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National Advisory Committee for Aeronautics, Technical Notes - Consideration of Dynamic Loads on the Vertical Tail by the Theory of Flat Yawing Maneuvers

Dynamic yawing effects on vertical—tail loads are
considered by a theory of flat yawing maneuvers. A com-
parison is shown between computed loads and the loads
measured in flight on a fighter airplane.

The dynamic effects were investigated On a large
flying boat for both an abrup_t rudder_ deflecti_on and a
sinusoidal rudder deflection. only a mederate amount
of control deflection was found to be necessary to
attain the ultimate design load on the tail. In order
to take into account dynamic effects in design,specifi—.
cations of yawing maneuverability or control movement
are needed.

The current use of semiempirical specifications for
the determination of critical loads on the vertical tail
of airplanes and the acknowledged inadequacies of this
procedure have led to a great deal of interest in the
theoretical approach to- the problem. The equatiOns of
lateral motion of an airplane are well known, (see, for
example, reference 1); but because of the inability to
obtain accurate values of the lateral stability deriva-
tives the. amount 0I labor involved in effecting the
computations has made impracticable the application of
the complete theory to the tail-loads problem. The
important dynamic aspect of verticalntail loads thus is
entirely absent from current specifications.

The purpose of the present paper is to consider e
dynamic yawing loads on the basis of a restricted theory
With the restriction of flat yawing maneuvers the loads
on the vertical tail that arise from abrupt deflections
of the rudder or from suddenly imposed moments from any
source may be determined. The loads were computed for
a fighter airplane for which loads measured in flight
were available, and, as evidence of the utility of the
restricted theory, the computed and measured loads were ' :
compared. The importance of consideri.ng dynamic effects
in the design of vertical tail surfaces is shown by com-
putations made for a large flying boat undergoing an .
abrupt rudder deflection and a sinusoidal rudder deflec-
tion.