Hovercraft Project

Attachment 3283I needed a big project once the last of the kids moved out of the house. I've always done woodworking, but wanted something different and fun.

I have always been fascinated by hovercraft and remembered seeing "personal" hovercraft on the opening of a James Bond file (one w/ Pearce Brosnan).

After looking into it, then looking more and looking even more - I decided I could do it.

It's been going on for about a year at a casual pace. I'm nearing completion.

It's been quite a project. I've learned a lot about fiberglassing and some about vacuum lamination. My overall approach is that I'm not trying to do a professional looking job - I want it to be fun to build and will be happy with half decent appearance and good performance. (It also provided an excuse to learn to weld, a lifelong goal.)

The drawing of what it should look like is attached.

Final weight is supposed to be 500 lbs (though I think that is actually heaver than it is). It's capacity is 850 lbs and the speed is 50 to 57 mph.

I got the plans from Universal Hovercraft (www.universalhovercraft.com). If you're interested, they have decent plans and they offer great technical support.

As I have time, I'll post pictures of the progress up to where I am now. (I'll try to do an update every day or so.)

Attachment 3285Attachment 3284The main body is 2" foam insulation board used in homes. I ended up using "green" from Lowes instead of the normal Corning pink. So, it started as a bunch of foam sheets.

The first step was to epoxy two layers of foam together in the rough shape of the hull. It is vacuum laminated using a big sheet of plastic folded over and duct taped together and a shop vac. Since my shop vac is crappy, I bought a refurbed vacuum pump to laminate. The second picture is of the hull while laminating (left under vacuum for about 30 hours).

(You have to put blankets over and under the vacuum hose to allow even air flow through the vacuum bag.)

This is a thread I will be following. Do you have a estimated budget or any budge figured out yet? What are you using for a motor to lift it?

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Originally Posted by EmptyNester

(You have to put blankets over and under the vacuum hose to allow even air flow through the vacuum bag.)

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I think I get what you're saying, is that inside the bag top and bottom and going to the nozzle so it provides air passages to the far end of the bag?

Did you just duct tape the vac hose into the bag at a seam?

Very cool project, looking forward to seeing how the powerplant and drivetrain is done.

Ed -

The detailed answer is, you have the following layers.

Bottom to top you have:
1) heavy gauge plastic big enough to fold over on top of foam
2) light gauge plastic to catch excess epoxy (and protect heavy gauge)
3) foam being laminated
4) light gauge plastic to catch excess epoxy
5) blanket to allow air flow underneatch vacuum line
6) vacuum line (hose/pipe with holes)
7) blanket to allow air flow
8) folded over plastic from bottom

You then seal the entire thing with duct tape. It's easy to find leaks as you can hear them and some leaking is okay. I've been told shop vac's use air flow for cooling, so they have to have some leakage to prevent overheating.

Jason,

On the Universal Hovercraft site, they say you can buy the entire kit for about $3000.

I'm just learning to fiberglass, so I've used more epoxy (suprisingly expensive) and fiberglass than expected. Mistakes also cost some. But, the biggest cost has been using the hovercraft as an excuse for tools. But, I'd have to say between $3k and $4k is ballpark. (I buy stuff as I go so that there is no big cash outlay.)

The plans call for an 18 to 24 hp riding mower engine. Since the "American Way" is "bigger is always better" - I got a 26 hp engine. They actually said that is a real sweet spot for performance. You can go for two separate motors (lift/thrust) or one. I'm going with one and the fan and prop are belt driven.

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Originally Posted by EmptyNester

The plans call for an 18 to 24 hp riding mower engine. Since the "American Way" is "bigger is always better" - I got a 26 hp engine.

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http://cumminsengines.com/every/appl...st_tier3.page?

Or if the American way is truly better... http://cumminsengines.com/every/appl...st_tier4.page?

MigPlazArc,

That looks great. LOL But, does it come with a snorkel? I'm guess I'd be driving a very fast submarine with that.

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Originally Posted by EmptyNester

MigPlazArc,

That looks great. LOL But, does it come with a snorkel? I'm guess I'd be driving a very fast submarine with that.

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Haha no, but they are turbo charged! If you have a plasma cutter and a welder you could put a snorkel on :)

Attachment 3292Attachment 3291

After vacuum laminating the two layers of 2" foam, I used a hot wire cutter to get the rough shape of the hull. I cleaning it up with a "sure foam".

After the shape was complete, a wood strip was attached to the sides. It will be the attachment point for the outer side of the skirt.

After that was done, the top of the deck is shaped with a downward slope. In the second picture you can see a dent down the middle of the foam. I used PVC with holes drilled in it for distributing the vacuum. The vacuum was a little too high and it ended up compressing the PVC into the foam.

That was a pain to fill. I used epoxy and glass microspheres.

Attachment 3294 Attachment 3293
After the hull is shaped, 1/8" marine plywood is attached with epoxy and vacuum laminated onto the foam hull. That's the layout in the first picture.

After the top of the hull is done, the bottom of the hull gets a foam "runner" around the edges. It's toped with plywood and will have a wood strip glued on for the inner skirt attachment.

The LP tank is to put weight on plywood expoyed into the hull. It is used for reinforcing the bottom of the hull to bolt the engine on.

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Originally Posted by MigPlazArc

Haha no, but they are turbo charged! If you have a plasma cutter and a welder you could put a snorkel on :)

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turbocharged....now you are talking :-) Lets put my bike engine in that thing.

Project is looking good empty nester. Any idea on payload on something like that or how fast they will move?

Quote:

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Originally Posted by MigPlazArc

http://cumminsengines.com/every/appl...st_tier3.page?

Or if the American way is truly better... http://cumminsengines.com/every/appl...st_tier4.page?

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Quote:

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Originally Posted by sportbike

turbocharged....now you are talking :-) Lets put my bike engine in that thing.

Project is looking good empty nester. Any idea on payload on something like that or how fast they will move?

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You both are a little off...... I'm going to "steel" an AT-802, take the turbine out and put it my oversized, 3x size of plans, hovercraft. :cool: Like the bike engine idea ;) And the cummin's turbo-ed. But turbine's are pretty light for the power.

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Originally Posted by sportbike

turbocharged....now you are talking :-) Lets put my bike engine in that thing.

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Yeah a 500 hp bike engine would work pretty good...But a turbocharged 15 liter with 400-600 hp stock!... Lets "chip" it and make it 750+ :D

And I'd have to agree...That hovercraft is coming along great it looks like.

P.S. you may need more than bolts to hold that 15l Cummins in ;)


Btw If you turn your hovercraft into a submarine I want to see a video of everybody's reaction to the strange turbulence under the water, thick black smoke bubbles coming to the surface, and the beautiful stainless steel "snorkel" air intake sticking out of the water! :)

Sportbike,

It has an 850 lb capacity and is supposed to have a top speed of about 50 to 55 MPH (cruise at 45).

The thing that makes me wonder how fast I'd really want to go is that they say not to run it if there any wind until you have experience.

I've read a number of funny stories about minor crashes because the test flight is the first time they ever flew a hovercraft. (One was a guy in the UK who was going to test it in a field. He said he hadn't really thought about the fact that he had to go up hill to get to the field. He said his first reaction when he started sliding sideways down the hill was to cut the power. With no power you lose all steering control, but it takes a couple seconds for the skirt to deflate. He said the second test flight was two weeks later after repairing all the damage from sliding sideways into a fence.)

Rege

If you loose power over water will this hovercraft float and will you be using it mainly on land or water ?

Quote:

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Originally Posted by EmptyNester

Sportbike,

It has an 850 lb capacity and is supposed to have a top speed of about 50 to 55 MPH (cruise at 45).

The thing that makes me wonder how fast I'd really want to go is that they say not to run it if there any wind until you have experience.

I've read a number of funny stories about minor crashes because the test flight is the first time they ever flew a hovercraft. (One was a guy in the UK who was going to test it in a field. He said he hadn't really thought about the fact that he had to go up hill to get to the field. He said his first reaction when he started sliding sideways down the hill was to cut the power. With no power you lose all steering control, but it takes a couple seconds for the skirt to deflate. He said the second test flight was two weeks later after repairing all the damage from sliding sideways into a fence.)

Rege

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Hmmm...kind of like some jetski's (needing to be under power to steer). Some jetski's even have sensors to open the throttle if you try to steer and cut gas at the same time.

Seems if may be easier to control with two separate engines, one for lift, and one for propulsion, although I am sure you can run a prop shaft or similar to use a singe power source.

When you get this thing done and tested, hit me up, I just might have to take a ride out a see it if you don't mind, Pittsburgh's not too much of a trip.

John

It does float. One of the strengths of the design is the bounancy of the foam. They say it can still float even if you cut it in half.

Some designs do have two engines. One drawback of two engines is that if you accidently cut the life engine instead of the thrust engine - you "plow in" (front starts diving underwater).

Quote:

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Originally Posted by EmptyNester

if you accidently cut the life engine instead of the thrust engine - you "plow in" (front starts diving underwater).

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In a two-engine configuration, the lift throttle and the thrust throttle could be mounted side by side with a horizontal tab on the lift throttle that overlaps the path of the thrust throttle, so that the act of reducing the lift simultaneously reduces thrust. You could reduce thrust without reducing lift, but you couldn't reduce lift without reducing thrust. There's got to be a name for that.

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Originally Posted by DaveO

In a two-engine configuration, the lift throttle and the thrust throttle could be mounted side by side with a horizontal tab on the lift throttle that overlaps the path of the thrust throttle, so that the act of reducing the lift simultaneously reduces thrust. You could reduce thrust without reducing lift, but you couldn't reduce lift without reducing thrust. There's got to be a name for that.

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At 45 to 50mph momentum would still be a problem.

Quote:

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Originally Posted by MigPlazArc

Btw If you turn your hovercraft into a submarine I want to see a video of everybody's reaction to the strange turbulence under the water, thick black smoke bubbles coming to the surface, and the beautiful stainless steel "snorkel" air intake sticking out of the water! :)

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Haha that would be awsome. Id also love to see that.. I could only imagine the look on some boaters face when this pipe goes past them puffing black smoke.

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Originally Posted by Jason

Haha that would be awsome. Id also love to see that.. I could only imagine the look on some boaters face when this pipe goes past them puffing black smoke.

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It would be awesome! Be even better to put a hinged rain cover "chinker thing" (I don't know what they call them) on it lol :D

Quote:

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Originally Posted by MigPlazArc

It would be awesome! Be even better to put a hinged rain cover "chinker thing" (I don't know what they call them) on it lol :D

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aw yes I know what your talking about.. That would be even better lol.

Off a couple days because I drove a cotter pin deep into my finger (darn HF trailer kit). Nothing a couple hours in the ER and a couple stitches won't fix.

The next step I did (last November) was to build the duct for the lift fan. They recommend an 1/8" clearance between the fan tip and the duct wall. The wall is made out of 1/8" marine plywood. It's amazing how you can bend that stuff. You glass two pieces together, then glass the outside of the wall. After that you wrap it around a form.

Attachment 3309

The next picture shows the top deck after I cut a hole in the hull and fiberglassed the lift duct in it place.
Attachment 3308

Attachment 3311The first picture shows the bottom after it's been finished and painted. The skirt attaches on the unpainted wood on the edge of the hull and the inside attached on the wood strip at the top. You can see a hole between the inner skirt attach strip and the outer edge of the lift duct. That is how the skirt is inflated.

The next picture shows the mounting strips for the cockpit wall and the center seat. The center seat also covers the steering mechanism and the lift fan drive belt.
Attachment 3310

You use two part marine foam to fill the void between the cockpit walls and the lift duct. The foam is as strong as a glue and it gives some structural integrity to the lift duct.

Attachment 3313

The foam expansion rate is based on the temperature. At 70 degrees it doesn't do much. They recommend 80 degrees. I did this in March, so it was pretty cold. I ran the torpedo heater pointed at the void I was filling. I poured the foam when it was about 105 degrees. It grew like crazy.

The last picture it after trimming the foam and glassing a piece of 1" foam insulation on top.

Attachment 3312

So how long is this boat and how big are the air motor blades gonna be?

It's 14 1/2 feet long and about 6 1/2 feet wide.

The lift fan has 4 blades and is 22" in diameter. The prop for propulsion is a normal 2 blade prop and is 56" in diameter.

Quote:

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Originally Posted by EmptyNester

It's 14 1/2 feet long and about 6 1/2 feet wide.

The lift fan has 4 blades and is 22" in diameter. The prop for propulsion is a normal 2 blade prop and is 56" in diameter.

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That ought to fly lol :)

Quote:

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Originally Posted by EmptyNester

It's 14 1/2 feet long and about 6 1/2 feet wide.

The lift fan has 4 blades and is 22" in diameter. The prop for propulsion is a normal 2 blade prop and is 56" in diameter.

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Is the one 26 HP engine going to power all of that prop? Are you going through two gear boxes or just one with two output shafts?

I Love Plasma -

My build only has a single engine and it uses belts. The sheave size is used to set the ratio of lift to thrust.

The lift fan has an 8" sheave while the prop has a 12". The sheave on the engine is the same size for both belts.

Okay I understand that part now. But one prop will be blowing towards the back of the craft and one blows down correct? How are you belt driving both props having both the props' shafts being perpendicular (If I am understanding the design correctly).

You do understand it correctly.

If you look at one of the first posts there is a blue print drawing. At the bottom of the mount for the prop there are two idler pulleys that give it a 90 degree bend.

Ah I see. Still a little confused. I will be keeping a close eye out for pictures, I think it will be easier for me then. :D

haha it's going to be done just in time for the rivers to freeze over, so either you'll have to wait til spring or have a cold ride out on the ice!

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Originally Posted by I_Love_Plasma

Ah I see. Still a little confused. I will be keeping a close eye out for pictures, I think it will be easier for me then. :D

haha it's going to be done just in time for the rivers to freeze over, so either you'll have to wait til spring or have a cold ride out on the ice!

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They say that they run fastest on ice. Not sure the cold weather operation has much appeal to me though. Plus, any breakdown is more interesting.

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Originally Posted by EmptyNester

cold weather operation

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If there was a light snowfall you could blow snow off the driveway and get the mail in the same trip!

Quote:

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Originally Posted by EmptyNester

They say that they run fastest on ice. Not sure the cold weather operation has much appeal to me though. Plus, any breakdown is more interesting.

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Yeah, it's not a simple "drive the pickup and car-trailer out with 6 big guys" retrieval. !! Yeah as you said interesting situation ;)

The thrust duct goes around the prop. If built correctly, they say you can get up to a 15% performance improvement. The first step was to build the form to bend the 1/8" plywood on. Then, cut the wood and fiberglass it together to get one long piece. The first picture shows the wood duct build on the form.
Attachment 3378
After that, you need to cut 2" foam to a specific arc to wrap around. It needs an arc rather than straight cut because you need to form the foam into a wing shape. So, compounding the precise arc of the plywood and the precise wing shape you form with the foam - it didn't go very well.

I got to the point of "this is no longer fun". So, I did the best I could just so I could move on. I ended up having to cut the foam into smaller chunks so I could work with it and get it to fit. Then, I either filled the gaps with foam or just glassed over them. Worst case, I can always redo it later and replace the one I did. A picture of it with the foam partially installed is below.
Attachment 3377

Not being a particularly artsy or talented at graphics design - I decided to go with a military look. I used "battleship gray" for the paint and I painted the props similar to military plane props. (Cheesy - but hey, it's the best I could do.) Friends have suggested I mount guns on it :)

The model is called the UH-14P, so I figured I'd do a big "UH-14" on the sides of the thrust duct.

Attachment 3379 Attachment 3380

type in "kari byron machine gun myth busters" on youtube THATS what you need minus the incendiary rounds ;).

Which prop is for lift? the big one what looks like maybe 40" blade?