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C/n 801A/801B/802 - The Test Specimen
Not all the VC10s built were fliers. In the development of large airliners - and the VC10 is still the largest airliner built solely in the UK - it is normal for complete aircraft to be constructed for the sole purpose of taking them apart again, obviously after testing has been carried out. The VC10 was no exception to this rule. Looking at the production list for the VC10 it is easy to see that the first two construction numbers on the list never came close to a buyer or even an operator, these are the test fuselages constructed. But the story of the 'testing times' starts earlier; with the mock-up. VC10 full-scale wooden mock-up
In aircraft design the mock-up has an important place. In these modern times they are often made using plastics but in the VC10 days wood was the material of choice. The purpose of the mock-up is to transfer the ideas from the drawing board to the production line, and as such it is an important aid to designing an aircraft. It enables the engineer to plan in three dimensions, and provides a check on the layout of the thousands of integrated components which make up an aircraft. Besides this, it also serves as a demonstration of layout possibilities for the customer. Sometimes it is only in the mock-up stage that important decisions can be made. Specific dimensions in cabins, galleys and cockpits can easily be set on a drawing but until you can find out for yourself if a cupboard is positioned at the right height you cannot be sure if your design will really work when used on a day-to-day basis. Because of this the mock-up can get quite crowded as it is being built with many different designers wandering about, checking on the feasibility of their ideas or complaining about someone else's air-conditioning ducts positioned just where they wanted to put a box full of electronics. As an example, the VC10 mock-up featured a fully equipped flight engineers station which was used for night lighting trials amongst other things. The mock up also featured several areas were components such as the freon packs and pipework or the hydraulic reservoirs and associated components were trialed for fit and any interference issues. For this, the large components were also built out of wood and painted black. Besides the complete mock-up that is pictured on this page, a separate mock-up was built of the freight door for the RAF version of the VC10. This was probably used to test the size of the door against many different types of military cargo that the VC10 was destined to carry. The mock-up for the VC10 was set up, together with the 1-11 mock-up, in the mock-up hangar at Brooklands, or to use the official terminology: British Aircraft Corporation - Weybridge division. This mock-up hangar was a wartime structure that is positioned on what used to be the 'Finishing Straight' of the pre-war Brooklands racing circuit. This hangar is still in existence as the sole survivor on the Brooklands site. The ex-mock-up hangar is now the main hangar for the aircraft collection of the Brooklands Museum, and as such provides shelter to: Wellington R for Robert, the Vickers Vimy replica, Harrier G-VTOL and several other aircraft. In 2016/2017 this hangar was restored and moved off the finishing straight. It now houses the 'Aircraft Factory' exhibition. C/n 801A/801B - Forward fuselage test sections Two forward fuselage test sections were constructed for the VC10 in 1961. Both consisted of a section from the forward bulkhead to (approximately) the back of the forward freight hold. C/n 801A is a test section without a main deck cargo door. This test section is preserved at the Brooklands Museum as detailed below. C/n 801B is believed to be s a similar test section but with a large main deck cargo door. This section was only used for water tank testing and has not been preserved. The test sections were used to validate the fuselage design for the maximum pressure differential of 9 lb/sq in. There are two cases to validate here, the first being the maximum attainable pressure differential before failure, and the second the fatigue problems arising from the repeated pressurization cycles during its life. The possibility of fatigue problems in jet airliner's fuselages came to the public's eye in 1954 with the mysterious crash of de Havilland Comet I G-ALYP off Elba, Italy. After the second crash under similar circumstances occurred the Comet I was grounded, and a thorough investigation finally pointed to metal fatigue after repeated pressurization as the culprit. The Comet featured almost squared off cutouts for the windows and some other fuselage openings, and the stress concentrations in the corners of these cutouts gave rise to fatigue cracks after repeated pressurization. This problem had never surfaced before, mainly because the propliners of the previous era never flew as high as the Comet did and therefore the pressure differential acting on the fuselage was a lot less. Also, with the limited knowledge available about metal fatigue in those days, the Comet fuselage had been tested to 2 times the design pressure differential and when it passed this test it was thought that metal fatigue would not be a problem. In the Comet crash investigation a complete fuselage was placed in a water tank and repeatedly pressurized to simulate many flights, and after many cycles the fuselage eventually failed, providing the investigators with clear cut proof. This test was to be the benchmark for many such tests as all airliners since that day had to prove that they could actually withstand the repeated pressurization cycles for which they had been designed. This was until more sophisticated calculation methods, based on a better understanding of the fatigue problem, could be used instead of actual fatigue testing of an aircraft's fuselage To test the VC10's ability to withstand these problems Vickers had an excellent tool in the Stratosphere Chamber designed by Barnes Wallis. In the 'Strat Chamber' altitudes up to 80,000 feet could be simulated and thus the fuselage would be subjected to the same forces it would experience during its service life. Initially the fuselage carried out tests in a water tank as a failure in a water tank will be safer for the surrounding test equipment (including the personnel). In one of these tests of the forward fuselage section it was pressurized to failure, this occurring on a skin line between the side and top fuselage skin panels on the left side of the section. It was repaired and then tested for fatigue in the Stratosphere chamber. The fuselage section was used for a variety of other tests until the mid-1980 after which it was donated to the Brooklands Museum by the British Aerospace Weybridge factory in 1986. In 1992 the fuselage section was repainted in BOAC colours by British Airways. This was not the end of its days as a test article though as RAF St. Athan borrowed the fuselage section in 1996 to test a front bulkhead replacement. In return they made the fuselage section fully weatherproof, fitted perspex viewing panels to the underside of the section as well as cabin windows, and they also supplied the trailer on which the fuselage rests. In 2016 initial steps were taken to refurbish the test fuselage, this progressed slowly during the subsequent years. At the end of 2020, the test fuselage section was in the first stages of being repainted into the overall white scheme it carried during testing.
C/n 802 - Structural test airframe The airframe that was constructed for structural testing was not a complete airframe as it lacked the nose of the aircraft. It did however include the complete wing torsion boxes on both sides. This was a necessity as this airframe would be used to validate other features of the VC10 structure; the wings and centre section as well as the wing to fuselage attachment points. To do this the entire airframe was mounted in the so-called 'Cathedral frame' which could subject the airframe to forces similar to those encountered during flight from manoeuvres and turbulence. As with the front fuselage section the test airframe would also be subjected to both alternating loads to simulate many flight cycles and large static loads to validate the ultimate loads that the airframe could withstand. One such test case was validated on 22 May 1962 to clear the structure for the beginning of flight trials and this is illustrated in photo number four shown below. The text that accompanies the photo is as follows: "A complete VC10 airframe has been built for
static, fatigue and fail-safe tests. This picture was taken just before the
successful completion of a proof load test (two-thirds of ultimate) which
preceded first flight. The airframe was held down by several concrete blocks which were attached to the fuselage underside and the forward end through a steel frame and cables. This represented the weight of the airframe and the load carried by it, while the aerodynamic forces were applied through a multitude of pads which were firmly affixed to the top of the wings. Power for the whole test rig was supplied by a six-cylinder diesel engine which drove hydraulic pumps. A large array of pipework and valves transmitted the hydraulic pressure to several jacks which pulled the wings up through interconnected beams and cables, thereby simulating the lifting force on the upper wing surface. The test rig was controlled from a room in which the various pressures could be monitored as well as the stresses measured in the airframe, for this purpose several large plotters were running. A monitoring room was next to the right wing leading edge and this featured readouts for some of the pressures and stresses and also a relative safe place from which to observe the airframe during testing. A separate tailplane was also subjected to these tests in a smaller setup. After the static load testing was completed the airframe was subjected to a representative fatigue program in which alternating loads were applied to check out how the structure would 'age' during its life as an airliner. The final batch of tests were fail-safe tests in which alternate load paths throughout the structure were validated. The fail-safe principle states that in the event of a failure in the structure a second load path must be able to withstand the design load on the airframe, allowing it to operate in safety until regular inspections allow the failure to be rectified. The eventual fate of the test airframe is unknown to me, but as a spare VC10 airframe would probably not go unnoticed in someone's backyard I'm guessing that it was scrapped after testing was complete.
The Fuel Test Rig To test the fuel-feeding properties of the wing tanks a complete left wing and center section was constructed from mild steel as a test rig for the fuel system. With a test rig like this it is possible to tilt the wing and figure out whether the fuel will feed to the engines under all flight conditions. Optimal locations for fuel pumps can also be verified from this rig, and the amount of unusable fuel can be determined. The fuel lines to the engines but also refuelling points were included so that every conceivable situation could be simulated.
Not just the structure of the VC10 was tested, various other rigs were constructed for the systems that would enable the crew to safely operate the aircraft. One of the largest of these was the flight control test rig which featured a full size representation of the airframe with all the moving surfaces, control cables, Power Control Units (PCU) and a complete cockpit with all the relevant controls and indications. The test pilots who would carry out the first flight spent quite a lot of time in this rig trying out the controls and practicing the emergency drills which would be needed if for example a PCU would fail in flight. Another important decision which was made by them was how much friction was acceptable in the flight control system. Any control system with cables has a certain amount but it was up to the test pilots to decide whether it would impair the pilot's ability to safely control the aircraft as too much friction can actually make an aircraft unstable, as well as increase the work load of the pilot.
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