Traction motors are 2 EE 506 motors with double reduction gear drive. Variant differences included compression ratios, propeller reduction gear ratios and accessories. The 18R was available with or without a Farman (bevel planetary) reduction gear. A large variety of reduction gear arrangements are used in the industry. Attached to the transmission was an "underdrive" with a reduction gear of 1.75/1. A reduction gear turns the propeller at 90 rpm. The circular air inlet behind the reduction gear has a de-icing device using hot air. A reduction gear on the driving shaft drives the layshaft. The high-speed propulsion turbines drive the shaft and propeller through a reduction gear. Each diesel engine drives one controllable pitch propeller via a two speed main reduction gear. EE506 axle-hung, nose-suspended, force-ventilated traction motors with 21.7&colon;1 double reduction gear drive. Each diesel engine drives one controllable pitch propeller via a two-speed main reduction gear. The reduction gear is a standard unit known from the art. A reduction gear and a crawler gear were available as additional accessory. This used two gears on a layshaft behind the headstock, giving a double reduction gear.