Experimental evaluation of low-band-pass landing-gear shock absorber for pulse loadings

Emanuel Schnitzer
Sep 1958

An experimental investigation was conducted to determine the practicality of constructing a low- band-pass landing-gear shock absorber and to evaluate its effectiveness in reducing rapidly applied loads. The band-pass principle was first introduced in NACA Technical Note 3803 from a theoretical point of view. For the experimental investigation presented herein, a low-band-pass shock strut was designed, constructed, and tested in conjunction with a high-pressure tire which was used in order to develop and transmit steep pulses. Taxiing runs were made over individual bumps to determine the strut pulse rate response and over consecutive closely spaced bumps to determine strut recycling characteristics. Duplicate tests were made with a comparable shock absorber having a fixed main orifice area. Design details are presented for the shock struts tested and also for a proposed band-pass vibration absorber. The loads for the low-band-pass strut for single rapidly applied pulses were 50 percent of the loads for the fixed-orifice strut whereas for cyclic loading the low-band-pass loads were less than 25 percent of the fixed-orifice strut loads. Smaller reductions were achieved for rapidly applied pulses superposed on slowly applied pulses. There was no attempt in this investigation to develop an optimum control unit to minimize loads for both single and multiple superposed pulses over the entire spectrum of load application rates. The load reductions achieved, however, were accomplished by the addition of a 1-1/2 pound control unit to the shock strut of a 5,000-pound airplane.

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