Oliver Garrow has been working with a convertiplane design concept since 2007, and has flown over 100 “sorties” with large scale models to test the concept and demonstrate flight characteristics.
Reported here in 2010, the aircraft initially looked a bit like an annular-wing configuration with pivoting engines or electric motors for lift and propulsion. Now, in its most current version, it looks a bit more like a box wing design with pivoting propulsion. Oliver’s company has changed its name from Verticopter to Elytair. As explained in company literature, “Elytair, named with the goal to offer Elite personnel Air transportation solutions, will be offered as a design platform through selective licensing agreements, for either manned or unmanned applications.”
As with the Verticopter, the Elytair can land and take off in every conceivable mode; conventional take-offs and landings (CTOL), vertical take-off and landing (VTOL) and short take-offs and vertical landings (STOVL). As with helicopters, Elytair can hover, but because it can pivot its propellers to give horizontal thrust, its forward speed can be two to three times greater than the best helicopters, with much better fuel economy.
The company explains, “To achieve this, Elytair blends two airframes each with an optimal wing configuration: a small Tilt-Wing for vertical flight and a Box-Wing for conventional flight. The result is an all-lifting three-wing configuration which provides the best ratio of lift versus drag. Another major benefit of this configuration is the excellent stability in all flight regimes including the conversions.”
Oliver flight tested his earlier designs at Moffett Field, California. This testing included all CTOL, STOVL and VTOL envelopes, and proved the design’s capabilities in a variety of winds.
Oliver and his team used computers for full-size airframe modeling and CFD simulations. One design models a mid-size personnel transport for 10 people with a Maximum Take-Off Weight (MTOW) of 11,500 pounds, and his well-tested flight simulations report a cruise speed of 325 knots at 30,000 feet and a fast cruise of 350 knots at 35,000 feet, comparable to best turboprops in operation today. The web site lists several advantages of the configuration, including:
- Box-wing solution provides best lift and control authority in CTOL mode
- Most neutral stall characteristics, using higher lift coefficient in the forward wing, borrowing from canard planes.
- All positive lifting surfaces, all 3 wings are creating positive lift for best L/D
Because Verticopter licensed its simulator technology to over 1,200 testers, the designs are well proven on the small screen. With that and the ongoing flight testing of their models, Elytair may end up with their goal of “an optimal airframe design for STOVL operation.”
Where the Verticopter was intended for sizes ranging from small personal aircraft to larger commuter planes, current literature shows two models, a commercial commuter liner and a smaller military troop carrier. Their material doesn’t mention too much about propulsion sources, but with the heavy lifting required for vertical take-offs and landings, Elytair will probably rely on a twin-turboprop setup for now, with greener power coming with the development of better batteries or fuel cells.