Homework

For Systems Architecture, subject “Modeling” Рin case you were curious (many pretty pictures for the bandwidth constrained to beetle their Luddite brows over):

In 1972, the US Air Force went to the aviation industry with Request for Proposals for a new, lightweight fighter design. Northrop contended with the YF-17, while General Dynamics competed with the ultimately successful F-16 design. Although not successful in the USAF’s lightweight fighter competition, the YF-17 had desirable characteristics satisfying the US Navy’s emergent requirement for a high volume, “low end” strike fighter to replace both the F-4 and A-7 aircraft, especially on the Navy’s smaller, conventional aircraft carriers Рships like USS Coral Sea and Midway - whose flight decks were not large enough to accommodate the “high end” fleet air defense aircraft, the F-14 Tomcat.

The translation of Northrop’s YF-17 fly-off demonstrator into the McDonnell Douglas (later, Boeing) FA-18, equipped for both the fighter and ground attack roles, as well as carrier suitability enhancements required the use of a number of models in the developmental process. The first model was the mental, or conceptual model – one airplane to replace two, an affordable, lightweight fighter that that could also perform ground attack (and eventually, sea control) missions, all of these capable of operating in the carrier environment. Significantly for the program as it evolved, that environment had at least as much to do with endurance and specific fuel consumption as it did with conventional carrier suitability requirements such as gross weight, approach speed and angle of attack, landing gear and arresting hook strengthening, provisions for catapult launch, etc. At this level, the mental model’s had a fairly high level of abstraction, notwithstanding the head start the YF-17/lightweight fighter fly-off had given the program – it’s primary purpose was to focus the design team on the gross performance characteristics required, as well as the cost constraints.

Scaled models were used both for wind tunnel testing, as well as drop testing. These models were designed to evaluate the aircraft’s aerodynamic qualities. Importantly, the YF-17 was designed with robust anti-spin performance and exceptional high angle of attack flying qualities. The latter especially had resulted in slotted leading edge fuselage extensions, to ensure good airflow over the rudders in a regime normally prone to wing blanking Рvery high angle of attack. The slots are visible in the photo below, from the same source.

As the design team experienced increasing cycles of knowledge translating the YF-17 into the FA-18, other models included spin test and drop test models. The spin test model was designed to ensure that the high angle of attack qualities were maintained even as the wing and fuselage underwent changes to ensure proper approach speeds on the carrier. The wind tunnel and drop test models also identified an adverse specified range result from the slotted leading edge extensions – at first the models predicted a 12% margin failure against specification, a seemingly insuperable gap. Further testing revealed that filling the gaps in the LEX would enable the models to meet spec without overly adverse effects on high AOA maneuverability.

While these aerodynamic models were being tested, qualitative models were also under evaluation. Data flow diagrams were being tested against flight control computers, weapons and navigation computers, all of which were to be highly integrated in the ultimate FA-18 design. Also integrated at this level were the weapons sensors, such as the APG-65 multi-mode radar and AN/AAS-37 Forward Looking Infrared Pod, or FLIR. These models were initially modeled at low levels of abstraction with the data flow diagrams moving into higher levels of abstraction (breadboards) and finally into the cockpit mock-ups for human systems engineering. Systems engineers tested cockpit mock-ups to validate the pilot’s interaction with the flight controls as well as “hands-on-throttle-and-stick,” or HOTAS weapons system manipulation. External effects were also modeled, including required radar detection ranges, fighter missile ranges and probabilities of kill versus threat aircraft profiles and weapons systems.

Full-scale models of form ensured that the various aircraft systems were physically interoperable, moving forward to early prototype test articles dedicated to stress-to-failure testing for both fatigue and overload. Moving into the final levels of higher abstraction, follow on DT&E articles ensured the essential specifications were met, or that the customer had room to make educated trade-offs. Finally, low-rate initial production aircraft were provided to the Navy‚Äôs Operational Test and Evaluation community for thorough testing of the aircraft and its associated systems. These models approached the initial operating capability of the fielded product, and underwent comprehensive test plans commensurate with their position on the waterfall process model.”

Or else, I could, you know: Post more about the cranium of Argghhh! Which is huge, let me tell you.