In 2005, Bevilaqua was elected as a member of the National Academy of Engineering for his theoretical contributions, practical innovations, and increased operational utility in vertical takeoff and landing aircraft.
Hans von Ohain inspired Bevilaqua to think like an engineer rather than a mathematician[4][5] - "in school I learned how to move the pieces, and Hans taught me how to play chess",[6] although he said that about Purdue as well.[2] Ohain also showed Bevilaqua "what those TS-diagrams actually mean".[3]
While at WP, Ohain,[7] Bevilaqua and others investigated and patented[8] various flow related concepts, some of them being flow multipliers related to vertical take-off and landing.
Bevilaqua was working for Lockheed Skunk Works in 1986, when DARPA and the similar British agency launched a program called ASTOVL[11] and issued a 9-month contract to develop concepts[12] for a stealthysupersonicSTOVL plane, in accordance with USMC wishes, but without the usual strict technical requirements.[3]
The challenge in combining supersonic flight and STOVL is that an engine powerful enough to lift an aircraft would be too wide to be supersonic, as shown by the Harrier.[3][5] A smaller engine with higher air flow was needed, but seemed impossible. Inspired by the General Electric CJ805-23 aft-turbofan[13] and the Rolls-Royce tandem-fan,[3][14] an appropriate system seemed to be a dual thrust system with a lift vector at the front and a swivel nozzle at the back for the jet engine, counterbalancing each other.
Many options were investigated,[13] but with one month left and no results, Bevilagua took another look at the situation. Three elements were clear:[5]
aturbine is the best way of extracting power from a jet
a shaft is the best way of transferring that power forward
a fan is the best way of converting power to thrust or lift[15]
Exploiting bypass air is the usual way of increasing thrust, but when air flow drops so does pressure, which increases engine speed at the risk of failure. This apparent flaw suddenly turned to a benefit when it dawned upon him that the extra engine power could be put to good use by turning a lift fan.[5] "It took eight months of brainstorming to program the computer in my head, and ten seconds to come up with the idea."[2]
The solution involved transforming some of the jet blast to vertical air flow by extracting energy from the hot jet blast with a turbine that turns a shaft driving a fan pointing down, thereby increasing impulse and thus lift, without increasing drag.[2] The transition between horizontal and vertical lift needs to be precisely controlled, and the two lift columns need to be carefully balanced, to maintain control of the aircraft.
The system works similarly to a turbofan, with an extra bypass fan moved and tilted 90 degrees to move cool unburned air vertically instead of horizontally,[12] or a turbine helicopter whose rotor is shrunk and encased. This effect is similar to the previous flow multiplier concepts investigated by Bevilaqua (see #List of Papers) and others (although methods are different), achieving a lift/thrust-ratio of 1.5:1[12] where previous successful aircraft were limited to 1:1 at best.
Bevilaqua is not[6]apropulsion engineer, and got help from various Lockheed experts in propulsion, materials, and other specialized fields to verify the theories of the concept, which were then patented in 1990-93.[1]
Both DARPA and the Marine Corps approved of the concept,[10] and from there, it developed through various defense programs such as CALF and JAST[11] into the Joint Strike Fighter Program and through to the X-35B and F-35B. Bevilaqua was a key figure in persuading[10] the Air Force in 1992 that the concept aircraft could be useful as a conventional aircraft without the LiftFan. When the US Navy also came on board,[10] the road was paved for the JSF concept of similar aircraft with different applications, in accordance with JAST Concept Exploration findings.[11]
One of the key factors in handing the $200B[3] JSF contract to LM is said[18] to be when the X-35B took off from 150 feet of runway, went supersonic, and landed vertically in one flight on July 20, 2001[19] - a performance that only the X-35B had done, and only because of the LiftFan concept.
^ abShort take-off, low fundingFlight International, 29 March 1995. Retrieved: 19 September 2010. Archived July 10, 2010, at the Wayback Machine. Quote: "[we] spent three weeks in a room going over every propulsion system ever used"