Aluminium gearboxes drive lightweight US Army guns

Dean Palmer reports on a range of lightweight spiral bevel gearboxes that have been specially designed to elevate the gun on the US Army's new lightweight Howitzer

Custom spiral bevel gearboxes have been developed for use on the M777 Howitzer artillery field guns for the US Marines, to elevate the gun barrel. The gearboxes, which have been in development over the last five years, have special designed shafts and end fixings and are chemically treated to withstand the harsh conditions and temperatures of the desert. Three variations of gearbox are being supplied for each Howitzer gun - two are based upon a standard N35 Neeter Drive gearbox, the third is a custom-designed one based on a set of N35 gears. Two of the gearboxes are power-driven, the third is used as a manual wind facility for elevating the gun prior to firing. The M777 Howitzer is an ultra lightweight version to allow the US Marines to fly the gun in to battlefield situations by helicopter. The gun uses lightweight materials including aluminium and titanium. Neeter Drive, part of the Power Jacks group based in Aberdeenshire, has been working closely with BAE Systems on the gearbox designs since 2000. The main contractor, BAE Systems, used standard Neeter Drives range N spiral bevel gearboxes, which are already compact (they have a central bearing mount rather than an extended hub), and which usually have spheroidal graphite iron housings. For this application, the housings were manufactured from aluminium, for reducing the overall weight of the gearbox. The gearbox uses precision cut Gleason gears, for noise level reduction, has taper roller bearings and shouldered through shafts, for greater torque handling. The gearboxes use special high temperature seals and oil for withstanding desert conditions and the drives were all chemically-treated prior to field testing. According to Bruce Hamper, product and marketing director at power transmission company Power Jacks based in Scotland, "many different prototypes were manufactured and tested in vigorous terrain and weather conditions, each design slightly different until the final design was settled upon. The final design has not yet seen service, but has been put through a more rigorous test than the prototypes."