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| Testing times ahead for HAL |
| Ajai Shukla / Bangalore Jul 05, 2010, 00:36 IST |
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The Russian designers stared transfixed at the monitor as the model of India’s Sitara Intermediate Jet Trainer (IJT) went into a spin, rotating like a fan uncontrollably. Despite every attempt to straighten it out with the aircraft controls, the Sitara kept spinning. If this had been a real flight, rather than just a “spin tunnel” test in Russia, both pilots in the Sitara would have died as the uncontrollable trainer smashed into the ground.
Instead, Indian designers at the Aircraft R&D Centre (ARDC) in Bangalore — which is designing and testing the Sitara — have tweaked the Sitara’s aerodynamics until it has passed the “spin tunnel” test.
But now, Chief Test Pilot Baldev Singh has to actually test-fly the Sitara, deliberately throwing the trainer into a hair-raising spin and then coaxing it into level flight again.
Only after that can the Indian Air Force use the Sitara to teach rookie pilots the vital skills needed to recover an aircraft from a spin. During training, IAF instructors will put the IJT into a spin and then hand over controls to the trainee, allowing him or her to stabilise the aircraft.
These are literally testing times at the ARDC, a unit of Hindustan Aeronautics Limited, which is preparing for several risky test flights that will determine the success or failure of its key projects.
Although the Sitara has cleared the “spin tunnel” test in Russia, that is no guarantee that the Sitara will recover from its first real life spin. Therefore, to minimise the risk to the test pilot, a special parachute is being fitted on the aircraft’s tail, which the pilot opens if he is unable to recover from a spin. Acting as an aerodynamic drag, the parachute retards the spin, allowing the pilot to recover control.
“There are always uncertainties in testing something for the first time”, explains HRS Prasad, the general manager of ARDC. “So we make doubly sure there is a system that will enable (the pilot) to recover from a potentially disastrous situation. But we are confident of demonstrating that the Sitara can recover from a spin… that is a basic requirement for a trainer.”
Even more dangerous are the flight tests ahead for the Tejas Light Combat Aircraft (LCA), to demonstrate its ability to handle higher angles of attack, or Alpha, as the designers call it. Simply put, a flying aircraft’s angle of attack is the angle it makes, nose to tail, with the horizontal. A high Alpha provides several benefits to a fighter, especially letting it fly slower to land on shorter runways.
The Tejas has currently tested an Alpha of just 22-24 degrees, and will go up gradually to 28 degrees. But flying a higher Alpha risks stalling the fighter; its engine could go off (or flame out, as pilots call it) leaving the Tejas, without propulsion power, or electrical and hydraulic power for its fly-by-wire controls, to fall out of the sky like a stone.
To guard against that, the ARDC is fitting a test Tejas with a fast-response power pack that US company, Honeywell, manufactures for such flight-testing. Within milliseconds of the Tejas main engine going off, the hydrogen-operated power pack starts up, providing power to the fighter’s hydraulic and electrical systems, and re-lighting the main engine.
“In flying a single-engine aircraft, there is no bigger emergency than a flame-out”, says a former Tejas test pilot. “But no fighter engine should flame out at just 28 degrees Alpha. However, the Tejas air intakes have not been well designed and, as the Alpha increases, the intakes constrict the airflow, and the engine dies for want of air.”
In contrast to the Tejas’ maximum Alpha of 28 degrees, India’s Sukhoi-30MKI can comfortably handle an Alpha of over 50 degrees. The US Navy F/A-18 Super Hornet can manage an Alpha of 58 degrees.
The Tejas flight test programme, India’s first such testing process, has been controversial, with critics charging that the slow speed of testing has delayed the Tejas’ induction into service. On the positive side, the Tejas testing has given birth to the National Flight Test Centre (NFTC), a test facility that is of global standard. The Aeronautics Development Agency (ADA), which oversees the Tejas’ development, has now engaged European aerospace giant, EADS, to advise on how to speed up testing.
“We have to proceed cautiously”, the Tejas programme director, PS Subramaniam told Business Standard, while witnessing a test last year. “We have managed to come so far without a single mishap. An accident would seriously damage the credibility of the Tejas programme.”
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