Summary of Methods of Measuring Angle of Attack on Aircraft Page: 3 of 30
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NACA TN 4351
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.
The overall error of an installation includes errors peculiar to
the sensing device in addition to the errors due to the location of the
device. The errors of the sensing device are generally determined by
wind-tunnel tests. The position error, on the other hand, must be deter-
mined by calibration of the installation in flight. In accelerated
maneuvers, additional errors may be introduced by such items as the
pitching velocity of the aircraft, boom bending, fuselage flexibility,
and lag in the transmission system of the angle-of-attack instrumentation.
A description of various types of angle-of-attack devices and their
application to stall warning is presented in reference 1. A comprehen-
sive survey of possible types of instrumentation for the measurement of
angle of attack on aircraft is given in reference 2. In a similar study
(ref. 3) a method is developed for determining angles of attack and side-
slip from measurements of the motions of the aircraft.
The present report sumnarizes experimental data on sensing devices
which have found practical application in the testing of airplanes and
missiles or which have been test evaluated for possible use on aircraft.
The position errors of several types of installation and some flight
calibration methods for determining these errors are also presented.
SYMBOLS
a, angle of attack (angle between relative wind in the plane of
symmetry and the longitudinal axis of the airplane), deg
al local angle of attack, deg
to angle-of-attack error (al - m), deg
p angle of sideslip, deg
Ap pressure difference between orifices on differential pressure
tube2
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Gracey, William. Summary of Methods of Measuring Angle of Attack on Aircraft, report, August 1958; (https://digital.library.unt.edu/ark:/67531/metadc57244/m1/3/?rotate=0: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.