British Concorde Static Test Airframe

 

In the development of the world’s first supersonic airliner there were to be many unknowns to be explored, and design calculations to be verified or validated. Once the materials had been selected, it was necessary to carry out an exhaustive programme of laboratory test to reproduce the supersonic flight environment that Concorde would spend her life flying in, both in terms of the thermal cycles that she would be subjected to, and the structural loadings and resistance to fatigue of the articles under test.

An understanding of the thermal demands of the supersonic flight profile could be gained from extensive laboratory testing. The rapid rise in the temperature of materials during acceleration, coupled with prolonged heat-soak in supersonic cruise, followed by rapid cooling under deceleration, could all be reproduced using relatively small articles in the laboratory. Because of the pioneering nature of the project, it was decided to build two test airframes, one for the purpose of static testing, and another for fatigue testing. The use of these test airframes would provide valuable data relating to the ability of the production machines to withstand the rigours of supersonic flight and give confirmation of the calculated in-service life of the complete aircraft.

 

FATIGUE TESTING – (British Airframe)

Conducted at – Royal Aircraft Establishment, Farnborough, England, UK.

As well as the static tests, there is a requirement to ensure that the structural integrity of the airframe is maintained throughout the life of the aircraft. In isolation, the number of hours flown is no longer a sufficiently adequate indicator of the condition of an aircraft, as the stresses imposed by the number of landings, cabin pressurisation cycles, and in-flight manoeuvres can all be measured, and must be taken into account. Most aircraft are fitted with a ‘fatigue meter’ that records many of the physical stresses involved in flight operations. The information recorded is compared against data gained from the fatigue testing of a representative airframe in order that assessment of its absolute fatigue status, and remaining operational life, can be made. Conventional airliners are not usually subjected to extremes of temperature, as in the case of Concorde.

Fatigue testing of the Concorde airframe was, at the time, the most complex and exhaustive ever carried out. At the Royal Aircraft Establishment, Farnborough, the airframe was surrounded by a jacket that formed a duct around the aircraft through which hot or cold air could be circulated to replicate the thermal cycles of supersonic flight. Five fans, each rated at 2,300 horsepower, pumped the air through the jacket. Warm air was provided by hot water heat exchangers and cold air was supplied via refrigeration units. Around  100 servo-controlled hydraulic jacks were used both to simulate external loading on the airframe and internal loading caused by cabin pressurisation cycle, air-conditioning, and fuel transfer stresses.

Earlier test had provided evidence that, if the maximum temperature for testing was increased, this would result in a reduction in the time taken to achieve the effects of heat-soak and thus reduce the overall test period. Effectively, every hour under test was equivalent to a typical three-hour flight.

Progress was fairly rapid; having commenced during August 1973. The certification requirement of 6,800 cycles was achieved by the end of 1975. Subsequent testing was carried out at a yearly rate of 7,000 cycles to maintain the fatigue life of the test specimen at around three times that of the fleet ‘fatigue leader’ aircraft in airline service.

A few bits and pieces of this airframe have survived and can be seen today at Brooklands museum, kept very close to Concorde G-BBDG