Flight investigation of effects of atmospheric turbulence and moderate maneuvers on bending and torsional moments encountered by a helicopter rotor blade

Leroy H. Ludi
Feb 1958

Flight tests have been conducted with a medium-size single-rotor helicopter, of which one blade was equipped with strain gages, to determine the relative effects of atmospheric turbulence and moderate maneuvers on the periodic rotor blade moments. The results indicate no significant increase in the total blade moments due to atmospheric turbulence or moderate pull-up maneuvers which produced center-of-gravity acceleration increments of less than about 0.15g (where g is the acceleration due to gravity). Because about 99 percent of the total flying time is spent at acceleration increments below 0.15g, the principal part of the flying time is thus found to be unaffected by atmospheric turbulence or moderate maneuvers. Therefore, the time spent in the various flight conditions, as determined by the NACA helicopter VGHN recorder, can be used at least for that part of the cumulative fatigue analysis involving the largest number of cycles in distinction to the largest stresses. Atmospheric turbulence and moderate maneuvers which resulted in center-of-gravity acceleration increments above 0.15g produced some increased moments which are of interest, particularly in the higher harmonics.

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