A long way to fly

Published : Sep 24, 2004 00:00 IST

The successful inaugural flight of Saras does not in any way alter the fact that India's first indigenous civilian aircraft has a serious problem to be solved before it can achieve its design goals.

in Bangalore

SARAS, India's first indigenous civilian aircraft, designed and developed by the National Aerospace Laboratories (NAL) of the Council of Scienctific and Industrial Research (CSIR), made its formal inaugural flight on August 22 in Bangalore in the presence of Kapil Sibal, the Minister of State for Science and Technology. Other key figures who witnessed the flight included R.A. Mashelkar, Director-General of the CSIR, V.S. Ramamurthy, Secretary of the Department of Science and Technology, and the directors of the various CSIR laboratories attending the CSIR Directors' Conference which took place during August 20-22.

The smooth flight, with clean take-off and landing, was, however, a subdued event. It lasted only 17 minutes and achieved an altitude of 900 metres much lower than the over 2-km altitudes achieved in the test flights in the run-up to the inaugural flight. The speed achieved was about the same, about 250 km. The aircraft veering off the runway on landing during its third test flight on July 19 may have been one of the reasons for the caution exercised, one NAL scientist remarked. Though the incident was explained as a "minor problem in direction control", it did result in the cancellation of the originally scheduled inaugural flight on July 24. The August 22 flight was the seventh flight of Saras which had logged a total flight time of three hours in the six earlier flights.

Saras is a 14-seater light transport aircraft envisaged to play multiple roles like feeder line aircraft, air taxi, ambulance, executive aircraft, aerial survey and reconnaissance. The original design values for its payload-range capabilities are 400 km with 18 passengers, 1,200 km with 14 passengers and 2,000 km with 8 passengers. Its design specific range is a high 2.5 km/kg of fuel and the operation cost is a low Rs.5/km.

The successful flight did not in any way alter the fact that the aircraft has a serious problem to be solved before it can achieve its design goals and become the prototype for production (Frontline, July 2). As against the design value for the empty aircraft of 4,125 kg, it currently weighs 5,118 kg, a near 25 per cent increase, which will affect its range, fuel carrying capacity and fuel economy, and, most important, its design payload capacity of 1,232 kg. As a result the payload-range characteristics have already been scaled down to 400 km for 14 passengers, 800 km for 12 passengers, 1,400 km for 8 passengers and 2,000 km ferry range with only crew. Indeed, all the seven flights so far have been only with four seats (and no other fittings) and a three-member crew.

A part of this increase (150-200 kg) has been attributed to the changed requirements in airworthiness standards (from FAR-23 to FAR-25) of the Directorate General of Civil Aviation (DGCA) for light aircraft carrying more than 10 passengers and another part (of a similar order) to alternatively sourced equipment and parts consequent to the U.S. nuclear sanctions. However, it still leaves a large increase for NAL to rationalise it as conservatism in the design and tolerance margins provided, notwithstanding the fact that this is the first civilian aircraft to be designed in the country.

"There was no legacy database to fall back upon as in established design houses like Boeing, Airbus Industrie etc.," says T.S. Prahlad, former NAL Director and Saras project director. According to him, the concept of `suit on assembly' was adopted consciously, to be optimised later for the production standard. Apparently, a reduction of 200-300 kg is possible by fine-tuning structural design, increased use of composites and optimisation of margins, electrical looming and so on. But that still leaves a significant increase. Also, it needs to be pointed out that Hindustan Aeronautics Ltd. (HAL), a partner in the venture, has been in the business of licensed production of aircraft and aspects of weight control would have been known to its engineers from experience.

"You cannot be afraid of going back to the drawing board in a complex programme like this, even though one ideally wants to avoid it," Prahlad adds. But in this case, going back to the drawing board has meant a change in the basic unit of the engine itself that naturally would result in significant time and cost overruns. The all-up production weight has now been placed between 6,900-7,100 kg as against the original 6,100 kg. Consequently, the originally chosen 850 hp PT6A-66 Pratt and Whitney engine is sought to be replaced by a 1,200 hp engine of the same PT6A family.

According to Prahlad, the second prototype (PT-2) will be built around the new engine.

According to NAL, besides providing a higher lift, the new engine will also meet the more stringent FAR-25 climb gradient requirements under conditions of one engine failure. Apparently, the basic structure and the landing gear have enough margins to handle this increased all-up weight. "A new structural specimen will be built and tested, if necessary, some limited flight testing will be done with the optimised aircraft of production standard to obtain the final DGCA certification," Prahlad says.

But when queried in detail about what kind of changes this would entail in the aircraft design and what kind of optimisation exercises are being envisaged, Prahlad says: "NAL is seriously addressing all the design optimisation issues. When the second prototype (PT-2) gets ready, we will have a much better grip on the whole issue for a more detailed analysis and discussion.

Stating that the criticism on the weight issue has been rather unfair, Prahlad says: "The first flight must be seen as an overall system engineering triumph, especially when it is done for the first time against many odds." He is confident that NAL will achieve performance success by the time Saras enters the market. "NAL is proud of what it has done and there are no apologies. We do realise, however, that there can be improvements - both technical and managerial and we will incorporate them in the programme as we go along," Prahlad says.

Clearly confident of NAL achieving success, the Indian Air Force has already placed an order for six aircraft and is expected to place an order for four more. For a limited series production, the CSIR has proposed the creation of a Special Purpose Vehicle (SPV) involving the CSIR, the HAL and private industry. NAL's expertise and confidence notwithstanding, it would seem a bit premature to moot a project to build a 50-70 seater civilian aircraft, as it did at the inaugural ceremony. It was equally early for HAL chairman N.R. Mohanty to seek a firm order of 30 Saras aircraft from the government to establish a full-scale production facility, which Kapil Sibal has promised to put before the government.

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