Frequently Asked Questions (FAQ)
Q - How can one engine and one fan provide both lift and thrust?
A - The use of a single horizontal axis fan with a splitter plate in its slipstream was pioneered by the author and two UK Hoverclub Members back in 1972. The splitter was positioned across the lower part of the fan duct. It takes the form of a chord of the diameter of the fan duct (forming a segment of a circle) which represented approximately 30% of the fan air. This portion of air is directed beneath the craft to form the air cushion on which the craft rides.
Q - What materials are the Canair 300 series & 500/2 made from?
A - Plywood (light mahogany door skins) is the major material for the hull. This is a readily available material, light in weight, low cost and very easy to work with. Areas susceptible to damage, such as the underside of the hull are covered with several layers of fiber glass mat. Because of the double curvature of the bell mouth fan duct, it is made of molded fiber glass. The other major material is the skirt and folding side covers which can be a light weight polyurethane, PVC or neoprene coated nylon fabric.
Q - Why do the side structures of the Canair appear to be fabric?
A - These sides are foldable, that is that when the craft is towed on its trailer or put away, the sides can be folded up vertically, to reduce the overall width of the craft to 4 feet. They are in fact composed of a wooden frame work, plywood covered on the underside, hinged at its base and supported by aluminum tubes. The top cover is fabric and forms a taught shape when hovering by a small air feed hole into the sides. Note: these side areas have a top zippered access portion in the middle so that paddles, bailer, anchor, rope camping gear etc, can be stored and carried aboard the craft.
Q - How does the Canair claim to have superior control and how does its reverse system work?
A - Canair's unique rudder reverse system provides the typical hovercraft aerodynamic yawing moment to produce a turn, with only its inner rudders being actuated. The outer set of rudders remain fixed to assist with a direct thrust into the turn. When both sets of rudders are closed all rearward thrust is stopped and redirected via fixed reverse vanes in the forward direction to achieve up to 35% to 40% effective reverse thrust. Slight variations in rudder position will result in turning while braking and moving in reverse.
Q - What type of engine does the Canair use?
A - The Canair was designed around a two cycle snowmobile air cooled engines. However, it can be fitted with liquid cooled two cycle engines as in personal watercraft or fitted with suitable four cycle engines. This is one of the areas of the Canair that is very much left up to its builder. A chart with the plan package list suggested engines that can be used based on the necessary power to weight ratios.
Q - Does the Canair float on water when the engine is not running?
A - The Canair has been designed with a sealed hull like a boat and also has built in buoyancy compartments to maintain floatation should the hull be damaged.
Q - What happens if the engine should stop while traveling at speed and making a turn?
A - Around the entire hull of the Canair craft is an up-wards inclined planing surface. It is designed so that should the hull come into contact with the waters surface at speed, it will produce an upwards force to aid dynamic recovery. The principle is similar to that of a thrown flat stone skipping on the waters surface. The force of Impact is kept to a minimum.
Q - If the craft ceases to operate and I'm on my own, how can it be loaded onto its trailer?
A - The Canair Construction Manual recommends a simple light boat trailer, 450 to 500 lbs. capacity. The addition of narrow 8 foot long 25 ½ " x ¾" thick plywood base or two longitudinal 2" x 4" runners, the craft can be loaded, engine off. This is accomplished by the aid of a support post, 8 foot long x 2" diameter galvanized metal pole and a loop ended rope. The ends of the rope are looped over the craft bow cleats, the bow of the craft is then lifted until the pole is able to support the craft nose up. The trailer can now be hand wheeled back under the craft and aligned with the landing pads. Lifting the trailer arm and craft, the pole is moved aside so that the craft and trailer can be lowered and hooked onto the tow hitch of the towing vehicle. Very simple and can be done alone.
Q - From pictures I've seen of hovercraft, they appear to generate large amounts of spray, do I have to wear rainwear while operating over water?
A - No, the Canair hovercraft with its low cushion pressure, segmented skirt and variable air flow can be operated over relatively calm water with almost no spray. When encountering waves and accompanying winds, and more lift air is applied, light amounts of spray can be generated. I am right handed and sit on the left hand side of the craft and have operated the craft for hours on end and at most have had a slightly damp left arm.
Q - It is hard to believe that the entire control of this craft can be accomplished using only one joystick, please explain?
A - Yes, the single joy stick or as some prefer, control column, controls the rudders for steering, side to side movement, and pull back for reverse. At the end of the joy stick is fitted a twist grip throttle for controlling engine speed and by pulling up on this grip, the air flow into the cushion can be varied.
Q - What is the purpose of variable lift air control?
A - Air for the cushion when operating over calm water need only be a minimum. When the craft begins to encounter waves, more might be needed. Transitions from water to land or visa versa may be made smoother with more lift air and when operating over irregular ground it might be wise to have a little extra air in the cushion.
Q - Why is pitch trim control so important and how does movement of the pilot seat help this situation?
A - Like any airborne vehicle correct attitude provides best performance. With variable weights in a hovercraft, i.e. one operator alone compared with operator and passengers, the pitch(fore & aft) trim can change. Bow down or stern down can increase skirt drag(resistance) and prevent the craft from attaining maximum speed. Continued running in either condition will accelerate wear on the bow or stern skirt. Level pitch trim is achieved by adjustment in fore and aft position of the pilot seat. A pull cord at the base of the joy stick releases locking pins that allow manual movement of the seat.
Q - I have heard that in small hovercraft the operator has to move their body weight around to help control the craft, in some cases by standing up is this true?
A - Not in a Canair hovercraft. You can remain seated at all times and during any maneuver. Changes in pitch trim are all handled by seat movement and with a strong side wind, carry on equipment can be moved from one folding side to the other.
Q - I've read that the HDL loop and segmented skirt is complicated and uses a lot of material, is this true?
A - Yes it is complicated, but only to design. It does use more material but has many other advantages. The upper loop portion for example, is not in contact with the surface and therefore sees next to no wear and should last the life time of the craft. The lower segments are all identical and are easily replaceable as they wear out. Besides having the lowest drag over waves and obstacles, compared with other skirts systems, it can also sustain major loss of segments, and the craft will continue to operate as if nothing had happened. The simple loop skirt uses much less material but minor tears can drastically affect the craft performance. Increasing the tear resistance of the loop material usually means a much heavier material resulting in a significant increase in skirt drag.
Q - Is the Canair a quiet craft when operating?
A - Not exactly. If the definition of quite is to compare it to a modern automobile, then defiantly NO. If compared to a light aircraft, then YES the Canair is quiet. The noise from a Canair hovercraft comes from 1. The fan, 2. The engine exhaust, 3. The engine block and the structure on which it is mounted and 4. The air intake of the engine. The fan is 31" diameter with nine to twelve, wide cord blades for minimum noise generation. The exhaust system needs to be matched with the engine for maximum noise suppression. The engine block is rigidly secured to a mounting plate which in turn is secured to a frame which is then mounted on resilient rubber mounts to lower noise transference. The final source of noise is the air intake to the engine, which should be fitted not only with a good air filter but also an air intake silencer.
Q - Why does the Canair use a small ducted fan instead of a large propeller?
A - Large diameter, slow rotating propellers can be highly efficient for thrust but cannot be used to also produce air at the pressure needed for the air cushion. If one is prepared to build in additional pulleys and a second fan for lift and a second bearing system, it will work. Canair is a strong believer in vehicle safety, not only for the pilot and passengers, but for the others outside the craft. Adequately guarding large propellers is not easy. The guards need to be big and strong with a mesh size to keep hands and fingers out. The problem is that a guard of this size can be heavy and the small mesh tends to restricts the airflow into and out of the propeller, thereby reducing the crafts performance. A smaller ducted multi-bladed fan may not be as efficient or as quiet as a large slow rotating propeller but has a low thrust line, is more compact and streamlined and is easily made very safe for all concerned.
Q - Do I need to be an experienced wood, fiberglass, metal and fabric worker to build a Canair?
A - No, I am none of these, yet I have built seven different craft during my life time, using these and many other materials. Some items such as welding of the engine frame and machining of the fan boss can be done by friends or farmed out to local work shops. To be proficient in one or more of these trades will no doubt mean that you can build your craft faster and probably finish up with a slightly better quality product.
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