Here's some info on three hovercrafts I constructed awhile back.
Each hovercraft is a rough implementation of the plans available from
Universal
Hovercraft. All are electric, and all were cut to the hull outlines
provided by the Universal Hovercraft plans. On all three models, I
deviated from the plans by using foam for the thrust ducts. Skirts are
constructed from plastic trash bags.
Some
additional info...
The one in the background was my first model hovercraft
that actually worked. It is free flight, and is fairly close to the
Universal Hovercraft plans for the UHM-23 (Universal Hovercraft Model - 23
inches). The rudder is fixed in place. It uses two $0.75 radio shack
hobby motors. The lift motor runs on four Energizer rechargable nicad 1.2 volt
AA bateries, the thrust motor uses just two of the same. You know you're doing
something wrong if you need more power for lift than thrust, but on
the other hand, I use this one inside my apartment to amuse guests, and
if it moves too fast, it'll just be that much less time before it crashes
into the wall..... Speaking of crashes, that St. Louis Arch shaped bit of
wood in front of the thrust duct serves as protection for the rather flimsy
foam thrust duct. Hovercrafts just weren't meant to operate in a world
populated by chairs and couches....
The two larger hovercrafts are a bit too powerful and much
too loud to use inside. The one on the left is still a work-in-progress.
It's my first radio controled model hovercraft and I've still got to get
the bugs out. It uses a stock r/c race car motor to blow some of the
air into a lift duct and some out a thrust duct and past dual servo-controled
rudders. Out of laziness, I deviated from the Universal Hovercraft plans
quite a bit here, and I paid for it: I couldn't get skirt right ( eventually
I cut out one that was too large so that I would have room to move it back and forth -- that's what you see here). But no matter how I set it, I still don't
really get enough lift and I think the trim is wrong too... Or it may be that
integrated craft are, in fact, a hoax and the Europeans and the Aussies are
having a good laugh at our expense as they hide little centrifugal fans
under the seats of their supposedly integrated craft.
To investigate this possibility, I built the craft at the bottom of the
pic. Stressing my 7.2 volt nicad battery to the limit, I used two stock
r/c race car motors. I get plenty of lift. And then on top of that, I
get plenty more lift. Lets put it this way: I can pile my shoes and an
extra 7.2 volt battery on top of the cockpit before I can detect a dip in
the hover height. Oh, and it is loud. Very, very loud. I love it. I
completely love it. Operating it is very much like my full-size craft
with one important exception -- there are only two radio channels, so I
can't turn off the lift motor. There's all the same hair raising moments
you get with my full-size craft (ie
I'm-giving-it-full-thrust-and-now-I-simply-have-to-see-if-I-can-get-out-of
the-way-in-time) but without the option of ditching the craft. Lots of
fun. The one downside is, of course, I get very short run times before
the battery needs to be replaced. What I really need is a lift motor
that spins at 7.2 volts but doesn't draw quite so much power (but there
are none to be found). Alternatively, an additional radio channel would
allow me to hook up an electronic speed control to the lift motor to
conserve power, and would give me an emergency stopping method. An
expensive solution for the future....
Just to be clear here -- I cut a lot of corners -- if you follow the
Universal
Hovercraft plans to the letter, you'll get some crafts that look
a bit more elegant than mine.
Finally, I'm sure that using twin
motors is the most important factor in the far better performance of my
twin motor craft, but simply being 6 inches longer and somewhat wider certainly
helps too (The smallest
craft is 23 inches long, the middle craft is 30 inches long, and the
largest craft is 3 feet long....)