Alex's twin motor hovercraft - RC Groups
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Aug 23, 2008, 11:20 PM
Engineer for Christ
IBCrazy's Avatar
Build Log

Alex's twin motor hovercraft

Well, technically a hovercaft does fly right? It just flies at low altitude.

Since my first hovercraft was a success, I decided to make a bigger and better one. This one will use two motors rather than only one. One is dedicated to the lift, the other is the drive. I'm thinking I will make a finger skirt for this one rather than the typical bag style that I employed on my first model. We'll see how it goes.

Another first for me, this one is mostly wood construction (ie. not foam). The bottom is foam so it can naturally float without the skirt inflated.

The craft measures 32"X20" and will have a 2" hover height. I estimate it will weight about 50 oz or so. So the bottom area will be ~600 square inches supporting 50 oz weight. That means the lift motor must produce 1/160 psi to lift the craft.
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Aug 23, 2008, 11:36 PM
Engineer for Christ
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frame construction

I build the frame out of Basswood. Balsa is a little too flimsy and takes on water easily. I would have used ply, but it is expensive and heavy. I used 3"X1/8" for the main rail. It will have foam glued to the bottom for flotation.

I glued a 1" strip along the bottom inner edge to begin the transfer chamber. The transfer chamber is 3" wide and will be fed by the lift fan. The transfer chamber will transfer the air around the craft and into the plenum chamber which lifts the craft.
Aug 23, 2008, 11:42 PM
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Making the bottom

The bottom of the craft is foam. It naturally floats and is water proof, so it works well here. I traced out a form of the inside of the frame on the foam. This will be glued to the bottom of the frame and will be the top of the plenum chamber. I made it 1" wider than the bottom of the craft to make a bigger transfer chamber. I secured the foam to the wood with gorilla glue.
Aug 23, 2008, 11:55 PM
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Finishing the transfer chamber

To finish the transfer chamber, I glued basswood at a 60 degree angle to the bottom of the craft. I then drilled many holes in it which will transfer air into the plenum chamber and the skirt. The angled chamber helps the craft overcome obstacles and such that are higher than the hover height. A squared edge will bring the craft to a jarring halt where the angle wants to rise over an obstacle.

The holes should act as individual air ports for each finger of the skirt. Before I get to the skirt, I'm going to set up the lift motor on the topside of the hull.
Aug 26, 2008, 10:16 AM
Registered User
critterhunter's Avatar
Looking good, Alex. I may build a RC hovercraft in the future. RC cars never interested me since I drive a car in real life but I'm pretty sure I'll never fly a plane. On the other hand, a hovercraft would be cool and it also doesn't have expensive wear and tear that the RC cars do.
Sep 29, 2008, 09:41 PM
Engineer for Christ
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Skirt construction

Ok, so after 5 weeks I'm finally getting back to this one. The skirt on this one is a finger skirt. I have never made a finger skirt before, so hopefully it will work.

The idea is that each individual "finger" acts as it's own, and will easily deflect if it hits an obstruction. I chose this type for two reasons:

1. The bag skirt had a tendency to take on water and was a pain to purge
2. I had never done it before

Each finer was glued on one side all the way around the craft with Goop. Once dry, I glued the other side to the frame.
Jun 19, 2009, 07:24 PM
Engineer for Christ
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Bag skirt

The finger skirt turned out to be too stiff. It would never have sealed so I went with a bag skirt. The entire skirt is sealed off except from inside the transfer chamber so it shouldn't pick up anything from the road or water. Again, the skirt is made from a cheap shower curtain and glued together with shoe goo.

I cut a 5" hole in the bottom of the craft for air to reach the plenum chamber. I then cut a cheap plastic bowl into a 2" cylinder and glued it into the hole. This will keep water out of the craft when I deflate the skirt.

The pressure vessel distributes the air to the rest of the craft. There are 6 ducts that transfer air into the transfer chamber and a hole every 2" along the transfer chamber to deliver air to the skirt. The vessel maintains pressure with a single small prop. Pressure in the chamber is approximately 1/5-1/8 psi.

I also glued an "H" out of 1/2" balsa wood strips. This way when I deflate the skirt at speed the craft drops on the wood and not the skirt. It's basically a set of brakes.

Last edited by IBCrazy; Jun 19, 2009 at 07:39 PM.
Jun 19, 2009, 07:29 PM
Engineer for Christ
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Drive system

The drive system is a rudder with the motor mounted to it. This basically gives me thrust vectoring for the best possible turns. The motor swings a large 9" prop for maximum acceleration and torque.

The rudder is made from coroplast with a flute cut out for a pivot.

The lift fan is a small 6" prop. Smaller props are better than larger ones as they require less power to generate the needed pressure. Remember that pressure is what lifts the craft, so all you need to do is keep up with the air flow once pressure is established.
Jun 19, 2009, 07:35 PM
Engineer for Christ
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Completed craft

The hovercraft performance is nothing short of exceptional. I can hover on as little as 30 Watts and it will lift a full 20 lbs at full power of only 60 Watts! I might increase the prop pitch from a 6X4 to a 6X5.5 to get more air flow in rough areas.

Weight on this one is a bit over 3 lbs, which is fairly light for a 30X21" craft. The size is great for stability on choppy water. Top speed is 22 mph at which point the front end lifts in the air and it back flips I need a bit more weight if I want to go any faster.
Jul 04, 2009, 10:06 AM
Registered User
it looks cool
Jul 04, 2009, 03:24 PM
Brunswick, Ohio
BrunswickOH's Avatar
Any chance of some video of this in action?
Jul 04, 2009, 05:14 PM
Engineer for Christ
IBCrazy's Avatar
I'll take some of it on water and land. I run it at the dock in downtown Paducah. It always draws attention when I charge it into the river at full power. It is a bit slower on water due to the drag of the skirt, but still works well.
Jul 04, 2009, 09:10 PM
Brunswick, Ohio
BrunswickOH's Avatar
Very cool

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