Static-Thrust Measurements of the Aerodynamic Loading on a Helicopter Rotor Blade Page: 2 of 23
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TECH LIBRARY KAFB, NM
NATIONAL ADVISORY COMMITTEE FOR AERONAUTIC f066b62
TECHNICAL NOTE 5688
STATIC-THRUST MEASUREMENT OF THE AERODYNAMIC
LOADING ON A HELICOPTER ROTOR BLADE
By John P. Rabbott, Jr.
An experimental investigation of the aerodynamic loading on a
15-foot-diameter helicopter rotor blade in static thrust was conducted
for a tip-speed range of 400 to 500 feet per second and disk loads of
zero to about 2.5 pounds per square foot. The chordwise pressure dis-
tributions at five spanwise stations are presented and a comparison is
made between the measured spanwise loading and a simple theoretical
loading modified by an approximate correction for a finite number of
The variation of spanwise load distribution near the blade tip with
thrust indicates that the blade tip loss is proportional to the thrust
Because of the very complex flow pattern in a helicopter-rotor wake,
the calculation of the aerodynamic loading on a rotor blade is a difficult
mathematical problem whose solution is possible only when many simplifying
assumptions as to the distribution of induced velocity across the rotor
disk are made.
The total thrust of a rotor, when calculated from blade-element
strip analysis and modified by a suitable tip-loss factor, has been found
to agree fairly well with the actual thrust. However, very little experi-
mental data have been available heretofore to compare with the calculated
spanwise distribution of loading. Reference 1 is an experimental inves-
tigation of the aerodynamic loading on a model rotor blade for a wide
variety of flight conditions, but it is limited somewhat by the relatively
low frequency response of the pressure measuring equipment in forward
flight. For the static-thrust condition, reference 1 presents the chord-
wise and spanwise loading on a rotor blade at one pitch angle and one tip
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Rabbott, John P., Jr. Static-Thrust Measurements of the Aerodynamic Loading on a Helicopter Rotor Blade, report, July 1956; (digital.library.unt.edu/ark:/67531/metadc55943/m1/2/: accessed January 17, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.