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National Advisory Committee for Aeronautics, Report - The Mean Aerodynamic Chord and the Aerodynamic Center of a Tapered Wing

A preliminary study of pitching-moment data on
tapered wings indicated that excellent agreement with test
data was obtained by locating the grader-chord point of
the average chord on the aaerage garter-chord point Qf the
semispan. The study was therefore extended to include
most of the available data on tapered-wing models tested
by the NAC’A.

The final comparisons were made on the basis of the
differences between the location of the aerodynamic center
asdetermined by calculation and by test. The agreement
obtained when the mean quarter-chord point was located
by geometry alone was appreciably better than that obtained
by introducing aerodynamic corrections. Since the wing
models included extreme conditions of taper, mepbac/c,
and twist, it is evident that the calculatimzc required to
determine the mean aerodynamic chord may be greatly
simplified and at the same time give improved accuracy.

The mean aerodynamic chord of any wing is defined
by reference 1 as, “The chord of an imaginary airfoil
which would have force vectors throughout the flight
range identical with those of the actual wing or wings.”

The mean aerodynamic chord is required in order
that the designer may have a ready means for evaluat-
ing the wing moments. By definition, the mean acro-
dynamic chord is to be so located that. its force vectors
are identical with those of the actual wing. Several
factors are involved in this substitution. In addition
to the length of the mean aerodynamic chord, its locar
tion must be determined.

Conventional methods for calculating the mean aero-
dynamic chord have attempted to apply corrections for
all factors known to be involved. The calculations
required to» allow for lift distribution, w'mg twist, and
tip shape tend to become very complex.