Experimental Flights for Testing of a Reactor as an Expedient for the Termination of Dangerous Spins Page: 3 of 20
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NACA TM 1221
expedient enforces a new steady-spin condition which can be terminated by
the customary control movements.
On the whole, a spin may be regarded as dangerous if high angles of
attack are attained where the tail surfaces are shielded or the flow at
the tail separated, so that the rudder effect is no longer sufficient to
disturb the gyroscopic moments responsible for the equilibrium. However,
exceptions are known: cases of dangerous steep spins with likewise too
small rudder effectiveness, or, inversely, cases of flat spins with
extremely high elevator forces which the pilot cannot overcome.
It would best serve the purpose to perform the investigation on an
airplane in a dangerous spin. However, since so far no flight tests
exist concerning another expedient that would offer 100 percent safety
and since the effect of the reactor itself is still unknown, the investi-
gation must, for the time being, be performed on an airplane the steady
spin condition of which may be satisfactorily terminated by control
In using the reactor the question arises whether the disturbance
should be applied about the Y or Z body axis. The designation "reactor"
is not quite justified, since the thrust increase of this arrangement
may only last 0.2 to 1 second overall. Nevertheless, it is used
here since devices of such type are known in literature under that name.
If the spin is to be terminated by a pitching moment, one starts
from the presupposition that the pitch of the spinning airplane
increases until subcritical angles of attack are reached where an
autorotation is no longer possible. The main fact in favor of this
arrangement is its symmetry due to which the same arrangement may be
used for left and right spins.
However, experience (particularly on dangerous models) and deliber-
ation show that a termination of spin by a damping of the rotation by
means of applied yawing moment is preferable.
The flight measurements described in the present report are for
the purpose of eliminating this lack of clarity in the opinions for
and against pitching or yawing moment, respectively. Furthermore,
the tests are designed to give information about the approximate order
of magnitude of the disturbance forces to be applied.
The symbols used here comply with the most recent flight-mechanical
standards. The coupling angles of the three coordinate systems are best
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Höhler, P. & v. Köppen, I. Experimental Flights for Testing of a Reactor as an Expedient for the Termination of Dangerous Spins, report, July 1949; (digital.library.unt.edu/ark:/67531/metadc64981/m1/3/: accessed January 24, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.