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National Advisory Committee for Aeronautics, Technical Notes - Summary of Methods of Measuring Angle of Attack on Aircraft

Wind-tunnel calibrations of three types of angle-of—attack sensing
devices - the pivoted vane, the differential pressure tube, and the null—
seeking pressure tube — are presented. The pivoted vane has been used
primarily in the flight testing of airplanes and missiles, whereas the
null-seeking pressure tube has been used ahmost exclusively in the serv-
ice operation of airplanes. The differential pressure tube has not been
used to any great extent as a flight instrument.

Flight data on the position errors for three sensor locations -
ahead of the fuselage nose, ahead of the wing tip, and on the forebody
of the fuselage - are also presented. For operation throughout the
subsonic, transonic, and supersonic speed ranges, a position ahead of
the fuselage nose will provide the best installation. If the shape of
the fuselage nose is not too blunt, the position error will be essen—
tially zero when the sensor is located 1.5 or more fuselage diameters
ahead of the fuselage.

Various methods for calibrating angle-of—attack installations in
flight are briefly described.

Angle of attack is defined as the angle between the relative wind
in the plane of symmetry and the longitudinal axis of the airplane. The
measurement of this quantity has received increasing attention in recent
years because of its requirement for fire control, cruise control, and
stall warning.

Sensing devices for measuring angle of attack may be located either
ahead of the aircraft (usually on booms mounted on the wing tip or the
fuselage nose) or on some part of the aircraft itself. For any position
on or near the aircraft, however, the sensing device will measure the
local rather than the true angle of attack. The amount by which the
local angle of attack differs from the true angle of attack is called
the position error of the installation. This error varies with the lift
coefficient and Mach number of the aircraft. For some locations of the
sensing device, the position error may also vary with changes in the con-
figuration of the aircraft, for example, flap deflection, landing-gear
extension, and so forth.