Static-Thrust Measurements of the Aerodynamic Loading on a Helicopter Rotor Blade Page: 4 of 23
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NACA TN 5688
q local dynamic pressure,(rt)2
R blade radius measured from center of rotation, ft
r radial distance to blade element, ft
T rotor thrust, lb
Tm measured rotor thrust from wind-tunnel balance, lb
vf value of rotor-induced velocity at fuselage, taken as induced
velocity in ultimate wake, fR /Yi, ft/sec
x distance from leading edge to any point on chord, ft
e blade-section pitch angle, deg
p mass density of air, slugs/cu ft
a rotor solidity, bc/iR
rotor angular velocity, radians/sec
EQUIPMENT AND TESTS
The rotor blades are of rectangular, untwisted plan form with a
15-foot diameter, an NACA 0012 airfoil section, and a rotor solidity of
0.097. One blade of the two-bladed teetering rotor was instrumented with
NACA miniature electrical pressure gages (ref. 2) to measure the differ-
ential pressures of the upper to the lower surface at ten chordwise
locations for each of five spanwise stations. The uninstrumented blade
has a very slightly greater thickness than the instrumented blade, as
some additional layers of covering material were added for balance. Fig-
ure 1 is a sketch of the instrumented rotor blade showing the principal
dimensions and the pressure-orifice locations, and figure 2 is a photo-
graph of a section of the instrumented blade taken during its construc-
tion. This figure shows the location of the pressure gages and the asso-
ciated wiring and tubing. The wires to the gages were imbedded in the
surface of the blade and led to a terminal strip at the root where con-
nection to the hub and slip rings was made. The forward portion of the
blade, from the leading edge to the quarter chord, was formed of an alu-
minum D-section spar covered with balsa fairing strips. The rear portion
was built up of plywood ribs and balsa planking, and the whole blade was
then covered with one layer of fiber glass impregnated with Paraplex resin.
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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/m1/4/: accessed October 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.