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Old 10-10-2019, 10:31 AM
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BMatthews
 
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For smaller size like this to maintain good lower speed manners you need to keep the model quite light. Add to this that the lifting surfaces of a canard cannot be pushed to as high a coefficient of lift so you cannot slow a canard down as much as you can a conventional setup. All this means that for a 35 inch span you need to keep the model fairly light. It'll fly with the best performance if you can keep the weight to 20 oz or less. But up to around 24 would be OK but the slow speed manners will not be as nice. Start crowding up to 26 or more though and you'll find that the stall speed is high and the model needs to be kept moving fast ALL the time. And at that point it may start trying to snap out of things like steep fast turns or fast loops if you pull too tight

So my suggestion is to not try to get too fancy with the scale detailing on a model of this size. And pick construction methods which you know will result in a lighter structure. Keep things light in the structure and that could allow you a bigger allowance for weight in a nice paint job where you can add shadow lines and panels and such with an airbrush to give the model a really nice "full size" look. Paint like this is fairly heavy though so keep an eye on the structure weights as you go. You'll want to start with a target of 20 oz ( 560 gms). Subtract the weights for the radio package, motor and flight battery. Then give yourself a 2 oz (60gm) allowance for covering and paint just to be sure. Then split up the weights from there into your components in proportions you hope to achieve. Then hopefully picking a construction method that is suitable start building and watch the target weight vs real weight as you build. If your first component or two is way over the target then clearly you are not going to make the target weight overall and need to shift to a lighter manner of building.

If you are wondering the reason why canards cannot be pushed to wing angles as high as a conventional model is due to the fact that there really is only one sort of wing layout. At least as far as the air matters. On a canard the front wing is still the "main wing" from an aerodynamic standpoint. So it can only rise up to an angle where it stalls and then it produces a lot of drag and the aircraft slows and falls away. Meanwhile the large rear stabilizer is restricted by the design's trim angles to fly at a slightly lower angle. And that means that while it is the major lift producer it still never gets to produce as much lift as it might simply due to being restricted on the angle of attack it can achieve due to the limit set by the canard surface. And that would be why we don't see canards used in styles of aircraft where such things matter.

Hope that helps out with the design exercise.