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Aviation History
1956
1956 - 1728.PDF
892 FLIGHT, 7 December 1956 MISSILE TESTING . . . mentioned, and also to investigate quantities not directly con- cerned with the main object of any particular firing. For example, it should be possible during the series of firings to check the performance of the sustainer motor, and also to measure the saturation temperature of the nose, the air pressure in and around the body and the vibration levels throughout the structure. One might expect a typical development programme to pass through the following stages: —(1) Stability and boost-separation trials—measuring in addi- tion such items as nose temperature and base pressure. (2) Sustainer-motor trials—also measuring internal tempera- tures and vibration levels throughout the structure. (3) Control trials: It is likely that these will begin by feeding in a pre-determined programme to check that the complete system operates properly during various manoeuvres and at limiting control-surface angles. Measurements would be taken of control-surface power, hinge moment and aerodynamic damping. (4) Guidance trials, either with or without the control equip- ment. At the end of the development period the near-production rounds would be fired against radio-controlled target aircraft— such as the Firefly U.8 and the Jindivik—and a number of rounds would be fitted with explosive warheads. At the end of such a programme the development of the basic missile might well be complete. Service evaluation is the next stage, for up to this point the eventual user has had to base his personnel and stores requirements on extracts from the reliability studies and similar documents produced by the manufacturer. The Services will therefore evaluate the weapon to confirm these estimates and will also examine every aspect of the operational performance of the system against various types of targets and under all kinds of climatic, geographic and other conditions, paying special attention to extremes of atmospheric temperature, moisture content and, in naval missiles, the effects of salty air and shipboard life. Large numbers of men have to be trained at this stage to carry out the various new specialist tasks. Unlike most other industries, that concerned with the develop- ment of guided weapons requires concurrent development of the measuring instruments used, so that there arises the peculiar situation of instrumentation determining the condition under which it will have to operate. Examples are the continued develop- ment of vibration accelerometers and of the telemetry transmitters associated with them. At times the answers obtained, although Taken from a Firefly U.8, this is believed to be the first photograph yet published showing a targets-eye view of a surface-to-air missile. Slight distortion is caused by the wide-angle (145-deg) lens. Clearly visible are the sun, the weapon's tracking flares, and the motor imoke-trail extending back to the distant Welsh coast. All photographs illustrating this article are Crown Copyright. later proved correct, are difficult to explain or even comprehend, and require a com- pletely new approach to the design. Stress levels may become unexpectedly high as a result of the extreme vibration which may be experienced in certain rounds, and fatigue is quite likely to cause the failure of at least one link in the complex guidance and control chain. It is therefore essential to provide a statistically evaluated number of spare missiles to take the place of diose which fail. In parallel with the flight trials a number of static tests have to be carried out in order to prove the ability of all the equip- ment to withstand one or more aspects of its future environment. Various compon- ents and complete missiles are vibrated through whole ranges of frequencies to determine the points at which resonance occurs and to reveal any inherent weakness. Other tests include temperature cycling, humidity tests, experiments in altitude chambers and tests which impose high accelerations or impulses. The latter are necessary to ensure that the complete air- borne system can withstand the shock of launching, and they are frequently carried out by dropping the items under investiga- tion on to lead blocks in special rigs while the performance of the equipment is monitored. Sustained-g tests are executed with the aid of large centrifuges. Not only do all such tests have to be made on the statistical number of specimens of every type of component after the com- pletion of design, but they also have to be completed, and any necessary modifications effected, before the components are required for flight. It is also necessary to test "production" com- ponents throughout the programme to ensure that the original design and workmanship is being adhered to. At various points in the development, complete missiles will be "fired" without ever leaving the ground. The launching and flight sequence will be simulated in special test-beds to confirm the performance of the motor and also to check the operation of all other equipment, including the effect of flame and smoke on radar and guidance signals and telemetry transmissions. The actual conduct of an individual trial depends on the object in view and on the methods of the establishment or com- pany concerned. Nevertheless, one principle remains unaltered throughout: the firing is part of a controlled experiment and must be conducted with the minimum of unknown factors. Not only is every development round most carefully manufactured and inspected, but even the most trivial departure from standard must be recorded, in case it contributes towards some unpredicted performance. Casual onlookers might conclude from observing such trials that, in view of the tremendous number of factors which can (and usually do) delay its departure from the launcher, the missile concerned would be utterly useless as a weapon. It is, however, inevitable that protracted pre-flight checks should be conducted both on the missile and on the great array of observers, radar, cameras and recording equipment through- out the entire range in advance of each firing, virtually none of which would be necessary in the firing drill of a Service weapon. Frequently a test firing has to wait for perfect weather condi- tions, because it is necessary for ground kine-theodolites to follow the missile for many miles down the range to enable the trajectory and other factors to be correlated with the estimated performance. High-speed photographs taken from the ground, or even from the target aircraft, provide valuable additional information and some- times gives the only clue to the solution of a problem. In operational service the conditions are entirely different. The sole object then is that the target should be hit; and high winds, fog, rain, "deviations from standard" (which should be negligible) and other factors can all be ignored. Should any missile fail, a good round must be fired at once to replace it. Investigation of the failure is a wholly secondary undertaking. R. A.
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