Boeing Vertol XCH - 62 The Boeing Vertol XCH - 62 ( Model 301 ) was a three turbine - engined , heavy - lift helicopter project designed for the United States Army by Boeing Vertol . Approved in 1971 , only one aircraft was built before it was cancelled in 1974 . An attempt by NASA to resurrect the program was aborted in 1983 . Design and development . While the CH - 47 Chinook is a large helicopter by American standards , its payload of 28 , 000 lb is dwarfed by the huge Soviet - Russian heavy - lift helicopters such as the Mil Mi - 26 ( 44 , 000 lb ) and the experimental Mil Mi - 12 ( 55 , 000 - 88 , 000 lb ) , and for a long time Boeing and the US military had an urge to match or top the Mil heavy lifters . In the late 1960s , Boeing came up with designs for machines with broad similarities to the Sea Knight and Chinook , but about twice the size of the Chinook in terms of linear dimensions . Proposed machines included the " Model 227 " transport and the " Model 237 " flying crane . Following award of an Army contract for a prototype of a " Heavy Lift Helicopter ( HLH ) " in 1973 , Boeing did move forward on building an oversized flying crane machine , the " XCH - 62 " . Rotor diameter was to be 28 meters ( 92 ft ) , fuselage length 27 . 2 meters ( 89 feet 3 inches ) , and footprint length 49 . 5 meters ( 162 feet 3 inches ) . Its widely - spaced landing gear would allow it to straddle heavy cargoes such as armored vehicles , and still carry twelve troops in its slender fuselage . Boeing also considered selling a commercial version , the " Model 301 " . The helicopter was powered by three Allison XT701 - 700 turboshafts , each rated at 8 , 079 shp , which fed into a combining gearbox capable of absorbing 17 , 700 shp . The XCH - 62 prototype was in an advanced state of assembly in 1975 , being readied for a planned initial flight in 1976 . Failures in the spiral bevel gearing of the main transmission were experienced in tests because the method of analysis employed had not considered the effect of rim bending . Consequently , new gears with strengthened rims were designed and fabricated . For a more accurate prediction of the load capacity of the gears , an extensive Finite Element Method ( FEM ) system was developed . The U . S . Army ' s XCH - 62 HLH aft rotor transmission was finally successfully tested at full design torque and speed , but the US Congress cut funding for the program in August 1975 . The designers of the Mil Mi - 26 avoided similar problems by using a split - torque design in the main rotor transmission . The incomplete XCH - 62 prototype ( 73 - 22012 ) was stored at US Army Aviation Museum at Fort Rucker , Alabama . It was to be pulled out of storage in the mid - 1980s when the Army , the US National Aeronautics & Space Administration ( NASA ) , and the Defense Advanced Research Projects Agency ( DARPA ) collaborated on a scheme to finish the XCH - 62 for experimental flights . However , Congress declined funding , and it didn ' t happen . The XCH - 62 prototype , the largest helicopter ever built in the western countries , was displayed at the US Army Aviation Museum until scrapped in 2005 . In 2008 , several parts were sent to the Helicopter Museum at Weston - super - Mare ( United Kingdom ) , to be exhibited there .