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Fast closing of actuator servovalves in airplane hydraulic systems can often cause unacceptably high pressure spikes in these systems. This paper describes and discusses a method of reducing these hydraulic system pressure spikes by suitable limiting of the rate at which the servovalve current can change. Analytical and test results are presented to show that with this method, the pressure spikes can be reduced without significantly affecting the actuator dynamic response characteristics.

Hypervelocity endo/exoatmospheric vehicles experience extremely severe thermal conditions, requiring an integrated vehicle-wide approach to thermal management. The paper presents a discussion of key thermal management and environmental control issues with examples from two classes of vehicles, namely a Mach 6 interceptor aircraft and a single-stage-to-orbit vehicle. The elements of a general thermal management optimization methodology are discussed. Trade study results between a single-phase and a two-phase cooling loop used on the single-stage-to-orbit vehicle are also presented.

Modern transport airplanes use precooled engine bleed air as a source for cabin pressurization, air conditioning, engine cowl and wing deicing, cross-engine starting, air-driven hydraulic pumps and other pneumatic demands. The Boeing Model 767 airplane air supply system consists of separate sets of equipment for each of the airplane's two engines and a remotely located built-in-test equipment (BITE) module. Each set of equipment independently regulates the pressure and temperature of the extracted engine bleed air. The normal control functions are completely pneumatic, not relying on electrical signals or interconnecting wires to provide their control or protective features. Electrical signals are used only for failure conditions using latching-type shutoff solenoids and for the BITE provisions. The digital BITE module monitors inputs from dedicated BITE elements throughout the system on a time-shared basis to isolate 95% of all failures to the LRU (line replaceable unit) level.