The use of aerial drones for combat purposes has a lengthy history, but the story is also ongoing as the development of unmanned combat aircraft/drones is still in its relative infancy. The US Navy employed Remotely Piloted Vehicles (RPV) for gunnery spotting and direction during the First Persian Gulf War of 1991, and the War on Terror introduced the world to the armed combat drone such as the MQ-1 Predator.

However, these early platforms had relatively low-performance figures, as allowed by aerial vehicles operating in a permissive environment such as an insurgency in an undeveloped country. Obviously, something else would be needed for combat missions in a heavily defended area of operations, and the concept of the Unmanned Combat Aerial Vehicle (UCAV) was born.

With the step up in requirements, there was a corresponding step up in capability, and aircraft manufacturers needed to experiment with a range of technologies, with most companies choosing to prove concepts through the assembly and Testing of a technology demonstrator airframe.

One of the first of these was a program for the US Navy in 2001, which showcased the X-47A Pegasus experimental unmanned aerial vehicle.

Contents

• Design and Development
• X-47A
• Conclusion and Legacy
• Specifications

Design and Development

The Pegasus was borne out of a Defence Advanced Research Projects Agency (DARPA) evaluation and test proposal for a joint US Navy/USAF unmanned technology demonstrator, which was known as the Joint Unmanned Combat Air Systems (J-UCAS).

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Both the Navy and Air Force realised that they had a range of different operational requirements, and J-UCAS was terminated in 2006. The services began pursuing separate demonstrator projects, with the Navy’s being known as the Unmanned Combat Air System Demonstrator (UCAS-D).

The US Navy awarded a contract under the auspices of the J-UCAS program to the Northrop Grumman Corporation for a naval UCAV demonstrator in 2001. The design specifications were exacting: the ability to resist corrosion in a maritime operating environment, to incorporate stealth characteristics, capable of launch and recovery from a carrier and able to operate in an intense electromagnetic environment and the performance necessary to operate in a hostile battlespace.

At this stage of development the Navy was envisaging the X-47A would lead to the development of unmanned aircraft that would act as stealthy scouts probing ahead of manned combat aircraft to penetrate heavily defended airspace, at less cost to manned platforms.

The Northrop Grumman design team realised that a project with multiple design specifications would require a multi-stage approach; with basic Flight operations being realised before carrier testing commenced.

The company introduced the X-47A ‘Pegasus’ UCAV demonstrator on the 30th of July 2001, and ground testing and further experimental development followed. To reduce costs several measures were adopted; the basic airframe design and manufacture were subcontracted to and undertaken by Burt Rutan Scaled Composites at Mohave Spaceport, and the non-afterburning turbofan had a standard tailpipe instead of a more expensive stealth-optimised version.

The Pegasus was transported to the Naval Air Warfare Center at China Lake, California for further evaluation and flight testing by the US Navy. The first flight of the X-47A took place on the 23rd of February 2003, but ongoing developments in the J-UCAS project meant that this was the only flight of the platform to date.

With several concepts proven by this flight, Northrop Grumman decided ahead of the termination of the J-UCAS program to concentrate on the design and manufacture of a full-sized carrier-capable demonstrator, and this led to the X-47B UCAV intended to compete for the UCAS-D contract.

The X-47A was a modestly-sized aerial vehicle, and as a proof-of-concept demonstrator was manufactured to test several emerging aviation technologies. With no pilot to accommodate and support the size of the airframe could be kept down to minimal proportions, which obviously helped with the planned stealth characteristics of the design.

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Composites were mainly used in the construction of the Pegasus, which lowered the total weight of the airframe, and helped diffuse/refract hostile radar signals to increase the stealthy nature of the design.

These stealth enhancements were augmented by the shape of the Pegasus, which resembled a large arrowhead without any vertical tailplane, with swept-back wings at an angle of 55 degrees.

All control surfaces were on the wings, and consisted of two elevators and four ‘inlaids’; small flaps mounted on the top and bottom of the wings near the wingtip, which provide both flap and airbrake functions.

The X-47A was fitted with retractable undercarriage in a tricycle configuration, with the front having a single wheel and the main trucks equipped with two wheels each. The main turbofan engine received its air through a ‘serpentine’ or slit diffuser just behind the nose of the aircraft, this was done to remove the possibility of radar ‘scatter’ off the rotating turbine blades by shielding the air intake from electronic view.

The centrally mounted engine has an enclosed weapons bay on either side of it, and although these were not employed during the test flight, it was speculated that each could accommodate a smart bomb up to 500lbs in weight, though only dummy weapons would have been carried had further test flights been authorised.

X-47A

As a technology demonstrator used to test a limited number of proof-of-concept theories, the Pegasus only needed to be manufactured to modest proportions, as the type was never intended to take part in any onboard testing on a carrier out at sea.

Still, the airframe had to be large enough to test a full-sized turbofan engine and other test equipment, strong enough to be operated at subsonic/transonic speeds, and capable of allowing testing of the airframe in high-G manoeuvring.

The X-47A had the following dimensions: a height of 6 feet 1 inch (1.85 metres) and a length of 27.9 feet (8.51 metres) and a wingspan of 28.8 feet (8.5 metres). Empty, the basic aircraft tipped the scales at 3,840 lbs (1,740 kg), and the gross weight was 4,870 lbs (2,210 kg). Max Take-Off Weight (MTOW) was 5,900 lbs (2,670 kg).

The single-engine of the X-47A was a Pratt & Whitney Canada JT 15D-5C non-afterburning turbofan, which generated 3, 190 pounds of thrust. A full test program had aimed at a top speed of Mach 0.8, along with a range of 1,700 miles (2,800 kilometres) and a service ceiling of 40,000 feet (12,000 metres). The thrust-to-weight ratio of the Pegasus was 0.65.

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The twin weapons bays were optimised to carry 500 lb-class guided bombs like the GBU-12, but could also have carried a number of Small Diameter Bombs (SDB) or other guided munitions. Another possibility was employing the bays to carry payloads for surveillance or reconnaissance missions, or even extra fuel tanks for an increased range.

Conclusion and Legacy

After the eventual messy end to the War on Terror, the international community realised that an increased emphasis on planning for heavy intra-national warfighting scenarios was necessary, instead of the recent focus on low-level conflict such as anti-terror operations.

Strategies and equipment that had worked well in Afghanistan and Iraq were obviously inadequate for employment against Russia and China, and an MQ-9 Reaper would have little chance in hostile skies above either nation, as has just been shown over the Black Sea.

The concept of the UCAV matured as a force-multiplication factor, allowing unmanned airframes to perform highly hazardous surveillance or strike mission, as well as sacrificing themselves in aerial combat to shield their manned counterparts from battle damage.

A multitude of companies have fielded successful designs for UCAVs in many countries, and further testing and technology advancement means that even more capable designs will be showcased in the near future.

Testing and development continued to investigate possible new capabilities for supersonic flight, and having the necessary aerodynamics and performance for repeated high-G manoeuvres. The Royal Australian Air Force has been the first air arm to introduce a UCAV into general service, in the shape of the MQ-28A Ghost Bat.

While the test program of the X-47A Pegasus was severely truncated and only one test flight was performed, the design can be said to be a success. Several important proof-of-concepts was tested and confirmed by the Pegasus, and the airframe and power plant combination worked well in both ground testing and on the test flight.

Northrop Grumman decided to let any further testing of the X-47A to lapse, but the aircraft was the design inspiration for its successor, the X-47B, which was a full-sized airframe for UCAV testing aboard a carrier.

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This lineal development of the Pegasus was a great success, using a combination of AI and human control to launch and recover aboard a carrier, perform most flight manoeuvres and even act as an aerial tanker, refuelling other aircraft while in flight.

The X-47A Pegasus may have had a very short career, but it can be said that its short period of service as a technology demonstrator was a success. The basic design was obviously deserving of merit, as its direct descendent the X-47B earned the US Navy and the Northrop Grumman Corporation the award of the prestigious Collier Trophy for aeronautical excellence in 2013.

Specifications

• Length: 27.9 ft (8.5 m)
• Wingspan: 27.8 ft (8.5 m)
• Height: 6 ft 1 in (1.85 m)
• Empty weight: 3,836 lb (1,740 kg)
• Gross weight: 4,877 lb (2,212 kg)
• Max takeoff weight: 5,903 lb (2,678 kg)
• Powerplant: 1 × Pratt & Whitney Canada JT15D-5C turbofan, 3,190 lbf (14.2 kN) thrust
• Range: 1,700 mi (2,800 km, 1,500 nmi)
• Service ceiling: 40,000 ft (12,000 m)

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