Laminated fuselage. Two pieces of 1/16" balsa stuck together. The glue must be PVA, because the adhesive line will provide some flexible strenth. Hopefully, it won't weigh too much. The taper in the fuselage, wing on top and stab underneath means that there is some built in decalage, but it is very close to 0-0.

8. Longish moment arm (distance between aerodynamic centres of wing and stab), for stability.

9. Try to keep the back end light. This means sanding down the stab and fin so that they are quite thin, a tapered fuselage with a sharper taper over the last inch or so and using glue sparingly.

10. I have guestimated the amount of polyhedral and the areas of fin and stab.

I'll build her and post photos as I go. I'm hoping that the weight without ballast will be under 14g (ideally, the flying weight with ballast should be under that). That would make the wing loading about:

0.5 / (46 / 144) = 1.6 oz/ft^2

That's lighter than a typical outdoor HLG, but heavier than an indoor duration HLG (which are ridiculously light). Have to think of a name....

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