Paul Bevilaqua

Life and career

Paul Bevilaqua earned a Doctorate in Aeronautics and Astronautics (subject: Turbulent wakes) at Purdue University in 1973. This seems to be concurrent with activities as an Air Force Lieutenant at Wright-Patterson Air Force Base (WP-AFB), where he began professional work in 1971. At some point he became Deputy Director of the Energy Conversion Lab at WP-AFB, managed by jet inventor Hans von Ohain. In 1975 Paul left the Air Force to be a Manager of Advanced Programs at Rockwell International's Navy Aircraft Plant. Ten years later, in 1985, he was appointed Chief Aeronautical Scientist at Lockheed, trying to come up with a new line of business.

Hans von Ohain inspired Bevilaqua to think like an engineer rather than a mathematician - "in school I learned how to move the pieces, and Hans taught me how to play chess", although he said that about Purdue as well. Ohain also showed Paul "what those TS-diagrams actually mean".

While at WP, Ohain, Bevilaqua and others investigated (see #List of Papers) and patented various flow related concepts, some of them flow multipliers related to vertical take-off and landing.

Invention of LiftFan

In the 1980s, the United States Marine Corps wanted a Vertical/Short Takeoff and Landing (V/STOVL) aircraft with more speed and payload than the Harrier/AV-8B.

Bevilaqua was working for Lockheed Skunk Works in 1986, when DARPA and the similar British agency launched a program called ASTOVL and issued a 9-month contract to develop concepts for a stealthy supersonic STOVL plane, in accordance with USMC wishes, but without the usual strict technical requirements.

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. A smaller engine with higher air flow was needed, but seemed impossible.
Inspired by the General Electric CJ805-23 aft-turbofan and the Rolls-Royce tandem-fan, 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.
To leave no stone unturned, all kinds of options were investigated, some even bordering on the ludicrous (using a cannon for lift, transferring power with a laser beam) - Skunk Works employees are no strangers to cartoon antics.

With one month left and no results, he took yet another look at the situation. Three elements were clear:

but that was tried by many and found insufficient - something more was needed.

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. "It took eight months of brainstorming to program the computer in my head, and ten seconds to come up with the idea."
In other words; 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. 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, 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 where previous successful aircraft were limited to 1:1 at best.

Paul is not a propulsion engineer, and got help from various Lockheed experts in propulsion, materials and other specialised fields to verify the theories of the concept, which was then patented in 1990-93.

Both DARPA and the Marine Corps liked the concept, and from there it developed through various defense programs such as CALF and JAST into the Joint Strike Fighter Program and through to the X-35B and F-35B. Bevilaqua was a key figure in persuading 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, the road was paved for the JSF concept of similar aircraft with different applications, in accordance with JAST Concept Exploration findings.

The practical development and testing of the F135 engine and system was performed by Pratt & Whitney, Allison Engine Company, NASA, Rolls-Royce and others.

One of the key factors in handing the $200B JSF contract to LM is said to be when the X-35B took off from 150feet of runway, went supersonic, and landed vertically in one flight on July 20, 2001 - a performance that only the X-35B had done, and only because of the LiftFan concept.

The JSF team was awarded the Collier Trophy 2001 for the working system, and Bevilaqua received the Paul E. Haueter Memorial Award (American Helicopter Society) in 2004.