毕业设计(论文)方案论证报告提要【范本模板】

To ascertain the performance capabilities of the prototype development hardware under the new two-fail/operate requirements，the BA609 Flight Controls IPT initiated a program of pilot-in-the—loop testing of actuator failure modes。These tests comprised pilot evaluations of BA609 flight control system handling qualities following the occurrences:

•Dual electrical system failures.

•Dual electrical component failures.

•Dual hydraulic system failures.

•Dual hydraulic component failures。

•Single electrical system combined with single hydraulic system failures。

•Single electrical component combined with single hydraulic system failures.

•Single electrical system combined with single hydraulic component failures.

•Single electrical component combined with single hydraulic component failures.

For each test condition，the worst case system or component failure mode was either initiated or simulated。For EHSV failures，second

stage spools were failed hard-over in both directions, as well as at null position, causing the cylinder to hydraulically lock。Solenoids were failed both open and closed。LVDTs were shorted and cores were simulated to structurally fail。Bypass，pressure relief, and delta pressure sensor hydraulic spools were simulated to be stuck in any position，and their springs were simulated as failed。For any component whose proper functioning could not validated either in flight or during preflight built—in testing （PFBIT）, the component was considered to be an existing dormant failure。Because the BA609 is a tiltrotor aircraft，it has three different modes of flight: airplane, conversion，and helicopter。As a result, testing of each relevant failure mode condition in each of the three flight modes was required.

One area in which the VMSIL testing was not representative of the actual aircraft was the structural strength of the simulated flaperon and elevator surfaces. Although the flaperon and elevator actuator test rigs had been modified to represent the aircraft structural stiffness, it was impractical to simulate actual aircraft structural strength with the test rigs. Therefore，actuator loads were monitored during testing to determine if acceptable structural loads were exceeded。

Based on VMSIL pilot—in-the—loop evaluations, test data from the failure mode testing，and a revised failure mode analysis，it was concluded that all actuator installations (collective，longitudinal, flaperon, and elevator) of the prototype development actuator design provided unacceptable performance for the production BA609 aircraft。Dual failure mode testing revealed a critical failure mode combination that impacted all prototype development actuator installations。The

BA609 hydraulic system architecture，utilizing three hydraulic cylinders to actuate each flight control，places a unique importance on the proper functioning of the prototype manifold bidirectional pressure relief valve (PRV）。Proper operation of the PRV becomes critical for failure modes that result in blockage of the cylinder ports （even momentarily）, such as an EHSV and/or bypass valve failure. Functional integrity of the prototype PRV，however，could not be verified on the aircraft，leading to a potential dormant failure。Figure 15 compares the potential actuator internal pressures generated by a blocked cylinder port for the conventional two-cylinder architecture and the BA609 three cylinder architecture。Both architectures illustrated represent fly-by—wire systems using 3,000 psi system pressure, equal extend—and—retract cylinder piston areas, and an external air load equivalent to 50％of stall of one cylinder。

With a conventional two-cylinder hydraulic architecture，a blocked cylinder port can generate 4，500 psi internal hydraulic pressure. The hydraulic component proof pressure （as defined in both ARP—5440 and in FAR Part 27）requires hydraulic cylinders to withstand 150％of operating pressure （4，500 psi) with no evidence material yielding. Therefore，the effect of a blocked cylinder port has minimal impact on structural sizing。

With the BA609 three-cylinder architecture，a blocked cylinder port can generate 7，500 psi internal hydraulic pressure。This

dual-failure—mode generated pressure not only exceeds the 150％of operating pressure standard, but it also reaches the limit of the recommended cylinder burst pressure (250％of operating pressure）. The effect of a blocked cylinder port for this condition is more detrimental in the flaperon and elevator actuators cylinders, due to their unequal extendend- retract piston areas, which amplify internal pressure to 8,955 psi and 9，676 psi，respectively. Therefore，to prevent damage from

occurring either to an actuator or the aircraft structure from a blocked cylinder port, either the actuators or the aircraft structure needs to be sized to withstand the higher resulting pressures and loads，or a reliable PRV must be incorporated into each actuator manifold.

Pilot—in—the-loop VMSIL testing also revealed that although all the actuators shared a common prototype manifold design，the impact to the aircraft handling qualities was very different when the same failure mode combinations were applied to different actuators. Degradation of aircraft handling qualities resulting from failure modes induced in the longitudinal or collective rotor control actuators were of greater severity than for the elevator and flapperon fixed—wing control actuators. This was in part due to the capability of the left flaperon，right flaperon，and elevator control surfaces to aerodynamically compensate for the loss in performance of any one of the three surfaces. In airplane and conversion flight modes, undesired roll from a slow or jammed flaperon surface can be compensated by the opposite flapperon。Uncommonded pitch from a slow or jammed elevator can be compensated by the pilot’s manual operation of the flapper on surface flap position control.

Other major factors influencing the actuators failure mode performance degradation were the margin of actuator stall load over flight loads and actuator cylinder configuration （triplex versus simplex）. The impact of these factors became especially apparent when evaluating the prototype manifold’s performance with dual failures that included failure of the solenoid-controlled bypass valve。Combined with other probable failures （FCC, wiring，EHSV）, some bypass valve failure cases require the two unaffected cylinders on the flight control to fight against the failed cylinder。The magnitude of this force fight condition was dependent on the failed position of the EHSV second stage spool。Loads ranged from 100％of cylinder stall load, if the EHSV failed off its null position, to 150% of stall load （PRV opening setting），if the EHSV failed at null, blocking the cylinder ports。

Under these failure mode combinations, the simplex actuator flaperon and elevator surfaces suffer a reduction in flight control load

capacity equal to the force fight load imparted by the failed cylinder。From pilot—in—the—loop simulation it was concluded that, for the flaperon and elevator surfaces，these failure modes were recoverable。With the rigidly joined three—cylinder triplex collective and longitudinal flight control actuators, however，these failure modes are considerably worse. Force fight loads between the cylinders bent the piston rods，inducing large friction forces that reduced flight control load capacity even further. In the case of the collective control that has a small margin of actuator stall load over flight loads (15％）, this failure mode rendered the actuator inoperable。For the longitudinal control that has a large margin of actuator stall load over flight loads （400%），this failure mode was recoverable but with extreme difficulty by the pilot。

The high susceptibility of the collective actuator to performance degradation from force fight loads was even apparent during tests that simulated dual failure modes that included the delta pressure sensor。In tests simulating worst-case delta pressure sensor false readings，friction resulting from force fight loads severely reduced the collective actuator frequency response and position control accuracy. Both frequency response and position control are critical to the collect ive actuators’ capability to function properly as a rudder in airplane mode and minimize

loads in the drive train connecting the proprotor gearboxes。Complicating this failure mode further was the inability to positively verify the integrity of the delta pressure transducer during PFBIT。It had been planned to use the prototype development manifold PFBIT concept to verify collective delta pressure transducer accuracy by initiating a controlled force fight between the triplex cylinders, in order to provide a cross reference with rotors turning (no APU）. However, frictional loads generated from collective cylinder force fights made the concept impractical. The ramifications of a single collective delta pressure transducer failure were determined to be unacceptable for meeting both handling qualities and fatigue loads requirements。