Bengaluru: The next key task for India’s Light Combat Aircraft Tejas is to undertake auto low-speed recovery (ALSR) flights. This is part of the last leg of activities towards the Final Operational Clearance (FOC), likely to be accorded to the programme, this December.

ALSR is a state-of-the-art-feature that guarantees complete carefree manoeuvring of the aircraft. In a conventional dogfight situation, the fighter jets need to perform extreme manoeuvres. To enable the pilot to concentrate on his combat task, the Tejas fly-by-wire system automatically limits the aircraft parameters to ensure no departure from controlled flight and also ensures that none of the structural limits of the aircraft are exceeded.

Unlike in a conventional fighter aircraft (MiG 21, MiG 27 or Jaguar), where the pilot has to continuously monitor all the parameters while doing combat, Tejas with this feature becomes completely carefree.

Engineers and designers from Aeronautical Development Agency (ADA), Hindustan Aeronautics Ltd (HAL) and the test crew from National Flight Test Centre are all geared up for this impending test.

The Initial Operational Clearance (IOC) version of the Tejas (16 fighters) already automatically limits many of the aircraft parameters. The only parameter not being limited automatically is low speed which the pilot needs to monitor in flight. But for the FOC versions, even the speed limiting is made automatic, making the aircraft carefree.

In this mode, the flight control system (FCS) continuously monitors the pilot's manoeuvres and once it detects that the current manoeuvre if continued for some more seconds could lead to a low-speed departure, it gives a warning to the pilot to take corrective action.

However, in case the pilot ignores this warning the auto-low speed recover function takes over control of the aircraft and recovers it to a safe condition in the shortest possible time.

The Tejas MK-I is capable of pulling up to a maximum of 8 G at 24 degrees Angle of Attack (AoA). Photo: Praveen Sundaram.

Professors and students from IIT Bombay assisted the ADA team to optimise the auto recovery procedures. The advantage of this feature is that it allows the pilot to fly at the limits of the aircraft capabilities by toggling on the low-speed warning during combat. However, it weaves around a safety net, if the pilot makes any error of judgement.

If pilots get disoriented

Another related feature in the FOC version of the control laws which is also being tested simultaneously is the Disorientation Recovery Function (DRF).

Pilots may get disoriented at times while flying into clouds or while flying over the sea. In such situations, a switch (panic button) is provided in the cockpit.

If pressed by the pilot, the FCS takes over the controls and recovers the aircraft to level flight optimally (with minimum loss of speed or altitude). Here again IIT Bombay is said to have done some cutting edge work in creating the optimal algorithms. Thus while the auto low speed recovery mode cuts in automatically, the DRF mode is engaged by the pilot when he needs it.

The trials for ALSR and disorientation recovery will be done in various air-defence and ground attack configurations.

As reported by Onmanorama earlier, Tejas had made its first ever air-to-air wet contact with an Indian Air Force (IAF) tanker over Gwalior in September this year.

A Tejas variant (LSP-8) made the wet contact with an IAF IL-78 tanker for the planned air-to-air refuelling. About 1,900 kg of fuel was transferred during the in-flight refuelling process at an altitude of 20,000 feet.

The scientists now say that during the subsequent air-to-air refuelling trials, up to 2,700 kg of fuel was transferred with the maximum fuel carrying load of Tejas being 4,000 kg.

“Air-to-air refuelling is one of the most difficult exercises for a pilot and is a high-gain piloting task. The FCS came out with flying colours during this tight tracking task and remarkably the pilot could achieve contact with the refuelling drogue in the first attempt. The skills of Tejas were also tested during Gagan Shakti (military exercise) and it changed the way IAF perceives the programme,” an official said.

The Tejas MK-I is capable of pulling up to a maximum of 8 G at 24 degrees Angle of Attack (AoA). The control laws (CLAW) are the defining factors that will help pilots manoeuvre safely during these situations.

Weapon trials on

Currently the Tejas team is embarking on final FOC weapon trials at Jaisalmer. Tejas has performed very creditably in the Flying Daggers Squadron during their weapon trials.

The accuracies of the weapon drops have been very good. While the air-to-ground bombs for FOC have been already deployed successfully, there is a need to have a statistical measure of the accuracy of each weapon, which is called as the Circular Error of Probability (CEP).

With the CEP, the Flying Daggers can then plan the number of aircraft and their configurations to ensure success in destroying an enemy asset. During the ongoing weapons trials at Jaisalmer, hundreds of bombs of different types are being dropped from Tejas to establish the CEPs.

With the FOC now at a striking distance, the Tejas programme has been surely heading with a clear flightpath in sight. The software fine-tunings will continue even as the FOC fighters start rolling out from HAL hangars. These fighters will be fitted with the fuel probe, GSh-24 gun and a SDR (software-defined radio) among others as mandated by the IAF.

(The writer is an independent aerospace, defence journalist, who blogs at Tarmak007 and tweets @writetake.)

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