1、Lessons Learned Entry: 1604Lesson Info:a71 Lesson Number: 1604a71 Lesson Date: 1994-11-14a71 Submitting Organization: DFRCa71 Authored by: Al Bowers / Victoria Regenie / Brad Flick Submitting Organization: Dryden Flight Research CenterSubject: F-18 High Alpha Research Vehicle Lessons Learned Abstrac
2、t: The F-18 High Alpha Research Vehicle has proven to be a useful research tool with many unique capabilities. Many of these capabilities are to assist in characterizing flight at high angles of attack, while some provide significant research in their own right. Of these, the thrust vectoring system
3、, the unique ability to rapidly reprogram flight controls, the reprogrammable mission computer, and a reprogrammable On-Board-Excitation-System have allowed an increased utility and versatility of the research conducted. Because of this multi-faceted approach to research in the high angle of attack
4、regime, the capabilities of the F-18 High Alpha Research Vehicle were designed to cover as many high alpha technology bases as the program would allow. These included aerodynamics, controls, handling qualities, structures, instrumentation, flight avionics systems, and propulsion. To achieve these go
5、als, new capabilities were developed to enable this research to occur some were outstandingly successful; others were not. Description of Driving Event: To better address the need for improved high angle of attack capabilities, NASA formed a High Alpha Technology Program (HATP). The focal point of t
6、his program was selected to be a highly modified F-18 airframe. Lesson(s) Learned: 1. Use of an all-inclusive steering committee of all the stakeholders was an outstanding asset to the execution of the program. Being all inclusive meant all voices were heard, and even when unanimous decisions were n
7、ot reachable, consensus was achieved, which maintained long term viability of the program and the project. Frequent communication was essential for this to happen Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-within the steering committee. 2. Insuf
8、ficient systems approach to the facilities, equipment, and planning occurred. Despite having extensive experience within the team with systems engineering, insufficient excess capacity was designed into the system because the entire lifecycle was not understood at inception. Requirements creep resul
9、ted in taking additional time, effort, and energy to incorporate research which was not mature at the start of the design. 3. Careful attention to risk management, both programmatic and technical, was a valuable asset in every phase of the program. In particular, sensitivity to the aircraft systems
10、was paramount. 3a. In one instance, the aircrafts flight control computers failed to pass the Built-In Test on several occasions during the Day-of-Flight checks before passing the Built-In Test. As the pilot and crew continued the preparation for flight, several engineers in the control room stopped
11、, took stock of the situation, and decided to cancel the mission until the reason for the failures was understood for the aircraft not passing the Built-In Test. 3b. In another instance, the Spin Recovery System (spin parachute) was reinstalled on the aircraft. The convention at that time was to fir
12、e the chute system from a benign flight condition as a system test. In most spin parachute systems, there is a small (but finite) potential for loss of the aircraft if the chute cannot be jettisoned. In the case of the F-18 HARV, the project team decided to fire the chute on the ground in a high-spe
13、ed taxi test only (this was done twice) and to NOT fire the system in-flight as a system test. This reduced the risk exposure to the aircraft and flight crew, while still testing the system in a representative environment. It should be noted that two other high angle of attack programs decided to fi
14、re the spin parachute in-flight as a system test (X-29A and X-31A). 3c. As well as making careful estimates for improvements and changes, be sure to define, well in advance and with careful planning, the deletion of specific envelope expansion hardware (or safety hardware). This needs to be carefull
15、y coordinated as part of the continuing airworthiness and flight safety process. In the case of the F-18 HARV, after the envelope expansion was complete, the need for the spin recovery system and the emergency power systems (battery back-ups, another system that was tested and demonstrated in ground
16、 tests) could have been removed from the aircraft. A current example might be the Fight Termination System onboard a UAV, or a system augmentation of the Flight Termination System. 4. Testing, both ground and flight, always uncovers deficiencies and contingencies that need to be planned in. This is
17、true in the integration phase, but also (and in particular with one-of-a-kind research systems) in the flight phase. One aspect of this was the use of carrying extra flight cards in the briefed cards for a mission. Even though we knew we could not achieve all the test points, excess cards were alway
18、s carried. If one piece of instrumentation failed during a mission, then other cards could be substituted and a full mission could be flown. Up to 140% of a missions cards would be carried on every mission. Having these contingencies in mind during planning is useful as well. If a particular flight
19、control load developed unforeseen problems, a previous load (for which lower priority test points are still waiting to be flown) can be reloaded and lower priority missions continue Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-while the unforeseen
20、 difficulties are resolved. The ground testing of the system wa greatly streamlined by the presence of the Hardware-in-the-Loop simulation residing at Dryden. The hardware simulation, being co-located with the aircraft and the research team, minimized impacts to the schedule. 5. Use of a Class B env
21、elope for Class B software (flight control laws) is very useful. However, careful attention needs to be paid to the corners of the Class B envelope to assure that, truly, the envelope is Class B. In particular, the lower right corner (for static structural loads) and the upper right corner (for flut
22、ter), and the upper left corner (for aeroservoelastics). Class B software is quickly reconfigurable, and flexible. Recommendation(s): 1. Use of an all-inclusive steering committee of all the stakeholders was an outstanding asset to the execution of the program. Being all inclusive meant all voices w
23、ere heard, and even when unanimous decisions were not reachable, consensus was achieved, which maintained long term viability of the program and the project. Frequent communication was essential for this to happen within the steering committee. 2. Use of a Class B envelope for Class B software (flig
24、ht control laws) is very useful. However, careful attention needs to be paid to the corners of the Class B envelope to assure that, truly, the envelope is Class B. In particular, the lower right corner (for static structural loads) and the upper right corner (for flutter), and the upper left corner
25、(for aeroservoelastics). Class B software is quickly reconfigurable, and flexible. Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: NASA TM 4772, “An Overview of the NASA F-18 High Alpha Research Vehicle”, Albion H Bowers, Joseph W Pahle, R Joseph Wilson, Bradley C Flick
26、, and Richard L Rood, Oct 96.Mission Directorate(s): a71 Exploration Systemsa71 Aeronautics ResearchAdditional Key Phrase(s): Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 Aircrafta71 Flight Operationsa71 Ground Operationsa71 Policy & Planninga71 Program and Project Managementa71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 2008-10-09a71 Approval Name: mbella71 Approval Organization: HQProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
