Piloting a Hovercraft



Piloting a Hovercraft

We have provided a comprehensive guide to learning to operate a hovercraft. While this guide is not intended for use with all hovercraft, it will provide and insight into the best procedures and practices for successfully learning to operate most air cushion vehicles.

Most homebuilders elect to train themselves to operate their own craft. Follow the instructional information below for best results. Individualized training is available through Universal Hovercraft either in your craft or ours. Please contact us for details.

Before we begin:
First time drivers should practice in a empty lake or field. A hovercraft will travel faster over land, ice, or snow than over water. On water the air pressure that supports the craft presses the surface of the water down. As the craft is pushed forward a wave is created in front. A hovercraft must have sufficient propulsion to push itself over the wave at which point the craft achieve hump speed. After exceeding hump speed the hovercraft will require very little power to maintain speed.

At speeds greater than 4 times hump speed (30 to 40 mph) other drag types take effect. Aerodynamic drag, momentum drag, wave impact drag spray drag and skirt drag. Aerodynamic drag depends on the size, shape, and frontal area of the craft. Momentum drag due to lift systems (usually located in the front of the craft) depends on the amount of air you are supplying to lift the craft. In addition to these forms of drag over water you have wave impact drag, water spray drag, and drag by the skirt occasionally contacting the water.

Learning to drive:
These craft have multi-surface capabilities. They can operate over solid surfaces, water or ice, hard packed or loose sand and various types of mud and snow. The cushion of air virtually eliminates contact with the surrounding surface. Contact is occasionally through the skirt material which produces a minimum amount of drag. The amount of drag created varies according to the surface over which the hovercraft is traveling. For example, tall grass creates high skirt drag while operating over smooth, flat ice surfaces skirt drag will be minimal.

Maneuvering on land
Determine departure path, slope, wind, and surface conditions. Set the hovercraft's rudder position before lifting off. When the craft is located on an incline, during liftoff, the craft will tend to move in the direction of the down slope. The craft must be oriented to allow the thrust to counteract the downward motion unless the craft is to be flown down the slope. Strong winds, gravity, and surface conditions will effect maneuvering. The following should be considered prior to lift off:

  1. Rough surfaces increase skirt drag which reduces the tendency to slide
  2. Smooth surfaces decrease skirt drag causing the craft to slide more easily.

Climbing slopes
Depending on the power to weight ratio of the craft and the incline of the slope, surface conditions, and the wind's speed and direction it is best to face the bow up the slope. Thrust can be used to counter movement down the slope. This is called "hanging on the thrust"Ł.
WARNING: When maneuvering on slopes, be careful to look far enough ahead to make sure there aren't any obstacles present that the hovercraft might run into on the way down. Higher grade slopes will have more effect on the craft than shallow slopes. Be sure to spend an ample amount of time learning how to safely and accurately navigate this terrain.

Clearing obstacles
The craft can clear 8 - 12 inch obstacles. Hovering over large obstacles should be performed at low speeds, not to exceed 5 - 15mph. Clearing larger obstacles will require more air flow under the craft to maintain cushion. This is achieved with higher lift fan rpm's.

Turning
Maneuvering around obstacles on a path of travel will be influenced by wind, surface conditions and closing speed:
On open water a turn must be started well before approaching the object. Obstacles should be given as wide a berth as possible. Most turns on plane are performed under 15 mph. Slower speed turns can be performed by bringing the craft to a complete stop before turning.
On hard packed gravel, asphalt road surfaces or grass; a slope in the surface will cause the craft slide toward the downhill side unless counteracted by thrust.
Operating on loose or dry gravel can be very challenging. Air is continuously escaping from the perimeter of the craft causing dust and debris to be kicked into the air. Visibility can be hindered. The best procedure is to move slowly across these surfaces using just enough lift power to stay on cushion. A low power setting and slow speed will greatly reduce the amount of dust being kicked into the air. Slow speed reduces wear on the skirt and landing skids.
When traveling on ice, lower cushion pressure to drop lightly on skids, acting like a brake and perform the turn to clear the obstacle.
WARNING: In congested areas people should be moved away from the craft to allow a clear area to maneuver.

Operating on Ice
Hovercrafts have ice-breaking characteristics. Operators should avoid snowmobile trails or other special activity areas where the hovercraft may break or weaken the ice surface. This will typically happen when the ice is less than 1.5 inches thick. To minimize the risk of breaking ice, speed should be maintained above 15 mph. Broken ice can become hazardous to the crafts skirt system. Broken ice chunks can be very sharp and can cut the vinyl skirt if proper care and procedure is not followed.

Stopping on ice: Hovercraft have very little friction when traveling over ice. Reducing power will help to slow forward momentum. Typically this will not be enough to slow or stop the craft in a short distance. There are four methods of slowing or stopping over ice: 1) Side slide method: In this method the craft is steered from side to side while maintaining the direction of travel. Turning the craft from side to side increases the air drag on the craft helping to more quickly decelerate. 2) 180 reverse stop method: In this method the craft is quickly turned from its forward coarse 180 degrees in the opposite direction of travel. Partial or full thrust can be applied causing rapid deceleration. This maneuver should not be performed over 35 mph IAS. 3) Ditching method: In this method the operator quickly reduces power allowing the crafts landing skids to come into contact with the surface. The craft will then slide to a stop. The craft must be fitted with upgraded landing skids for this method to be effective over most ice. 4) Combination method: In this method the pilot will use a combination of the above maneuvers to successfully slow the craft.
For example: If the craft were traveling at 65 mph IAS over ice and needed to stop the pilot may use a combination of the above methods. First the pilot would begin by side sliding the craft to reduce excessive speed. When the craft decelerates to under 35 mph a 180 reverse stop may be executed.

  1. Experienced pilots typically use the combination method to stop.

Hump Speed
The term describes the characteristic behavior of the hovercraft as it gains speed over water. A hovercraft hovering in a stationary position will displace its own weight of water beneath its cushion. This induces a bow wave which the hovercraft must climb over to attain cruising speed.
Operating below hump speed causes a hovercraft to respond much like a boat. The slow craft speeds can help when maneuvering; however can be undesirable when in swift water where the water will tend to affect the speed and direction of travel of the craft.

Getting over hump: Rotate the throttle to increase engine RPM. From a standstill (0 mph) the craft must be slowly be brought up to the accelerating power setting (3,500 RPM). While increasing RPM verify the skirt is clear of water (see skirt drain procedure). Set lift fan RPM to low lift. Maintain 3,500 RPM until the craft is over hump (about 11 mph). Immediately after the craft has accelerated over hump speed the throttle should be adjusted for cruise RPM and lift fan RPM should be adjusted.

Operating Over Water

Accelerating: Rotate the throttle to increase engine RPM. From a standstill the craft must be slowly be brought up to the accelerating power setting (3,500 RPM) until the craft is over hump. Immediately after the craft has accelerated over hump speed the cruise RPM setting should be adjusted.

Trimming the craft: While the craft is accelerating the trim lever should be in the nose down position. This reduces spray and drag. After cruise speed has been reached; proper trim must be attained. Keep the nose level. Use the trim lever to fine tune. If more back pressure is required to keep the craft level a change in balance may be necessary. Begin by moving ballast items such as tool bags or cargo toward the rear of the craft until proper trim has been achieved.

  1. Craft trim should always be set before accelerating to fast cruising speed.

Turning (slow speed): Slow speed turns allow the most precise maneuverability. Turns should be planned as far in advance as possible. Entrance speed into a turn should be between 11 - 30 mph. Higher speed turns will use a larger radius while slower turns can be accomplished in a very small area. In this example the entrance speed is 15 mph IAS. Enter the turn above plane speed. Adjust lift fan RPM to a low lift setting. Apply pressure on the joystick to achieve the desired turn angle. After the turn has begun apply slight pressure in the opposite direction to stop rotation. Continue the turn by adjusting the throttle and rudder position to keep the craft on course. The goal is to complete a controlled turn with the least amount of water spray possible. Achieving this requires careful coordination between trim, throttle position and lift fan rpm.

Turning (high speed): Higher speed turns (30+ mph) will use a large turning radius. Turns should be planned as far in advance as possible. Apply slight pressure on the handlebars to achieve the desired turn angle. After the turn has begun apply slight pressure in the opposite direction to stop rotation (at higher speeds this may not be necessary). Continue the turn by adjusting the throttle and rudder position to keep the craft on course. The goal is to complete a controlled turn. Achieving this requires careful coordination between trim, throttle position and lift fan rpm.

  1. Controlled turns require careful coordination between trim, throttle position and lift fan rpm.

Draining the skirt: It takes a very short period of time (2-5 minutes) for the skirt to begin filing with water. Water in the skirt must be evacuated through the rear skirt drain hole before accelerating to speed. Excess water in the skirt will increase drag, wear and could result in damage if not properly drained. The amount of water in the skirt will dictate the length of the draining procedure. Typically it takes between 20 seconds and two minutes to completely drain the skirt.

Skirt draining procedure: 1) Trim the craft nose down. 2) Bring the craft up on cushion (1,600 - 1,900 RPM) allowing the front of the craft to rise out of the water. This allows the water to rush toward the rear of the skirt and out the skirt drain hole. 3) Slowly increase thrust throttle to 2,200 RPM. You will feel the increased drag caused by water in the skirt. Drag will decrease as the skirt drains. Maintain this RPM (or less) until the skirt feels completely drained. 4) Increase throttle to accelerating RPM. If the craft does not immediately begin to accelerate over hump speed, reduce RPM and continue the skirt drain procedure. The craft should begin to rapidly accelerate as normal if the water is completely drained.
NOTE: Trying to accelerate with a skirt full of water could result in damage to the skirt.

Maneuvering on water: All maneuvers should be performed with the goal of staying in control and maintaining low water spray throughout all operations. Low spray keeps component maintenance and repair to a minimum while increasing comfort and vision.

CAUTION: Salt water - The craft should be washed after each use giving special attention to the engine compartment and drive components. Protect electrical and mechanical components with a corrosion resistant spray such as T-9 or WD-40. Most components on the craft are protected from corrosion by a coating or paint; however well maintained components will always increase reliability and require less overall maintenance.

Stopping the craft

Stopping: Hovercraft have very little friction when traveling over most surfaces. Reducing power will help to slow forward momentum. Typically this will not be enough to slow or stop the craft in a short distance. There are four methods of slowing or stopping over any terrain: 1) Side slide method: In this method the craft is steered from side to side while maintaining the direction of travel. Turning the craft from side to side increases the air drag on the craft helping to quickly decelerate. 2) 180 reverse stop method: In this method the craft is quickly turned from its forward coarse 180 degrees in the opposite direction of travel. Partial or full thrust can be applied causing rapid deceleration. (WARNING: This method should not be used over sticky mud terrain) This maneuver should not be performed over 35 mph IAS. 3) Plow / Ditching method: This method should only be used while the craft is aimed within 15 degrees of its straight line course.┬ In this method the operator reduces power allowing the crafts plow plane or landing skids to come into contact with the surface. Contact will increase drag resulting in a controlled deceleration. The operator can vary the degree of deceleration by coordinating lift fan RPM and position of the elevator. 4) Combination method: In this method the pilot will use a combination of the above maneuvers to successfully slow the craft.

  1. Hovercrafts are not equipped with brakes. The pilot must always keep this in mind as he is traveling over different terrains and in close proximity to other operators.
  2. 180 reverse stop method should not be used over sticky mud or any terrain that may stick to the skirt. It is possible for the craft to stop suddenly while traveling sideways over mud causing a rolling moment.
  3. Hovercraft will decelerate at the same rate as a boat when operating over water.

Stopping or landing on a slope: Pin point landing on sloped surfaces takes practice. Begin by: 1)Approach the intended landing site like it is an aircraft runway. Line the craft up with the landing site as far away as possible 2) Approach the landing site taking into consideration wind direction, wind velocity, current and grade of the slope 3)Keep the craft on a "straight in"Ł approach path. Adjust speed accordingly taking onto account the grade of the slope and the intended landing site. Typical approach speed is just above plane speed (6-9 mph). 4)The crafts momentum will carry it a certain distance up the hill. Apply additional thrust if necessary 5)Try to carry just enough momentum to climb the slope and not overshoot the intended landing site. 6) Apply thrust to hold the craft in position while lowering the lift rpm. Reduce lift RPM to idle, then reduce thrust RPm to idle.

  1. This maneuver takes practice.
  2. Do not let the craft slide backwards after landing. Backsliding can cause excess wear and damage to the skirt.


Copyright © Universal Hovercraft of America, Inc. Unauthorized use of any content on this site is prohibited.