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Aviation History
1962
1962 - 0226.PDF
228 FLIGHT International, 8 February jofo INDUSTRY International Flight Systems Products Company News Right Systems Rotax Garrett ADCs By the formation, as part of a planned diversification, of a joint company with the Garrett Corpora tion, Los Angeles, California, Rotax can now design and produce in England air data computers based cm the very success ful AiResearch models. The American company has been active in the field for some time and has designed central air data computers for the A3J Vigilante, F4H Phantom, Canadian, NATO and Japanese versions of the F-104, the XB-70 Valkyrie and for the now defunct F-108 interceptor. With the exception of the XB-70 unit, all of these are in quantity production and some of them are of the so-called "second generation," miniaturized type, weighing half as much as earlier units of equivalent capability. AiResearch are also making strenuous efforts to enter the civil market, where commercial jet trans ports are raising their own special problems. As a first step, prototypes of a lightweight, short 3/8 ATR size unit with outputs of t.a.s., i.a.s., Mach number and altitude were made, and have been turned over to operators such as PanAm for operational evaluation. PanAm alone has completed nearly 2,000 hours flight and ground testing. It is noteworthy that computers for the F4H and A3J weigh about 401b, whereas the "second generation" unit for the F-104G weighs 251b. Both have outputs of pressure height, rate of change of height and for height-lock datum, total pressure, impact pressure, Mach number, Mach number rate, Mach-hold datum, t.a.s., angle of attack and density ratio. Primary quantities sensed are ratio of static to dynamic pressure and static pressure, angle of attack and total temperature. Mach number is related directly to pressure ratio, whereas the differential P-S is related to i.a.s. Accurate Mach number provides accurate t.a.s. and also, with angle of attack, provides an accurate correction factor for static pressure. Angle of attack is also useful for judging approach speeds at widely varying landing weights. All the basic computation is performed with only three synchros. Digital computation was considered, but was rejected because the outputs are in any case required in analogue form. Computations are done with mechanical gears and cams which translate the sensor movements into output shaft rotations. Garrett have prepared elaborate curves of the fundamental relationships between various parameters and the two-dimensional cams can be replaced in 24hr to allow for different errors arising from a change in pitot head and static port characteristics. Gear and cam modules have been designed for rapid installation, and the outputs are in the form of syncjiros and potentiometers, mostly the latter. Outputs can be provided for flight instruments, inertial navigator, autopilot, in-range computer, bombing system, Position and Homing Indicator, fire control and undercarriage warning circuit. The sensors have an extremely low thres hold, O.OOlin of mercury change in pressure giving a useful output signal and 0.001 change in Mach number giving a change in S : P ratio. Rotax state that the accuracy of their force balance beam sensor is approaching the limits of present test equipment and that only the most accurate equipment is capable of checking the sensor. Garrett have worked for some years in this field in an intensely competitive market. They feel able to offer, for both military and civil applications, air data computers as advanced as any now available. Rotax Garrett Ltd have all the know-how at their disposal. A prototype can be prepared in six months, and a flight unit in nine months. All the modules of the AiResearch air data computer (see "Rotex Garrett ADCs," above) coupled for initial calibration. Note the extensive use of gears and two-dimensional cams, together with potentiometers. Right, absolute-pressure sensor of the computer. The output shaft is brought out through the front of the unit. The paper clip gives scale
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