APPLICATION | AEROSPACE
No operator license is needed under most North American safety agency ‘One ton and under’ rules. Precision is everything in aerospace.
Unintended contacts between load and aircraft, or between the lifting device and the aircraft, must be at all costs avoided. Yet normal overhead gantry cranes suspend the load from ropes, and ropes by their nature sway. A swaying load is not helpful for precise positioning. There is a solution: the stacker crane.
A stacker crane resembles a normal overhead bridge crane, including the trolley and winch, but it has an additional component: the load is steadied by a telescopic mast which runs vertically between the trolley and the load. The mast does not take the weight of the load, which is carried as before by the winch ropes; instead, it is a guide. Its function is simply to prevent sideways sway, hugely increasing accurate and steady positioning. Major hoist and crane manufacturer
Casper, Phillips & Associates (CP&A) is involved in aerospace as well as many other sectors. It recently designed a trolley,
mast, and platform for a stacker crane used for painting aircraft at a large aerospace manufacturer. Precise control of the load was especially important in this case, since the hoist travel range, of 57ft. (17 metres), was so large. Further, the crane needed to allow the loaded platform to get close to the plane – within touching distance – to allow painting, but never to contact it. Even a small dent in the bodywork would result in expensive repairs and downtime. The scope of work was to replace an
existing three-rail stacker crane, including full mechanical and structural design services. It was a design-bid-build contract. CP&A was awarded the structural and mechanical design; it produced all the design documents, then the aerospace manufacturer put out a tender for the cranes to be built to the drawing set. CP&A’s involvement with the project
began with the creation of a design that satisfied the performance specification. The design went through multiple reviews, both by the owner and by a third-party peer. CP&A was able to re-use the existing bridge
structure but replaced all the electrical and mechanical components. Keeping the bridge structure dictated some design decisions such as retention of a round mast. In this case, four axes of motion are possible: bridge (longitudinal), trolley (transverse), hoist (vertical) and rotation (of the load at the bottom of the mast). Each axis is powered by a different motor: the hoist motor moves the load up and down while rollers (wheels) running in vertical guide rails along the length of the telescopic mast allow smooth motion of the mast system. The guide rollers allow the mast to move up and down and prevent the mast from swinging. Stacker cranes have different designs
for these guide rails. Some have two such rails, diametrically opposite each other across the mast cross-section; some have three, spaced equally around the circular circumference of the mast. The facility’s existing cranes had both these designs, with the load platform offset at the bottom of the mast. Such two and three-rail systems always experience a load-force applied in the radial direction of the mast,
PENNY ENGINEERING DESIGNS CUSTOM AIRCRAFT HANGAR SYSTEMS
www.hoistmagazine.com | February 2025 | 25
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