The British Aerospace EAP was an experimental aeroplane designed to address a variety of aeronautical concepts planned to be implemented in a new generation of European advanced fighters. Despite the rather bland name, the Experimental Aircraft Program had a rather glitzy developmental path, appearing in many top European airshows.
Considered by many as the most successful research vessel ever made, it was later repurposed as a test bed for the Eurofighter 2000 Typhoon, helping to reduce developmental costs by a considerable margin.
From the late 1970s, in response to the desire of NATO-aligned European powers to produce an advanced modern fighter, the staff at British Aerospace began to research a twin-engined jet with a big centerline fin, large rear delta wings, and canards.
These would go on to become signature features of a research plane known as the Experimental Aircraft Program (EAP).
The EAP would also grow out of several earlier projects spearheaded by many powerful Western nations. The first, known as the European Combat Fighter (ECF), was originally a partnership between the German and British governments in 1979, but when the French manufacturer Dassault got involved the next year, the name was changed to the European Combat Aircraft (ECA).
However, the ECA soon broke apart when the French, at odds with its multinational partners, demanded that the craft be fractionally lighter, while the rest of the members remained divided over whether a carrier-based naval version should also be assembled.
Unperturbed by the breakdown in governmental cooperation and sensing that a lot of money could be made, aviation manufacturers were the next to pitch their ideas. In response an Industrial Avionics Working Group comprising of BAE, GEC Avionics, Ferranti, and Smith Industries was formed in the UK, while Aeritalia, Rolls Royce, MBB, and other industry bigwigs undertook their own private assessments.
Efforts culminated in April 1982 when BAE, MBB, and Aeritalia offered a joint proposal called the Agile Combat Aircraft (ACA).
After a mock-up was exhibited at the 1982 Farnborough Air Show, the ACA was allocated government support from Britain, Germany, and Italy who expected a flyable prototype, imaginatively known as the Experimental Aircraft Program, to make its first flight on April 30th 1986.
Soon after though, the Germans and Italians both decided to pull out of the project entirely, leaving only the British.
Despite their governments’ unexpected withdrawals and against official advice, many German and Italian companies still played a major part in the EAP, supplying many of its components and hardware often for free.
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Overall, the EAP was to be primarily a demonstrator built from advanced materials tasked with experimenting many novel concepts such as a departure prevention system that kicked in at high angles of attack, and the extent to which the EAP could be digitally controlled.
More broadly, it would evaluate the characteristics of an unstable aircraft and the merits of flight control systems and delta canards at speeds of up to Mach 2.
Painted with a mixture of pale blue, dark blue, black, grey, white and yellow, the EAP was 17.72 meters in length, 5.52 meters high and had an empty weight of 10,000 kilograms, while its wings had a span of 11.97 meters and an area of 48.31 meters squared.
Fitted with an area rule fuselage to minimize the drag from supersonic waves, a radome nose, and a modified Panavia Tornado fin, the EAP’s aerodynamic profile was further assisted by the inclusion of a set of large cranked delta-wings for high lift and a pair of streamlined canard wings at the front.
Similar to the Grumman X-29, the wings of the EAP were aero-elastically tailored so that they didn’t deform under heavy pressure. Roll and pitch control was determined by full-span trailing edge flaps while leading edge flaps could be electronically manipulated by a flight control system which optimized wing camber and maximised manoeuvrability in accordance with flight conditions.
The EAP had a top speed in excess of Mach 2 and was blasted through the air using a set of Turbo-Union RB.199 MK 104D engines, also found in the RAF Tornado F.3 Interceptor, which were fed by approximately 10,000 pounds of fuel housed in 14 receptacles lined along the fuselage as well as two integral wing tanks.
However what set the EAP truly apart was the catalogue of cutting-edge avionics covering communications, navigation, utility services management, and flight control. Particularly impressive was the demonstrator’s utility services management system (USMS), which linked over 600 different kinds of input and output signals from electronically controlled devices located in every part of the aircraft such as those regulating hydraulic systems control, anti-skidding, cockpit temperature monitoring, and secondary power system control to name just a few.
Being an experimental craft the EAP was highly unstable, meaning that the Flight Control Computers (FCC) had to work three times as fast as contemporary aircraft. One pilot even described it as: “like steering a bicycle pushed rear-end first by the handlebars whilst sitting in the front of a 60 mph car.” Perhaps for the best then, no military equipment was ever fitted on the EAP apart from dummy weapons carried in a low-drag position.
Following the competition of a series of weighing and ground tests with a partly complete unit on October 27th 1985, the single EAP, ZF534, which was the first British single-seat ‘fighter’ prototype since the 1960s, was proudly unveiled at BAE’s Warton plant by chief executive Sir Raymond Lygo on April 18th 1986.
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Going forward, the initial flight testing program was to be funded by BAE and would last 3 and a half months and cover 50 flights, while the UK Ministry of Defense would cover the costs afterwards.
With the ground engine and text tests completed over the summer, on August 8th 1986 the EAP flew for 67 minutes with Tornado test pilot David Eagles at the controls, reaching a maximum speed of Mach 1.1 at an altitude of 30,000 feet.
On the other hand, the EAP’s dream start was somewhat marred by a test flight in September when test pilot Chris Yeo lost power on all the computer screens while attempting a 1g to 4g ‘rollercoaster’ manoeuvre.
With the backup power system, fortunately, switching on, Yeo was able to safely land the craft and the fault, a 10-millisecond power interruption, was swiftly dealt with to prevent repeat occurrences. All fixed up, that same month the EAP made its first public display at the Farnborough Air Show for its 21st flight without a hitch.
In October and November, high-angle of attack trials were commenced, and by May 1987 the EAP had been installed with an anti-spin parachute in preparation for the main phase of flight research.
During one particular trial on May 1st, the EAP was flown with a 25-degree angle of attack and a 200 degrees per second roll rate, with assessors noting a considerable improvement in turn performance in comparison to other aircraft. For the EAP’s 100th flight, it was exhibited at the 37th Paris Air Show, where pilot Peter Orme had the privilege of taking it for a spin in front of the French president.
Following a further spurt of experiments focusing on flight loads, on March 28th 1988 the EAP was modified to fix stability issues at high speeds, permitting it to fly at speeds above Mach 1.64 and to travel through the wake of other aircraft if necessary.
Eurofighter Development Program
The beginning of the fourth phase of testing on July 27th 1988 also marked the moment that the EAP became involved in the Eurofighter development program that would go on sire the Eurofighter Typhoon.
That day the EAP was used to compare flight load data with a wind tunnel tested scale-model of the Typhoon, eventually leading to a fifth round of examinations commencing in 1989 in which the EAP was fitted with a Eurofighter airbrake and also entered into Electromagnetic Compatibility trials at facilities in Warton and Boscombe Down.
Towards the end of this fifth stage on October 4th 1989 the EAP was publicly showcased at the Red Arrow’s Silver Anniversary Airshow in anticipation for the next phase of Eurofighter testing which was to begin on October 14th. After 259 test runs and a total of 195.21 flying hours, the EAP performed its last flight on May 1st 1991 at the BAE airfield at Warton.
With its engines dismantled the EAP was next repurposed as an educational tool at the Department of Aeronautical, Automotive Engineering and Transport Studies at Loughborough University, where from June 27th 1996 it was used by undergraduates for design appreciation exercises.
Finally, on November 5th 2013, the EAP was placed on public display in the Test Flight hangar at RAFM Cosford where it can still be viewed today.
As a result of the EAP program, a House of Commons Accounts Committee proclaimed that 850 million pounds had been saved on the Eurofighter’s development cost, making it perhaps the most successful research aircraft ever built.
- Crew: 1
- Length: 48 ft 2.75 in (14.7003 m)
- Wingspan: 38 ft 7 in (11.76 m)
- Height: 18 ft 1.5 in (5.525 m)
- Wing area: 560 sq ft (52 m2)
- Empty weight: 22,050 lb (10,002 kg)
- Max takeoff weight: 32,000 lb (14,515 kg)
- Powerplant: 2 × Turbo-Union RB199-104D 3-spool turbofan engine, 9,000 lbf (40 kN) thrust each dry, 17,000 lbf (76 kN) with afterburner
- Maximum speed: Mach 2 at 11,000 m (36,100 ft)
- Service ceiling: 60,000 ft (18,000 m)