Attenuation of Propeller-Related Vibration and Noise

Abstract

The potential sources and paths by which the propeller produces structural responses resulting in vibration and noise in the cabin of a transport aircraft are discussed. New low-cost, convenient experimental and analytical techniques are described for evaluating the excitations-propeller airborne pressures on the fuselage shells, slip-stream-induced forces on the wing and tail, and oscillatory forces on the propeller. The techniques described make use of ground-determined structural signatures to relate forces with vibrations or noise, and of propeller signatures from flight tests which define the vibroacoustic contributions of individual propellers. Knowing these, the propeller-produced excitation forces can be deduced by the relations shown; design approaches to control the fatigue and vibroacoustic environment can then be enunciated logically.

Unsteady Pylon Loading Caused by Propeller-Slipstream Impingement for Tip-Mounted Propellers

“…The unsteady loading caused by the impingement of the propeller slipstream on the wing or pylon results in structural vibrations, which are transmitted to the fuselage [21]. These vibrations are then perceived as additional noise inside the cabin, reducing passenger comfort.…”

“…This shows that the unsteady pressures caused by the impingement of the propeller slipstream can be an important source of cabin noise. A secondary source of structure-borne noise can be caused by unsteady loading on the propeller blades [21,31]. However, the contribution due to the propeller-slipstream impingement on the wing or pylon is considered dominant [21,23,28].…”

Estimate of human control over mid-air collisions

“…4 Since there are 8760 hours per (365 day) year, the average number of general-aviation aircraft in the air at any given time is Comparing this number with the total number of registered general-aviation aircraft (Table 1) shows that at any given time on the average over the ten-year span 1.77% of the registered aircraft are in flight.…”

“…Table 2 presents data on civilian carrier aircraft miles flown annually during the ten-year period. 4 The annual miles traveled has been denoted by the symbol </>, which, in terms of the previous nomenclature of the previous section, is simply ($> = N J v 1 , where v l is the average velocity of carrier aircraft (expressed in units of miles/yr). The value is rather strikingly constant, the average over these ten years being </ > = 2.63 x 10 9 miles/yr.…”