HOVERCRAFT, THE THEORY AND TERMINOLOGY

A hovercraft travels over land and water on a cushion or bubble of low-pressure air.  A hovercraft has one or more blowers that blow air underneath the craft, which is contained by a skirt.  The skirt that is around the perimeter of the hovercraft performs an extremely important function in containing the air cushion.  By using a skirt, the amount of engine power required to lift the craft is considerably reduced and as an added benefit, extra hull surface clearance is obtained.  The skirt is a long strip of material that is mounted onto the underside of the craft.  When the skirt is inflated, it lifts the hovercraft.  The escaping air coming from where the skirt touches the ground is what creates a friction-less cushion of air.  Because the hovercraft has practically no friction, it takes little force to move the craft. 

The diagram above shows the basic principle of a hovercraft.  Air is directed underneath the craft by a blower, and the air that escapes out of the flexible skirt creates a near frictionless environment which enables the craft to hover.  The craft can move forward and turn by using propellers to propel the craft.

The hovercrafts shown on xinventions either use a leaf blower of vacuum cleaner engine for lift.  The larger hovercraft uses an engine for propulsion while the smaller hovercraft has none however one can easily be attached.

Weight and Balance

Center of gravity (CG): is the point at which a hovercraft would balance if suspended.
Center of lift (CL): is the center of area.
Reference datum: is an imaginary vertical plane from which all distances are measured for balance purposes.
Station: is a location along the hovercraft hull given in terms of the distance from the reference datum.
Empty weight: is standard weight plus weight of optional equipment
Maximum weight: is the maximum weight approved for general operation.
Maximum flight weight: is the maximum weight the craft will fly in ground effect.

Operational

Plow in: is when the hard structure in the bow of the craft comes into contact with the water. The contact has the ability to generate a high level of drag causing a controlled deceleration of the craft.
Side plow: is when the hard structure on the side of the craft comes into contact with the water. The contact has the ability to generate a high level of drag causing a controlled deceleration of the craft.
Landing skid: surface on the bottom of the craft in which the craft rests when not on cushion. Landing skids are also used to reduce wear on the bottom of the craft.
Hover height: distance between the lower hull and the surface when the craft is on cushion.
Cushion delay time (cdt): is the time it takes for the hovercraft to go from full hover (or 10 inches of hover height) to the landing skids touching the ground. This action is done by rapidly reducing the engine rpm with the throttle or by turning the key to the off position.
Thrust duct: is the tapered ring around the diameter of the propeller. Thrust ducts add protection; increase overall efficiency and stability of the craft.
Trim wing / elevator: Horizontal wing located behind the thrust duct. This wing helps to maintain proper trim of the craft while operating. When the craft is in Hoverwing™ mode the horizontal wing them becomes an elevator controlling the altitude and trim of the craft.
Plow plane: Angled bottom surface of the craft that first comes into contact with the water. This surface helps to break water from bottom helping to reduce drag.
Skirt drain hole: Hole located in the rear center section of the skirt. This hole remains open allowing water to continuously drain from the skirt.
Scooper hole: Hole or damage to the skirt resulting in water continuously being scooped into the skirt. These holes are typically found in the skirt contact area.
Skirt contact area: Portion of the skirt that comes into contact with the terrain. This portion of the skirt incurs the most wear.
Tail heavy: When the rear of the craft is excessively loaded. The rear of the craft squats in the water causing excess drag and hindered maneuverability.
Hovercraft: transport vehicle that moves on a cushion of air.
Radar: apparatus that detects objects through the use of microwaves.
Pylon: supporting post.
Dynamic propeller: two-bladed apparatus that provides motion.
Fin: steering device.
Rudder: apparatus that prevents drift.
Lift-fan air intake: opening to allow air to enter.
Main level drive gear box: compartment that contains and protects the gear mechanism.
Skirt finger: part of the flexible skirt.
Passenger entrance: opening on the side wall that provides access to the passenger cabin.
Flexible skirt: lower flexible part.
Bow door ramp: opening at the front.
Control deck: cubicle from which a hovercraft is operated.


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