Home AP1-88/80 AP1-88/100 CC5 Finger Trouble Griffon2000TD Griffon8100TD SR.N2 SR.N4 SR.N5 SR.N6 SR.N6 Mk6 BH.7 - 1:32 BH.7 - 1:16 SEDAM N300
General Guidelines Fans FAQ Resources Disclaimer Links Book Papers Calculator Plans Technology MHA In build

Model Hovercraft FAQ

Contents

Building Model Hovercraft

Finding Information

Q):- Where can I find information about full-sized hovercraft?

A):- Information on full-sized hovercraft can be obtained from books, manufacturers, operators, clubs and societies. Try the links on the links page.

Q):- Where can I find plans for model hovercraft?

A):- Model hovercraft plans are scarce. There are plans for a Griffon 2000TDX and SR.N5/6 on this web site.

General

Q):- Where should the balance point of the craft be?

A):- Balance depends on usage, whether over land or water. I have found that neutral balance (i.e. centre of gravity over centre of pressure) is best for overland. For overwater operation, experience shows that you should have the weight further back, so that the craft can rise out of the depression that it makes on the surface of the water easier, and thus get "over hump". Note that centre of pressure is the same as centre of area.

Q):- How do you waterproof model hovercraft undersides and buoyancy chambers?

A):- For wooden models, I use two coats of yacht varnish

Q):- How do you control the craft?

A):- I use 27MHz radio (Futaba). I sometimes use 2 channel for proportional control of rudder and forward/reverse thrust. I have an old three channel set that I sometimes use, which gives me control of the lift so that I can stop the craft in case of emergency.

Electric Power

Q):- Are electric-powered model hovercraft practical?

A):- Nearly all of the model hovercraft shown on these web pages are electric-powered . Electric power is not only feasible for model hovercraft, it is also practical for scale models.

Q):- What motors do you use?

A):- The motors that I use are based the Mabuchi or Johnson RS540 type. Graupner make a "Speed 600", which is ideal.

Q):- What performance should I expect over land?

A):- Overland speed is much better than over water. Obstacle clearance is poor, though. The craft should be able to travel over single obstacles the size of a matchbox (scaled up to a filing cabinet on it's size in real life!). The craft may operate over gravel, but such surfaces cause a lot of the lift air to escape.

Q):- What batteries do you use, and what duration do you get?

A):- I used two 6 cell packs, 1200 to 1400 mah. I only get about 7 minutes from these, but that is the disadvantage of using electric power.

Q):- Have you tried using IC engines?

A):- I have used IC engines in an early SR.N6 model. The most important aspect is to match the motor to the propellor size. In fact, you generally have to decide the motor based on the propellor size, which is determined by the size of the hovercraft. The only problems are that it can do more damage if you put your finger into a propellor driven by an IC engine, as opposed to an electric motor, and also that a lot of dirt and water get blown about, which tends to upset IC engines.

Lift

Q):- How do you get lift air into the skirt to fill it up?

A):- I generally use a straight duct with air bleeding off into the skirt bag. This is through slots cut into the side of the duct. More recently I have had all of the air going into the bag, and holes on the inner wall of the bag providing cushion air. On the SR.N5 model the air goes through the slots into the skirt bag, as the duct is stalled. When the skirt is full, it is easier for the air to go into the plenum, and the craft then lifts.

Q):- What is the cushion pressure of your models?

A):- Typical cushion pressure for my models is between 0.5 and 2 lb/sq ft.

Q):- In a single engined hovercraft, how much air should go towards lift?

A):- About a third of the airflow should go towars lift.

Q):- Do you need to use a speed controller for the lift motor?

A):- You do not need a speed controller for lift. If you are going to use the craft mainly on water, then have a switch and leave lift on all the time you are using the craft. If you are going to mainly use it on land (smooth surfaces) then have some form of radio control for lift, so that you can stop the craft quickly before it hits large obstacles. You could also do this by putting a microswitch at the end of the rudder travel to stop the lift motor.

Q):- Can you use fans from hairdryers and vacuum cleaners?

A):- It is important to match electric motors to the fan unit or propeller, and such fans are not usually well matched to high-revving electric motors. That is why I use small airscrews, rather than available centrifugal fans.

Propulsion

Q):- What gearboxes do you use on your models?

A):- I do not use gearboxes, I use separate motors for lift and thrust, and hence separate battery packs, all adding to the weight!

Q):- Can you use electric ducted fan units?

A):- Electric ducted fan units can be used for propulsion, and have the advantages that they are compact and efficient. They are also safer than free (unducted) propellors.

Skirts

Q):- How do you design model hovercraft skirts?

A):- My first skirt designs were based on profiles of intersecting tubes. This is shown in the Hoverclub of Great Britain guide to making hovercraft (i.e. full sized racing craft). Their method relied on producing a scale engineering drawing by hand. I worked out the trigonometry involved, and have now taken this further and have used it successfully for tapered skirts. I draw skirt cross-sections as a semicircular outer wall, and an arc of twice the radius for the inner wall. I then use simple geometry to develop the panels.

Q):- What material do you use for the skirt?

A):- I generally use the material that is used to make kites. You can use light sailcloth (e.g. ripstop nylon or terylene).

Q):- How do you join the skirt sections?

A):- I always sew skirt sections together. You can use a sewing machine for best results. Sew along the inner line, giving an overlap. When it is complete, turn it inside out so that the overlaps are on the inside. I have glued skirts using glues like that used to repair bicycle tyre punctures. Apply it very thinly and let it dry. Apply a second thin coat, and when that is dry, put the two pieces together. You must get it right first time! An impact adhesive like Evo-stik or Uhu clear would also work. Superglue is an alternative, but I tend to get my fingers stuck to the skirt.

Q):- How do you make the skirt fit the curves and corners of the hovercraft?

A):- The skirt can be made from a series of small straight sections. When inflated, they tend to follow a curve around the model.

Q):- How do you attach the skirt to the hovercraft?

A):- Impact adhesive allows you to remove the skirt. More recently I have used Velcro, and I have used the poppers that are used on quilt covers (these are expensive). If you use Velcro, stitch the Velcro to the skirt material. On the craft side, you should be able to glue it. I usually give the underside two or three coats of yacht varnish, and this gives a smooth surface for the Velcro to stick to.

Q):- Can fingers be used on model hovercraft skirts?

A):- Yes. Look at the Finger Trouble pages for this. I find that fingers tend to drag on electric models, but with the better power/weight ratio of IC models this is less likely to happen. I have recently tried fingers on my 1:12 SR.N6 Mk6, but with no great success. The material tends to be too stiff, and tailoring is very difficult. The result is that the fingers do not fill properly, and then they do not seal and drag in the water. The Finger Trouble model works OK, but it has a loop segment skirt, and not the more difficult bag/finger.

Model Hovercraft Parts and Accessories

Q):- Where can I buy model hovercraft parts?

A):- Hovercraft modellers have to borrow parts and accessories from other forms of modelling. Batteries, motors and speed controllers are used in model aircraft and buggies. Propellors that are suited for electric flight models are generally usable in modl hovercraft. Kite material can be used to make hovercraft skirts.

Personal

Q):- How long have you been making model hovercraft?

A):- I first made a glow engine powered Britten-Norman CC5 model in 1970. The models shown in my web pages start from 1980.

Q):- How many models have you made?

A):- I have probably made about 20 scale models, including:

Q):- How long does it take you to build a model hovercraft?

A):- Times vary. I can design & build in about six months, but in recent years I am so busy at work that it can take four or five years!