VTOL X-Plane

DARPA announced the programme in February 2013 with a requirement to create a new aircraft that uses the best features from both vertical take-off and landing technology and that used for conventional aircraft. The hybrid aircraft will try to improve on four areas: • Speed - achieve a top speed of at least 300 kts. • Hover - increase hover efficiency to at least 75 percent. • Cruise efficiency - achieve a lift-to-drag ratio of at least 10. • Load - ensure the solution can carry a useful load of at least 40% of the projected gross weight. ==Phase One - Preliminary design study==

The first two companies to be involved were announced in December 2013 when Sikorsky Aircraft was awarded a US$14.4 million contract and Aurora Flight Sciences was given US$14 million for preliminary design studies as part of the $47 million Phase One budget. On 18 March 2014, DARPA announced that Sikorsky, Aurora Flight Sciences, Boeing, and Karem Aircraft had been selected to compete for the VTOL X-plane. The four companies have based their designs on unmanned aircraft and will compete over the next 20 months. The name of Aurora's submission was revealed as the LightningStrike in February and although the design was unknown, the company has a history of producing ducted fan and hybrid propulsion aircraft. Karem Aircraft was expected to propose a tiltrotor aircraft with an optimum speed rotor. The Boeing PhantomSwift embedded twin lifting fans inside the fuselage with tilting ducted fans mounted on wingtips for lift and forward thrust; a scale demonstrator was built and flown by the company in 2013. Sikorsky teamed with Lockheed Martin for a "low complexity" design that combined fixed wing aerodynamics and advanced rotor control. A single design was to be selected in autumn 2015 for a $95 million contract to build a demonstrator in phase 2. • Rotor Blown Wing - Sikorsky and Lockheed Martin teamed to develop their unmanned rotor blown wing concept. They claimed it integrated fixed wing aerodynamics and advanced rotor control to provide a low complexity configuration. • LightningStrike - Aurora Flight Sciences' LightningStrike would achieve high overall efficiency by integrating the propulsion into the air vehicle's aerodynamic design. The company has experience with ducted-fan designs through Goldeneye series aircraft, also under DARPA programs, and with hybrid-electric propulsion with the Excalibur unmanned aerial vehicle proof-of-concept aircraft to create a design providing vertical takeoff and landing with high-speed horizontal flight. Levering this experience Aurora Flight Sciences' developed a revolutionary vehicle concept that employs Electric Distributed Propulsion (EDP) in eighteen wing fans, and six canard fans, driven by 3 MW of electricity. • PhantomSwift - Boeing's PhantomSwift concept had two large internal fans to provide lift with two wingtip fans that provide stability while hovering. In forward flight, the internal fans stop supplying power and the wingtip fans provide thrust. Boeing claimed that this configuration was 50 percent more efficient in the hover than a typical helicopter, and expected to have a top speed of . The full-size version would have had a wingspan of , a fuselage length of , and weigh . The demonstrator would be powered by one or two General Electric CT7-8 engines, ==Phase Two==

The design, development and integration phase is expected to last 18-months; Phase Two will allow companies to mature their designs. A 20 percent-scale demonstrator, weighing 325 lb (147 kg) using wings and canards made of carbon composites and 3D-printed plastics, was flown on 29 March 2016. The full-scale aircraft will be designated the XV-24A. ==Phase Three==

Phase Three was to last 12-months from February 2017 to February 2018 and consist of ground and flight tests of the experimental designs. ==References==