Measurements of Free-Space Oscillating Pressures Near Propellers at Flight Mach Numbers to 0.72

In the course of a short flight program initiated to check the theory of Garrick and Watkins (NACA rep. 1198), a series of measurements at three stations were made of the oscillating pressures near a tapered-blade plan-form propeller and rectangular-blade plan form propeller at flight Mach numbers up to 0.72. In contradiction to the results for the propeller studied in NACA rep. 1198, the oscillating pressures in the plane ahead of the propeller were found to be higher than those immediately behind the propeller. Factors such as variation in torque and thrust distribution, since the blades of the present investigation were operating above their design forward speed, may account for this contradiction. The effect of blade plan form shows that a tapered-blade plan-form propeller will produce lower sound-pressure levels than a rectangular-blade plan-form propeller for the low blade-passage harmonics (the frequencies where structural considerations are important) and produce higher sound-pressure levels for the higher blade-passage harmonics (frequencies where passenger comfort is important)

NACA Research Memorandums

Report presenting a cascade-general-momentum theory method for calculating the operating conditions of a supersonic propeller annulus throughout the flight Mach number range. General flow patterns about the cascade and adjustments to free-stream conditions are discussed

NACA Technical Notes

Report presenting a series of measurements at three stations of the oscillating pressures near the propeller at flight Mach numbers up to 0.72. The measurements were made at a single radial station and three axial positions. Results regarding effect of engine speed at constant flight Mach number and power and effect of flight Mach number at constant engine speed and power are provided

NACA Technical Reports

"In the course of a short flight program initiated to check the theory of Garrick and Watkins (NACA rep. 1198), a series of measurements at three stations were made of the oscillating pressures near a tapered-blade plan-form propeller and rectangular-blade plan form propeller at flight Mach numbers up to 0.72. In contradiction to the results for the propeller studied in NACA rep. 1198, the oscillating pressures in the plane ahead of the propeller were found to be higher than those immediately behind the propeller. Factors such as variation in torque and thrust distribution, since the blades of the present investigation were operating above their design forward speed, may account for this contradiction" (p. 999)