Enercon wind turbines have some special technical features compared to turbines of most other manufacturers. Characteristic is the gearless propulsion concept, which Enercon pioneered since 1993. The first generation of gearless turbines was the E-40/500 kW series. (Earlier Enercon designs had a transmission train.) The hub with the rotor blades connects directly to the rotor of the ring generator (direct drive). The rotor unit rotates on a front and rear main bearing about a fixed axis. The speed of the rotor is transmitted directly to the high-pole synchronous generator, where the rotor rotates in the stator, differently. The Enercon generator has no permanent magnets, allowing the company to not rely on rare-earth metals. However, the direct connection also causes grid losses. Rotation speed and the mechanical load changes over the service life are lower than geared systems. Rotation speed varies from 18 to 45 revolutions per minute (RPM) for the E-33 and 5-11.7 RPM for the E-126 depending on wind speed, while a geared generator has a speed of about 1500 RPM at rated power. Thus the large Enercon generators lead to high tower head masses, and construction and logistical challenges.