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Optimizing flying wing design

#1
My question is fairly simple: how does one decide on the ideal dimensions and ratios for a flying wing given the target cruising speed and payload or other relevant flight characteristics.

For a more conventional aircraft, I feel like I have a fairly good intuition as far as changing the wing design to get the desired characteristics. Wing area is roughly proportional to payload for a given flight speed. An undercambered airfoil will be slower and lift more, but not perform well inverted. A more symmetric airfoil will be faster and more acrobatic. A relatively thin airfoil will be faster, but may have a high stall speed. A higher aspect ratio wing will be more efficient. etc.

Those are not ultimatum, but rather rules of thumb and variables I consider when I am designing a new aircraft.

In the case of flying wings, I feel like I have much less intuition about how my design choices will affect the final aircraft.

Specifically, what are the (general) effects of increase sweep, more taper, a larger center section, and higher aspect ratio on flying wing flight characteristics?

The designs of many of the most popular flying wings follow a relatively similar ratio: the versa is pretty similar to the Ritewing Zephyr II is pretty similar to the TBS Caphirana.
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Is this some optimal shape? If so, how come the Ritewing Zephyr III and Ritewing Drak, which are entirely different, perform so spectacularly?
 

earthsciteach

Moderator
Moderator
#3
Flying wings are pretty interesting. They are far less forgiving in terms of cg location than conventional aircraft. The more sweep a wing has, typically the easier it is to get cg right, assuming you have a pusher motor. Center section, taper are probably more a product of utility and aesthetics, respectfully. Aspect ratio is related to the desired performance/efficiency of the wing, same as in any other plane, as you mentioned.