The Vertical Take-Off and Landing Experimental Aircraft (VTOL X-Plane) program was an American research project sponsored by the

Defense Advanced Research Projects Agency The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Adva ...

(DARPA). The goal of the program was to demonstrate a

VTOL A vertical take-off and landing (VTOL) aircraft is one that can takeoff and landing, take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust- ...

aircraft design that can take off vertically and efficiently hover, while flying faster than conventional

rotorcraft A rotary-wing aircraft, rotorwing aircraft or rotorcraft is a heavier-than-air aircraft with rotor wing, rotary wings that spin around a vertical mast to generate lift (force), lift. Part 1 (Definitions and Abbreviations) of Subchapter A of Chapt ...

.DARPA Awards Contracts in Search of a 460 MPH Helicopter
- News.USNI.org, 19 March 2014 There have been many previous attempts, most of them unsuccessful as of 2015.Whittle, Richard.
The Next X-Plane
''

Air & Space/Smithsonian ''Air & Space/Smithsonian'' was a quarterly magazine published by the National Air and Space Museum in Washington, D.C. Washington, D.C., formally the District of Columbia and commonly known as Washington or D.C., is the capital city an ...

'', October 2015. Accessed: 26 September 2015. A helicopter with a conventional rotor layout has a theoretical top speed of , after which it suffers from

dissymmetry of lift Dissymmetry of lift (also known as asymmetry of lift or asymmetric lift) in rotorcraft aerodynamics refers to an unequal amount of lift on opposite sides of the rotor disc. It is a phenomenon that affects single-rotor helicopters and autogyros ...

. Some designs have successfully created hovering and high-speed aircraft, including the

Bell Boeing V-22 Osprey The Bell Boeing V-22 Osprey is an American multi-use, tiltrotor military transport and cargo aircraft with both vertical takeoff and landing (VTOL) and short takeoff and landing (STOL) capabilities. It is designed to combine the functionalit ...

tiltrotor A tiltrotor is an aircraft that generates lift (force), lift and thrust, propulsion by way of one or more powered Helicopter rotor, rotors (sometimes called ''proprotors'') mounted on rotating shaft (mechanical engineering), shafts or nacelles ...

that can fly at and the Sikorsky X2

compound helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attribut ...

that flew at , but both made significant aerodynamic compromises to hovering efficiency or range. DARPA's goal was 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 An unmanned aerial vehicle (UAV) or unmanned aircraft system (UAS), commonly known as a drone, is an aircraft with no human pilot, crew, or passengers onboard, but rather is controlled remotely or is autonomous.De Gruyter Handbook of Dron ...

even though it was not required, but the technologies were intended to be applied to manned aircraft as well.

Aurora Flight Sciences Aurora Flight Sciences (AFS) is an American aviation and aeronautics research subsidiary of Boeing that specializes in special-purpose unmanned aerial vehicles. Aurora's headquarters is at Manassas Regional Airport. History In 1989, AFS was ...

was selected to create a test design, which would fly in 2018.VIDEO: Aurora’s LightningStrike wins DARPA VTOL X-plane comp
- Flightglobal.com, 4 March 2016 DARPA canceled the program in 2018 before the flight testing, citing growing commercial interest and the lack of a military partner. In September 2022, DARPA initiated the ANCILLARY program to develop a small VTOL uncrewed aerial system (UAS) with low weight, high payload, and long endurance capabilities, X-plane flight tests scheduled for 2026.

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: *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 Sikorsky Aircraft is an American aircraft manufacturer based in Stratford, Connecticut. It was established by the Russian-American aviation pioneer Igor Sikorsky in 1923, and was among the first companies to manufacture helicopters for civilian ...

was awarded a

US$ The United States dollar (Currency symbol, symbol: Dollar sign, $; ISO 4217, currency code: USD) is the official currency of the United States and International use of the U.S. dollar, several other countries. The Coinage Act of 1792 introdu ...

14.4 million contract and

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 The Boeing Company, or simply Boeing (), is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, and missiles worldwide. The company also provides leasing and product support s ...

, 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 In aeronautics, a ducted fan is a thrust-generating mechanical fan or Propeller (aeronautics), propeller mounted within a cylindrical wiktionary:duct, duct or shroud. Other terms include ducted propeller or shrouded propeller. When used in vertic ...

and hybrid propulsion aircraft. Karem Aircraft was expected to propose a

aircraft with an optimum speed rotor. The Boeing ''PhantomSwift'' embedded twin lifting fans inside the

fuselage The fuselage (; from the French language, French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds Aircrew, crew, passengers, or cargo. In single-engine aircraft, it will usually contain an Aircraft engine, engine as wel ...

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 The Lockheed Martin Corporation is an American Arms industry, defense and aerospace manufacturer with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta on March 15, 1995. It is headquartered in North ...

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. An artist depiction of Sikorsky's Rotor Blown Wing bore visual resemblance to the Boeing Heliwing, an unmanned

tailsitter A tail-sitter, or tailsitter, is a type of VTOL aircraft that takes off and lands on its tail, then tilts horizontally for forward flight. Originating in the 1920s with the inventor Nikola Tesla, the first aircraft to adopt a tail-sitter configu ...

intended to reach in forward flight; it first flew in April 1995 but crashed in July and the project was shelved. Sikorsky confirmed that the Rotor Blown Wing would be a tailsitter, with its name suggesting that the wing remains aligned into the proprotor wash during transition between vertical and forward, reducing download on the wing in hover mode. *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 ''GoldenEye'' is a 1995 spy film, the seventeenth in the List of James Bond films, ''James Bond'' series produced by Eon Productions, and the first to star Pierce Brosnan as the fictional Secret Intelligence Service, MI6 agent James Bond (lit ...

series aircraft, also under DARPA programs, and with hybrid-electric propulsion with the

Excalibur unmanned aerial vehicle The Aurora Excalibur was an unmanned aerial vehicle (UAV) developed by Aurora Flight Sciences between 2005 and 2010 capable of vertical takeoff and landing (VTOL). The design combined ducted fans and hybrid drive. A smaller scale model with a wing ...

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. *Karem tiltrotor - Karem Aircraft submitted a tiltrotor concept called TR36XP, employing a slender-bodied fuselage with a high-aspect-ratio

gull wing The gull wing, also known as Polish wing or Puławski wing, is an aircraft wing configuration with a prominent bend in the wing inner section towards the wing root. Its name is derived from the seabirds which it resembles and from the Polish a ...

. The outer sections of the wing, together with two 36 ft rotor/propellers, rotated through 90 degrees for transition between hover and forward flight, powered by two

Rolls-Royce Turbomeca RTM322 The Rolls-Royce Turbomeca RTM322 is a turboshaft engine currently produced by Safran Helicopter Engines. The RTM322 was originally conceived and manufactured by Rolls-Royce Turbomeca Limited, a joint venture between Rolls-Royce and Turbom ...

. *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, but a production version would be powered by an all-electric drive. - Defensetech.org, 28 August 2014

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 A turboshaft engine is a form of gas turbine that is optimized to produce shaft horsepower rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the ex ...

engine, the same type used on the V-22 Osprey, that generates electric power via three

Honeywell Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building automation, industrial automa ...

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 Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are t ...

) of electricity, as much as a commercial

wind turbine A wind turbine is a device that wind power, converts the kinetic energy of wind into electrical energy. , hundreds of thousands of list of most powerful wind turbines, large turbines, in installations known as wind farms, were generating over ...

, 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.Check Out the Military’s Experimental Helicopter Plane
- Defenseone.com, 4 March 2016You-Ain’t-Gonna-Believe-This Design Wins DARPA X-Plane Deal
- Breakingdefense.com, 4 March 2016 A 20 percent-scale demonstrator, weighing 325 lb (147 kg) using wings and canards made of carbon composites and

3D-printed 3D printing, or additive manufacturing, is the Manufacturing, construction of a three-dimensional object from a computer-aided design, CAD model or a digital 3D modeling, 3D model. It can be done in a variety of processes in which material i ...

plastics, was flown on 29 March 2016. The full-scale aircraft will be designated the XV-24A.DARPA’s sub-scale VTOL X-Plane prototype completes flight testing
- Gizmag.com, 5 April 2017

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.

References

External links

{{US STOL and VTOL aircraft DARPA projects 2010s United States experimental aircraft VTOL aircraft