TOPIC: HOVERCRAFT

River Rat

 

 

I would like to thank Guy for setting up this space to document my journey…

In the mid 1980’s, while I was in high school, seeing a hovercraft transition from shore to water with hardly a wave intrigued me… I was hooked and had to have one.  I ordered plans from Universal Hovercraft and built a UH-12T2, a twin engine craft designed for two people within a cockpit.  I learned a lot building this craft. 

Here is my second build… the hull comes from another builder and is a single engine design.  It is approximately 16.5 feet long by 8 feet wide.  I have a 22R-E (fuel injected) from a 1985 Toyota Celica, rated at 114 HP at 4800 RPM.   Here is where I am with the build…

 

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Engine and Drive

I removed the engine and all associated electrical from the car.  There were “gobs” of wiring and peripheral devices connected to the wiring harness.  I made an engine mount and connected all the wiring.  I was relieved to find no smoke arise when I connected a battery to the harness!  I wanted to see if it would turn over so I crossed my fingers and turned the key.  Nothing!  No click noises of relays, and even worse, the voltmeter on the console increased in voltage as I engaged the key to the start position.  Not good.  I did some more research and realized I did not have the “neutral switch” plugged in as the car had a manual transmission and I removed the bell housing and transmission.  I connected everything and the engine turned over.  I created a fuel system using an external fuel pump connected to a tank from a snowmobile I salvaged and had the “return” line go back to the tank.  I turned the key, it spun over about twice and purred like a kitten with little vibration!  Wow!  I was delighted!

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I spent a lot of time researching how to transfer the power to the reduction drive assembly and decided to go with a “Kop-Flex” sleeve and coupler.   We have a CNC plasma machine and I cut a ¼” steel plate that will bolt onto the flywheel in lieu of the “flex plate” from the old clutch assembly.  I had a local machine shop heat up the ring gear and remove the ring gear from the flywheel.  They then put the flywheel on the lathe with the plate attached and machine the circular plate on the edge to make sure it is completely round.  They then machined the face of the plate to seat the sleeve of the coupler about 1/16” into the plate.  This ensures that the coupler is completely centered on the flywheel.  Bolts were then drilled into the plate while the coupler was seated to secure the coupler. 

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I have the engine mounted on the frame by the two rubber mounts from the car body.  The engine is mounted exactly like it was on the car.  The two main mounts are at 45 degree angles exactly midway through the length of the motor, and the motor balances perfectly on those two mounts.  I then used a piece of aluminum angle iron and made a rubber isolated adjustable mount right under the end of the motor below the flywheel.  It is adjustable as each has a threaded rod with two nuts that can be easily adjusted so I can make the engine level with the mount below.

The coupler is designed for a 1 ½” keyed shaft.  The coupler is designed with teeth that are slightly ground that can accommodate up to 1.5 degrees of misalignment with the attached shaft.  If I can design the mount properly, the pillow blocks should be perfectly centred, hopefully ensuring a long life of the coupler with minimal drive train vibration.

For the “lower” shaft assembly, there will be a pillow block bearing unit as close as possible to the coupler, then a 4.75” 8 groove 3V profile pulley, followed by another pillow block.  The upper 1 ¼” shaft will have a pillow block, then a wooden 10.75” sheave, another pillow block and then the fan assembly.  The reduction ratio is 2.26, which would put the fan at about 2100 rpm with a wide open throttle rpm of 4800 on the motor.

I am making the upper sheave.  I am using plywood.  I cut good quality ¾” plywood into 11 ¾ circles and then laminated them together.   I used 5 pieces to give me a width of 3 3/4”.  The belt profile is a little over 3”.  I have the unit mounted onto a lathe now and have turned the unit so the outer edge is round.  It was fantastic to see the wood become uniform.  I am also cutting down the two faces (front and back) to make them true, as they were about 1/8” out of true.   I picked up two “weld-on” 1 ¼” bushings and will be cutting some 1/8” steel plate “doughnuts” with 8 bolt holes to weld onto those bushings.  I will cut into the front and back face of the wooden sheave to accommodate the hub assembly. 

I looked up the specifications of the 3V eight groove sheave and drafted that profile out to cut a ¼” steel tool for cutting the grooves in the sheave.  I cut out the tool and compared it against the 4.75” lower pulley.  It was close but took some filing by had to get it matching the profile exactly.  

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On my first craft, I designed a joystick to integrate the throttle and steering.  It was intuitive and I decided to go with it on this craft.  I used paper mache (newspaper pieces and flour and water) to make a custom grip for the stick.  I used two part epoxy to coat the paper mache.   When the epoxy cured, I immersed the unit into water for several days and dissolved out the paper, leaving the shell.  I will use a part A, part B foam to pour into that unit to attach it to the top of the joystick.  I can then fiberglass the handgrip and foam below it.

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I ordered a multi-wing 12 bladed ZL fan.  The fan is 44.75” is diameter that will have an 1/8” clearance to the duct.  I am not sure what balance I will need between the lift and thrust.  About 1/3 of the duct will split to direct air into the plenum for lift.   I know that more blades provide more pressure for lift but not a much thrust.  If the lift is to much compared to the thrust, I can reduce the number of blades.  I can also adjust the pitch on the blades to “absorb” the 114 HP, keeping the wide open throttle to a maximum of 4800 rpm.

I want to try a finger skirt design on this craft.  I like the idea of the ability to change damaged skirt sections as needed.  I have been trying to collect information on how finger skirts are designed.  I am finding that most folks, are using the bag design.   Presently, I will be making fiberglass panels to enclose the hull to complete the plenum.  I really could use some help here!  I think the most suitable material is urethane coated nylon with a weight of 6 ounces per yard.  From what I read, the skirt is angled in more at the front of the craft, less so on the sides and is most upright at the rear.  I am not sure how to design the “anti-scoop” flaps that prevent water from filling up the skirt in the rear sections.  I have heard of a special design that is supposed to prevent plow-in on the front but I have no idea how they are constructed.  Any comments, diagrams or information you could provide would be greatly appreciated.

I am not sure how to determine the optimum hover height.  I read that some people use 10 percent of the width of the craft.  My craft is 96” wide so that would put the designed hover height at 9.6”.  Is it right to use 10 percent of the craft width?

My goal is to get the craft functional before the lakes and river freezes.  I need to know how much weight the craft can carry before it has difficulty getting over the hump on water.  Once I have that determined, I would like to make a partial cabin to make the unit a “year round” craft and take long trips on the river.  I can spend all winter designing the cab, instrumentation and cosmetic work during the long winter months.

 

Comments   

Gone7
# Gone7 2015-09-01 20:36
You're very welcome Robert! Glad to see your new project post. Looks like an interesting build for sure.

My initial concern would be that you have a fairly heavy engine for that size hull. It's an awesome little motor, I love Toyotas, but most of it is made of cast iron. Too bad you can't trade it out with another lighter weight option.

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Author / Member : tymorobe

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