Len. There are several model hovercraft sites out there with some good info on them, modelhovercraft.com is one.  I am afraid your SLA battery is out of the question… one was too heavy for my Shorty, and that was only floating and not hovering!. Two channels will suffice for drive motor and rudder, but only if you accept the lift fan being on all the time, otherwise three channels looks like being needed. I suppose you could mix the lift and propulsion motors? The skirt as far as I can see is the tricky bit, ripstop nylon appears to be the material of choice and can be glued according to some previous research. A bit catch 22…the more bits there are to the skirt the more efficient it will be.  The larger the hovercraft the easier in this regard.I am not sure about run time as they require some fairly powerful motors, and weight, hence smaller batteries becomes an issue unless you want to go only slowly ! I also understand that fixed prop and rudder types are difficult to control, rather than a moveable prop or ducted fan set-ups. A nice true scale model is likelty to be even more difficult to this regard.

ALTERNATIVLEY-as an idea to throw in,  I am contemplating an SRN4, of fairly serious dimensions, but making it only a SEMI-hovercraft… ie a floater with air assistance. It will have essentially a catamaran hull (ish) hiding beneath a skirt and some sort of fan (but nothing too powerful) to blow air underneath. My experience of watching hovercraft is they only really perform on flat surfaces, and as this is likely to be yer usual pond then if it LOOKS like its hovering, all well and good. This gives you "the look" but without an endurance problem and having to worry overmuch about lift and getting the skirt dead right, besides which my spare time is relatively limited.. or is this too much like heresy ?????

There must be some hovercraft owning chaps out there to rubbish my thoughts……..Ashley

Len. You should see my space ship !!!!!      (only joking)

The skirt seems to me to be the stumbling block on this, but after much thought I am going (eventually) to try a simply tube of ripstop Nylon, constructed by folding a long strip almost in half and sewing along the length…the "almost" means that one side will have a flap hanging over the seam which would be placed at the botttom of the skirt and form the "fingers". Holes will have to be made and reinforced with glue along the inside bottom of this tube to let the air out, AS the really cunning bit to all this is using a  ducted fan unit (available from a shop the website of which i have at work) to inflate the tube, giving it the correct rounded appearance as its in flight. The loose flap may need a bit of gathering in to acheive the correct look, but the theory is dead good. A prototype would be required to get the balance of motor/holes etc etc rougghly right but this can be made with corrugated card box material, a hot glue gun to fix the bits and a quick coat of varnish. Quick and easy. If a semi hoverer is made then there would be nowt to stop you ganging the lift and thrust motors together, as a loss of lift at lower speeds doesnt matter on water. Ashley

Hi Len

Try http://www.hovercraftmodels.com/RC%20Hovercraft_SK5.htm this is a US site dedicated to model hovercraft.

Paul

HI Len

I have an old model maker plan for a semi scale free running model SRN1 hovercraft. It is designed to use a 3.5 cc ic motor and is about 40in by 30in  and is made from balsa ( no skirt).

If this is of interest let me know

cheers tom

Len. Went to the Hovercraft museum at Lee-on-the-Solent yesterday, Saturday, and discovered the secrets of model hovercraft, there being loads of models there. It also explaing the usually miserable performance on anything but a dead smooth surface. The skirt on the majority of them IS just a simple sausage tube, it is fed air to inflate it but it IS NOT vented. This skirt is inflated by the lift fan, but only a small amount of the total air is used, the rest is stuffed underneath the craft in the manner one would think. The inflated skirt, looking like a pukker hovercraft skirt, is used to contain the air and create the cushion, but simply drags along the ground to create the seal, very innefficient and so leading to poor rough-stuff hovering performance( it doesnt actually drag too much, there being air escaping under it). The answer of course is to do it properly and have a seperate finger skirt, or fingers underneath the main sausage, but having seen the complexity of this on one of the larger models that had a pukka fingered skirt, I fully understand why the sausage is the norm ! Besides which, the simple sausage works well enough in most situations. A centrifugal fan also seems to be the preffered lift mechanism, all hand made on those I  saw. So there. I will see pictures of your next week, eh?   Ashley.

Len, Basically its a disc with blades standing on the edge which is spun round. (think of a round model of stonehenge with very thin stones) if you have a cover over the top of this, the air goes in the centre of the dic and gets flung out the sides (hence the centrifuge bit). Think also of a flat shape hairdryer with a hole in the side, a Morphy-richards for instance. This sort of fan gets used in car interior heaters a lot. It produces a good volume of relativly low velocity air, and is generally quieter than a prop or fan. There are few centrifugal fans on the market small enough for model use however, and usually it seems that hovercraft makers have to make their own, which is a fag as they have to be reasonably balanced or they wobble or vibrate, a lot, depending on speed. Computer cooling fans also seem a good alternative and in a handy size but the problem here is mounting the fan on a more powerfull motor. According to more research, only perhaps 25% or the total power needed to get a working hovercraft appears to be needed for the lift, the rest is for propulsion. Propellers in a duct seem to be the next most used device, I am not sure why they dont use ducted fans, as these are available ready made in various power and dimensional sizes and very cheap. Alright, I will give you two weeks to make summat`    Ashley

Hi Guys50 years ago as a 10 year old, Christopher Cockerel was building his experimental hoovercraft, and my comic, the Eagle had a centrefold showing what this vehicle was all about. I had a thimbledrome aircraft enginewhich I mounted vertically on a sheet of balsa in which I had cut a hole for the air to be blown through to provide the cushion My radio control was a single channel valve driven unit by Electronic Developments (ED) with a sequential escapement which meant that I could only turn to starboard if I turned to port first and waited two marching pacesbefore pressing the transmit key and starting the real turn. Once the air got underneath the sheet balsa base, the cushion was established, and was strong enough to carry the weight of engine fuel radio and batteries. I remember the thing whizzing off down the road totally out of control because the road camber overcame my ducted air control, so take my advice, steering is not at all positive, allow plenty of time to manoevre ‘cos you have NO BRAKES. Good luck, work it out and do it
Havefun. Mike D

Hello Len

Oddly enough Model Boat Mag will be covering a skimmer and a hovercraft in next months issue.

Paul

I like it. Perhaps we could have a think and suggestions on more esoteric (not a dirty word) and unusual models to build. Thats what I like. Makes a change to turn up at the pond with something with a "wow" factor  (another fishing boat or tug does not cut the mustard at teddington).   NO OFFENCE INTENDED TO ALL THOSE WHO LIKE TUGS AND FISHING BOATS. I LIKE TUGS AND FISHING BOATS, ITS JUST THAT THERES LOTS OF THEM>  Before i get another snotty reply post !!!   Ashley

Paul, That was so snotty I have been forced to take a large Brandy and rest on the sofa

When ,eventually and if, I make my SRN4 I will only take it out after dark and not tell anyone about it     Ashley

I have been a busy chap, besides drinking, and made myself a prototype SRN4 hovercraft to test the wonderful theory. Hot glue is a wonderful thing for quick constructing!

It is made out of 3mm MDF; the top is flat, there are 4 ribs underneath and a 1" shelf around the bottom to stick the skirt on to, with cardboard sides about 3 inches deep. It is 19" by 30" overall, skirt sticks out another 3/4"-1". It is lifted by two EDF64 fans (electric ducted fan for those not in the know) . the 64 being the diameter in mm. Propulsion is by 4 Graupner speed280 race motors and 3 bladed 85mm props. It weighs about 1.6Kg, without batteries or controller. The skirt is 45mm foam pipe lagging and looks the business. I tried it on an "instant" pool in the garden. it floated, even with two 6v 4.5Ahr SLA batteries aboard in only about 1" of water and positivly leapt into the air (you know what I mean) when power was applied to the EDf`s. It picks up speed nicely across the kitchen floor and I cant wait to try it tethered with string on the pond to see just how well it does go. The props are a bit small size wize compared to the overall dimensions which means larger props and will have to mean larger motors, I am looking for about 4.5" 4-blade props, an extinct animal according to my surfing. raupner do some wonderful 6" 4 bladers, but this would mean making the craft EVEN BIGGER and would mean another prototype. I do not want to make a smaller craft, size is everything in the WOW! stakes on our pond. Current draw with the set up as is , is 13A, however as it will carry 2 batteries then I will have 9A capacity for a reasonable run time.    Ashley

Len. The trouble with making aircraft props is keeping them in one peice, guaranteed…as if a blade comes off at full revs (and we are talking 16,000 rpm+ for these little monsters) near the pond side………   I did see a 4-blade prop made my simply putting two 2-bladers on the same shaft and from any angle other than dead sideways on it looked ok. I am taking the monster to the weedy pond today just to see how it copes with a bit of surface muck, and how fast it goes (on a tether) . I am likely to have to use a couple of speed 400`s at the rear, which will probably give me sufficient speed on their own, and perhaps a couple of slightly lower power , but same can-size, at the front….370`s or something, to keep the current consumption down.   Ashley     pics today if i can manage to post them.