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I have some questions regarding the Cri-Cri design. If some of them can't be answered directly, I would like to read what theory says about it.

  • Why is a T-tail used? What are its advantages for an LSA over a classic tail?
  • The plane has a polygon-shaped fuselage which is not streamlined. How much efficiency was traded for production simplicity?
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  • $\begingroup$ @SteveV. Hi Steve, I've cut the question. There are still two points in it, but probably they aren't worth opening separate post for each one. Hope this is ok. $\endgroup$ – Eugene May 24 '17 at 12:14
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    $\begingroup$ I have the impression that your first question might be answered here: aviation.stackexchange.com/q/1400/1467 and as for the second question, "is it worth" begs the answer "it depends", as it in the end is a matter of opinions of the designer (and what were their design goals) $\endgroup$ – Federico May 24 '17 at 12:32
  • $\begingroup$ @Federico, thanks for the link. It certainly an opinion of the designer, but probably this was (or can be) explained, since the aircraft is in production for over four decades. In the second question I try to understand how to evaluate losses due to rigid forms. $\endgroup$ – Eugene May 24 '17 at 12:51
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The T-tail positions the horizontal stabilizer out of the turbulent "prop wash". This reduces the strength and weight that would be required of the structure if it had to endure the aerodynamic stress behind the two propellers (which is terrific).

This simple shape has everything to do with parts and assembly simplicity and low cost for the homebuilder. Drag increases exponentially with speed; so for slow aircraft, draggy shaped components are much less a problem.

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  • $\begingroup$ Thank you, STWilson. Never thought downwash from these two small propellers would be so strong that it makes sense overhead for having reinforced tail structure. Regarding fuselage shape, is the "boat-like" shape really simplier to manufacture for a homebuilder than a conventional oval shape? What does make this difference? $\endgroup$ – Eugene Jun 11 '17 at 22:20
  • $\begingroup$ Contored surfaces require stretch forming the skins to obtain a compound shape. The skins in this design are not formed, just cut and trim. $\endgroup$ – STWilson Jun 12 '17 at 1:53
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    $\begingroup$ Turbulence aft the propellers would not be characterized as downwash. Think of it as a spiraling mess to be avoided, very hard on airfoils (like stabilizers) behind it. youtu.be/1z6M0NrDM2U?t=1m56s $\endgroup$ – STWilson Jun 12 '17 at 15:32
  • $\begingroup$ Are skins carry any load in cri-cri (and likewise LSA)? $\endgroup$ – Eugene Jun 13 '17 at 1:48
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    $\begingroup$ Stretch forming: youtube.com/watch?v=Kh4MBHyHAtg. @Eugene I encourage you to join in the chats when the system grants you that privilege. It's discouraged to carry on conversations here in the questions. Good luck in your pursuits! $\endgroup$ – STWilson Jun 13 '17 at 15:25

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