VTOL X-Plane

The Vertical Take-Off and Landing Experimental Aircraft (VTOL X-Plane) program is an American research project sponsored by the Defense Advanced Research Projects Agency (DARPA). The goal of the program is to demonstrate a VTOL aircraft design that can take off vertically and efficiently hover, while flying faster than conventional rotorcraft. There have been many previous attempts, most of them unsuccessful.
A helicopter with a conventional rotor layout has a theoretical top speed of , after which it suffers from dissymmetry of lift. Some designs have successfully created hovering and high-speed aircraft, including the Bell Boeing V-22 Osprey tiltrotor that can fly at and the Sikorsky X2 compound helicopter that flew at , but both made significant aerodynamic compromises to hovering efficiency or range. DARPA's goal is to demonstrate a VTOL aircraft that can achieve a sustained top speed of 300 to 400 knots ().
All competitors for the program opted to demonstrate their concepts using an unmanned aerial vehicle even though it was not required, but the technologies are intended to be applied to manned aircraft as well.
Aurora Flight Sciences was selected to create a test design, which will fly in 2018.
Requirement and programme.
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:
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.
Phase Two.
The design, development and integration phase is expected to last 18-months; Phase Two will allow companies to mature their designs.
On 3 March 2016, DARPA awarded Aurora Flight Sciences $89.4 million to build and demonstrate their LightningStrike concept, beating out the other three competitors. The LightningStrike is a tilting-wing design powered by one Rolls-Royce AE1107C turboshaft engine, the same type used on the V-22 Osprey, that generates electric power via three Honeywell generators to run 24 distributed ducted fans, three each in the forward canards and 18 across the main wing. Rather than using conventional engines like all the other entrants, the aircraft relies on "distributed electric propulsion," where the three generators that produce three megawatts (4,023 horsepower) of electricity, as much as a commercial wind turbine, power individual motors that drive the fans; each wing fan uses a 100 kW motor, and each canard fan a 70 kW motor. The air vehicle will weigh between , about the size of a UH-1Y Venom, and cruise faster than 300 knots, 50 knots faster than the V-22. Phase II of the VTOL X-Plane project will fabricate two air vehicles before flight testing, planned by September 2018. 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.
Darpa cancelled the project before flight testing.