A hovercraft uses a series of fans to create a pressurized cushion of air underneath the hovercraft's chassis. This air cushion is held in place by the skirt of the hovercraft. There are three basic types of hovercraft air skirt known as jute, bag and segmented skirts. Each type of skirt has specific benefits and drawbacks that affect hovercraft stability, efficiency and lift. Lift is the amount of upward force that a hovercraft can generate as a result of the air cushion it creates below it. The amount of lift that is generated by a hovercraft's air cushion is one of the main determining factors governing how much weight it can support.
Although the amount of lift on a hovercraft determines the gross weight that it can carry, how that weight is distributed on the hovercraft has a significant impact on its performance. Trim describes the balance of weight on the hovercraft relative to its horizontal and vertical axes. A hovercraft that has more weight on one side or end will tilt in that direction unless there is a roughly equivalent amount of weight on the opposite side of the hovercraft. Adjusting the trim of the hovercraft involves changing the balance of weight on the vehicle by adding or subtracting weight in specific locations. Hovercraft are specifically designed to accommodate trim by placing heavy components, including fuel tanks, motors and fans, on or near the vertical axis.
Hovercraft use separate sets of fans to generate lift and thrust. Thrust is the force that turns the vehicle and propels it forward and backward. Weight corresponds to mass which determines the amount of inertia the hovercraft has. Heavier hovercraft have a corresponding increase in inertia which requires more thrust to overcome. Since hovercraft ride on a cushion of air, they rely almost entirely on thrust to turn, accelerate and brake. Adding wieght to a hovercraft increases its turning radius, lowers acceleration and increases stopping distance.
Weight plays an important role in hovercraft design and how cargo and passengers are distributed on the craft. While traveling in a hovercraft, it is important to remember that changing positions on the hovercraft can change its trim, which can cause the hovercraft to tilt. Since hovercraft ride on a cushion of air, tilting can cause a dangerous loss of lift potentially resulting in a crash.
