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National Advisory Committee for Aeronautics, Technical Notes - The Logarithmic Polar Curve - Its Theory and Application to the Predetermination of Airplane Performance

The logarithmic polar curve has for several years been used by
the most prominent aerodynamical laboratories as well as by airplane,
manufacturers in Europe.

The vast possibilities of the method, when once thoroughly mas—
tered and properly used, and the saving of time and expense in—
volved in the analytical treatment of performance, amply justify
i its use. Any one who familiarizes himself with the method will,
within a short time, find a large number of stadications, not men—
tioned in this note, which, h0wever, will come up in connection
with airplane design. As examples, some additions to the original I;:'
method which I have made myself and which may increase the useful—
ness of the method for performance estimation, are described and
their construction shown.

To show more clearly the practical application of the polar
curve, a series of examples are appended hereto with suggestions
for solutions. I am indebted to Mr. Elliott G. Reid of the N.A.C.A.

Langley Memorial Aeronautical Laboratory for his thorough checking
of the manuscript and also for the valuable suggestions-he has made.

In making up the appended chart, engineering units have been used
throughout, as they are more convenient to use in a design office,
giving directly the results in easily visualized units.

In working on the problems connected with aerodynamics and re—
lated subjects, graphical solutions are often used due to the facil~
ity with which the designer can obtain from them his data and thence-
forth make suitable changes in his design, if needed, to meet cer—
tain requirements. To show graphically the relations between the
air forces acting on an airplane, its velocity, angle to the rela—
tive wind (angle of attack), climbing ability, etc., is therefore
desirable — and several attempts have been made to obtain a satis-
factory graphical method.