Hydraulic systems help give military transport jet wings a lift

Paul Boughton
the AirbusA400M multi-role military transport aircraft versatile and innovative aircraft is by any standards an impressively large machine.
"At 45m long, and with a span of 42m, the AirbusA400M multi-role military transport aircraft...  

At 45m longand with a span of 42mthe AirbusA400M multi-role military transport aircraft versatile and innovative aircraft is by any standards an impressively large machine. Its 23m long by 4m wide wing boxeseach of which weighs 3tonnes arein factbelieved to be the largest carbon fibre reinforced plastic composite wings ever made.
For jigs to simplify the manufacture of these enormous wingsthe Airbus Wing Manufacturing Facility based at Filtonnear BristolUKturned to Electroimpact of SeattleUSAthe company that had previously supplied the jigs used in the production of wings for the Airbus A380the world’s largest passenger aircraft.
After an extensive tendering process that included a thorough technical evaluation of the solutions proposed in the competing bidsElectroimpact awarded Bosch Rexroth a contract for the complete hydraulic systems to operate the total of 16 hydraulic platforms needed for two wing jigs. Bosch Rexroth was also awarded an additional contract by Electroimpact to supply hydraulic systems for use with ancillary equipment on the two jigs.
Following the successful completion of the first two jigsElectroimpact has now placed an order for a third wing manufacturing jig.
The wing jigs incorporate two elevating platforms on each side of the wingone platform having a lift of 3.5mthe other with a lift of 2.5m. An essential requirement is that the motion of the cylinders used to lift the platforms should be accurately synchronisedso that the platforms remain absolutely level under all conditions.
A key factor in the success of Bosch Rexroth’s tender was that it was able to demonstrate this synchronisation on a simulated assembly. In factsynchronisation better than ±2mm over the whole of the longer 3.5m stroke was achievedcompared with the specified requirement of ±5mm.
Bosch Rexroth was also able to show that it could produce cylinder and valve block assemblies that were compatible with Electroimpact’s existing design for receivers – the chambers sunk into the concrete floor below the elevating platforms to accommodate the lifting assembliesso that the platforms can be lowered to floor level.
Further factors which aided the success of the Bosch Rexroth offer were a power unit design that allows up to three rigs to be operated from a single power packand the company’s proven capability in the areas of designsite installation and project management.
In the final systemthe platformsthat have a worst-case total load of 13tonnes are each driven by two cylinders. The cylinders used are customised versions of Rexroth CDL products.
Additional guidance and support for the lifting system is provided by linear slides and the cylinders are fitted with linear transducers to provide the accurate positional feedback needed for the control system to maintain synchronism.
All of the cylinders are fitted with safety manifold blocks to prevent the platforms descending unexpectedly should the hydraulic system be damaged or develop a fault.
The cylinders have a maximum working pressure of 210barand are fitted with seals to suit the Castrol AnvolSWXFM hydraulic fluid that was chosen for the project because of its fire-resistant properties. To protect the lifting mechanism from the abrasive effects of the carbon fibre dust and swarf produced during the manufacture of the wingsthe lifting assemblies are fitted with flexible gaiters.
Power for the lifting systems is provided by a 2000litre hydraulic power unit which incorporates two 55kW electrically driven pumpseach delivering 220litres per minute at 135bar. The pumps are arranged in a duty/standby configurationso that normal operation can be maintained even if one of the pumps is out of service. To save valuable space in the assembly areathe power unit is mounted within a GRP enclosure and is installed outdoors.
To maximise energy efficiencythe pumps are fitted with pressure control arranged so that they deliver only the pressure and flow necessary to satisfy the current demand on the system. This energy-saving feature is another factor that helped to set the Bosch Rexroth design apart from the other proposalsas these had pumps which would have run continuously at full outputeven when the jigs were not in use.
The control system for the elevating platforms is built around RexrothHNC100 digital axis controllers used in a closed-loop configuration and arranged to provide the accurate synchronisation needed between the two cylinders used on each platform. The control system also incorporates a pressure/force controller to detect overloading of the platformsand a cable-break monitoring safety feature for the linear position transducers.
Hydraulic equipment supplied by Bosch Rexroth for ancillary functions on this project includes valves and cylinders to operate the lower leg deploymentboom liftboom extend and end gate systems. As in the case of the systems for the main platformsextensive use is made of dual redundancy in the ancillary systems to ensure that the risk of downtime is minimised.
To further help in keeping downtime to a minimumBosch Rexroth has given careful attention to making the installation easy to maintain. In particulargreat care has been taken to ensure that equipment installed below floor can be easily serviced. Numerous isolation points arefor exampleprovided so thatin the event of a faultindividual sections can be quickly isolated as an aid to maintenance.
The AirbusA400 military transport is a new breed of aircraftthe design of which takes full advantage of the latest developments in aviation and materials technologies. Manufacturing such a genuinely groundbreaking product presents many challengesbut those associated with the production of the wings have now been effectively addressedwith a little help from hydraulic systems developed and supplied by Bosch Rexroth.
For more informationvisit www.boschrexroth.co.uk

"

Recent Issues