DARPA / Navy Common Affordable Lightweight Fighter (CALF) 1993-1994

The DARPA / Navy Common Affordable Lightweight Fighter (CALF) program has also been called the Joint Attack Fighter (JAF), but the two seem to be separate and distinct efforts.

The ASTOVL/SSF concepts were originally seen as developing a replacement for the US and UK Harrier jump-jet. As the ASTOVL/SSF concepts became multi-service with the suggestion of multiple variants, the program was re-christened as the Common Affordable Lightweight Fighter (CALF). The management of the CALF program was handed by DARPA due to the experimental nature of the concept. DARPA was also managing the ASTOVL program, which was used by the SSF program as their unclassified, white-world cover story.

The CALF program's aim was to develop the technologies and concepts to support the ASTOVL aircraft for the USMC and Royal Navy (RN) and a highly-common conventional flight variant for the US Air Force. Although the CALF program was organized upon a suggestion from Lockheed, the government still wanted multiple contractors involved in the program. Initially, the only two contractors involved were Lockheed and McDonnell Douglas. Boeing later approached DARPA and offered to meet DARPA's financial contribution if they were allowed onto the program.

Under DARPA management, the joint DARPA/Navy CALF program was a three-phased program culminating in a low cost, two-aircraft flight demonstration of a single STOVL concept. Phase I encompassed all of the previous design study activities, and was denoted Phase I after the fact. Phase II was a three year Critical Technology Validation Phase to conduct technology maturation and risk reduction activities in preparation for Phase III, Detailed Design, Fabrication and Flight Test.

DARPA competitively awarded two contracts in March 1993 to conduct critical technology validation of two CALF concepts. Lockheed was awarded a $32.9M contract to conduct risk reduction of a shaft driven lift fan and McDonnell Douglas was awarded a $27.7M contract to conduct risk reduction of a gas driven lift fan. The competition had emphasized the use of new partnering and incentive approaches and both of these contracts included unique features. The Lockheed contract included an innovative fee structure wherein Lockheed could recoup up to $4M in the event of an underun. The McDonnell Douglas contract included cost share in which the government would provide $45.6M and McDonnell Douglas would be required to match no more than $13.5M of their own money. Formal negotiations were still in progress with the UK for an additional $12M contribution to be used to fund options on the Lockheed and McDonnell Douglas contracts. These options were ultimately exercised in August 1994 upon signature of the CALF Memorandum of Understanding with the UK.

In March 1994, Congress appropriated an additional $6M to fund a direct lift STOVL concept. Following a procurement competition, Boeing was selected to conduct this effort, offering to cost share an additional $6M to enable a similar level of risk reduction as the Lockheed and McDonnell Douglas and put them in a competitive position to vie for a follow-on demonstration program. Further provisions included a $10M contribution each from Congress and Boeing for the following year, bringing Boeing's total contract up to $32M.

For all three contractors, the Critical Technology Validation Phase included continued design work on both operational and associated low cost demonstrator aircraft, affordability analyses, and small scale and component testing culminating in large scale powered model testing to validate not only propulsion system performance but to ensure no adverse performance effects from operation in ground effect such as stability and control problems, lift losses and hot gas ingestion. The CALF program employed a unique design approach for the time - rather than defining specific performance requirements for the operational aircraft, the government defined a set of mission goals and asked the contractor to conduct design trade-studies to find the most cost effective solution. The government imposed only a single requirement - that the aircraft weight empty be less than 24,000 lbs. This weight target was set for two reasons. First, this weight was consistent with the thrust available for vertical landing from an F-119 class engine. Second, since parametric cost estimating relationships show strong correlation with weight, this also ensured that a low cost design would be achieved. The demonstrator aircraft would be based on this design, employing a common outer moldline, to validate performance predictions and demonstrate manufacturing affordability initiatives. However signature reduction materials and treatments would be left off the demonstrator to reduce cost. The demonstrator aircraft would also demonstrate the commonality between the Air Force and Marine Corps variants by using common tooling and producing both configurations.

In 1994, Northrop Grumman entered into a no-cost agreement with DARPA to begin critical technology validation activities. However, their efforts were merged with those of McDonnell Douglas following the merger with JAST since they were teammates on that program. Several aircraft configurations developed under the CALF program. In preparation for Phase III, DARPA applied for and received the X-32 designation for the planned demonstrator aircraft.