Air boat

you only need the engine not the gearbox. i think the small airboat pictured will disappoint you with its performance unless you want to cruise at slow speeds. build a 13 or 14 footer and use a larger engine. just as easy as an 8 footer and 100% increase in performance and fishing room. look up glen-l plans 13 foot air boat for vw power.

 

Do a websearch for flounder gigging boats - they use 13hp Honda motors with about a 3-foot prop. It won't get you on plane, but it will scoot you around in the shallow stuff pretty good.

I could see Tom Kane's idea possibly working as a hovercraft. Maybe a centrally-located motor driving four (one at each corner of the craft) downward-ducted props for lift and a fifth ducted prop at the back for propulsion and rudder...

 

I know what you mean, BUT
If I got an VW engine or any really, would be worked into a bigger boat, but this would be a little fun project, hence a old lawn mower motor and a small 8ft boat

 

Might I suggest a fairly modern liquid-cooled snowmobile engine? Many of the relatively late model engines make quite a bit of horsepower, and by virtue of being liquid cooled, one needs only add a larger radiator to keep it cool enough during the summer months.
Seems to me that weight-to-power considerations would make one a rather viable candidate for something like an airboat.
A guy would have to do something about final drive ratios, but a gearbox or pulley/belt jockeying should do what is needed to get prop RPM down to subsonic.

Roger

 

Experimental Air Boat with a horizontal fan.

 

Different quite different lol

 

Helicopters and many other craft have horizontal fans and all work well. Any air a fan displaces is replaced from all directions not just from the direction of travel particularly at slow speeds. Air comes down from above even at high speed.
If you just want to skim the surface and not fly you do not need a big fan or collective, and cyclic pitch control. Ducted fans are more efficient for this type of work. A horizontal fan reduces the possibility of an air boat rolling over from rotational torque and is better controlled. Directional control can be from changing the direction of the airflow without any reduction of thrust and without using ducting.

 

Tom, would you have any more information on this?

 

First off, a helicopter doesn't use a horizontal fan, it uses a rotating wing that generates lift in just the same way that an aircraft wing does. Because it's rotating, it can generate lift without forward motion, that's all. When in flight the disc is tilted to provide thrust as well as lift, but as anyone who's operated a helicopter will know, it is very far from being an efficient way of moving through the air. Helicopters use more power, and hence fuel, for a given speed and payload, because they are less efficient than conventional aircraft.

Tom, you seem to just carry on ignoring the high losses of a horizontal fan/prop system for this application, both in this thread and others where you've tried the same sales pitch. The evidence is indisputable; turning the inlet air through 90 deg when in forward motion and turning the outlet air through 90 degrees all the time creates a lot of additional loss. Your repeated mention of the "air being replaced from all directions" is also incorrect when in forward motion. Forward motion of a system such as you suggest will reduce efficiency, as the air flowing over the upward facing intake will suffer a pressure drop, reducing fan efficiency. This was discovered back in the 50's with the first hovercraft, and since then vertical intakes have been abandoned for all systems of this kind where efficiency is important.

The directional torque roll over is a non-problem in practice. Like many others here, I've designed, built and flown a very light air boat (mine was on TV to prove it). The torque effect with 50 hp and a very light, top heavy, air boat made from three of sailboards and microlight aircraft engine and prop was non-existent - or at least undetectable by this particular air boat pilot.

Similarly, as I said before (and was studiously ignored) the losses from rudders are small, smaller by far than the ducting losses from turning all that mass flow in a horizontal fan design.

 

Jeremy,

Do by chance know a Canadian by the name of Bob Sturick?

He made significant progress in hovercraft design in the 60's.

Thread drift... sorry Liighthead.

 

I'm afraid not, Tom. I never really played around with hovercraft much, apart from building one at school in the late sixties as a class project with a lot of other kids.

I did design and help build an air boat for a TV show here, Scrapheap Challenge (the show's called Junkyard Wars in NA, I believe), a few years ago. It worked OK, despite being very light, bodged together in just 10 hours from scrap and having all the weight up fairly high. Here's a shot from one of the stills the TV people took of me racing it across a lake in the final:

 

Not bad for ten hour build time!

I like the geometry.

 

You might consider a small, horizontal fan hovercraft from Universal Hovercraft.

Check out the specs and video at:

UH-6F Trainer

 

I am quite happy with my experiments and have a lot of fun and people keep on saying it will not work or be efficient and pointing out problems which do not exist for what I want. Just a quiet motor across shallows and lowering down a
pivotal drive surface propulsion for a bit of extra speed when the water is deep enough. When I fit the bigger fan I expect to even be able to skim in ground effect. Lots of boats are pushed around by small fans.

 

That was a great show. I missed that particular episode.