A new class of frequency-selective shock absorbers called band-pass shock absorbers which were conceived as a means of overcoming some of the limitations of conventional shock absorbers is described. These shock absorber designs are introduced, special emphasis being given to their use in landing and taxiing problems of high-speed aircraft. For such aircraft operated on rough land or water runways, conventional oleo struts approach a rigid condition for bumps with steep slopes and thereby develop and transmit severe shock loads to the aircraft fuselage. The operation of the band-pass shock absorbers in the reduction of loads in certain selected frequency ranges is described. Theoretical equations are derived and solutions are made for several cases for the purpose of comparing the low-pass and conventional shock-absorber actions. The results indicate that the band-pass shock absorbers should alleviate high-frequency or rapidly applied impact loads but should retain the characteristics of conventional oleo struts when taxiing and design landing loads are slowly applied. A number of variations in design are presented for low-pass shock absorbers and reference is made to double-acting band-pass vibration absorbers for other applications.
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