The aerospace sector demands heavy lifting, delicate handling, and precise po... - Digital Dream Technology support

“One of our aerospace customers in the UK has been with us since 2004,” he says. “We delivered our first hoist to them then, and since then have been able to become their main supplier through our partners Granada Materials Handling. We are probably the main brand in their factories all over the UK. They have somewhere in the region of 1,000 cranes altogether, which is a lot of equipment.

The sometimes-considerable length of wings and of fuselage sections calls for other special measures. “Due to their dimensions, the handling of wings poses a challenge that cannot be met by single hoist units,” says Berns. One hook or support point is rarely sufficient; Demag offers cranes and hoists that handle aircraft wings in tandem mode. Two cranes are coupled to form a tandem unit and can be operated by synchronised radio control. Demag has supplied quadruple suspensions for transporting wing sections. Signal transmission to the synchronised units is bidirectional for reliability and safety.

The control systems ensure that large parts are lifted smoothly and precisely, eliminating any twisting of the load. Rotating crabs give positioning accuracy in up to 13 axes of motion. Similarly, again using synchronised hoists, fuselage sections can be turned from the vertical to horizontal positions and then back again, and placed accurately and gently into assembly jigs without any risk of damage. Even complete fuselages can be transported.

Robinson of SWF makes the same point. “We also do tandem lifting,” he says, “and you need inverter controlled hoists for that. They are very common now, because finished items can be 13m or 15m long, so you need two hooks to support them.

“You need two cranes also, working in fixed ratio together. One master sender controls both cranes. If one crane stops, the other stops as well, so there is no possibility that one would continue on its own—which could have catastrophic results. We do systems like that more or less regularly.

“We have a client in Northern Ireland, also serviced through Granada, who makes smaller aircraft. The requirements there are a little bit different. We do tailor-made solutions for them, and one of them is a a double girder hoist with two hooks, one at each end, but the hooks are set a fixed 20m apart; they cannot move towards or away from each other. They have synchronised pickup: they just lift the fuselage and the whole load moves along the shop. No sideways transport is needed.

Below-the-hook arrangements can be specialised, he adds: “Last year for an aerospace client we did four very special underslung double girder trolley cranes with fancy technology for locking an electrically-controlled pin. The hoist is PLC controlled, as is the latching system. All controls are on the hoist unit. There was no hook, simply a pin that located into a hole in the load. Once located, small arms in the pin extended and slotted into recesses in the hole, locking the job into place. That was unique.”

Nor are these the only specialised below-the-hook arrangements. Frans Heilmann is director of Aerolift Industries, based in the Netherlands and specialising in vacuum lifting for large and delicate loads such as plane wings and aerofoils for wind turbines. Currently Aerolift is in discussion with a Chinese aircraft company. “In aerospace we lift sensitive plates with complex surface shapes,” he says. “Only rubber touches the surfaces; so vacuum lifting avoids damage to them. We have a new type of rubber compound that is soft and protective against wear; and if is it scratched or damaged it closes the gap automatically: it is self-sealing.

“We calculate the curvature of the wing into our design. Traditionally a 0.5cm error in curvature can be accommodated by the rubber seal but ours can seal a gap up to 1cm. If you are working with 80% vacuum, and a leak does occur, an alarm will go off but the safety margins are such that it will still hold even at a 40% vacuum.”

Aircraft maintenance is another sub- category of the industry, again with its own requirements. SWF has a client in the Middle East, doing aircraft maintenance in a hangar, and also has hoists in hangars in Switzerland.

“Hangar cranes are underslung,” says Robinson. “They can have very very large spans, up to 60m, with multi-end carriages. One long hangar can have up to four 3.2t trolleys underslung.”

The sheer size of aircraft factories is another factor that needs to be taken into account. The solution is to use interlocking overhead cranes. “Suspension cranes that have multiple suspensions, with total spans of more than 100 metres, are the most efficient solution,” says Berns. “This leaves the entire ground area available for production. “Interlocking suspension cranes transport the highly sensitive components within facilities and between neighbouring assembly bays. The load does not have to be deposited between bays, which saves on assembly time and minimises the risk of damage. By integrating crane girder overhangs into the design of the building, virtually the entire production area can be served.”

Similarly, for the Boeing manufacturing facility in North Charleston, South Carolina, where Dreamliner aircraft are made, American Crane installed an 80t custom underhung crane system. The system has 14 bridges and three trolleys. The bridges can be interlocked to allow the trolleys to transfer from one bridge to another throughout the system. The 460 x 1,000 ft (140 x 300m) building is designed without columns, which allows 100% accessibility from the crane system.

Each trolley, hanging from the bridges, can rotate ±180°, and itself supports two single girder cranes which in turn support two hoists each, for a total of four 10t hoists. The hoist-below-a-hoist system allows for movement and rotation of the load in all directions. The control system has infinite position possibilities and provided precision control. Objects of various shapes with problematic centres of gravity can be moved anywhere throughout the factory.