The Puma is a twin engined helicopter of medium lift capacity used by French military forces for tactical and logistical transportation operations. With a length of 14m and rotor diameter of 15m, it can bear a live load of 1.5 metric tons at its cruising speed of 250 km/hr over a distance of 550 km. This tough and reliable helicopter has proved itself on a daily basis for several decades and in more than fifty countries. In France, maintenance and servicing are carried out on air force bases; one of them has recently had its operations hangar fully renovated with the installation of two MANULEC powered gantry cranes fitted with VERLINDE EUROBLOC VT hoists and VERLINDE lifting components.
On this air force base assigned the task of Puma maintenance, it was urgent to carry out a large-scale renovation of hangars so that maintenance could be carried out rapidly and safely. Indeed, the original hoist system made use of mobile cranes that were difficult to manipulate and whose loading arms had insufficient slew angle to ensure rapidity and facility of maintenance operations. Furthermore, the complex equipment also required frequent maintenance operations to ensure 24hr availability.
The 45 m deep covered hangar is divided into two identical spaces. This layout enables the simultaneous maintenance of four helicopters, mostly involving the engines and mechanical, electrical and hydraulic parts. Heavy parts to be shifted, located at the top of the helicopter's fuselage, include the two engines each weighing 225 kg and the main rotor system providing lift for the helicopter. The 418 kg main rotor system combined with the main gearbox, that together weigh 720 kg, is a complex mechanical assembly and a key part of the machine because it provides not only the transfer of power to drive the blades but also provides their pitch angle. Other maintenance work is necessary on the tail rotor drive shaft.
Two identical powered gantry cranes meet precise technical specifications
The mission of design and positioning of the two powered gantry cranes was assigned to MANULEC, Verlinde's partner specialized in the study, design, building, installation, maintenance, training and load testing of lifting systems. François MATHYS, the company CEO, is fully acquainted with the aviation industry for having been an air force officer and helicopter pilot. Taking a personal interest in the project, he realized that two unique and free-standing identical structures had to be designed. Two important factors figured among the constraints. The first was that the building's structure was unable to support the handling system and the second was that it was vital to be able to move from one work space to the other without hindrance from obstacles on the floor. To meet these constraints, the main beam of the 23m long powered gantry crane is set on two 11 m high legs.
The specification for an obstacle-free central area meant that, to ensure gantry crane travel, a metal roller path was required anchored to the floor by countersunk flush head bolts. The gantry crane control system is offset to one side and is made up of an assembly of a rail fixed to the floor and metal wheels integral with the crane end carriage. To prevent the gantry crane from twisting during travel, since the control system is on one side, the two legs are driven by the matched and synchronized motors with a variable speed drive system. The gantry crane main beam on which the hoist travels is also very specific. Its closed box section with a steel diaphragm welded inside, contributes to the rigidity of the assembly and to keeping the legs aligned. With its design for a rigid "girder-gantry crane" assembly, MANULEC defined the most uniform equipment possible in terms of efficacy, space requirements and weight.
Original electrical power supply
The company gave proof of originality in this domain as well by using a contact-to-rail power supply solution. Needing little space, light and easy to install, suspended at the top of the building structure, this solution was decided in preference to the conventional trailing cable that is problematic for travel in excess of 40m. Safety was not neglected either as four emergency stop buttons were fitted at the four corners of the gantry crane together with proximity sensors with limit switches along the guide rail and an alert system to sound and flash when the crane is in movement.
The selected model is a VERLINDE EUROBLOC VT1 type electric wire rope hoist with short headroom enabling a load of 3.2 metric tons to be lifted to a height of 11m. For this type of operation, the load limiter was calibrated to 1.5 metric tons classifying the hoist in frame structure FEM 3M (6 ISO). On the girder, the hoist travels a distance of 22m with lifting height of 11m. Hoisting or changing of an engine requires accurate load positioning. Due to its design, EUROBLOC VT offers very limited lateral travel of the hook block when lifting in order to keep the load aligned; what is more, the variable speed system on all travelling motors for lifting, travel or long travel prevents load rocking. Lastly, among the many other characteristics of EUROBLOC VT hoists, it should be noted that the tropicalised motors as standard are a guarantee of their reliability and long life span, and for greater freedom of operation the remote control radio with infra-red validation enables control of all manipulations of the crane and hoist.
This new equipment will enable the officer in charge of the maintenance shop to carry out operations on Puma helicopters much more quickly and with greater safety for mechanics.