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National Advisory Committee for Aeronautics, Technical Notes - Flight Determination of Wing and Tail Loads on a Fighter Type Airplane by Means of Strain Gage Measurements

A flight investigation was conducted to determine the contri-
butions of wing, tail, and fuselage to the total airplane lift of
a prepeller-driven fighter-type airplane. The tests covered a
Mach number range from 0.2 to 0.8. The loads on the various airplane
components were measured by the use of calibrated strain-gage
installations located at the roots of the wings and horizontal tail
surfaces.

The results of the investigation showed that the center of pres-
sure of the wing additional air load remained constant near the
lifting-line-theory value up to thephighest Mach number (0.8) attained
in the tests. The fuselage load-per unit normal acceleration appeared
to be unaffected by Mach number changes. Adequate correlation was
obtained between various tail-load parameters derived from the flight-
test results and from wind-tunnel tests. Strain-gage measurements
have been found to offer an accurate and convenient method for ‘
determining loads in flight.

Although there are numerous wind-tunnel tests of airfoils and
airplane models available at speeds which extend into the transonic
range, the flight-loads data available for correlation are not only
meager but for the most part are confined to relatively low Mach
numbers. In order to obtain flight-loads data at high subsonic speeds,
the National Advisory Committee for Aeronautics investigated a
Specially reinforced fighter-type airplane for the purpose of
determining buffeting and transient loads. Some results of the
buffeting tests have been published in reference 1. The strain-
gage instrumentation used in the buffeting tests was adequate for
the evaluation of wing additional-air-load center of pressure,
fuselage load per unit normal acceleration, wing-fuselage zero-lift
pitching-moment coefficient, wing-fuselage aerodynamic center, and
tail loads due to angular acceleration in pitch below the buffeting
boundary.