STEWART PENNEY / VENEGONO
Years of work will be rewarded in November when Aermacchi's M346 advanced trainer takes to the air
The planned maiden flight of the Aermacchi M346 in November marks the culmination of years of development, mainly with Yakovlev, and kicks off a test programme that will see the advanced trainer entering service in 2007.
The M346 is the latest in a line of advanced trainers from the Italian specialist, based in Venegono, northern Italy, and can trace its heritage through the MB326 and through three generations of MB339.
While developing glass cockpits and other upgrades for the MB339, the Venegono, northern Italy-based company conducted a series of studies, first with Germany's Daimler-Benz Aerospace (DASA, now part of EADS) in the late 1980s and early 1990s, and then with Russia's Yakovlev.
Aermacchi and DASA worked on preliminary designs that included intensive trade-offs between single- and twin-engined configurations and transonic and supersonic performance, says M346 programme director Massimo Lucchesini. This led to Aermacchi's decision to opt for a twin-engined, highly agile aircraft able to operate at high angles of attack and with transonic aerodynamics.
The 50:50 joint programme with Yakovlev started in 1993 and lasted six years, during which the Yak/AEM-130 (YA-130) demonstrator was built and flown. The YA-130 became the basis for Aermacchi's M346 as well as the Yakovlev Yak-130.
The most significant differences between the demonstrator and the M346 are the adoption of Western avionics for the latter, including a quadruplex fly-by-wire (FBW) system, and Honeywell F124-200 engines replacing the Slovakian PSLM DV-2S. In addition, the fabricated, built-up structure of the demonstrator has been replaced with one incorporating the latest manufacturing techniques, such as multi-axis machining, and composite materials.
The aircraft was built at the Sokol plant at Nizhny-Novgorod, Russia, but much of the flying was performed from Venegono because of Aermacchi's flight-test capability. Of the 300 YA-130 flights, more than 200 were carried out in Italy. During testing, the aircraft demonstrated a maximum angle-of-attack (AoA) of 41° and 35° with full control power. The highest speed achieved was Mach 0.9.
At the end of 1999 the M346 and YA-130 became separate programmes, leaving Aermacchi to begin detail design of the M346, a decision allowing it to prepare for two major contracts - the pan-European Eurotraining and the UK's Military Flying Training System (MFTS).
The M346 is lighter than the YA-130, has a shorter wingspan and length and a narrower forward fuselage, reducing the cross-section area. The demonstrator programme included extensive windtunnel studies as well as flights to prove aerodynamic fixes.
Wooden components were used to test solutions, albeit in a limited flight envelope. From an aerodynamics standpoint, the YA-130 is important to M346 risk reduction, says Aermacchi.
The YA-130 was cleared for carefree handling in the tested envelope, although the FBW system used analogue technology. The aircraft is designed to be "representative of" a modern combat aircraft, Aermacchi believing that a high-performance advanced trainer can cover more of the training programme. This allows the "downloading" of some operational instruction to the training school from the operational conversion unit.
As well as being offered as an advanced trainer, the M346 will have secondary combat roles, including close air support, interdiction, point defence, homeland defence and low-level air defence. "These take advantage of the trainer's low operational costs," says Lucchesini, while stressing that the roles are secondary to the M346's main purpose.
"Aermacchi thinks the M346 is the right solution," says Lucchesni, as training platforms need to mirror frontline aircraft with carefree handling, including at high AoA. Pilot training demands an aircraft with high energy and good manoeuvrability, as well as complex mission and systems handling in such environments. Higher safety levels are also required, he adds.
These requirements drive the design, says Eligio Trombetta, deputy programme director and systems engineering manager, although upgrading old designs with new avionics can allow the instructors to teach systems and mission management, "which Aermacchi has implemented on the MB339", he adds.
Using FBW on existing, conventionally designed aircraft "would be a big effort with a limited return, as the aerodynamics won't allow more performance", says Trombetta.
Safety is also driving the need for a new design. "The requirements are increasing all the time. In Italy it is one catastrophic failure every 1 million hours. This is our national requirement and also in the Eurotrainer requirements," says Trombetta. Aermacchi signed a deal with the Italian defence ministry in March for the latter to certificate the M346. The Italian defence ministry is also the lead organisation in the 13-nation Eurotraining programme.
Safety standards
This less than 1 x 10-6 failure rate designed into the M346 is better than that for any existing military aircraft, according to Trombetta. For certification, Aermacchi is using a combination of historical datawith military and commercial aircraftcertification guidelines.
Trombetta says Aermacchi conducted a hazard analysis early in the design at the aircraft, system and equipment level. The company also performs regular critical function analysis of all software and holds periodical safety review boards. Achieving high safety standards has a knock-on effect on aircraft costs - the higher the safety level, the fewer attrition airframes are needed, believes Aermacchi.
Trombetta says the safety requirement "drives the architecture and functional choices of hardware and software design". The safety criterion is a key driver for twin engines, he adds.
Aermacchi's M346 design targets are:
Transonic aerodynamic configuration with a variable camber wing providing a wide flight envelope; twin-engined configuration for energy and safety; FBW for safety and flight quality; "fighter-like" cockpit and digital avionics; high reliability and reduced maintenance for low operational costs.Life-cycle costs are viewed as crucial, with Aermacchi striving for costs no higher than those of its current products or of its competitors.
High reliability reduces maintenance, and therefore costs, says Trombetta. To ensure Aermacchi achieves its goals, safety, reliability and maintenance specialists have been integrated alongside other engineers for the first time on an Aermacchi programme, "to ensure the requirements are embedded into the design and not bolted in at the end. It is a parallel, not series approach," says Trombetta. When M346 design work started in January 2000, it also marked the first use of an integrated project team at Aermacchi, he adds.
The Italian ministry of industry is financing development of the aircraft. As a result, the company has to meet schedules and targets, which are checked annually. Aermacchi also has to repay the government, which will receive money from every M346 sale.
The industrial programme comprises six risk-sharing suppliers of the principal systems. These include Teleavio, which is responsible for the flight control system, including integration of the BAE Systems North America flight control computer; Microtecnica, providing the hydraulics; ASE, responsible for the electrical system; Martin Baker's Italian subsidiary SICAMB, providing the ejection seat; and Honeywell, teamed with Fiat, which is supplying the powerplant.
Seven partial risk-sharing partners - such as Liebherr, which is contributing the nose landing gear - nine component and subsystem suppliers and 45 vendors are also on the programme.
Aircraft responsibility
For the three prototype aircraft, Italian companies are responsible for 50.6% of the aircraft with US organisations contributing the second largest slice - 30.2%. This could change for production aircraft, as Aermacchi is aware it will have to meet national offset needs in future competitions. "There are no rigid agreements with suppliers and we have the freedom to rearrange industrial participation to cope with local industrial offset requirements," says Lucchesini.
The programme schedule calls for the first flight of M346 P01 at the end of November. This aircraft was due for roll-out on 7 June and will now undergo extensive ground trials. Aircraft P02 is due to fly in the late third quarter or early fourth quarter of next year, with the third prototype to follow 12 months later.
Although P03 will be assembled in the experimental shop, it will be the first built to production standard. Two structural test articles will also be manufactured to the same standard as P03. The first production M346 is due to fly in January 2007. Initial operational clearance for the aircraft is planned for late 2006, with full clearance scheduled for the following year. This timetable allows Aermacchi to meet MFTS and Eurotraining schedules, according to Trombetta.
Aermacchi's M346 performance predications include a thrust-to-weight ratio "close to one" at half fuel load, while the aircraft's sustained turn rate is "close to that of operational fighters", says Trombetta. Landing and take-off performance are better than that of existing trainers, with the landing run achieved without the requirement for a brake chute, which is "an operational cost".
The low-speed performance is achieved with leading-edge flaps and double-slotted, constant chord trailing-edge flaps. Stall speed is below 100kt (185km/h), with the high lift devices lowered. A knock-on effect of the low landing speed is that the braking system dissipates less energy, which increases system life.
The maximum Mach operating number of M1.2 has been verified in windtunnel tests and will be confirmed in flight tests. Trombetta says that the M346's performance sits between that of today's advanced trainers and fighters, although he points out that the latter achieve much of their improved performance through use of afterburning engines.
Much of the performance is due to the twin F124-200 turbofans, which as well as a high thrust-to-weight ratio also have a throttle response "representative of modern fighters", says Trombetta. The engines are also dressed identically, allowing any engine to be put in the left or right hand bay without requiring additional preparation work. The aircraft is also designed to allow ground operations with only the starboard engine running.
The 207bar (3,000lb/in2) hydraulic system is split, with the No 1 system supplying the flight control system only and the No 2 supplying the flight controls and utilities. Trombetta says the system has growth potential and includes two emergency accumulators for the undercarriage.
Because of the 1 x 10-6 catastrophic failure requirement, the aircraft will be recoverable after a double failure. The Microturbo Rubis auxiliary power unit (APU) is to be cleared for in-flight restart and will supply hydraulic power as well as energise the aircraft's batteries. The Rubis will supply the electrical and environmental control systems, providing 5kW and 7kg/s (15lb/s) at 4.4bar respectively. It will be cleared for airstarts up to 20,000ft (6,100m).
The flight control system is divided between primary and secondary controls. The former, comprising the ailerons, elevators and rudder, are protected even in the event of a double failure. The secondary controls comprise the leading and trailing edge flaps, and the dorsal-mounted airbrake. The variable camber wing results from the leading edge flap being "continually tuned" by the flight control computer, says Trombetta.
Carefree handling is a function of the aircraft's aerodynamics and the flight control system's control law design. Control and stability augmentation is provided throughout the flight envelope. The autopilot is also part of the flight control system.
Failure modes are available for training missions "to expose the student to failure conditions", but in a real failure the system will automatically reconfigure, says Trombetta. The FCS is integrated with other systems through dual 1553B databuses. Dual 1760 buses are used in the weapons system, while radar, electronic countermeasures stores management and forward looking infrared (FLIR) sensor information are also carried on a common bus. A basic avionics bus integrates the communications, navigations and cockpit display functions.
"Quadruplex, fully digital fly-by-wire is a significant effort in the M346 development and certification programme," says Valerio Cioffi, flight control systems chief engineer.
Tailoring training
FBW also offers the potential to allow the training organisation to "tune" tuition, increasing the difficulty level as a trainee becomes more experienced. To maximise the M346's mission efficiency, it will be able to continue with a training mission despite a failure. If a mission is scrubbed before completion, it has to be reflown, incurring additional costs.
At the heart of the FCS is a BAE North America flight control computer. The same company is supplying the air data sensors, which are already flying on the Korea Aerospace Industries/Lockheed Martin T-50 and the latest Lockheed Martin F-16 fighters. These will be arranged in a skewed configuration around the nose, which does not disturb the airflow, says Trombetta.
Smiths Aerospace is providing the primary actuators, while Microtecnica is providing the same devices for the leading- and trailing-edge flaps. A rotary actuator is used to drive the leading-edge flap while a ballscrew is used on the trailing edge. OMA is providing the airbrake actuation.
Aermacchi's FCS experience dates to the late 1980s, when it built a rig with a triplex flight control computer and a duplex direct drive valve actuator. The M346's quadruplex FCS provides full operation for the essential functions even after two electrical failures. After the loss of the airflow signals (angle of attack, angle of sideslip) the FCS reverts to alpha-fail mode while in case of loss of pressure signals it reverts to fixed-gain mode. The M346 is marginally stable, so stability augmentation is used.
As the system is quadruplex, it has four air data probes, and the same number of inertial sensors, flight control computers, and pilot input transducers (on each inceptor). Each primary actuator has four input signals and four feedback loops.
The "high performance" leading-edge flap is controlled by "dual duplex system", while the trailing-edge high lift devices and airbrake are managed with straightforward duplex systems as there is less of an implication for safety. All surfaces have fail-safe modes - the airbrake fails closed, for example.
Flight testing will validate the transition to failure and reversionary modes, says Cioffi, adding that the interim software releases will be used to fix any issues.
Cockpit set-up
As with today's fighters, the M346 has a glass cockpit and hands on throttle and stick inceptors for the two crew. The displays can be set up independently in either cockpit or mimic the other pilot's screens. The displays are also a key part of Aermacchi's embedded training system that allows pilots to be instructed for combat operations, forcing the trainee to use radar and other "sensors" - all simulated within the embedded training system - to take on opposition forces.
Each cockpit is dominated by a head-up display (HUD) with three 250 x 250mm (5 x 5in) colour multifunction displays (MFD) arranged horizontally across the cockpit with the central unit slightly lower than the two outboard screens. Trombetta says each MFD has the same part number, while the HUDs are also common to reduce spares costs.
The vertical stagger between the two seats is enough to allow use of the HUD and not require a repeater as used in other tandem-seat trainers, says Trombetta. Italy's Galileo Avionica supplies the HUD, MFDs and the mission computer, the "core avionics".
The crew sit on Martin Baker MK16L zero-zero ejection seats, similar to those fitted on the Eurofighter Typhoon, but lighter. The first ejection test is due next month in Venegono with high-speed tests to be performed by Martin Baker at its Northern Ireland, UK, facility later. Aermacchi has already delivered the structural components for the high-speed rig.
At the heart of the navigation system is a Honeywell inertial reference unit incorporating an embedded GPS-satellite navigation system and ring laser gyros.
Software is Aermacchi's responsibility, says Trombetta. "Configuration change, upgrades, and so on, can be managed by Aermacchi directly and we are quick to react". Aermacchi is also providing the software in the embedded training system and for the terrain profile matching system used for ground proximity warning.
"We can integrate a multimode radar," says Trombetta, adding that Fiar's Grifo is used as the baseline unit for design purposes, while the two Italian companies are also talking about the radar simulation within the embedded training system. A radar, which could be housed in the redesigned nose, would be provided to some customers to meet navigation and combat requirements. Similarly, a navigation and attack FLIR can be provided.
Operators will be able to refuel the M346 with engines running to increase the aircraft's operational use. The aircraft can carry 2,000kg fuel internally: distributed between a 315kg-capacity tank in each wing, the main 1,195kg tank in the centre fuselage and a 175kg collector tank. In addition, two wing pylons and the centreline station can each carry a 450kg external tank.
All aircraft, including the first prototype, will have an in-flight refuelling probe. Although the nozzle is the tried and tested unit used on the MB339, the probe is different, being shorter with a direct entry into the aircraft's fuel system. It is also fitted with a composite fairing to improve its aerodynamics, says Trombetta.
The M346 electrical system comprises two independent systems, each driven by an ASE 20kVA generator. These are linked to 300A/10kW transformer rectifier units also from ASE, which is co-operating with Hamilton Sundstrand on the electrical system.
Aermacchi is also designing in growth potential into the M346, providing more cooling and 50% more electrical power, says Trombetta.
A major difference between the M346 and the YA-130 is the airframe structure. The Russian-built aircraft relied on fabricated components, whereas Aermacchi's trainer structure comprises a significant amount of machined metallic components and carbonfibre with small amounts of Kevlar used for fairings around the base of the fin and on the tailcone.
Trombetta says the structure is built to the latest international standards which "don't dictate solutions, but guidelines. The design organisation is left to find the solution". The M346 structure is designed for a 10,000h life with a planned 20% follow-on. Ultimately, the goal is to achieve a 15,000h life.
Damage tolerance, corrosion prevention and durability criteria have been adopted for detail design to minimise structural maintenance costs. Aermacchi is aiming for only four maintenance man hours per flying hour to keep support costs low. Damage tolerance extends to the primary structure. "It's a trade-off between static strength and durability," says Trombetta.
Striving for simplicity
Simplicity is a driver, and the company has striven to reduce parts count and use simple manufacturing processes, "The M346 is heavier than the MB339 by around 2,000kg, but has 40% fewer parts," says Trombetta. Interchangeability is another driver, Aermacchi having ensured that ailerons, flaps, panels and access doors can be used on any aircraft, rather than fitting only one. The tailplane is interchangeable, the same part number being used for the left- and right-hand stabilisers, "which keeps support costs low".
The control surfaces and the airbrake are manufactured from metallic bonded composite. Roberto Mantelli, M346 programme structural integration and test manager, says each stabiliser comprises seven components, but this will be reduced to five as it has been found possible to remove two bearing supports.
Aluminium honeycomb is placed on the lower skin, and the leading edge added before the assembly is bonded in an autoclave. The top surface of the honeycomb is then machined to shape, the trunnion is added followed by the top skin before a second curing, says Mantelli.
The trunnion is also riveted in place "for back-up". Mantelli says "the same technology is used on the flap rudder and aileron", adding that the auxiliary leading edge aerofoil on the slotted flap is manufactured by extruding the metal into an aerofoil cross-section with integral twin spars. Tooling used to produce the initial aircraft is production standard, says Mantelli.
The wing comprises three main and two auxiliary spars with an integral fuel tank. The main spars pick up one to three one-piece mainframes, which, like all other fuselage frames, are machined, says Mantelli.
Aermacchi has started testing the M346 on an array of test rigs at its Venegono facility, including an iron bird, avionics, electrical and structural test rigs and a research flight simulator, as well as the three prototype aircraft.
Meanwhile, suppliers have also built rigs, including Microtecnica, which has a hydraulic system rig at its Turin plant, while Secondo Mona has a fuel rig at its factory near Venegono. These will be used to clear the systems before first flight and Aermacchi's iron bird will clear the flight-control laws.
The iron bird comprises the M346's FCS, hydraulics systems, undercarriage and control surface, all linked with pipes and wiring looms matching the size, shape and configuration of those of the aircraft. This allows the systems to be tested on the ground and flight control laws to be evaluated before the first flight takes place, the iron bird either being flown by a human pilot in a cockpit mock-up or a virtual pilot, the latter principally used for endurance or testing or where precise repeatability is needed.
Prototype use
Aircraft P01 will be used for handling and performance trials, including envelope expansion, high AoA work and FCS proving. It will also be used for general systems tests and flutter trials.
As well as similar handling and performance work, Aircraft P02 will in addition be the main avionics testbed, including the onboard simulation system. The aircraft will also be used to test the in-flight refuelling system and FCS structural testing.
Aircraft three, the first production representative M346, will be used for avionics development, including more work with the embedded simulation system, trials with the definitive main landing gear, radar integration, electronic warfare work and external stores testing.
P03 will be the first aircraft with the definitive main landing gear. Liebherr is already supplying the nose gear, and is competing with APPH and Messier Dowty to supply the main gears.
As a risk reduction measure P01 and P02 will have main gears from the Alenia/Aermacchi/Embraer AMX light attack aircraft. The winning supplier will provide an integrated design comprising the legs, wheels, brakes and systems.
Many of the YA-130 flight trials were performed in Italy because Aermacchi has a tradition of flight testing, whereas Yakovlev is a design bureau and Sokol is a factory, says Trombetta. For the M346 programme, the Italian manufacturer has upgraded its flight-test centre, improving its real-time capability.
Flying is to be divided between Venegono and Sardinia. The Italian air force test centre will also participate in the flight-test programme as part of the Italian defence ministry's agreement to certificate the aircraft.
Trombetta says around 700 flights are planned, leading to full operational clearance (FOC) as an advanced trainer. This will include the onboard simulation and initial weapons trials. Specific weapons will be cleared during additional flight-test programmes. Aircraft P01 and aircraft P02 will perform the bulk of the trials, each being programmed for 300 sorties.
An initial operational clearance is planned for late 2005 as a stepping stone to FOC in 2007.
Source: Flight International
