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National Advisory Committee for Aeronautics, Report - Initial Results of Instrument Flying Trials Conducted in a Single Rotor Helicopter

Instrument-flying trials have been conducted in a single-
rotor helicopter, the maneuver stability of which could be
changed from satisfactory to wwatisfactory. The results
indicated that emisting longitudinal flying-qualities require-
ments based on contact flight were adequate for instmment
flight at speeds above that for minimum power. However,
lateral- directional problems were encountered at low speeds
and during precision maneuvers.

The adequacy, for helicopter use, of standard airpldne in-
straments was also investigated, and the conclusion was
reached that special instruments would be desirable under
all conditions and necessary for sustained low-speed instan-
ment flight.

If the capabilities of the helicopter are to be fully realized,
instrument and night flight must be readily accomplished.
Since comparatively little instrument flying has been at-
tempted with helicopters, the Langley Aeronautical Labo-
ratory has undertaken a flight investigation to determine
whether the flying-qualities requirements for helicopters sug-
gested in reference 1 are adequate for instrument flight and
whether any unknown or unusual problems exist. In addi-
tion, information was sought as to whether special flight
instruments are necessary for successful instrument flying in
rotary-wing aircraft. The initial results of this program are
given in the present report.

The single-rotor helicopter used in this investigation is
shown in figure 1. An additional set of controls, a flight-
instrument panel, and a cloth hood (fig. 2) were installed
in the rear cockpit to enable the pilot to fly solely by instru-
ments.

The flight instruments provided (fig. 3) were those that
are normally considered adequate for an airplane and in-
cluded a directional gyro, an artificial horizon, and a turn-
and-bank indicator, all of which were electrically driven.
The artificial horizon was somewhat more sensitive in pitch
than a standard instrument, 27° providing full-scale deflec-
tion. The trim range of this instrument was kept within
desirable limits by tilting the entire instrument panel ap-
proximately 6° to compensate for the nose- -down flight atti-
tude of the helicopter.