STEWART PENNEY / YEOVIL
Westland's Lynx has been around for more than 30 years. The latest version of the helicopter is re-engined and equipped with a glass cockpit
Conceived more than 30 years ago as an agile battlefield and naval helicopter, Westland's Lynx has received an injection of power and an infusion of technology and is again a force to be reckoned with on the export market.
The Super Lynx 300 first flown by AgustaWestland's UK arm in April is significantly different to the machine that first flew in March 1971. The Super Lynx is fitted with a glass cockpit and 1,200kW (1,620shp) CTS800-4N engines from Honeywell/Rolls-Royce joint venture LHTEC in place of 835kW Rolls-Royce Gem 42s. The CTS800 is the commercial version of the T800 turboshaft developed for the Boeing Sikorsky RAH-66 Comanche. The first Super Lynx 300, a naval machine, is destined for Malaysia, which has ordered six. Other customers include Thailand, for two naval helicopters, and Oman, which is to take 16 multirole battlefield machines.
Westland chief engineer Geoff Byham says the T800 gives the Super Lynx 300 a hot and high capability that earlier Lynxes lacked. While maximum take-off weight at 5,330kg (11,740lb) is the same as for the UK Royal Navy's Lynx HMA8 maritime helicopters, says Byham, this weight can also be lifted in hot-and-high conditions. The new engine and glass cockpit are the major improvements to the Super Lynx. They required significant engineering development, much privately funded before the company won orders.
Malcolm Davidson, Westland head of mechanical systems, says the bigger engine has greater mass flow and a larger diameter, which means the T800 sits further from the helicopter's centreline so the engine mounting and helicopter's outer mould line are different.
The engine also has more drains and access points, reflecting current design and safety practice, which need incorporating into the fuselage. The T800 is a two-shaft engine, comprising the gas generator - with a two-stage centrifugal compressor driven by a single-stage turbine - and the power turbine. On the Super Lynx there is also an integral reduction gearbox. The three-shaft Gem has a two-spool gas generator and a power turbine.
Davidson says the T800 was considered alongside the MTU/Turbomeca/R-R MTR390, but the US engine was, at that time, funded for development and provided the best power and specific fuel consumption figures. The engine provides around 15% more take-off lift capability on an ISA+35°C (50°C ambient temperature) day, giving the Lynx access to markets in Asia and the Middle East to which it was not previously well suited.
Byham says the new engine meant making structural changes to the top deck above the cabin to take a new load path and the heavier, more powerful engines. Alterations to the Lynx's aerodynamics reflect the T800's side intake, while a new exhaust was also required. Davidson says the engine also has an integral particle separator in the inlet, whereas the Gem only has such a system as part of additional role equipment. The particle separator has an exhaust above the engine. Westland is also working on a design for an exhaust infrared (IR) suppressor, says Davidson.
The cowling shape is also different, which could affect the rotor wake, but it has been checked and "it's okay", says Byham. The bolted, semi-rigid rotorhead, actuators, controls and composite rotor blades are the same as on the RN's Lynx HMA8.
Canada's Bombardier did much of the structural design work as offset for an AgustaWestland EH101 Cormorant search- and-rescue helicopter sale to the Canadian Forces. Byham says the redesign has allowed some "clean-up" of the engine deck and load carrying structure following earlier modifications.
Davidson says the T800's direct output from the power turbine means LHTEC developed a reduction gearbox to step down the engine shaft speed to that of the Lynx's main gearbox. As the T800 delivers more power and because of the likely higher ambient temperature operating conditions, the main gearbox has improved cooling with a higher-flow oil pump and a higher capacity filter, with improved filtration. This will improve main gearbox durability, says Davidson.
The Gem's hydromechanical engine controls are also replaced by a dual redundant digital system. Engine-control laws have been refined on the Lynx T800 demonstrator, which first flew in June 2001. Earlier Lynxes have two power condition levers and a speed select lever to match the engines. The digital controls replace these and automatically match the engine speeds, says Davidson, adding "starting is more or less automatic".
The rotor speed (NR) "greenband" has also been tightened, although it is still wider than routinely required to provide a safety margin for any tailrotor problems, says Byham. Digital controls will also help in the event of an engine failure, says Davidson, as engine loads will be automatically limited, although pilots will still need to monitor torque levels.
Byham says: "Fundamentally, the helicopter shouldn't detect any difference between the engines," which is partly because of the Lynx's semi-rigid rotor.
The T800 digital controls and the Super Lynx 300's constant speed rotor also make it possible to improve vibration absorber fine-tuning, "allowing us to manage aircraft vibration better".
During Lynx/T800 demonstrator trials, engine-bay environment assessments, including temperatures, have been made while the modified fire detection, warning and suppression system, main gearbox and hub oil cooling, and the engines' reduction gearbox cooling, have been evaluated. Davidson says the T800 installation includes new bay cooling with air introduced through two intakes using an exhaust-induced flow system.
Michael Robertson, Westland chief project engineer/designer-Lynx, says the electrical power system has been upgraded for the Super Lynx. The AC generators are modified EH101 systems producing 25kVA each compared to the 18kVA on earlier Lynxes. The generators are mounted on the forward face of the gearbox along with a new accessory drive and oil pump. The additional power is for the larger intake anti-ice system as well as the avionics. The rotor brake is also bigger, to hold the main disc stationary at higher power inputs, but it is also more useable as it is more progressive than before, adds Robertson.
The winch is electrically rather than hydraulically driven as the T800 does not have a hydraulic pad. Both main gearbox-driven hydraulic systems supply power to the flying controls, but only one supplies utility systems, such as the brakes.
As a driver for the Super Lynx 300 is the improved hot and high performance, the tailrotor was given increased pitch range - now 30° - to provide the necessary control forces in thinner air densities. Although the change was relatively simple, just moving the stop, Westland still had to qualify the modification, says Byham. The main rotor had enough pitch availability, he adds.
Hot and high trials
The T800 demonstrator programme will end this year, says Davidson, with hot and high trials planned for this month and next in North Africa. The machine will probably then be used for other trials, such as the new exhaust IR-suppressors. The flight-test programme was planned to last 180h, but will fall short of this as potential problem areas, such as control law matching and engine bay cooling, have been easier than predicted, says Davidson.
The other major development on the Super Lynx 300, the digital cockpit, is to be proved on the first production aircraft, as the Lynx T800 demonstrator has only engine integrated display units (IDU), says Byham. Ahead of the machine's first flight in April, Westland integrated the glass cockpit and avionics systems on its rig at Yeovil. The cockpit has four 150 x 100mm (6 x 4in) Smiths liquid crystal displays, two 5ATI-configuration displays for engine data and 3ATI standby instrumentation - all of which are "smart-head" displays with embedded processing and graphics generation - and a similar, non-smart-head, 3ATI unit for the threat warning display. The displays are in a panel that is machined, rather than fabricated. Avionics and instruments are controlled through the avionics management system (AMS) in the central pedestal. The rig is linked to aircraft equipment including a radar and forward-looking infrared (FLIR), rather than emulated sensors, says Geoff Webster, Westland chief crew station engineer.
The right-hand display (IDU4) is likely to be dedicated to primary flight instrumentation by service pilots, although this can be transferred to the inboard right IDU3. The two screens ahead of the other cockpit crewmember can show standard cockpit instrumentation, navigation, tactical or sensor information as required, says Webster. Integration of the sensor data is dependent on the customer's requirements. Some, for instance, want standalone FLIR imagery, others want the picture integrated with flight information, radar or electronic surveillance data, and weapon cueing. "We can do whatever the customer wants," says David Tyler, Westland head of electrical and avionics systems. Much of the display philosophy has been developed from the EH101/Merlin, and the Super Lynx work, including the display hardware, will be introduced into the latest EH101s, he adds.
Webster says that, to reduce risk, Westland ensured that its suppliers tested subsystems before they were delivered to prove functionality early. In addition, the engine instruments, attitude heading reference system (AHRS), and standby instruments have been flown on other helicopters before incorporation on the first Super Lynx 300 production vehicle. Much flight testing will be scenario-based to test the equipment as a system, he adds. At the same time the systems suppliers are concluding hardware and software qualification tests.
Westland has linked the mission systems on the Super Lynx with a military standard 1553 databus while the remainder are connected using the commercial ARINC 429 architecture - a similar scheme is used in the EH101. As some sensors are carried over from earlier Lynxes, analogue to digital conversion is required, which is performed by the same system as that which drives the engine instruments, says Webster. Some analogue equipment is already digital compatible - the air data system, for instance, is ARINC 429 compatible - and Westland has integrated the radar altimeter (radalt) with digital systems in earlier programmes.
System controls are split between soft keys around the displays "as we've tried to put controls with the systems" and two Thales-supplied control display and navigation management units (CDNU) in the centre console. These are primarily used for communication and navigation systems management. The CDNUs, with a data transfer system and the communications system are combined into the AMS. Webster adds that sensor data is fed to where it is required, for instance AHRS data is directed to the CDNUs and the displays.
Westland intends to be able to offer the customer whatever systems and level of integration are required. "The intention is that the [core avionics] hardware doesn't change, but the software will," says Tyler. Sensors and avionics would be plugged into the integrated core. This allows a range of radars, FLIRs and other sensors to be offered.
The navigation system has an embedded global positioning/inertial navigation system (EGI) primary sensor and an optional Doppler navigation mode. The system can also take data from the radalt and, if specified, drive a moving map. The dual AHRS provide a reversionary navigation capability, and also replace the earlier machines' vertical gyros and compass. Aircraft motion data from the AHRS is fed to the autopilot and display system.
Westland does not offer standard weapons packages, but it can offer a range of equipment for each role, says Westland chief defensive systems engineer Rowlie McBeath. Weapons tend to be bought as separate packages. "We discuss with the customer what they want and give what they want," says McBeath. Westland has already integrated many of the standard missiles and torpedoes. For the naval role, the Lynx is cleared with standard torpedoes and is also cleared with a range of air-to-surface missiles and various machine- gun options, including pintle-mounted door guns, while a 20mm cannon pod and rockets are being integrated.
Although the Super Lynx 300 already has the equipment for the naval role, Westland is preparing a series of systems to improve the machine's battlefield credentials, including a stores management system (SMS) which is in development, a head-up display (HUD) and a new weapons carrier to integrate battle-field munitions with the Super Lynx's wheeled undercarriage.
Integration of battlefield weapons is more difficult to read across from earlier generations as the installations were developed for skid undercarriage-equipped British Army Lynxes. This mounting interferes with the main gear sponsons so cannot be reused. British Army Lynxes are armed with the ubiquitous Raytheon BGM-71 TOW anti-tank missile and studies have been done into integrating the Lockheed Martin AGM-114 Hellfire, today's Western standard helicopter-launched missile.
"We're looking at a new pylon for missiles as we need to take them away from the fuselage. We're looking at a single store station either side [of the fuselage]," says McBeath. The design under consideration sits ahead of the sponson and places the weapon "slightly outside the undercarriage system". The pylon would be a "standard carrier" compatible with a wide range of weapons and is a study at present, but can be offered at a "short lead-time" to a customer, says McBeath.
Air-to-air weapons have also been considered: "We've certainly talked to MBDA, Raytheon and Thales Missiles from time to time," says McBeath.
The "glass cockpit makes quite a difference", when integrating new weapons, says McBeath. Modern avionics are more compact, so additional capabilities can be added without the requirement to find more space in the avionics bay.
Initially, Westland plans to integrate the HUD as a weapons' sight. A further step from HUD to helmet-mounted sight would be "relatively easy", says McBeath. "We're keen to be positioned so we can do it swiftly when it's needed for a customer," he adds.
The Super Lynx 300 is a more integrated platform, so introducing new weapons has to take this into account. Whereas each weapon would previously have had a separate control system in the cockpit, this is no longer the case, with only the master arm and safety systems being a standalone panel, he continues. Westland aims for a series of common firing cues for classes of weapons, so all anti-armour weapons would look the same to the pilot, which reduces development and integration costs. These can be changed for individual customers, but would cost extra, says McBeath.
As well as a range of weapons, Westland offers a raft of defensive aids subsystems (DASS) for the Lynx, says principal survivability engineer, Alan Haggerty. Export customers will frequently have pre-ordained DASS and electronic warfare equipment, often because commonality across a number of fleets is important.
Customers have a wide range of potential equipment, he says. Radar-warning receivers (RWRs) on offer include BAE Systems' Sky Guardian or the fuller defensive capability of the same company's Helicopter Integrated DASS (HIDASS) or one of the US equivalents, such as ITT's Suite of Integrated Radio Frequency Countermeasures (SIRFC), while Israel has "a lot of systems which are proving popular, and some countries have their own systems, South Africa for instance," says Haggerty.
Equipment of choice
Westland will fit other companies' equipment, says Haggerty, and although it can take already integrated systems such as HIDASS or SIRFC, it has previous experience of integrating disparate manufacturers IR countermeasures (IRCM), laser warning, RWR and countermeasures dispensers into a single system.
Previous installations and the Lynx's compactness mean that dispenser and antenna locations are familiar, says Haggerty. "RWR positions don't change much - they want the four corners. Hence it's the same two points on the nose and rear fuselage just ahead of the [tailboom]," he adds. Westland did consider the sponsons for the rear-facing antennas, but returned to the current position. This is unlikely to change unless a customer requires an RWR with a significant electronic-surveillance capability, as such detectors produce much finer range and direction measurements.
With the potential of battlefield operations and the increase in naval littoral operations, which increase the risk of exposure to IR-guided surface-to-air missiles (SAMs), suitable countermeasures are becoming a necessity. The Northrop Grumman/BAE AAQ-24 Nemesis directed IRCM is offered as a customer option, but Westland also offers the less expensive ALQ-144 lantern-based IRCM with an upgrade path to Nemesis, as both systems can be mounted in the same rear fuselage position. "We've contemplated a move but we found this is the best-placed location for the ALQ-144 and the DIRCM position is best here as well, bearing in mind the most likely threat, SAMs," says Haggerty. This is, he says, a compromise as the forward hemisphere "where the signature is much less" is not well covered.
"We like to integrate the DASS within itself and report the information to the aircraft for display," says Haggerty, as this keeps the response speed and allows DASS to be maintained as a package, making customer systems easier to accommodate.
Source: Flight International