Sea Power: AWD flight deck choices may impact helicopter decision | ADM Apr 2009
Gregor Ferguson Sydney
The RAN has decided its three Hobart-class AWDs will be equipped with the Curtiss Wright ASIST (Aircraft Ship Integrated Secure and Traverse) system to secure helicopters landing on their flight decks, and then move them across the flight deck in and out of the hanger.
ADM has been told this element of the AWD platform design will not be put to tender.
ASIST is a development of the RAST (Recovery Assist, Secure and Traverse) system developed by the same manufacturer, and which already equips the RAN's FFG and Anzac-class frigates as well as the US Navy's DDG-51s and the Spanish Navy's F-100 family, from which the AWD is derived.
The RAST system requires a helicopter to hover above the flight deck while a messenger cable is lowered and manually connected to the system's recovery assist tethering cable.
This is then hauled up to the helicopter and automatically locked into the retractable main RAST probe on the underside of the aircraft's fuselage.
The tethering cable is then tensioned, which helps centre the aircraft over the flight deck so the pilot can steer the descending helicopter onto the system's Rapid Securing Device, which then secures the probe to hold the helicopter down.
The RSD is then used to move the helicopter into the hangar by traversing along a rail inset into the flight deck.
The system is designed for use in Sea State 6 conditions.
The ASIST system's machinery is mainly located in the ship's hangar and offers a considerable saving in weight and space below the flight deck compared with RAST.
It requires no manual assistance on the flight deck itself. Sensors mounted on the flight deck and helicopter track the aircraft's position and feed steering cues to the pilot; simultaneously, the RSD moves fore and aft automatically along its rail to align with the helicopter.
On touchdown the RSD captures the probe to lock the aircraft down and then traverse it across the flight deck.
Thus far some 30 ASIST systems have been installed on seven ship types in five navies, including the Italian Navy's FREMM and Horizon frigates which operate the EH-101 and NH90 NFH (for NATO Frigate Helicopter).
The Italians use a variant dubbed TC-ASIST, for Twin-Claw ASIST, which seizes the helicopter's landing wheels if the aircraft isn't probe-equipped, as the NFH90 isn't.
However, the RAN ships will not be equipped with the TC-ASIST variant, ADM has been told.
Importantly also, the US Navy has specified ASIST for its Zumwalt-class DDG-1000 destroyers, which will also operate the MH-60R, so a ship-helicopter integration path has already been explored for both of the contenders in Project Air 9000 Ph.8.
And the US Navy has also asked Curtiss Wight to study the not-insignificant engineering issues involved in converting a RAST installation aboard existing DDG-51s to ASIST.
Deck handling
However, UK engineering firm MacTaggart Scott believes the capabilities of its Trigon deck handling system, which has been in service with the Royal Navy and over 20 other customers for 40 years, haven't been sufficiently examined within the context of the AWD project and the RAN's future choice of ASW and ASuW helicopter.
The design philosophy of Trigon is quite different from that of RAST/ASIST.
The aircraft is equipped with a Decklock such as the Harpoon, which grips and holds a bar on a static 3m diameter grid installed on the flight deck.
Once secured, deckhands attach three wire ropes to the existing strong points on the helicopter undercarriage; two are mounted on hydraulic winches below the aft or side edges of the flight deck and the third is mounted on a winch located on the hangar's forward bulkhead.
The cables are tensioned automatically by a central processing unit which controls the winches and automatically aligns the stationary helicopter to draw it into and out of the hangar
The differences between Trigon and RAST/ASIST are immediately obvious: first, Trigon doesn't require a steel rail embedded in the flight deck with a traversing mechanism capable of shifting a 10-tonne helicopter.
All of the Trigon cabling lies above the deck, although the winches and pulleys themselves are buried at the deck edge or mounted on the forward hangar bulkhead; and a twin-hangar aircraft still needs only one Trigon system - the hangar cable can be rerouted easily through the bulkhead dividing the two hangars.
MacTaggart Scott says that this set-up is inherently lighter, simpler, less intrusive in structural terms and more reliable; and that many RAST and ASIST operators are reporting high preventive and corrective maintenance costs keeping their systems operational.
And the company estimates that Trigon costs between one third and one quarter of the price of its rivals to buy, and about the same difference to install.
Secondly, the Trigon system is designed to be used with all types of helicopter, without the aircraft requiring modification.
RAST and ASIST can be used only with helicopters already modified to be compatible with them.
Furthermore, ASIST requires the aircraft to be fitted with at least four infrared ‘targets' so they can be tracked by the automated control system.
And what will land anyway?
The dilemma for the RAN is this; at the start of 2008 it issued a Request for Information (RFI) to two manufacturers for the supply of 27 new maritime helicopters to replace its existing Seahawks and recently cancelled Super Seasprites.
The contenders are the Lockheed Martin/Sikorsky MH-60R Seahawk and Eurocopter NH90 NFH, one of which will equip the RAN's AWDs and Anzac frigates from the middle of the next decade.
The MH-60R, like the RAN's current S-70B2 Seahawk, has a RAST/ASIST probe; the NFH90 does not, and nor does the MRH90 which will be the RAN's new utility helicopter; but they are designed for the Decklock system, which, ironically, is manufactured by Claverham Ltd, a sister company of Sikorsky in the extended United Technologies family.
If the AWDs are fitted with the ASIST (and not the TC-ASIST) deck handling system, this doesn't necessarily dictate the choice of the MH-60R.
Defence told ADM, "Both Australian Aerospace/Eurocopter and Sikorsky have confirmed that their airframes can be configured to utilise the ASIST system without major redesign requirements.
"Choice of this system to equip the Hobart-class destroyers will not therefore have a major impact upon the choice of aircraft to satisfy the requirements of AIR 9000 Phase 8."
ADM understands the ADF Capability Development Group studied this question very closely.
While the ship-helicopter integration issues with the NH90 NFH are not trivial, in the opinion of one aviation specialist they're not considered such that they become a determinant in the choice of aircraft.
Eurocopter told ADM, "To guarantee adequate operational capabilities, several specific features have been implemented in NFH design such as decklock (Harpoon system) and traversing systems (including SAMAHE, TC-ASIST, Trigon V)."
Nevertheless, MacTaggart Scott argues that equipping the AWDs with a deck grid and Trigon, and the aircraft with a Decklock system, would be cheaper, less expensive (both to buy and in terms of aircrew and operator training and maintenance) and would enable the AWDs to embark helicopters of all types from any of Australia's coalition partners, including its own S-70Bs.
It points to an installed customer base of 220 systems in 24 navies; interestingly, one of the most recent adopters is the US Navy whose LCS-1 Freedom is equipped with the Trigon system to handle both the MH-60R/S helicopters and the RQ-8A Firescout UAV.
Both deck handling philosophies have relative advantages and disadvantages and it's easy to understand why the RAN would specify ASIST: its current inventory of Seahawks are already equipped for just such a system so specifying ASIST for the AWD simply extends an existing family.
The difficulty for the RAN will come of it selects the NH90 NFH: this is not RAST-compatible and therefore the Anzac frigates would likely need some kind of non-trivial modification to either upgrade RAST to ASIST, or install an entirely different deck handling system.
Retrofitting the entire Anzac fleet with a new deck handling system would be disruptive and expensive.
This, rather than any platform performance or capability issue associated with the AWD or its embarked helicopter, may have some bearing on the Navy's final choice of helicopter.