By Wg.Cdr.P.Ashoka
The Gnat mk1 made its appearance in the Indian skies in the late Fifties, when transonic aircraft with powered flight controls were first procured by the Indian Air Force. These were the French Mystére IV, the British Hunter, followed by the Gnat from a British Company called Follands.
The Gnat handling flight was formed in January 1960 at Kanpur with the task of flight evaluation of the aircraft before it entered squadron service with IAF. It was a part of Aircraft and Armament Testing unit (A&ATU), later to be renamed Aircraft and Systems Testing Establishment (ASTE), now located in Bangalore. The Handling flight consisted of three pilots initially – Sqn Ldr MSD Wollen, Flt Lt VK Singh and Flt Lt P Ashoka, who carried out the bulk of flying. Two other pilots joined later for short periods – Flt Lt .Jakatdar and Flt Lt Satwant Singh. The mother organization i.e. A&ATU, was commanded by Wg Cdr S Das, the legendary test pilot, and had a number of other pioneer test pilots on its strength – Sqn Ldr CKV (Chandu) Gole, Flt Lt IM Chopra, Flt Lt A Sudhakaran, Flt Lt MW (Chuchu) Tilak and Flt Lt Jagat Mohlah. We in the Handling Flight were the only 3 Non-test pilots in that group!
Sqn Ldr Mally Wollen (who later became Air Marshal and after retirement, was appointed Chairman, HAL) was a renowned fighter pilot with tremendous energy and commitment. Flying under his stewardship was not only educative but also very challenging. Flt Lt VK Singh was an excellent fighter pilot and a great friend of mine. We were both bachelors then and roommates in the Officers’ Mess at Chakeri. We did a lot of vigorous flying together which was both exciting and rewarding.
During the tenure of the Gnat handling flight from January 1960 to July 1961, we carried out all the operational exercises that the aircraft would be required to do in Air Force Service. These included general handling of the aircraft, aerobatics, formation and tactical flying, dog fights, air to ground weapon delivery i.e. gun firing, rocket firing and bombing, as well as air to air gun firing on a towed target. All the weapons work was done either at Tilpat range near Palam or at Air Force Station, Jamnagar. The Gnat Handling Flight was disbanded in July 1961, when the first Gnat squadron (No.23 squadron) was formed at Ambala.
Now to the Gnat aircraft itself. If I were asked to use one word to describe flying the Gnat, it would have to be simply DELIGHTFUL. That does not mean easy or necessarily pleasant, but just plain thrilling. It was partly its naughtiness that made it such an attractive challenge, and hence its taming so rewarding. The basic design concept of the Gnat was to have a small and light fighter aircraft with excellent performance. Small and light makes it cheaper to produce, and of course, less visible to the enemy. It was about 6200 lbs in weight, a mere third of LCA type of light fighter, and had a 4500 lbs thrust engine. In order to make it small and light, a number of unique concepts were used. The cockpit had excellent visibility but was very compact and cramped. Small sized pilots felt snug and cozy in it, but for heavier and taller pilots, it was a real squeeze ! It had a light weight ejection seat, which did not have ground level ejection capability – a few pilots lost their lives on this account. Of course, this was rectified in the Ajeet. The pilot’s sitting posture was quite unique, as his legs were close to horizontal. This gave a sizeable advantage in terms of ‘g’ threshold in tight turns, as the blood from upper body did not flow down to the lower limbs quite as easily as it did in more ‘dining chair’ like seats. Consequently, the pilot could hold tighter turns without the risk of ‘blacking out’ – a clear advantage in close combat. Not only, that, its high power – weight ratio enabled it to sustain a healthy 7g turn through 360 degrees at speeds around 400 knots. The high power weight ratio also gave it an exhilarating rate of climb of around 10,000 ft per minute, almost double that of other contemporary fighters. The nose would be way up into the sky and the altimeter would wind up at a rate not seen earlier !
But the high power of the Orpheus engine (for its size) required a relatively higher pressure across its air compressor, leading to certain complications. Since all compressors have a limit to the pressure ratio that they can handle while maintaining smooth airflow through the engine, this limit was more easily reached on the Orpheus engine. It was thus necessary to have a device to ensure that this limit was not crossed – it had a Pressure Ratio Limiter (PRL) to do this job. The PRL would automatically reduce engine speed to keep the pressure ratio from going beyond limits. During test flights, if the PRL setting was high, we would get an abrupt engine failure, and many Gnat pilots would have had such an experience. Fortunately, the engine restarting system was almost always successful and a safe landing was normally possible. Another novel feature of the Orpheus engine was the fact that it was started with compressed air supplied by a ground trolley. Not only did this make the engine starting system very simple indeed, but what is more, it made for an astonishingly quick start up. This enabled the Gnat pilots to ‘scramble’ for interception in an unbelievably short time. I had once attained a timing of 45 seconds from ‘scramble’ order to getting airborne !
The Gnat had no separate flaps for landing. But to get similar lift benefits, the ailerons (for lateral control) would droop down through a mechanical linkage, whenever the undercarriage was lowered; and act as flaps in addition to acting as ailerons. Also, the wheel brakes were simple car type brakes operated by master cylinders located behind the rudder pedals – there was no complex brake system as such. Also, there was no anti-skid device in the system. In spite of such simplicity, we operated happily from a 1700 yard runway at Kanpur.
The Gnat had a unique system for longitudinal control, with an integrated control unit called Hobson Unit. This unit enabled both hydraulic as well as electrical operation of the tail plane. The datum of the tail plane was altered electrically by operating a switch on the pilots’ control stick. Subsequent movement of the tail plane away from the datum was achieved by fore and aft movement of the stick. However, the authority of the control stick was limited. Thus, depending upon what tail plane angle was likely to be required, say, for landing, the datum had to be appropriately adjusted early enough to ensure adequate control during landing ! The system also implied that irrespective of where the datum was set (by tail plane trimmer), the stick would always be in neutral position. Such control system characteristics were quite unique, and the design for the same was ingenious ! However, the flight control system as a whole gave a lot of technical troubles and was not popular with the hard worked maintenance staff.
To end the story, notwithstanding the problems it gave, the Gnat would remain etched in the minds and hearts of its pilots as an irrepressible machine, and a delight to fly !