Screaming Skull
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It is the raison d’être for the Advanced Light Helicopter (Dhruv) with Shakti engines, and the very mention of the mission starts the adrenaline rush in a helicopter pilot.
Picture the stark landscape of the Siachen Glacier comprising just three colours: the Brown of the craggy mountains with peaks so sharp that they resemble fangs, the almost alien dark Blue of the high-altitude sky, and the dazzling White of the perennial ice cover. Then throw in a stupefying mix of high-air temperature and rarified atmosphere, add a postage stamp-sized helipad situated between deep ice crevasses at a geographical elevation of 5,940m (19,480 ft). The mission is to land on that postage-stamp helipad at a temperature of ISA+20 (-5°C), hover the helicopter Out of Ground Effect (OGE) with 200 kg of load and fuel for one hour of flying plus 20 minutes of reserve.
To add a further bit of spice as if all this were not enough, there are also tactical considerations in the approach and getaway due to extreme proximity of the helipad to a very ‘friendly’ neighbour on the west. Simply impossible you say? Well you were right — up to now that is. Demonstration of the mission was well beyond the performance envelope of most helicopters and in fact it was one of the reasons for development of the Lama (Cheetah) helicopter from the Alouette-III (Chetak) in the 1970s.
Although the Cheetah manages some payload in the hot summer months,it is unable to meet the above mission requirement. Also, its payload drops significantly in ISA+20 conditions at that altitude. The mentioned mission requirements appear beguilingly simple — however at those stated conditions, everything (aerodynamics, engine performance, control margins, handling and stability) tapers off to a point, usually well short of the target for most helicopters.
It is not just about additional power from powerful engines. There are helicopters that can fly at the required altitude. However, they invariably are at the limits of control margins, stability and handling due to their conventional hinged rotors, and therefore are practically not suited for such missions in the harsh flying environment which is invariably accompanied by extreme turbulence. Also, the technical trick is to translate the additional power available from the more powerful (but invariably heavier) engines into rotor thrust and still have a useful margin of payload. Usually, at that altitude, the power required by conventional rotor systems to hover with useful payload and fuel rapidly outstrips the power available from most turbine engines.
So, it is that sort of a target that would make most helicopter designers and test pilots frown, shake their heads and mutter darkly under their breath —“elusively out-of-reach and quite simply impossible”. However, the ALH was designed to stringent manoeuverability requirements specified by the IAF and Indian Army. Some of its capabilities are routinely demonstrated by the Sarang Display Team. In fact when various combinations of manoeuvres were initially tried out by this scribe as a former team-member to define the display manoeuvre sequences, there were always generous margins available on all controls.
The ALH’s highly manoeuverable rigid rotor system has some beneficial spin-offs at high altitude — good control power, good control margins and easier handling for pilots. The typical high-altitude sluggish handling and inertia in other helicopters is absent in the ALH. The controls remain crisp, with adequate control margins and good stability. The only compensation on approach to a helipad is to cater for the higher True Air Speed (TAS) and reduce the IAS appropriately at an earlier point.
On 11 Aug 2009, at 0750 hrs, the shrill whine of two escorting Cheetah helicopters mixed with the deeper roar of the ALH’s Shakti engines broke the morning silence on the glacier as the ALH-Shakti made an approach to the helipad.
The observed temperature was between -1°C and0° C (ISA+22) and Wg Cdr (Retd) Unni Pillai (Chief Test Pilot (RW), HAL) was at the controls with Lt Col T. Srinivas. The two experimental test pilots wereintensely focused on the difficult approach, which under the best of conditions usually approaches near white-out condition.
This was the beginning of the culmination of years of hard work by the dedicated team of designers, who had toiled hard to achieve the ‘impossible corner point’. They had strived to achieve the near-perfect mix of carefree handling of the ALH’s rigid rotor system with abundance of power from the Shakti engines at extreme altitudes. While ‘Srini’ called out the approach and reserve power parameters, Unni manipulated the controls and brought in the ALH to a hover over the tiny helipad.
On the approach, the ALH hadan equivalent mission payload of175 kg on-board. Unni brought in the ALH to a low hover, pulled up into a hover OGE, while Srini checked the power and other margins. After the sit-down, personnel from the post loaded upthe helicopter with an additional 160 kg and the crew pulled up the ALH to hover OGE above 12m (35 ft) on radio altimeter.
The hover was a tricky exercise — too low and they would be ‘in Ground Effect’ which would affect the accuracy of the test, and if too high, the crew would lose sight of the tiny helipad under the helicopter’s nose and would enter white-out. The crew observed the power margins and carried out a second sit-down. Another 80 kg was added and the ALH was hovered OGE for the third time. The power margin was adequate and so the crew carried out another sit-down and added a further 240 kg. The ALH was picked up for the fourth hover OGE. At that point, after catering for fuel burn during the successive hovers, the ALH had an equivalent of 619 kg of mission payload on-board, with fuel for one hour plus 20 minutes of reserve.
It was best summarised by the marshaller at the post who gave the thumbs-up to Unni and Srini, walked up to them after the last hover andy elled to them above the noise of the engines and rotors: “Jhahaz mein bahut dum hain (the craft has plenty of power)!” The ALH-Shakti had gone well beyond the mission requirement of 200 kg of load and had beaten the dreaded ‘corner point’.
It was an elated team of designers lead by Ms Rama Bhat who received thehelicopter back at Leh. The Chief Aerodynamist Mr Girish who had been into serious number-crunching into the late hours, notwithstanding the rarified atmosphere of Leh was especially happy since the performance had been as predicted. The team had also been supported very well on-site by representatives of the certification and inspection authorities. Team ALH-Shakti had proved true the ALH slogan — Any Mission, AnyPlace, Any Time.
(Gp Capt Nair flies for HAL's Rotory Wing Flight Ops team. He was commissioned in the helicopter stream of the IAF in December 1983. He has been associated with the Dhruv (ALH) programme, and commanded a combined Chetak-Cheetah unit in the Western Sector. He formed and commanded the Sarang Helicopter Display Team comprising Dhruv helicopters, during 2003-2005. He served as Chief Operations Officer, in an IAF base in the North-East)
Courtesy: LiveFist
Copyright: HAL
