A transmission system for use with a microturbine engine that includes an input shaft operably coupled to the output shaft of the microturbine engine. The output shaft of the microturbine engine and the input shaft of the transmission system operate at a rotational speed in a range between 50,000 and 250,000 RPM with an output power between 200 and 5 HP. The transmission system includes a gear train having a first gear that interfaces to a second gear, the first and second gears employing teeth with opposite handed helix-angled surfaces that apply axial forces to the input shaft during both normal operation and start-up operations, which pushes the input shaft toward the output shaft of the microturbine engine. Preferably, the helix-angled surfaces on respective normal drive sides of the teeth produce an axial force during normal operation that will not be overcome with the axial force produced by the mass time acceleration of the first gear. The gear train interfaces to a starter-generator preferably through the second gear. The gear train preferably provides a reduction ratio having a value greater than 24.