Airbus has introduced a number of important developments to the aircraft systems to save weight and improve performance and reliability
Despite the sheer scale of everything about the A380, it is easy to be left with the impression that there is nothing radically new about the platform once you have digested its daunting dimensions and weights. Where are the technological marvels, the innovations to excite engineers? Is the A380 simply an overgrown derivative of every jet airliner since Boeing decided to hang the 707's engines from under the wing?
Those who take this view will realise their mistake once the skin is peeled back to look at the systems design. From the outside, the A380 appears as "conventional" as any aircraft that is 30% bigger than its predecessors can be. But inside, a raft of redesigned systems reveal that Airbus is re-setting the standards.
The aircraft's major systems - landing gear, electrical power, environmental control system (ECS), flight control system (FCS) and avionics, fuel quantity and management system (FQMS), hydraulics - all incorporate new technology to varying degrees.
Many of the innovations have been driven by Airbus's need to stem weight growth. When dealing with huge numbers, seemingly small margins can make a big difference. Roy Langton, group vice-president, engineering, of Parker Aerospace, which is designing the FQMS, uses an apt example: "With 310,000 litres [68,200 gallons] of fuel on board, a 1% measurement error equates to the weight of about 30 passengers."
Muscle within
Of the A380's numerous systems, only the landing gear offers the external viewer a glimpse of the muscle within. Goodrich's impressively large four-post main landing gear (MLG) has been designed to bring the 560t aircraft to a halt from 174kt (322km/h) in 32s. The nose gear, made by Messier-Dowty in Velizy, France, stands 5m (16ft) tall from the ground to the top of the dragstay, and the body-mounted main six-wheel body landing gears measure 5m from wheel base to retraction point. The bogie beam on the rearward-retracting body gear is 4m long, and the aft two wheels steer up to 16° for improved ground handling. The steering mechanism includes local hydraulic generators within the brake cavity, dispensing with hydraulic fluid transfer from the main system. The braking and steering systems are supplied by Messier-Bugatti.
The wing-mounted landing gear, which retracts into the belly, is an enlarged version of the A340 MLG, with a 3.07m long shock strut outer cylinder. The aircraft was originally configured with the six-wheel gears on the wing, but the arrangement was swapped to alter pavement loading and to allow greater keel structural rigidity. "We have unique single-body landing gear bays that allow for a stiff longitudinal structure, and we can use the space in between them for a bit more cargo in the centre bay, or even a crew rest area," says Paul Beazley-Long, Airbus's systems leader for landing gear. The layout also provides room for a fifth central MLG leg with twin wheels should Airbus develop a 650t A380-900.
Goodrich says the main challenge for its MLGs is to provide a weight-optimised gear while maintaining structural durability throughout operational life. Titanium is used extensively - the bogie beams are machined from a one-piece titanium forging. As on previous Airbus aircraft, 300M steel is used for the main fittings and sidestays.
Goodrich is incorporating high-velocity oxy-fuel (HVOF) coatings on the gear, an environmentally improved replacement for chrome. Noise reduction features include "capped" open-ended pins and locating dressing as close as possible to the gear. Provision for a noise-reducing fairing is also included in the baseline design.
First gear deliveries are due later this year for Airbus rig tests early next year at the company's UK plant in Filton. Drop, endurance, environmental, fatigue and strength qualification testing are still to be conducted by the manufacturers. Flight test gears will be delivered in the first quarter of next year.
Wheels and brakes on all the gears are being provided by Dunlop Aerospace and Honeywell, which is designing and manufacturing the metal matrix composite (MMC) MLG wheels and brake piston housings. Dunlop is responsible for the MMC nose wheels, torque tubes and the 20 high-density carbon brake packs on the MLGs.
Barry Ecclestone, vice-president of Honeywell Aerospace Europe, claims a 25% weight reduction against today's "base technology" by using the MMC wheels, and says the high-density carbon brake packs allow a 15% volume reduction for the same heatpack mass and energy absorption capability.
"Total [wheel and brake] system weight is around 4,000kg [8,800lb]," says Ecclestone, "and we reckon we've saved between600kg and 700kg over one built using conventional technology." However, the Dunlop-Honeywell team is also pursuing a backup design using older technologies as a contingency, he adds.
Carl Trustee, director of engineering and quality assurance at Dunlop Aerospace, says some major hurdles were overcome in developing the MMC wheels, adding: "The breakthrough was in being able to forge MMC." He says the material contains silicon carbide (SiC) particles, with properties that do not vary with direction as they would with SiC strand reinforcement.
Trustee says Airbus has increased the severity of its rejected take-off (RTO) braking requirements, with the test now to be conducted with 100%-worn brakes rather than the previous 90% limit. Airbus has also added a flapless landing case.
Goodrich is the largest single subcontractor on the A380 programme and, as well as the MLGs, is supplying the primary and standby air data systems, the primary and secondary FCS, the cargo mechanical system, the engine pylon aft fairing and rear secondary structure, exterior lighting and emergency evacuation system.
The primary and secondary air data systems provide information for the flight controls, cockpit displays and standby instruments. The system uses SmartProbe multifunction sensing probes and processing, and Airbus will receive the first prototype units for laboratory testing in September. The following month, Goodrich will deliver a prototype of its automatic ice-detection system, which uses a small probe vibrated at ultrasonic frequencies to detect ice buildup as small as 0.13mm. The cargo mechanical system follows from Goodrich's systems on the A340, and initial examples are due to be delivered next year. The A380 has 23 exterior lights, either high-intensity discharge xenon or light-emitting diodes, including landing, taxi, take-off and anti-collision lights.
Goodrich is also involved in the Aerolec joint venture with Thales Avionics Electrical Systems to develop the A380's variable-frequency (VF) electrical power generation system (EPGS), one of the most vaunted systems innovations.
Vaunted innovation
It will be the first time VF electrical power has been available on a large commercial aircraft, and follows Goodrich's experience of using a VF system on the Bombardier Global Express. Aerolec is supplying four VF generators for the main engines, two constant frequency 400Hz generators for the APU and six generator and ground power control units (GGPCUs).
The first VF generator - each of which will provide 150kVA in the 370Hz to 770Hz frequency range - was delivered to Rolls-Royce in March for testing on the Trent 900 engine. Alain Marthes, Thales Avionics' vice-president A380 programme, says generator endurance tests have already been completed for the generators. "Total power output will be 600kVA, compared to 360kVA at a fixed 400Hz on the A340," he adds.
Peter Crouchley, vice-president engineering and quality at Goodrich Power Systems, says the major advantage of the VF system is the "elimination of the complex hydro-mechanical constant-speed drive (CSD) required by conventional systems".
Crouchley says the generator main rotors are made smaller and lighter by using a hollow shaft with the windings inside. "The arrangement was developed for the two-pole APU generators, which run at a constant 24,000RPM, and was carried across to the four-pole VF generators," he says. First deliveries of system components are required for Airbus "iron bird" testing by November, with first-flight production versions following next year.
Hamilton Sundstrand's ram air turbine (RAT) also reflects the scale of the A380's power requirements, delivering 90kVA at between 480Hz and 640Hz. "The 62.5in [1.6m] diameter RAT is 58% bigger than anything we've done before and 25% more efficient by weight than that on the A340-500/600," says David Hess, president of Hamilton Sundstrand's Aerospace Power Systems. It is the first all-electric RAT for Airbus. The first generator is currently in test and the first full RAT test is scheduled for the first quarter of 2004.
Honeywell is developing the secondary electrical power distribution system (SEPDS), fed by the primary system, which will be the first to incorporate solid-state power control in place of traditional electromechanical circuit-breakers, providing load management benefits and improved diagnostic health monitoring and system upgrade potential.
Airbus has demanded an equally radical rethink on hydraulics. The A380 has a partially decentralised 350bar (5,000lb/in2) hydraulic system, with many of the flight controls powered by electro-hydraulic actuators using a local hydraulic reservoir - the first of its kind on a commercial transport. The system, including eight engine-driven pumps (EDPs), hydraulic lines and hoses, is being supplied by Eaton, while Messier-Bugatti is supplying the hydraulic fluid collectors and filters, and the electro-hydraulic actuators for the fight controls.
All previous Airbus aircraft have used a more conventional 210bar hydraulic working pressure, and the 66% pressure increase on the A380 was driven primarily by weight requirements. John Halat, director of R&D at Eaton Aerospace, says narrower tubing and less oil volume are the chief advantages. "Total weight savings realised in the system are about 2,200lb [1,000kg]," he says. There is an estimated 1,000m of hydraulic piping and tubing in the A380, about one-third of which is pressurised to 350bar.
Halat says the first production configuration EDPs are scheduled to be delivered to Airbus this month, having already completed 1,000 hours of testing with Airbus and R-R. The production EDPs will have a clutch - new to Eaton's commercial products. Halat says Airbus asked for clutches so that EDPs could be isolated in flight if required, and to allow flight dispatch with an inoperative pump. "Other new features include impellers for improved low-pressure operation and attenuators which can guarantee less than 1% pressure error," he adds.
The relatively narrow hydraulic lines benefit from Eaton's Rynglok titanium tube fittings, 1,100 of which are used on the A380, and 150 more are used for tube assemblies on the MLGs. The fittings were designed specifically for the 350bar hydraulic systems on the Boeing F-18E/F Super Hornet and the Bell Boeing V-22 Osprey programmes, and can be installed in-situ in the aircraft, says Eaton. To withstand the higher pressures, Eaton's Aeroquip hosing, which is used on the landing gears, also has titanium fittings and Kevlar reinforcement, while traditional stainless steel-reinforced hosing is used on the lower pressure return lines.
Brian Mack, Aeroquip product manager at Eaton, says the qualification of the Kevlar reinforced hosing, which includes 300,000 impulse cycles at 150% of operating pressure, should be complete by June, and Halat says first hardware for the MLG's hydraulics will be handed over to Goodrich in September.
Reliability requirements
A major challenge for Eaton was Airbus's increased reliability requirements for the system. Phil Galloway, engineering manager at Eaton's Vickers Fluid Power, says: "Traditionally, we aim for 25,000 hours' mean time between failure, which sizes our bearing and rotating components. For the A380, Airbus requested 50,000 hours. We compromised at 40,000, but it's still a real challenge."
In its partially decentralised hydraulic system, the A380 will have only two main hydraulic circuits instead of the three previously used on Airbus aircraft. The third emergency circuit will consist of independent decentralised hydraulic generating systems located close to the actuators, allowing the third circuit to be replaced by an electrical circuit, saving a considerable amount of weight.
The primary and secondary FCSs use electrically powered instead of hydraulically powered systems, resulting in the near disappearance of hydraulic circuits in the A380's wings and fin. The "more electric aircraft" developments have led to the adoption of electro-hydrostatic actuators (EHAs) and electric backup hydraulic actuators (EBHA) in the FCS.
The EHAs convert electrical power into hydraulic power locally through an electric motor and a pump which then moves the piston jack. The hydraulic circuit is constrained within the actuator and is totally independent of the aircraft hydraulic supply, saving weight and hydraulic complexity. The EBHAs, on the other hand, are more conventional in that they remain connected to the main hydraulic supply and use the supply in normal operation, transitioning to electrical power supply in backup operation. Although not cost- and weight-effective, the EBHAs improve safety by having a backup to potential hydraulic failure.
A further saving in hydraulic demand comes from the use of an electrical thrust reverser actuation system (ETRAS). Developed by Honeywell and Hispano-Suiza, the ETRAS also offers a reduced risk of inadvertent deployment, says Honeywell, as well as improved maintainability compared with traditional hydraulic or pneumatic solutions. Thrust reversers are fitted only to the inboard engines on the A380, again to save weight.
The software for the FCS, along with all the other system software on the aircraft, sits on the 32-unit Thales Avionics-supplied integrated modular avionics (IMA) suite, developed with Diehl Avionik Systeme of Germany.
The IMA suite comprises standardised electronic boards and modules and uses a common Arinc 653 operating system. The architecture means that common module processing resources can be shared by several functions, and software and hardware can be updated independently. Thales is supplying 18 of the line-replaceable unit modules, the remaining 14 coming from Airbus.
Easy upgrades
The IMA approach will aid system upgrade potential, because new software can be loaded into the modules without physically removing and replacing the module. Several functions can be run on one module. Power-on on the first flight-test aircraft is set for the end of 2004.
Application software for various systems is coming into Thales from 15 different suppliers, each of which is working with Thales to validate the programs on the modules.
The IMA modules communicate with each other and with the cockpit using Thales' AFDX system bus, for which first examples of the terminals were handed over to Airbus last June. More than 100 have now been delivered for testing, and production of the final versions for the first A380 is about to begin.
Thales is also supplying the flight control unit (FCU) and has been contracted by Messier-Bugatti to develop the braking and steering control unit (BSCU) software, the first time the company will provide both the module and the software for the BSCU. It is also supplying the high-lift control and monitoring equipment, which includes two slat and flap control computers (SFCCs) and the doors and slides management system (DSMS). The first SFCCs are to be delivered to Airbus's Bremen facility in the third quarter of this year, with the DSMS due to go to Bremen by year-end.
With a maximum capacity of 840 passengers in a high-density layout, the A380 also has environmental systems of an unprecedented scale compared to other aircraft. The primary part of the ECS is the Hamilton Sundstrand-supplied air generation system (AGS).
Hamilton's AGS features four air cycle machines (ACMs), each of which has four stages - one more than on Hamilton's previous "state-of-the-art" ACMs used for the Boeing 777. The additional turbine stage incorporated in the ACMs increases their efficiency, and David Hess, president of Hamilton Sundstrand's aerospace power systems, says that along with overall packaging density, this feature accounts for Hamilton landing its first Airbus AGS contract. "Each of the two 2 x 2 x 1.8m air generation units will use just one heat exchanger per two ACMs," he adds.
The two 235kW air-conditioning packs are 85% more powerful than any previous packs made by Hamilton, and despite the A380's huge passenger capacity, Hess claims a 5% improvement in air capacity per passenger over previous aircraft.
Phil Brigham, programme manager for A380 air management systems at Hamilton, says: "The first ACM, the heart of the AGS system, is on test now at Windsor Locks, Connecticut. We'll deliver the first full system to Airbus's Finkenwerder, Hamburg, plant by the end of the year, where it will be tested on the 'Cabin Zero' integration rig."
Ratier-Figeac is providing the largest-ever trimmable horizontal stabiliser actuator (THSA) for the A380. The fail-safe 2.9m THSA is hydraulically actuated, with electrical backup. First units are to be delivered in October.
Hamilton's German subsidiary, Nord-Micro, is supplying the quadruplex-synchronous cabin pressure control system, the first of its kind to have four channels operating simultaneously rather than in backup mode. "It is a much safer and more reliable system, and we can eliminate three major valves in the control system", says Hess. Nord-Micro is also supplying the avionics ventilation and ventilation control systems for all of the A380's distinct pressurised areas. The AGS's heat exchangers are being designed and manufactured by Hamilton Sundstrand-Nauka, a Moscow-based joint venture with NPO Nauka.
Fuel shift
The A380's wings and horizontal stabiliser trim tank can accommodate an incredible 310,000 litres of kerosene, and as on the A340-500/600, Parker Aerospace is supplying the fuel system, this time dubbed the fuel quantity and management system (FQMS).
The basic functions of controlling the burn sequence, tank usage and aircraft centre-of-gravity management during flight are not new for Airbus aircraft. However, Roy Langton, group vice-president engineering at Parker Aerospace, says the lightweight flexible structure of the A380's wing imposes significant new challenges. "We can't push fuel out to the wingtips when the aircraft is on the ground, so we only begin once the wheels leave it," he says.
The fuel system is controlled by four IMA modules in simplex mode providing the required integrity and reliability. The system also features refuel/defuel control, jettison control, and automatic temperature and fuel density calibration. More than 100 AC capacitance probes measure fuel quantity.
"For fuel quantity, Airbus stipulated less than a 10-9 chance of erroneous but believable indications, a more stringent requirement first introduced on the A340-500/600," says Langton. "The measurement accuracy is a nominal 0.5% on the ground and 1% in flight."
The system also acquires fuel properties directly each time new fuel is uploaded onto the aircraft. "Fuel density and capacitance is measured during upload and calculated on a per-tank basis," says Langton, adding that his "1% of fuel equals 30 passengers" analogy conveys the sheer scale of the masses involved.
| A380 main systems suppliers | |
| Supplier | Country |
| Aerolec (Goodrich-Thales JV) | France |
| Dunlop Aerospace | UK |
| Eaton | USA |
| FR Hi-Temp | UK |
| Goodrich Landing Gear | Canada, USA |
| Hamilton Sundstrand | USA |
| Honeywell | USA |
| Hurel Hispano | France |
| Messier-Bugatti | France |
| Messier-Dowty | France |
| Nord-Micro | Germany |
| Parker Aerospace | USA |
| Ratier-Figeac | France |
| Smiths Aerospace | UK, USA |
| Thales Avionics | France |
| Zodiac-Intertechnique | France, Germany |
| Zodiac-ECE | Germany |
Source: Flight International
