Introduction: Launch It: the Improved CD Hovercraft.

The CD hovercraft is a tried-and-tested Make, but technological improvements have tended to be in the method of connecting the balloon to the CD. I have attempted to apply some of Sir Christopher Cockerell's original developmental research to this old favourite.

Step 1: Materials and Tools

In addition to the basic materials (an old CD, a balloon and a plastic bottle cap and hot glue), you will need a sheet of paper or light card, a thin sheet of expanded polystyrene, ordinaryglue and a sharp knife.

The type of glue is not vitally important, since it will not be under any strain greater than the weight of the polystyrene and paper. If you use a water-based glue, though, try and be very sparing with it, as excess water will make the paper "cockle" and cut the vehicle's efficiency.

Step 2: What Are the Improvements?

Hovercraft gain lift from pressure-drops. More rapid changes in pressure and downward air-velocity give rise to greater lift.

Early attempts at a hovercraft simply blew air down an open shaft towards the ground. However, when the bulk of the shaft was closed off, and the air-flow restricted to the edges of the craft, the increase in lift was startling.

In the traditional CD hovercraft, the drop in pressure is gradual, spread over the whole surface of the CD. We are going to use the polystyrene and paper to create channels that will restrict the airflow so that the pressure-drop occurs more rapidly near the edge of the disc.

Step 3: Restricting the Flow.

The air is restricted by using channels cut in a layer of polystyrene, capped by a layer of paper.

Using the attached templates, cut pieces from the polystyrene and the paper. If you are doing it by eye, remember that the CD has a diameter of 12cm.

It is easier to glue the polystyrene to the paper, and then both to the CD. Use the "normal" glue to do this, being careful not to clean off any "ooze" before it dries: blobs of glue on the bottom of the hovercraft will catch on the surface below the craft and slow it down or even stop it completely.

Step 4: The Traditional Bit

Drill a hole in the middle of the bottle cap, as large as the hole in the CD.

Hot-glue the cap to the CD, upside down. As you press the cap in place, gently twist it to ensure the glue forms an air-tight seal. You must be very careful to avoid glue oozing through the hole in the CD, as it will block the channels you have just made.

When all the gluing you did has dried and/or cooled, blow up your balloon and twist the neck to keep the air in.

Stretch the neck over the cap, place the hovercraft on a smooth surface and let the neck untwist. Air will rush down the channels, under the craft and lift it on a cushion of air. The slightest nudge should send the hovercraft scudding away.

Step 5: Launch It!

Time to be honest - things did not go as well as expected.

The hovercraft worked, but the large hole in the cap meant that it only ran for a couple of seconds.

Restricting the air-flow seemed to cure this, but I left things a bit late to finish this Instructable, and did not wait until the glue dried before testing. (Bad Kiteman, naughty Kiteman!)

This meant that the glue oozed through the paper and stuck to the mat while I was holding the hovercraft still.

Have a look at the video to see the results so far, but the deadline is too close to be able to try it with a dry, non-adhesive base.


Step 6: Lacking Motivation?

If your smooth surface is also level, the hovercraft will not move unless you nudge it.

You may want to add one or two narrow extra channels through the outer ring of polystyrene to the edge of the disc.

The portion of air that leaks through these channels should provide enough thrust to propel the hovercraft across the desk.

Build two or more CD Hovercraft with thrust channels, and you can race them across the kitchen floor - the loser washes up!

Comments

author
agishero (author)2013-01-03

Word File Can't Be Downloaded

author
Kiteman (author)agishero2013-01-03

(Thanks - I've submitted a bug report)

author
ilpug (author)2011-08-28

These are really fun to make. I recognize that set of craft knives, i bought mine for 99c at a discount store and most of them broke in a week. How did yours hold up?

author
Kiteman (author)ilpug2011-08-28

Fine, I'm still (ab)using them.

author
ilpug (author)Kiteman2011-08-28

Wow. Maybe i am just more prone to breaking things.

author
kiteguy (author)2011-04-19

Hummmm,

Quote: "being careful not to clean off any "ooze" before it dries: "

Perhaps this is one reason it would not "fly" as wanted.

author
Wyle_E (author)2008-01-31

If you have a source of dry ice, a small plastic bottle of dry ice chips would last longer than the air in a balloon. The original version of this gadget is the "dry-ice puck" that's been used in physics classes for almost a century. It has a thick, polished steel puck instead of the CD, and a copper ball (remember copper toilet-tank floats?) to hold the dry ice. With that much mass, it would glide *slowly* for several yards without visibly slowing. One of these days I may dust off my old Unimat lathe and make one.

author
Kiteman (author)Wyle_E2008-01-31

That is true, of course, but most readers won't have access to lumps of dry ice.

author
hintss (author)Kiteman2010-08-21

buy them at Ralphs?

author
a918bmxr (author)2009-05-21

this is the latest in self propelled balloon hovercraft technology
(klik linc)
https://www.instructables.com/id/the-better-cd-hovercraft/

author
Kryptonite (author)2008-12-11

I've tried this the "Original" way, and I think it worked better than yours, any ideas why? I thought that yours would go better, oh well, better luck next time.

author
astro boy (author)2008-07-04

replace the cd with another piazza base more power or smaller hole longer run

author
Kaiven (author)2007-10-17

do you kkow where polysterine can be found in a house? where i live, we don't have that kind of pizza stuff. Alos, is there anything else i can use? thanks

author
shadowgravity (author)Kaiven2007-11-21

isnt styrofoam polystyrene?

author
Wyle_E (author)shadowgravity2008-01-31

Yes. It's clear that you want polystyrene foam, aka styrofoam, and not solid polystyrene. Open-cell foam (the original Styrofoam) won't work here, because it won't hold air. Closed-cell foam, used in disposable cups and plates, is what works.

author
Kaiven (author)shadowgravity2007-11-21

uh...Dunno...

author
Kiteman (author)Kaiven2007-10-17

Ceiling tiles? DIY stores sometimes sell thin sheets of expanded polystyrene as insulation (maybe to go behind radiators), craft / modelling stores will sell it as a modelling material, or be able to advise on other alternatives.

author
Kaiven (author)Kiteman2007-10-18

oh! i found something! maybe a styrofoam meat tray. Mine had chicken :)

author
Kiteman (author)Kaiven2007-10-19

That's fine - as long as it'a big enough to cover the CD.

author
Kaiven (author)Kiteman2007-10-17

ok, i might try something i can find

author
pyrotecnix (author)2007-09-20

dude no way i have the same blade kit thing as you soz i am a bit lame...

author
zachninme (author)2007-09-17

This seems... too complicated... it seems your air channels actually allow too much air coming out too easily, decreasing run time. I'm not sure, but maybe...

author
Kiteman (author)zachninme2007-09-18

The excess air-flow seems to be through the central hole, which is why I restricted it there.

However, v2 will involve few/narrower channels from the centre to the edge, a change of glue and possibly plastic to cover the bottom instead of paper.

author
Weissensteinburg (author)2007-09-16

Hot glue dries a matter of minutes, if not seconds...

author

But its not low-friction. You need something that will be smooth.

author

It says you need ordinary glue, it can be used the same way as normal glue.

author
Kiteman (author)Weissensteinburg2007-09-17

I couldn't use hot-glue on the base because the gun melted the 'styrene and it cooled too quickly, before I got it completely smooth.

author
Weissensteinburg (author)Kiteman2007-09-17

Ah, gotcha.

author
ProfessorZ42 (author)2007-09-16

Wow! Five projects for one contest, and all fantastic!

author
Kiteman (author)ProfessorZ422007-09-17

I seem to have had a rush of blood to my 'ibles, don't I? It could have been six, but the local plumbing supplies stores all close on Sundays. That will have to wait, now - I have costumes to make!

author
bobbyk881 (author)2007-09-16

fuji film rules !!!!!!!!!!! and its not badly printed

author
Kiteman (author)bobbyk8812007-09-17

The balloon is badly printed.

author

Then why is there a big bubble of "FUJIFILM" missing?

author
awoodcarver (author)2007-09-17

Kite you must want that prize , I started a tater launcher-gold bearing gravel sucker for this contest but cant get to my tools to cut/round off some parts (garage is full of someones couches and such)good luck and do a new vid when it is done , I will have some of the kids at school make a few of these

author
MisterSlippy (author)2007-09-16

I believe this instructable calls for liberal use of the ubiquitous double-sided sticky tape! Excellent instructable, I like the design mods to the classic cd-hovercraft. Pity you had to rush it at the end there, though. Waiting anxiously for an update, lol

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