Sikorsky is planning to fly a subscale uncrewed aircraft in its Rotor Blown Wing (RBW) vertical-takeoff-and-landing (VTOL) configuration, according to a petition for exemption to certain airworthiness regulations filed with the FAA in June.

Sikorsky is seeking experimental-category certification of the aircraft for flight testing.

The RBW is a tailsitting configuration for a fixed-wing aircraft that takes off and lands vertically and transitions to wingborne cruise flight. The design was revealed in 2013 when Sikorsky was awarded a contract for the first phase of DARPA’s VTOL X-Plane program.

As studied for the VTOL X-Plane, the RBW had a single turbine engine powering two wing-mounted semi-articulated proprotors generating slipstream that flowed over the wing to increase lift. The aircraft could hover on its proprotors like a rotary-wing aircraft or cruise like a conventional fixed-wing aircraft.

Sikorsky Innovations, the Lockheed Martin company’s technology development arm, submitted the exemption application. The document says Sikorsky plans to fly a subscale, electric-powered version of the RBW to inform designs of future larger full-scale uncrewed aircraft.

The aircraft Sikorsky plans to fly has a maximum takeoff weight of 115 lb. and can reach a maximum speed of 125 kt, the application says. The 12,000-lb. uncrewed RBW studied for DARPA’s VTOL-X-Plane was powered by a single Rolls-Royce AE1107C turboshaft mounted in the righthand wing nacelle.

To be able to flight-test the subscale RBW, Sikorsky has requested the FAA grant an exemption to Part 91.151 regulations requiring fuel reserves for at least 30 min. of fixed-wing flight or 20 min. of rotary-wing flight while operating under day visual flight rules.

Justifying the request for an exemption, Sikorsky says the aircraft uses batteries and not fuel for energy storage and, being subscale, does not have the volume and payload capacity to carry enough batteries to meet the reserve requirements of Part 91.151.

Instead, Sikorsky proposes using a minimum reserve power level of 20% of battery capacity that always will be available after flight to ensure an equivalent level of safety to Part 91.151 is maintained throughout RBW operations.

This is nearly identical to relief granted by the FAA previously, the company says, citing the exemption provided to Amazon Prime Air for its electric-VTOL delivery drone. Any delay in providing the exemption would “put Sikorsky and Lockheed Martin at a potential disadvantage to competitors within this very competitive segment of the aerospace industry,” says the petition.