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My interest in hovercrafts was first incited by Junkyard Wars. I absolutely loved that show. From the constantly changing cast of characters to the equally unique challenge posed every week, I couldn't get enough of the weekly scrap heap showdown. I really wanted to make my own version of whatever the teams where creating any given week, but the hovercrafts really caught my attention. Something about the odd way hovercrafts slide across the ground like everything is covered in ice caused dreams of such a machine for me to pilot. I'm a little big to ride the radio controlled hovercraft that resulted from my obsession, but it's still a fun vehicle to drive around...

For a dimensioned drawing, check out my website: thewidgetforge.com

Step 1: Design

The design is based around an 0.049 cubic inch un-throttled Cox engine that came off a control line airplane. It is very powerful for its size and can really move the craft along. Unfortunately, the downside is often difficult to start, especially if you feel the urge to run the craft in the cool air of fall. The glow plugs which cost about $10 and are difficult to find also burn out very easily. There is a fine line between enough juice to start the engine and a fried plug. It would help to have a larger, throttled engine for the greater control and less finicky starts. If you're interested in a Cox engine, eBay has many on sale, often in lots with plenty of extra parts included.

To help with the control issues of an un-throttled engine, I came up with the most unique part of the design: The radio controlled deflector which splits the air between thrust and lifting. It can deflect a maximum of 50 percent of the available thrust to the lift the craft or close off the lift duct completely. While it lets you control the ride height of the craft to some extent, it is most useful for panic stopping by completely cutting off air to the skirt, allowing the craft slid to a stop on the ground.

Steering consists of two balsa uprights which support the two rudders. The rudders are two inches wide and provide plenty of maneuverability, although more rudder surface would probably make it even more maneuverable. A cowling would likely make the rudders more effective too, but the hovercraft is very maneuverable as it is, so it isn't really worth the added frustration in starting the engine to add one.

Materials and Parts
The body is pink insulating foam from a local home center. This stuff works great for this purpose: it is easy to work with and quite stiff on its own. It comes in a variety of thicknesses and usually two foot by eight foot sections. The one inch thick foam is plenty strong for a craft this size. The rest of the structure is made of 1/8 inch thick balsa and, for the engine mount, 1/8 inch plywood from a local craft store.

The remote control system is a two channel set-up meant for cars, boats or other crafts that ride on the surface. It has a range of about 100 feet which is plenty for this hovercraft. The 2 oz fuel tank, fuel lines, fuel, control horns and pusher prop were all bought online at an RC specialty site.

Step 2: Routing

After I laid out the main features on the base with a red marker, I routed the necessary channels with a Dremel using the small base attachment that comes with the tool and a 1/8 inch bit. I clamped a ruler down to the foam as a straight edge. This made for some very accurate and clean cuts. The engine mount structure and the uprights for the rudders are all glued into routed grooves.

The servos sit in routed cavities and are firmly screwed into balsa blocks which are glued down to the foam. I free handed the holes for the rest of the RC gear. The routed cavities for the RC gear worked out real well. They can be easily removed when necessary but don't slide around or come loose.

For extra stiffness, you can use balsa strips glued into routed cavities It wasn't necessary on this craft, but I did this on a future design to stiffen the compromised structure of the foam around the lift duct hole.

Step 3: Engine Mount

The engine mount is a simple 1/8 inch plywood stand which bolts directly to the engine. The fuel line simply connects underneath the engine to a connector on the carburetor. It may be a good idea cut out a hole in the back of the mount to better feed the air intake even though there is clearance as it is. The main engine mount is supported by the four balsa braces, which are also mounted in routed slots in the foam.

Step 4: Control Surfaces

The rudders are connected to 1/8 inch by one inch wide balsa uprights. The top section is just glued with a butt joint. As a future improvement, this structure could be stronger and the top section could be better connected to the uprights but it is still strong enough as it is. The lift deflector is attached to two pieces of 1/16 thick balsa glued directly to the foam on the top surface, which is visible, and the inner surface of the lift duct.

All of the movable surfaces where attached with the same technique: fabric hinges. I cut a basic fabric into one by two inch strips. Four of these strips per surface were plenty on my craft. I sanded the leading edges of the surfaces to a sharp edge so the fabric could cross over the edge cleanly. I used glue (Weldbond or any heavy craft glue would work) to attach the fabric to the control surface, saturating the material similar to the way fiber glass is used and alternating sides of the control surface as shown in the pictures. Once that dried, I could attach the other half of the fabric to the uprights and lift duct respectively in the same way.

The control surfaces attached to the servos with simple metal connecting rods made form a metal wire that comes covered in plastic. I'm not sure what it's for, but I think it is used for training plants. Z bends at either end of the rods connect to the plastic control horns. To actuate the second rudder, I drilled small holes in the top of the rudders and used more wire bent in a c shape to connect them. This works, but they had to be secured with rubber-bands when the connecting rod popped out of place. This made the rod dig into the top of the rudder. It would be much more secure to go ahead and use two more of the control horns and a connecting rod with z bends to link the two rudders.

Step 5: Fuel Tank

The current set-up includes a piece of foam which holds the tank up high enough for the engine to be able to easily suck in fuel (around or above the height of the carburetor.) The foam kept coming loose in the beginning, but was fixed with a tighter fitting piece. It can't be glued in since the tank and foam need to be removable for filling the tank and priming the fuel lines, which can already both be difficult and frustrating tasks. Unfortunately, the tank soon loosened up and was moving around and falling out of the foam support, so it is currently held in place with rubber bands lashed around the tank and foam.

Instead of this design, I would suggest gluing balsa braces on either side of the foam so the stand can securely slot into the body without using glue. That would keep the tank upright and secure without making it any more difficult to work with. A rubber-band would still be needed to hold the tank from falling out, but the stand would be much more stable.

Step 6: Skirt

The skirt made of four pieces of fabric sewn together at the edges so the edge that touches the ground is smaller than the edge which fastens to the craft in order to catch air efficiently. The top of the skirt is pined onto the sides of the foam body with regular straight sewing pins. This holds the skirt on well with little air loss, but could be more secure, as pins often come loose and become ineffective. The picture at left was taken after running the craft on a gravel covered parking lot.

This open-bottom skirt design is very simple and effective at holding air while creating little friction, but it does have some issues. When running on surfaces with sand and other loose debris, it tends to scoop up said debris and weigh down the rear end of the craft. Running on rough surfaces also tends to wear and fray the skirt. A tube like design with holes on the inner wall would help to solve this problem and would still be easy to attach to the foam, but I haven't tried this design yet.

Step 7: Adjusting the Center of Balance

Hovercrafts seem to be relatively resistant to a mispositioned center of gravity. It is still important to check that the craft is level while the engine is running. Air running through the lift duct at the rear of the craft and the engines torque can both affect the balance enough to change the way the craft handles. It's a good idea to test the running balance before permanently securing the radio equipment. Since the engine and servos were positioned in relation to the rudder and lift duct fans, the positions of the receiver, batteries and fuel tank were the main variables. I started by positioning the fuel tank as close to the center of the craft as possible so it wouldn't change the center of gravity as the fuel is used. The rest of the RC equipment was positioned to place the center of gravity in the correct place: about an inch towards the tail end of the center of the body to counter the thrust of the lift duct and about 1/4 inch to the left side to counter the torque of the motor. I then tested out the running center of balance by taping everything on for a test run. After a few tries I was ready to route out the cavities for the RC equipment.

Step 8: The Finished Hovercraft + Video

After some tweaking and testing, I got the hovercraft working consistently, although it could still use some further improvements such as a better skirt design and a better fuel tank stand set-up. Its biggest drawback is the difficulty of cold starting the engine. Once running the craft performs quite admirably. Acceleration is decent while the speed tops out at about 15 mph. It can also do standing 360s and takes high-speed, sliding turns with ease.


Can i use a Asp 52 flow engine
<p>That engine is 10 times the size of the one I used! I'm sure you could make a great hovercraft with it, but it would need to be a lot sturdier than my design :)</p>
Sry Asp glow engine
Sry Asp glow engine
may i make a own hovercarft instructable with another design (dont like to kill your copyright) and with a better to start cox engine
I don't mind. Post back here when you're done with the instructable cause I'd like to see it!
<p>i did make the hoovercraft back then</p><p>but i never got around to make a instructable of it</p><p>(it even had skirts)</p>
XD oke
hi I'm starting a hovercraft group to share experience and designs to make the best hovercraft s possible I was wondering if you were interested
http://www.youtube.com/watch?v=MArNYYv7eIc&amp;feature=youtu.be
Judging from the engine size you could circumvent the start problems by using an electric motor
can it also be used on water, like a real hover craft?
I haven't tried it, but you probably could with a better skirt as long as the water was glassy smooth and wave free.
That is sick!!!!! How big is the nitro motor?
0.049 cubic inch displacement.. it's really small even by rc engine standards!
Just a tip for cheap linkage rods, etc... I have been using the rods or wire they use to make marking flags to make linkage rods for the race engines I build for racing karts, a very popular country sport. They even make a tool to bend short 90 degree turns in the rods to allow more complex rods. Anyone who has worked on a small briggs engine will understand the linkage concept. My point is you can use this high carbon steel wire to make so many things and it is inexpensive. If you have to buy some, they sell it at all the farm supply stores for about 10.00 a bundle, with about 100 lengths of wire with a colored flag on the end, which is easily removed. They come in two or more lengths, and cost about the same for either, so I just bought a bundle of the long ones, and still have a bunch left to use.<br><br>They also sell it at the Harbor Freight stores for less then 10.00, if you are fortunate to have this kind of store near you. I don't. so I paid the premium price, but have more than got my money's worth for the many projects I have used this on.<br><br>One caution when using this wire, it is possible for it to &quot;break&quot;, when making tight bends and will leave a wickedly sharp end when it does, so use with care, and use safety glasses when working with stiff wire, as it can easily poke you in an eye or other places for that matter..<br><br>Just thought of another use that I have used coat hangers for, and that is to put a straight length into a drill and use it to mark holes like when locating a place to run cables, heating ducts, etc This will drill through the depth of a 2x12 easily, so it will drill through your floor like butter and just leave a tiny hole if you cannot use that location.This flag wire should work well for this application. This is a great tool when working alone, as you can make up a bunch of them about 12&quot; long, drill them in to the floor to mark your locations, remove the drill with them still in the floor, and then go locate the other end in the basement, crawlspace, and make sure that you are in a good spot before making a larger hole. Use a side cutter or like tool to cut the rod end at an angle to make it drill better. You will be amazed at how well it drills through most any floor, and even allows you to drill in tight places, as you can literally drill around corners, the wire is that flexable. <br><br>Well, they don't call me &quot;motor mouth&quot; for nuthin.......<br><br>Dan
http://bentley-marine.com/images/BM_Hovercraft.jpg
do they go on water
Hovercrafts do go on water in general, but this one doesn't since the skirt is not designed for it.
no of any type of skirt that would work?
Your best bet is probably to look up skirt designs for full size hovercrafts to get some ideas for better designs.
so, you know those hover crafts that kids build as science fair projects? would that type off bottom work?
It could as long as you use a water resistant material. That design doesn't give you much ride height or stability though. It would probably only work well on calm water and smooth land.
okay, thanks for the information.
big black trashbags
how did you connect the rudders to the servos
I actually used two sewing pins and strapped a piece of cardboard to my servo so I get 90 degree travel, it is slightly flimsy though
I used a thin metal rod bent to the right shape that connects the servo arm to a plastic connector (I got it from a hobby shop) that screws into the rudder.
I am done with mine, it doesn't look as nice but it works great, I used old parts from a sky fly2 and love how much lift and speed I get. I will post a video soon.
do u run this engine in reverse to move air in the correct direction and how do u start it if the spring for staring it is wound the wrong way
I use a pusher prop that's made with the blades reversed. It turns the right way when pointing backwards. Probably easiest to get an electric starter if you want to start it in the other direction and use a standard prob pointing backwards.
ahh ok i dont have time to get a pusher prop so i will run it backwards thanks though
Cool, I might try that with my spare .25 airplane engine.
just bought thanks for your suggestion!! BTW KOOL INSTRUCTABLE!! THANXXX
Hi guys i need to actually repair my hovercraft i don't have the remote is there any way to make one thanxx
Buy one! You cant make one
I have a quick question. I'm making a hovercraft of my own and I'm looking at servos to try to figure out what specs would be best. The servos you used are the Futaba S3003, right? That clocks them in at about 3.2 kg-cm at 4.8. Are the servos you used strong enough? I am using a smallish brushless RC motor so I probably wouldn't need something that powerful but.... Just trying to figure out what I need. Thanks!<br />
They are futaba s3003 and they are more than powerful enough. In fact, you could probably get away with micro sized servos if weight is an issue and especially if you're using a smaller motor. The standard size servos are often cheaper and I had a few lying around already so I used them.<br />
Thanks for the quick reply! Ok, seeing as they are powerful enough I think I will use some micro servos with about 2 kg-cm, they should be enough. If/when I get my hovercraft finished I will post a picture or two. Thanks!<br />
Hmmmmm, on other hovercrafts I've seen there are two motors:&nbsp;one to propel air downwards to keep the hovercraft lifted, and another to thrust it sideways and forward and whatnot. On yours I only see the one motor, to thrust it. What keeps it off the ground?<br />
The lift flap deflects some of the thrust from the engine under the craft so the one engine can do both jobs.<br />
did you see the junkyard wars where they made the gliders
I think I remember that one. I'm pretty sure I've seen every episode except maybe one that I had to miss and forgot to tape. Wish I could get them all on DVD...
Would this work on water? XD love it
Hovercrafts do go on water in general, but this one doesn't since the skirt is not designed for it.
What size engine is that? Where did you get it for how much?
It's a Cox 0.049 cubic inch engine. It was originally used on my dads 30 year old control line airplane that was broken, so I got mine for free. I don't think they make them anymore, but you can find them all over ebay. They aren't to expensive there as long as you can find one in good condition.
buy a cox sure start 2006 engine. and a adapter head. (no more need to buy expencife heads)
if anyone is familiar with those RC cars that suck on to the walls I modded one to become a hover craft also and it does go very nicely on water. (c)
i love junkyard wars too!

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