Wet friction clutch is the key functional component of the high-speed helicopter variable-speed transmission system. which is used to change the power transmission path. In the engagement process of wet friction clutch. the driving/driven disc will produce drag torque under the shearing of lubricating oil. https://www.diegojavierfares.com/amazing-price-Kicker-48CDF104-Comp-10-Down-Firing-Loaded-Subwoofer-Enclosure-special-find/