The Indian Navy’s Dhruv: falling between two stools

by Ajai Shukla

Prodded by questions from visitors to this blog, I have spoken in some depth to the Indian Navy as well as to the designers of the Dhruv Advanced Light Helicopter (ALH) at Hindustan Aeronautics Limited (HAL) about why the Indian Navy remains reluctant to accept the Dhruv into service; and also about what HAL has done to address the issues that the Navy has raised.

So here are the findings of this quick enquiry.

Currently there are 8 Dhruvs on the Indian Navy’s inventory. They operate mainly on communications, training and administrative duties from shore-based airfields. The navy does not plan to order any more Dhruvs.

The Navy believes that its helicopters (hereafter helos) must all have the capability to land on the deck of ships. That is in contrast with some brown-water navies that find it perfectly acceptable to operate the bulk of their aircraft primarily from the shore. For a helo to operate from a ship, the navy is demanding three additional “specific-to-navy” criteria

1.   Strengthened Undercarraige.  The undercarriage must be specially adapted for deck landings. Unlike landing on terra firma, where the impact is primarily in one dimension (that of the weight of the helicopter impacting on hard ground) a ship is moving in three dimensions (roll, pitch and yaw) and the undercarriage must be capable of absorbing the impact of landing in all three dimensions. The navy says that the Dhruv’s undercarriage does not meet that requirement.

2.   Folding Main Rotor.  An on-board helo has to be accommodated into a very small hangar space, which means that the main rotors must have a system of hinges, which allow them to be quickly folded before putting the helo into the hangar (and then, equally quickly, unfolded when it is brought out for another flight). The navy’s initially stated requirement was for the rotors to be folded within a width of 3.5 metres.

Furthermore, the navy wants an automatic blade folding facility, of the kind that is installed in its Sea King helos. In this, onboard electrical or hydraulic actuators fold up the blades quickly, rather than having to go through the longer and more painstaking process of manually folding the blades. Remember, that in the smaller warships, the tips of the main rotor blades extend beyond the deck, overhanging the sea. So manually folding them --- by removing bolts and supporting the blades during folding/unfolding --- is an exercise that the navy would rather avoid.

HAL had a problem with foldable blades, as well as with installing an automatic system. A senior Dhruv designer told me, “the requirement of Blade Folding with a width of 3.5 metres was not feasible due to the inherent design characteristics of the ALH hingeless Main Rotor Blade with an Integrated Dynamic System”.

However, HAL worked on the problem and came up with the concept of “segmented blades”, which would be 5.1 metres wide instead of the navy’s requirement of 3.5 metres. HAL says the navy has agreed to the 5.1 metre width, and that the process of manually folding the “segmented blades” has been demonstrated to the navy.

However, HAL has not installed an automatic folding facility. HAL tells me, “Automatic blade folding was not pursued due to weight penalty of about 100 kgs”.

It may be useful here, for the readers’ understanding, to describe what HAL means by “segmented blades”.

“Segmented blades” comprise of two blade parts. The outer part is folded inwards to obtain the desired folded width. The other option is that of “Hingeless blades”, which have no physical hinges. These are made of composite materials, which ensures “virtual hinges”.

3.   More “Time on Task”.  The navy is demanding that the Dhruv must be able to spend 2 hours and 20 minutes on task (i.e. airborne with its task payload), and have an additional reserve of 20 minutes.

The Dhruv is simply not capable of meeting this requirement. HAL points out that, “this (requirement) is beyond the inherent payload capacity of any 5.5 tonne class helicopter in the world and can be met with difficulty by a 10-tonne class helicopter, given the Naval specification and weight requirement.”

If the Dhruv were flying empty, additional fuel tanks could have given it the ability to meet the Time on Task requirements. But the navy demands that the Dhruv must carry a heavy weapons and sensor payload, which rules out the fitment of extra fuel tanks. The need to carry such weapons and sensor payload put most naval helos, e.g. the Sea King, in a much higher weight class (10-14 tonnes).

IN SIMPLE TERMS, THE 5.5 TONNE DHRUV FALL BETWEEN TWO STOOLS. IT IS TOO LARGE AND HEAVY TO PERFORM THE ROLE (SEARCH & RESCUE, COMMUNICATIONS, ETC) THAT 3-TONNE HELOS LIKE THE CHEETAH AND THE CHETAK CURRENTLY DO… AND TOO SMALL AND LIGHT TO REPLACE 10-14 TONNE HELOS LIKE THE SEA KING AND THE KAMOV.

Despite that, top HAL sources aver that torpedo/depth charge trials were carried out during 2001-02; and sonar, Electronic Support Measures (ESM) and High Frequency Communications Systems (HFCS) trials were carried out during 2004-05. Platform integration for an Anti-Submarine Warfare (ASW) role has been successfully completed, which includes ESM, sonar/sonics, torpedo and HFCS.

There were some problems faced during the 2004-05 trials with the reliability of the sensors, but HAL points out that the reliability issue needs to be dealt with by the vendors of the sensors, all of whom were selected by the navy.

And finally, there is no truth to the belief that a vibration problem is the navy’s main issue with the Dhruv. HAL designers say that, “With fine tuning of the Anti-Resonance Vibration Isolation System (ARIS), structural reinforcements and the introduction of Frahm dampers, the vibration problem has been resolved satisfactorily”.