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Aviation History
1981
1981 - 0034.PDF
32 FLIGHT International, 3 Jonuory 1981 Letters The Gnat—not as simple as it seemed SIR—I was interested to read the editorial in your December 6 issue, advocating simplicity in advanced fighter concepts by combining new aerodynamics and avionics with a proven structural design and an exist ing engine. However, I think your chosen example, the Gnat, is not a good illustration. As one of the early Gnat-trained RAF pilots who went on to enjoy well over l.OOOhr rewarding flying as an instructor on the aeroplane, I would not wish to knock the aircraft which gave me and many others so much pleasure and challenge, even though the latter was not always planned! But the Gnat, joy though it was to fly, could hardly lay claim to sim plicity. On the contrary, it was a demandingly complex little aeroplane, an engineering nightmare. The longi tudinal control system in particular, with three different modes of pitch control, was the source of much difficulty for many. Some respected and experienced pilots never really mastered it; a few in the early days died trying. Most, who had only the fleeting association with the Gnat that the AFTS course brought, passed on to greater things still pondering the witchcraft of manual control in a dark and gusty circuit. Crosswind landings in manual control from the back seat gave rise to the original legend of the legless blindfolded epileptic one-armed paperhanger. Similarly, the mysteries of the fuel system were still being unravelled as the aeroplane passed out of RAF service. During the introduction of the SIR—A recent letter from Mr G. L. Gillet (November 15) described a growing problem within air traffic communications which he attributes to "sticking transmitters." T believe that a different but closely related problem is the real cause of Mr Gil- lett's increased periods of anxiety. With today's congested airspace the number of aircraft operating on a common VHF frequency can reach an uncomfortably high level. When this level is reached the chances of two aircraft making simultaneous trans missions are greatly increased. Simul taneous transmissions are a problem known to both pilot and air traffic controller and, even with the highest level of R/T discipline, will continue to add an unnecessary hazard to flight operations. The whistles and garbled voices created by these transmissions are, at least, an irritating nuisance, at worst, the cause of loss of life. Undoubtedly the worst case was the Pan Am/KLM disaster at Tenerife, in Hawk to RAF service I was OC Stan dards Squadron at Valley, and had the unique opportunity to assess con currently the performance of Gnat, Hunter and Hawk in the air and on the ground. I am left in no doubt that the Hawk is a far better example of simplicity in design, and without any significant decrease in airborne capability when compared with the Gnat or Hunter. In fact, in several areas of performance, the Hawk/ Adour combination is streets ahead. Admittedly one would like a few more knots at the top end of the speed- scale and also a bit more CL and greater thrust to drag ratio at high altitude. However, take a look at any Hawk low-level aerobatics demonstra tion and you'll see that neither are lacking in thick air. (Nevertheless, if you must go to high level you'll find the Hawk will cruise on for many, many more yards per pint than the Gnat, Hunter or most other jets. Indeed it will at any level.) Add to this a head-rattling rate of roll, 9gs worth of "Yug" (for the ham-fisted, masochistic or simply over- enthusiastic) before overstress checks are needed, very good cockpit visi bility, nicely harmonised controls, short take off and landing rolls, high crosswind tolerance, etc etc. But I have strayed from the point—sim plicity. Most Hawk systems are more straightforward than those of the Gnat (except perhaps the electrics). Reliability and maintainability are much better than the Gnat (or Hunter). Although the Hawk possesses a which 560 died and two 747s were destroyed. While the KLM crew were receiving pre-take-off instructions, an unknown transmitter was "keyed," causing the KLM crew to misinterpret the ATC's requirements. They mis takenly commenced their take-off roll and, in the fog, collided with the Pan Am aircraft which had been authorised to backtrack on the run way. I propose that a solid state device of known simplicity be incorporated as part of the existing circuitry of current VHF transceivers to preclude unintentional overlapping transmis sions. Should two flight crews initiate transmissions at the same "time," the millisecond reaction of the squelch circuitry of the "lagging" transceiver is able to detect that it has been pre ceded to the transmit mode. To pre vent the "lagging" transceiver from overlapping the "leading" unit, the transmit mode of this transceiver is finely tuned wing, nobody could deny the basic ruggedness of airframe and engine, which have resulted in an enviably dependable record in safety of operation. From many aspects, the Hawk has already surpassed the Gnat as the kind of example (without the supersonic machismo) to which you refer. Evidence of that example is partly shown in the RAF decision to arm some of its Hawks with Side winders for operational use in the Air Defence role. The Hawk is not yet the match we need to beat the F-5, and I don't know what the development potential is for improvements in speed and high-level performance, but it is a cheap, reliable and agile day-fighter/ trainer. It is proven in service and has a lot of life left yet. (Please note that this is a personal view and does not represent official RAF opinion or policy.) Bradenham SON LDR ROY GAMLIN Beeches High Wycombe Bucks immediately disabled. In spite of their attempt to transmit, the "lagging" crew are automatically advised that they have been "beaten to it" by their still active receiver, which is by now monitoring the preceding crew's trans mission. After the conclusion of this message they may initiate their trans mission. A feature of the device is that, should an "overridden" crew for any reason elect to transmit, the second of their two key actions will cause by pass of the device and enable normal transmission. The design of the device is such that no change is made to aircraft wiring. Incidentally. I have already modi fied a Collins 618M-1, which has proven the technical viability at less than the cost of a good headset. NIGEL M. CORRIGAN CIO Heli Orient (PTE) Ltd East Camp Seletar Airfield Singapore 2879 Simultaneous transmissions can be avoided
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