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National Advisory Committee for Aeronautics, Technical Notes - Standard Symbols for Helicopters

A list of standard symbols for rotatingawing aircraft is presented.
The list of symbols is subdivided for ready reference under appropriate
headings, the symbols being restricted to those most generalLy used in
studies of helicopter aerodynamics.

Great interest has been shown by manufacturers of helicopters and
by various government agencies charged with the design, evaluation, and
procurement of helicopters in the standardization of symbols for use in
their work A survey was therefore conducted among members of the
armed services, industry, certain educational institutions, and various
government agencies in order to obtain an indication of their prefer-
ences. This survey was made by the Helicopter Committee of the Society
of Automotive Engineers in cooperation with the NACA Subcommittee on
Eblicopters. The results of the survey indicated a definite preference
for those symbols that had been most widely used in the past. Accord-
ingly, a list of symbols that have appeared in many papers on rotating-
wing aircraft has been prepared and correlated. This list, which is
presented herein, was approved as standard by the members of the
NACA Subcommittee on Helicopters at a meeting held on December 3, D9¢7-
The membership of this Subcommittee is considered representative of the
various groups contacted during the aforementioned survey.

The symbols listed have been limited for the present to those most
generally used in helicopter aerodynamic studies. Specialized symbols
necessary in vibration, stress, and stability work remain to be devel-
oped and standardized as these studies mature with time and use.

The units given in the definition of the symbols pertaining to
velocity and angles were chosen to make the equations compatible and
the coefficients of the correct magnitude- The units given are not
intended to preclude the use of alternate units that might be more
convenient for use in plots or tables, in which case the alternate
unit should be specified.