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• April 15, 2017 Create Date
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National Advisory Committee for Aeronautics, Research Memorandum - Buffeting of External Fuel Tanks at High Speeds on a Grumman F7F-3 Airplane

Attempts were made to alleviate the buffeting of external
fuel tanks mounted under the wings of a twin-engine Navy
fighter airplane. The Mach number at which buffeting began
was increased from 0,529 to 0.6h0 by streamlining the sway
braces and by increasing the lateral rigidity of the sway
brace system. Further increase of the Mach number, at which
buffeting began to 0.725, was*obtained by moving the external
fuel tank to a position under the fuselage.

High-speed combat aircraft have encountered serious
buffeting in flight at high Each numbers when carrying
external stores. As a typical example of this condition
the Grumman F7F-5 airplane encountered buffeting with the
installation of ISO—gallon fuel tanks mounted externally
beneath the wings. This buffeting effectively limited the
speeds to which the airplane could be flown with the tanks
installed.

At the request of the Bureau of Aeronautics, Navy
Department, flight tests were conducted at the Ames
Aeronautical Laboratory on a Grumman F7F—3 airplane to
obtain information on the sources of the buffeting and
on means for alleviating the buffeting.

Standard NACA continuous-f1lmprecording instruments
were used to record airspeed, altitude, free-air temperature,
and the motion of the tank; 55~millimeter motion pictures
were obtained of the tufts on the tank and surrounding
structure.

An airspeed calibration, obtained on an XF7F-l airplane
by flying in formation with an airplane on which the airspeed
installation was calibrated, was used for this investigation.
It was considered that the errors involved in the use of this
calibration and in extrapolating to the test Mach numbers
were negligible.