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I've been tasked with designing an RC aircraft that has the greatest lift force for a specified wingspan, total length and takeoff velocity, and thus have been studying the different wing configurations that could be used.

I've had ease in finding methods for designing more common configurations (using books such as Snorri Gudmundsson's and Jan Roskam's), even biplanes, however it seems there is no method specialized for estimating the aerodynamic coefficients for triplanes, which to me seems to be a very promising way to increase wing area with the given geometrical constraints. There are methods for biplanes such as Munk's General Biplane Theory, but not triplanes.

I've managed to use the XFLR5 software for simulating the configuration (wings and vertical stabilizer only, though - I've had to use the elevator as the third wing). However, I've learned it's not good practice to rely solely on a single method's results for obtaining the aerodynamic coefficients, and without some sort of semi-empirical method to compare it against, I'll unfortunately have to scrap that possibility.

If there are no such equations, can the biplane methodology be adapted in any way for a triplane? I've found two NACA reports comparing biplane and triplane wind tunnel results, but haven't managed to fiddle with the biplane equations and get accurate results from them.

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  • $\begingroup$ You could compare a biplane with a monoplane of the same planform and obtain a lift differential (which will be less than twice the monoplane lift). Then just repeat that differential for each extra wing in the stack. Why not go for a quadruplane or even more? $\endgroup$ – Guy Inchbald Feb 16 at 19:49
  • $\begingroup$ Something like Munk's "General Biplane Theory" proposed "k" coefficient to convert a biplane into an equivalent monoplane? Perhaps generating multiple triplane planforms in XFLR5 would allow for curve fitting such a coefficient for a triplane instead for a rough estimate of the final lift coefficient slope? $\endgroup$ – how-do-you-do-fellow-kids Feb 17 at 1:25

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