A twin turbine engine helicopter has a two-stage main reduction gearbox, the input stage having a speed reduction ratio exceeding 5.5:1, into an epicyclic gear train second stage ratio about 6:1 for approximately 30:1 or higher overall ratio output to the main rotor. In various embodiments, the first stage uses face gears, or bevel gears, with a reduction greater than 5.5:1 and a second stage epicyclic gear train using single or double row helical or spur gears. The first stage gears are straddle mounted in the housing.