From: gnreddy@cbnewsf.cb.att.com (G.Narotham Reddy)
Subject: India's New Advanced Light Helicopter - Technical Details
Organization: AT&T
Date: Thu, 10 Sep 1992 13:25:49 GMT


In fact, while many of the latest helicopters from the companies 
in advanced countries have some of the features supported by the ALH, 
but none has all the new features that this radar evading aircraft boasts of.

* HAL's Advanced Light Helicopter

June 29, 1992 was a red letter day for the Bangalore-based aircraft
manufacturing company, Hindustan Aeronautics Ltd.  On this day, after
a gap of nearly 15 years, a state-of-the-art aircraft, fully designed
and developed within the company, rolled out for flight trials.
( Infact, it was tested sometime in the first week of September).

The aircraft is the Advanced Light Helicopter(ALH), designed for
multi-role application in both defence and civil operations.  Designed
for a maximum take-off weight of five tonnes, the ALH is a long range
(800 km with 20 minute fuel reserve) helicopter incorporating the
latest thinking in airframe, rotor system, blade technology, flight
control and survivability features.  
	In fact, while many of the latest helicopters from the companies 
in advanced countries have some of the features supported by the LAH, none 
has all the new features that it boasts of.
	Extensive use of fibre composites is one of the main features
of the ALH.  Fibre comprising very fine fibres(typically ten microns
in diameter) of glass, carbon, kevlar and the like laid in a matrix of
epoxy resin. After hardening at controlled temparatures and pressures
in autoclaves, these materials achieve much higher strength to weight
ratios compared to metallic alloys.  The HAL is one of the few
companies in the world to have mastered this advanced process
technology and has a large, well-equipped facility at its Bangalore
complex to make aircraft components out of fibre composites.
	For military aircraft, an added advantage besides the overall
weight reduction of using fibre composites instead of metallic alloys
is that these materials absorb radar waves and render the  craft
'invisible' to radar surveillance.  The designers of the U.S stealth
bomber utilised this principle.
	The ALH has as much as 60 per cent of the surface area made up
of composite components. While many other brands of helicopters use
fibre for secondary and decorative structures, the HAL has for the
first time deployed these materials for primary stress bearing
structures such as the tail boom which uses a carbon composite.
	Thanks to the high usage of composites, the structural weight
of the ALH is 20 per cent or so less than what it would have been if
metal alone had been used.  This aircraft (without fuel) weighs only
2.5 tonnes and can carry a load of 2.4 tonnes, the highest in the
world for its class of helicopters.
	A number of new concepts have gone into the rotor system
design of the ALH. Unlike in the conventional helicopters, the main
rotor is hingeless. This rigidity ensures smooth, quick response from
the rotor to controls exercised by the pilot and much less vibration
induced by the rotor action. The four rotor blades are coupled to a
composite hub which incorporates a ingenious elastomer layered bearing
to absorb the oscillating movement of the blades in their own
flexure. Since there is no metal-to-metal contact or rotating contact
as in conventional bearings, this elastomeric bearing is maintenance
free.
	Yet another innovation which makes for lower maintenance
hassles is the bearingless tail rotor. In this, the rotor blades
consist of two spars joined in the centre.  Each spar has a fibre
composite blade moulded over both ends in the form of a tight fitting
glove.  Since the two blades at either end are part of a single beam,
the centrifugal forces during rotation are counterbalanced and the
twist is self-compensated.  This obviates the need for a bearing which
would require regular lubrication and replacement from time to time.

	Two features of the ALH which are yet to make their
appearance in any of the other modern helicopters available aboard are
the integrated Dynamic System(IDS) and the Anti-Resonance Isolation
System(ARIS) with six degrees of freedom.  The IDS comprises a compact
and short power transmission system between the engine and the main
rotor. This is why the main rotor blades are much close to the
fuselage in the ALH than other helicopters. Thanks to this, there is
much less vibration caused by the rotor action on the fuselage.
	The ARIS is a highly ingenious device with a carbon fibre
composite spring and diaphragm which isolates the vibration from the
engine and transmission. This protects the control instrumentation
from premature failure.
	The ALH is powered by two turboshaft engines (Turbomeca TM
333-2B), each capable of providing 747 kilowatts of power which enables
the helicopter to perform excellently in hot and high conditions. The
ALH has a cruising speed of 245 km/hr and a maximum continuous rate of
climb of Nine meters/second.
	This modern, modular, compact engine is equipped with Full
Authority Digital Electronic control(FADEC) which automatically
maintains high fuel efficiency for all power demands on the engine.
The specific fuel consumption of the ALH at 313 kg per kwhr is the
lowest in the world for helicopters of similar capacity. The ALH has
an endurance limit of 3.8 hours of flying time (with 20 minutes
reserve) which is the best for its class of helicopters.
	While the engine is at present being made by turbomeca of
France, the HAL plans to produce these engines at its Bangalore
complex in course of time.
	The ALH incorporates a number of survivability features such
as crashworthy fuselage, armour protection, self-sealing fuel tanks,
twin engines, duplex automatic 4-axis flight control system,
transmission module with 30 minutes dry running capability, large
vertical fin enabling continuation of forward flight even with damaged
rotor and low radar signature due to extensive use of composites.
The ALH can operate in adverse environmental conditions, be it sand,
rain, snow, ice, lightning or extreme temparatures. It can operate
with equal ease over sea, and at hight altitudes.
	The ALH can be outfitted for a variety of applications. It is
agile enough to operate in restricted areas like small ship decks or
off-shore rigs. With its two meter wide body, spacious and quite cabin
which can seat as many as 14 passengers(including two crew), sliding
doors, emergency exits, the ALH fits will into civilian roles such as
search and rescue, air ambulance, air taxi and police work.
	These is an Army/Air Force version with fuel tanks able to
withstand small arm bullets, infra red suppression, flame supressor
device and night attack capability. A navy/coast version comes with
tricycle retractable landing gear, foldable tail boom, stubwing to
accomodate landing gear, loads and batteries and harpoon system for
deck lock.
	The ALH project has been nearly eight years in the making and
some 750 engineers and technicians have been involved in the design
and development. Technical support has been received from Eurocopter
of Germany. Not only is the final product at par or even more advanced
than the latest offerings from the developed countries but, according
to HAL sources, the cost of the project has been not even one-fifth of
what it would have cost a developed country to design and develop a
similar aircraft.                              [ Source: The Hindu ]

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