On Mon, 18 May 2015 19:38:18 -0700, Andy Blackburn wrote:

Elliptical polyhedral is not part of any drag theory I ever learned
studying aerodynamics. The wing planform, airfoils, twist and the use of
winglets are used together to optimize the tradeoff between parasitic
and induced drag while maintaining desirable handling and stall
characteristics. My sense is that use of dihedral (or polyhedral) is
mostly motivated by handling (and perhaps ground clearance)
considerations rather than performance considerations. They may also
think it looks cool.

Elliptical polyedral and planform have been described as the ideal and
used for years in the design of high performance free flight competition
models. There are references going back to the early '60s: Jim Baguley's
articles on F1A design in Aeromodeller, several articles in the annual
NFFS Symposium reports since 1968. These suggested that approximating an
elliptical area distribution minimises tip drag, while doing the same for
polyhedral minimises the tip height and hence the total wing area for a
given projected area, with the added benefit that, because polyhedral
minimises the angle between adjacent panels, it also minimises
interference drag. Six panel wings have been common in the F1ABC classes
for the last 15-20 years.

But then, as Will Schueman said, this is to be expected since the model
design/build generation time is much shorter than that for sailplanes:
6-12 months vs 5+ years, so more rapid evolution is to be expected.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
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