As a conscript, a young Rafi Yoeli served in the Israeli Air Force (IAF) as an air traffic controller, studied aeronautical engineering at Tel Aviv University and joined Israeli Aerospace Industries (IAI) in the late 1970s when it was improving the IAI 1124 Westwind business jet, designing the 1125 Astra business jet and state-of-the-art Lavi jet fighter, and developing the Scout UAV for the Israeli Defense Force (IDF).
He then paused in his industry career to earn a Master of Science degree in aeronautical engineering and doctorate in artificial intelligence from Technion–Israel Institute of Technology in Haifa.
Upon graduating, Yoeli founded Aero Design & Development (AD&D) in 1987 to provide consulting aeronautical engineering services to defense agencies and aerospace companies.
Some of AD&D’s notable projects included the development of advanced flight control computers and software; development of the “Skylark” Mini-UAV (sold by Elbit to 20 nations); design of the Stingray unmanned maritime vessel; design and development of three different air-breathing jet powered UAV’s; and modification of an IAF MD500 helicopter to an unmanned role.
As an IAF reservist, Yoeli also spent several days each month for almost 30 years managing the maintenance and battle damage repair of F-16, F-15 and F-4 fighter jets, as well as AH-1F, MD500 and CH-53 helicopters.
Yoeli obtained his fixed-wing pilot license in 1980 and his helicopter pilot license in 1995, and soon began flying from home to his office in a Rotorway Exec helicopter.
At about the same time, Yoeli became intrigued with early internal ducted rotorcraft such as the Hiller VZ-1 Pawnee one-man flying platform. (See “Walking on Air: Individual Flying Platforms of the Past, Present … and Future?” Vertiflite, Summer 2004.)
In 1997, Yoeli designed, built and flew AD&D’s Hummingbird ducted fan flying platform kit, which was powered by four Hirth piston engines. Yoeli placed a small advertisement for Hummingbird kit aircraft in the Experimental Aircraft Association’s Sport Aviation magazine for the kit.
“I got more than 1,500 responses from the advertisement from people who wanted to buy the kit. But because the Hummingbird was designed to remain airborne after losing any one of its four single cylinder engines, when all engines where running it had a lot of extra power,” said Yoeli. “I decided not to sell the kit because I was concerned that irresponsible people would open up the throttle, climbing up rapidly and then getting hurt or worse.”
Using major components from the Hummingbird, AD&D developed the Hornet UAV, which was first flown in early 2000. The design was optimized to fly a large payload above the duct that could provide 360-degree coverage.
Yoeli’s interests then shifted to internally ducted tandem fan aircraft as represented by the Piasecki VZ-8Z and VZ-8P(B) AirGeeps developed with US Army funding in the late 1950s. (See “Driving on Air: 20th Century Flying Carpets,” Vertiflite, Spring 2005.)
To explore the tandem fan concept, Yoeli bought two Hummingbird kits from AD&D after he sold the company to Elbit Systems and joined them together to create a tandem ducted VTOL platform that he built and flew.
To fly the Hummingbird, the standing pilot provided directional control by shifting his weight; but that wasn’t an option in the tandem duct design. “It was obvious that the pilot (me again) would need a new way to control the vehicle in roll,” recalled Yoeli.
“The vane control system we’re now using on the Cormorant Fancraft actually started out as a ‘poor man’s’ alternative to rotors with cyclic control, which I couldn’t afford. That's how the patented vane control system was born and it was definitely these two Hummingbirds joined together that started it all."
Ken Swartz runs aerospace marketing communications agency Aeromedia Communications in Toronto, Canada. He specializes in contract public relations, freelance writing and social media marketing for the aviation and aerospace industry. He has reported on the helicopter industry for 40 years. In 2010, he received the HAI “Communicator of the Year” award. He can be reached at firstname.lastname@example.org.
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