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Individual Histories - The Test Specimen
Inside the VC10 forward fuselage test section Photo J. Hieminga 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 set 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. Besides the complete mock-up that is pictured above, a separate mock-up has been 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 one of only two that are still in use on the 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, Viking G-AGRU, Harrier G-VTOL and several other aircraft. Forward fuselage test section
The forward fuselage test section that was constructed for the VC10 consists of a section from the forward bulkhead to (approximately) the back of the forward freight hold. The test section was 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 it's life. The possibility of fatigue problems in jet airliner's fuselages came to the public's eye in 1954 with the mysterious crash of deHavilland 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. Still the fuselage also 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 the final 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. The failure can still be
seen as the fuselage section is preserved at the Brooklands Museum,
repainted in BOAC colours. The picture at the top of this page was taken there
during the summer of 2000. 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 another feature 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 non-alternating loads to validate the ultimate loads that the airframe could withstand. One such test case is illustrated in the second photo shown on the right. 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 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 final test that is usually carried out on these airframes is
loading of the wing to failure, and obviously the result of this is quite messy.
Preservation of the structure after these tests is therefore not really a good
idea. The sight of a wing failing is actually quite impressive, if footage
exists of the VC10 tests and someone is willing to provide a copy please let
me know. The Fuel Test Rig
To test the fuel-feeding properties of the wing tanks a complete
wing was constructed from mild steel as a test rig for the fuel system. With a
test rig like this it is possible to tilt and bank 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. |
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