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National Advisory Committee for Aeronautics, Report - Horizontal tail Loads in Maneuvering Flight

A method is given for determining the horizontal tail loads in
maneuvering flight. The method is based upon the assignment
of a load-factor variation with time and the determination of a
minim-um time to reach peak load factor. The tail load is
separated into carious components. fiamination of these com-
ponents indicated that one of the components was so small that
it could be neglected for most coneentional airplanes; therefore,
the number of aerodynamic parameters needed in this computa-
tion of tail loads was reduced to a minimum.

In order to illustrate the method, as well as to show the efect
of the main rariables, a number of examples are given.

Some discussion is giren regarding the determination of mari—
mu-m tail loads, maximum pitching accelerations, and maxim-um
pitching velocities obtainable.

The subject of maneuvering tail loads has received con-
siderable attention both experimentally and theoretically.
Theoretically, methods and solutions have been derived for
determining the horizontal tail load following either a pre-
scribed elevator motion (references 1 to 3) or an assigned
load-factor variation (reference 4).

The first approach has been adopted into some of the load
requirements where the type of elevator movement specified
consists of linear segments whose magnitudes and rates of
movement are governed by the assignment of a maximum
initial elevator movement consistent with the pilot’s strength.
The rates of movement and the time the elevator is held
before reversing are so adjusted that the design load factor
will not be exceeded. ,

The results of reference 5 show, as is to be expected, that
only when the aerodynamic force coefficients are accurately
known from wind-tunnel tests can good agreement be ob—
tained between measured and calculated tail loads. At the
design stage, however, only general aerodynamic and geo-
metric quantities are available and some of the more im-
portant stability parameters are not known accurately.
Thus, the work involved in the solution for the tail load
following a given elevator mot-ion is not considered to be in
keeping with the accuracy of the results obtained. Con-
sequently, there appears to be a need for an abbreviated
design method of computing tail loads which, although
incorporating approximations, will nevertheless be based on
the theoretical considerations of the problem.