Blade folding in indigenous naval advance light helicopter: what ‘automatic’ vs ‘manual’ mean

Photo: An indigenous Indian naval Advanced Light Helicopter landing on a warship deck.

By Commander K. P. Sanjeev Kumar

(Editor’s Note: A debate is raging on the suitability of the indigenous Advanced Light Helicopter (ALH) for an Indian Navy warship. This article is from an expert naval aviator and is a very important contribution for readers to understand the technical issues involved in the debate. The Defence Acqusition Council (DAC), the highest procurement decision making body in the Indian Ministry of Defence, was to meet in May 2020 to take a call on progressing with the Strategic Partnership (SP) project to buy and build 111 Naval Utility Helicopters in India for $3 billion. The meetings were postponed as the Department of Defence Production was pushing for including the state-run Hindustan Aeronautics Limited (HAL), as a bidder in the acquisition that was originally envisaged as private sector-only project through a DAC decision of 2018. This last minute interference in the SP project is delaying a decision in arming the Indian Navy with the NUH it badly needs to boost operational preparedness.)

This is a short post to address a debate that came up in media about main rotor blade folding requirements of naval variant ‘Dhruv‘ ALH.

The Naval Staff Qualitative Requirements (NSQR) for ALH were released in 1985. Messerschmitt-BolkowBlohm (MBB) of erstwhile West Germany was HAL’s design consultant in initial years (1984-94). Similarities between MBB’s BK 117 helicopter and the ALH are evident at first glance.

Air Marshal M. Matheswaran‘s paper in the Manohar Parrikar Institute for Defence Studies and Analyses (IDSA) on ‘ALH Dhruv and the Indian Helicopter Industry‘ is recommended reading before delving into single service issues. Another paper by test pilot Group Captain (Retired) Hari Nair, who has been associated with the ALH programme since 1992, presents design and tri-service challenges imposed on the programme. It can be accessed here.

With a hinge-less main rotor system (rigid rotor), four composite main rotor blades designed for high agility, integrated dynamic system (IDS) for battle survivability, and many challenging tri-service specifications, a simple and quick main rotor blade folding system — one of navy’s primary, non-negotiable requirements — already posed a design challenge from early days. So did the folded width, with three out of four blades having to fold backwards from the hub.

When first signs of trouble with manual blade folding system started to emerge, many rounds of discussion took place to explore if something can be done to ease the pain. Incremental changes based on feedback from the field were implemented. Life onboard a ship is hard enough without adding needless complications. Design has to cater for this reality.

Automatic blade folding system is a complicated electro-hydraulic mechanism with concomitant weight penalty. It is arguably difficult to build this into the small, hinge-less rotor system of the ALH. Auto-folding becomes “essential” in the larger naval helicopters such as the SeaKing 42B, Merlin HM Mk-2, or CH-148 Cyclone. Their large, heavy blades cannot be ‘manhandled’ without serious risk of damage to man or machine (rotor diameter often extends beyond ship’s deck edge).

Short, squat helicopter designs such as the Kamov 28 have fully articulated, small diameter, 3-bladed, coaxial rotors with a simple, manual blade folding system. Conventional helicopters in the 5-ton to 5.5-ton category do not accomodate fully-automatic blade folding; neither was it ever called-for in the naval ALH. Such a requirement does not exist for the 5-ton Naval Utility Helicopter (NUH) either.

NSQRs are “essential”, “must have” requirements that go through several iterations (draft, preliminary, joint SQR, etc) before finalisation and formal approval. ALH NSQRs never included a self-contained, automatic blade folding system.

Naval specifications were broad-based and only called for a simple and quick blade-folding solution. Extended parleys did take place between the navy and the HAL on the need to simplify the blade fold procedure. Meanwhile, the project gathered momentum; crossing crucial milestones; and closing some critical options for the navy variant.

In due course, the manual blade folding procedure on ALH evolved; with props like ‘bearing offloading device’ to take blade’s weight off the elastomeric bearings during folding, ‘big bolt’, ‘main bolt’, ‘small bolt’, a large number of spares, tools and accessories. Two decades later, the manpower and parts-intensive process, even after several improvements, still remains complex and impractical across the full spectrum of naval ships and operating conditions (day/night, heavy seas, small decks, etc).

The 2-segmented blade proposal, a rudimentary example of which is available on the Chetak (Alouette III) for the last 50 yrs, has now been offered for naval ALH by HAL. This blade design, meant for stowage and air transportation, is already flying on the Light Utility Helicopter (LUH).

The naval ALH blade-fold problem is thus intimately connected with basic design of ALH rotor head and rotor system optimised for Indian Air Force and Indian Army requirements. Why did navy go along with this? There are many reasons; prime among them being institutional support for an indigenous project. Why did HAL never call out this design contradiction? I don’t know. However, recent comments by officials do admit that mixing so many requirements on a single platform was “not possible”.

ALH was India’s first twin-engine light multirole helicopter. It was a learning process for all participants. It may be fashionable to say ‘navy was never interested in ALH’ or ‘navy loves imports’. But it is patently unfair and completely untrue. It does grave injustice to the sweat and toil invested by designers, test crew, operators and stakeholders from both sides into this maiden project.

The Indian Navy has remained engaged with ALH and continues to do so even today. From an initial order of over a 100+ ALH, navy almost closed the project, only to revive it ith orders for 16 more Mk-3 ALH in shore-based role. ‘Orders-versus-investment in new design’ is a ‘chicken and egg’ conundrum. A world-class manufacturer should target global customers. This is unlikely to happen if domestic customers are unhappy. Being dismissive doesn’t help either.

Finally, every helicopter is but a bundle of contradictions held together by the glue of extreme engineering. Going forward, all sides must learn to differentiate between “essential” and “desirable” requirements and clearly identify the fine line between science and science fiction.

No world-class product can develop in an atmosphere of mistrust. While the services have been “fighting with what we have”, it is time to reflect where such slogans often land us. Institutional memory is short. Past pain is easily forgotten. As we move towards increasing self-reliance in aerospace and defence, both sides must keep promises, demands, and expectations realistic. The blame game benefits nobody.

(The author is a retired Indian Navy aviator and an Experimental Test Pilot. The article was originally posted on his blog and is being republished with permission.)

1 reply »

  1. The LCA project started almost same time as ALH and the helicopter was inducted to the armed forces long time back compared to induction of LCA.Why and how did it happen ? The lessons learnt must be taken into account for all the stake holder for the future aircraft/helicopter design.

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