Hovercraft Project

[redbeard]

Is the lift fan something you manufactured or is it available off the shelf somewhere?

[EmptyNester]

Plasma - very cool. That would definitely look good, but would probably take up all the craft's weight capacity.

The lift fan is the 4 bladed one and is around 24" in diameter (I don't remember exactly). The Prop is for propulsion and is 56" inches.

You can either make them yourself, buy them in rough form and finish them, or buy them finished (from Universal Hovercraft, the place I got the plans). Since balancing them is critical and it seems like a poorly built one could probably disintegrate itself and the craft - I bought it finished.

[Tritium]

I always wanted a hovercraft when I was a kid but it would serve no practical purpose in the cactus, mesquite and bare dirt areas where I live(except as a dust cloud generator). Still though I find them very interesting. Good luck with yours. Now a Sky Car, that would fill the bill around here just fine.

Thurmond

[NRM]

Wow nice thread, keep up the good work. I want to build one now.

[EmptyNester]

These shots show the skirt laying on the floor before I attached it. I started painting the hull but didn't paint around areas that I though I might need to do more work.

The front has a mount for the forward navigation light. I'll still have to put a dashboard on the front and a bottom attach strip for the windshield.



The rear shot shows the engine mount (angled wood painted gray). Right behind that is the platform that the prop shaft and bearings connect to. Where the wood sticks off the back will become the bottom attachment point for the steering system (rudders).



The next welding project will be building braces out of angle iron (1" long) and conduit. The first angle will go against the top/back of the cockpit, the second will go against the top of the prop platform and the conduit will be between the two.

There will be one on each side of the prop platform. It's to prevent a catastrophic failure of the prop mount from killing you.

This is starting to catch up to where I am right now (I started this in Sept '10).

[redbeard]

You can either make them yourself, buy them in rough form and finish them, or buy them finished (from Universal Hovercraft, the place I got the plans). Since balancing them is critical and it seems like a poorly built one could probably disintegrate itself and the craft - I bought it finished.

Just curious, do the plans have fairly detailed instructions on how to make them? No doubt one would gain a whole new respect for the Wright Bros. if he went that route.

I always wanted a hovercraft when I was a kid

What kid didn't? Being a child of Arizona though, I always thought the 6x6 amphibious vehicle would have been the more practical choice.

[EmptyNester]

Redbeard,

I'd have to say the prop construction instructions are closer to "conceptual" than to "detailed" They give a cross-section of what it should look like and a broad description of the steps.

When I thought about the speed these things go, and how critical balance is - I knew it was beyond my capability to make it "safe", let alone "good perfoming".

They have a technical support line that I made a lot of use of, but in general I spent almost as much time research steps on the web and thinking through how I'd do any given step before I started. Had I not done that - I probably would have had to redo almost everything.

I'm not one to charge ahead blindly, but the blueprints are for the model I'm doing and the instruction book is general for all the models they make. So, the information you need for any particular part can be somewhat disjoint.

But, I would recommend the plans from the company. The $35 or $40 for the plans is well worth the free tech support you get with the build.

Rege

[DaveO]

I recall reading that for a long time ship propellers were created more as the result of art than science, and it wasn't until fluid dynamics became a studied topic and the advent of computer modeling did we get a really clear idea of what was going on. Compare a modern submarine propeller to your mind's eye view of what a propeller looks like (altho sub props are also built for silence). So I can see why leaving that aspect of your build to the experts makes sense.

[67cudafb]

I have been reading all the post and I think this thing could really hurt you but a lot of fun doing it be safe

[redbeard]

I know you're right on the professionally made prop, I just have this ridiculous credo that everything I build should be as close to 100% DIY as possible. It has bitten me in the butt more than once.

The plans and tech support do sound like a pretty reasonable deal, hopefully these guys will still be around if I ever get enough time to do something like this.

[Tritium]

I have been reading all the post and I think this thing could really hurt you but a lot of fun doing it be safe

So can an 8' shredder on a small tractor but like all things with big rotating blades you have to be VERY aware what you are doing and where you put body parts you want to keep

Thurmond

[EmptyNester]

Tritium - I had thought it would be humorous for my first flight to wear an old leather aviator helmet with goggles and scarf. Then I realized that could make the test flight very short and my last flight

I do have to make guards for the prop and fan. They say to use 4" square wire fence for the prop and 2" for the fan. I'm trying to figure out the best way to fabricate it.

I am currently thinking about 2 ways:

1) cut it bigger and then trim and bend pieces until it was round then weld it together

2) cut it round to size and then weld wire around it.

The second option seems like the easier path- but I'm not sure what kind of wire to use or where to get it.

Any thoughts anybody....

[redbeard]

How about making it an inch or so larger, folding it down and wrapping a strip of sheet metal around it to dress the edge? Hardware cloth comes in a lot more sizes and materials than they carry at the Big Orange Box, and could be something to consider using too, but might require some extra support. If you use a finer mesh, you probably could get away with wearing that scarf.

Another possibility would be just to fab your own entirely by building a frame out of 1/8 or 3/16 rod with concentric rings spaced at 2-3" supported by 8-12 spokes. More work, but it would look nice and professional and symmetrical, kind of like the guards on the oscillating fans of yore.

[sportbike]

How about making it an inch or so larger, folding it down and wrapping a strip of sheet metal around it to dress the edge? Hardware cloth comes in a lot more sizes and materials than they carry at the Big Orange Box, and could be something to consider using too, but might require some extra support. If you use a finer mesh, you probably could get away with wearing that scarf.

Another possibility would be just to fab your own entirely by building a frame out of 1/8 or 3/16 rod with concentric rings spaced at 2-3" supported by 8-12 spokes. More work, but it would look nice and professional and symmetrical, kind of like the guards on the oscillating fans of yore.

Speaking of guards for a fan, Perhaps you can stumble across a large barn style fan and use the guard from it? I kind of like the concentric ring idea. You could just calculatethe lengths of each ring (3.14 * diameter = circumference) , weld them together, then sort of 'squish' them into a circle.

[ogorir]

with that fence panel, you should be able to take a piece of cardboard cut to the diameter you need the guard and spray some paint around the edge to mark the circle.(remember when you're looking at the paint circle that the inside is what you want to keep). you can fold over the edge to give the guard some depth by cutting the crosswise pieces and bending the wire up where your circle is marked, then welding it back together(which direction you cut depends on where you are on the circle, obviously)*.

using bolt cutters and a big pair of vice grips for bending, it shouldn't take too long to knock it into shape. a 2" strapping band welded around the outside should finish it off nicely.

*I realize this isn't completely clear, I just can't think of a better way to say it.

[DVA]

That is an awesome project. When I was a kid my neighbor drove his hover craft up and down the dirt roads and made the hugest dust clouds, hope nobody was painting their home in the neighbor hood. Anyway, I will keep an eye on your progress.

[EmptyNester]

Lots of good ideas.....

I haven't looked for the material to make the guard yet. I'm not sure if it isn't actually the hardware cloth that I'd end up getting.

I think fabbing my own would be good, except I'm just getting started with metal and I'm guessing it wouldn't look that good.

One of the other things I've heard mentioned is that another purpose of the guard is to contain pieces should the prop break/fragment.

Ogorir - do they make banding material in anything other than stainless? I only have MIG and have only worked with mild steel so far.

DVA - I've seen videos of hovercraft running on dirt. Looked like it would be a mess. When I get it done, its going to kill me not to be able to cruise around the neighborhood to test it. I live in a plan - so that wouldn't go over well plus the roads are a little too narrow for comfort. It's going to be interesting that the test flight will also be my first training flight.

[EmptyNester]

These pictures show the skirt after just being attached.



The skirt is PVC covered cloth. I had to cut the fabric in half and then cut the fabric to a specified pattern for the joints. Glued it with a quick setting cement and it was ready to go.

The edges get folded over and screwed in. It took 300 screens starting with the corners. You have to gather fabric on the inside at the front because of excess due to the curve of the hull.

I tested it on the horses so that I could see how the skirt was hanging. I could see that there was some severe puckering. After that we took it down and did the test hover.

That was the big milestone since hovering is an issue if the air splitters aren't done right. You can see the top of one in the picture above. It is a piece of 1/8" wood that goes from the skirt attach strip in the lift duct to the bottom of the fan blade. It ensures that you get high pressure air in the skirt.

With my kids help, we did a test hover. Worked great! At high motor rpm the rear skirt would flap. After talking to tech support, I found out that I didn't add and extra 4" piece to it.



300 screws off, a little glue and 300 screws on - and it was good to do. No more flapping. On the reinstallation I used nylon string trimer line inside the folded over skirt material. It kept the skirt from twisting and make the installation go smoother.



This is the view of underneath. I marked the ground contact line with a paint pen so that I could ensure it was installed straight.

[redbeard]

with that fence panel, you should be able to take a piece of cardboard cut to the diameter you need the guard and spray some paint around the edge to mark the circle.(remember when you're looking at the paint circle that the inside is what you want to keep). you can fold over the edge to give the guard some depth by cutting the crosswise pieces and bending the wire up where your circle is marked, then welding it back together(which direction you cut depends on where you are on the circle, obviously)*.

using bolt cutters and a big pair of vice grips for bending, it shouldn't take too long to knock it into shape. a 2" strapping band welded around the outside should finish it off nicely.

*I realize this isn't completely clear, I just can't think of a better way to say it.

I think you did a much better job explaining it than I did, but I just thought of a more visual way to put it: form the mesh into the shape of a giant freeze plug then wrap the circumference with an appropriately sized steel band.

Another thing that occurred to me is that if you do fab your own, it might be easier to get a roll of stiff steel wire (10ga or better) and spiral it out from a circle in the center. Once you have the first wrap started, it should be easy to follow by using spacers (1/4 plywood with slots maybe?) to keep it nice and even.

You mentioned that part of the purpose of the guard is to contain shrapnel in the event of prop failure, if so, are the sides of the ducts themselves going to be able to slow down chunks of disintegrating propeller enough? If not you might consider lining them with sheet metal or building the cage extra deep if there is enough clearance.

[EmptyNester]

They say that one of the biggest mistakes new builders make is putting too much weight on the hovercraft. Everything is really light. The cockpit walls are only 1/8" plywood. Seats are 1/4". As a big guy, I plan to beef up the seats a little.

I've only seen pictures on one prop failure. I think the 1/8" plywood, foam and fiberglass of the duct were sufficient to slow it to the point that it wasn't a real threat. It turns out that the one failure I saw was from a prop the person made by themselves.

The clearance on the prop is supposed to be 1/4". My duct is a little out of round and it's good about 2/3 of the way around. I haven't decided yet if I want to glass the other part to make it consistent.