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Bell Shaped Lift Distribution - best compromise to achive it.

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John Newton

Well-Known Member
Joined
Dec 5, 2012
Messages
430
Location
Derbyshire, England
A question for the group, I have been looking into how best to achieve a bell shaped lift distribution for my latest R/C model. As
I understand it the Horten borthers achieved a BSLD by a combination of Geometric twist (washout), Aerodynamic twist (Reflexed
airfoil at the the wing root blending to symmetrical at the tip and strong taper. My question is why did they go this route, was
it simply to achieve good stall characterisitcs?

Could a BSLD be achieved just using a combination of Aerodynamic twist and taper OR Geometric twist combined with taper (or even
just planform shape (variable taper) alone with no twist?). The reason that I ask is that if I were to eliminate the geometric
twist I may be able to produce a foam wing on a large CNC router I have access to.

On a similar theme I recently stumbled upon a model called the "Norten" in a recent edition of quiet and electric flight magazine,
it looks a little like the northrop N9M with twin electric pusher props, it has a 6mm thick flat plate depron wing and no twist
whatsoever, it relies on having elevons on the outer portion of the wing which are raised at neutral trim. the model appears to
have little or no adverse yaw.

I calculated a static margin of 8% (assuming the neutral point is at 1/4 of the mac) this supprised
me as I thought it would need to be closer to 15-20% as per the Horten designs, are the twin props adding enough effective side
area I to compensate for the lack of a fin I wonder? Apparently it flies well inverted.

I have just modified an old Zagi (plus single pusher prop) in a similar fashion to see if it will work with the fins removed.

thanks for your time, John Newton
 
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