US Army Re­search Lab im­proves Apache per­for­mance


The US Army Re­search Lab­o­ra­tory (ARL) helped fig­ure out 20 years ago a rev­o­lu­tion­ary way to in­crease trans­mis­sion power in the Apache he­li­copter with­out in­creas­ing the trans­mis­sion’s size or weight. Split-torque face gear tech­nol­ogy is now inside the Im­proved Drive Sys­tem of the new Apache Block III he­li­copter that be­gan de­liv­ery in Oc­to­ber 2011.

With split-torque face gear tech­nol­ogy, he­li­copters can now have more power with­out be­com­ing heav­ier or big­ger, said Lt Colonel David “Blake” Stringer, Ph.D., who is the Chief, Ve­hi­cle Tech­nol­ogy Di­rec­torate Field El­e­ment Of­fice in Cleve­land. With in­creased power den­sity, the he­li­copter’s drive sys­tem now has ad­vanced from a horse­power of 2,828 to 3,400, with growth po­ten­tial, and the he­li­copter can fly longer, at higher al­ti­tudes car­ry­ing al­most 200 pounds more weapons with a fuel tank—thanks to, es­sen­tially, ba­sic sci­en­tific re­search be­gun by ARL decades ago.

The cur­rent Army ob­jec­tive is to field 690 AH-64D Apache Block III he­li­copters over the next 15 to 20 years. The ini­tial pro­duc­tion phase calls for 74 trans­mis­sions plus ini­tial spares.

“Face gear tech­nol­ogy is re­ally unique be­cause it al­lows you to send a lot more power through the same geo­met­ric foot­print than you could nor­mally do with any kind of con­ven­tional or other gear con­fig­u­ra­tion,” he said. “The big­gest ben­e­fit when we started the pro­gramme was weight re­duc­tion. The ini­tial pro­jec­tions from the project were 40 per cent weight re­duc­tion com­pared to the cur­rent base­line Apache trans­mis­sion.”

Face gears are a spe­cific type of in­ter­sect­ing-shaft gears that have been tra­di­tion­ally used in po­si­tion­ing mech­a­nisms such as clocks, but the army found an ap­pli­ca­tion to use them in high power trans­fer ap­pli­ca­tions. Think of gears as a cir­cu­lar disc, Stringer sug­gested. “The disc con­sists of the outer cir­cu­lar edge and two ‘faces.’ In spur or hel­i­cal gears, the teeth are on the outer edge of the gear disc. In bevel gears, the teeth are set at some an­gle be­tween the outer edge and the face. With face gears, the teeth are cut on the ‘face’ of the gear disc, or per­pen­dic­u­lar to the edge of the disc.”

The tests that the Block III and the PM have had with the face gears has been in­cred­i­bly suc­cess­ful, a lot more suc­cess­ful I think than they had an­tic­i­pated and so we’ll just keep go­ing and see how it evolves and if it’s as suc­cess­ful on Block III as it con­tin­ues through the ac­qui­si­tion process, it will prob­a­bly pro­lif­er­ate through most of the he­li­copter fleet even­tu­ally. Trans­mis­sion fail­ure is the sec­ond most dan­ger­ous in-flight emer­gency af­ter fires, Stringer said, which is part of the rea­son that the US Army be­gan an ef­fort in 1988 to im­prove drive sys­tem tech­nol­ogy. They fo­cused most of their ef­forts on re­duc­ing air­craft weight and noise. He said the Army also un­der­took a project to find a way to keep the air­frame it­self in ser­vice much longer, and to de­velop tech­nol­ogy for a fu­ture at­tack he­li­copter.

Other im­por­tant con­trib­u­tors in­cluded Boe­ing, North­star, the Army’s Avi­a­tion Ap­plied Tech­nol­ogy Di­rec­torate, the Univer­sity of Illi­nois, NASA, and DARPA.

An AH-64D Apache Long­bow Block III at­tack he­li­copter is mounted to the US Army Re­search Lab’s Ro­tor­craft Sur­viv­abil­ity and As­sess­ment Fa­cil­ity’s tilt-ta­ble for later live-fire and other tests and eval­u­a­tions

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