Airboat with Horizontal Fan

[tom kane]

An Airboat with a horizontal fan should be more efficient than a vertical fan.
Air particles entering a horizontal fan must stop,slow down,change direction allowing the fan to accelerate air particles better.Head winds should have less detrimantal effect.A horizontal fan can add lift to boat etc., Made from lunchbox, computer fan, electric drill battery. It does work.

[Ike]

Isn't that pretty much what a hovercraft does?

[mydauphin]

Tom you invented the hovercraft...

[tom kane]

Originally Posted by Ike

Isn't that pretty much what a hovercraft does?

Do you think this model could be scaled up for real passengers. And can you explain exactly how the model shown actually works.

[tom kane]

Originally Posted by mydauphin

Tom you invented the hovercraft...

Thank`s for giving me that dubious honour. Can you explain exactually how the model shown actually works. It is simple enough..it does weigh two pounds. Not good power to weight ratio but it can move quite fast for the restrictions.

[Leo Lazauskas]

Originally Posted by tom kane

Thank`s for giving me that dubious honour. Can you explain exactually how the model shown actually works. It is simple enough..it does weigh two pounds. Not good power to weight ratio but it can move quite fast for the restrictions.

Search for:
hovercraft
travelling pressure distributions
Surface Effect Ships

You should find more than enough to keep you busy for a long time.

[tom kane]

Thank`s Leo thats all old stuff to me,done that been there I have not seen the principle depicted by the model shown used anywhere. The model is a boat operating in the water not riding on a cushion of air which gives it better directional control. Not a lot different to most real size and models.
The difference is just how the air flow is put to use and the use of a horizontal fan. The need is for a very shallow water craft with no underwater obstructions manouverable, reasonably quiet,not speedy, not a rich mans ego driver. Did you know that the "inventor" of the so-called hovercraft used old tin cans to try the principle?

[mydauphin]

Originally Posted by tom kane

An Airboat with a horizontal fan should be more efficient than a vertical fan. Why would you say that? The only advantage is better aerodynamics, but that is offset by airflow reduce over prop. A ducted fan is probably best.
Air particles entering a horizontal fan must stop,slow down,change direction allowing the fan to accelerate air particles better.Head winds should have less detrimantal effect.A horizontal fan can add lift to boat etc., Only if air is pump under hull. Made from lunchbox, computer fan, electric drill battery. It does work.

A weird idea for an almost flying boat (WIG) is combining a boat with an autogyro. The propeller on top actually generates lift in airflow and pusher engine work same as airboat.

[tom kane]

I have already suggested some of the reasons why a horizontal fan would be more efficient. Aerodynamics are not a concern at low speeds. A ducted fan would be used. The air flow over the fan would not already have been accelerated as with a vertical fan which would make it less efficient,a propellor or fan needs stationary air to work efficiently. The lift to the hull would be applied through a thrust bearing (by the fan trying to rise ). Air pumped under a hull reduces contact with water making the boat harder to control. Wierd ideas are great if they do a job the way you need.

[tom kane]

How about this airboat,a bit wierd but does a job..but the noise and power that has to be generated to just move is terrific..

[Dave Gudeman]

Originally Posted by tom kane

I have already suggested some of the reasons why a horizontal fan would be more efficient. Aerodynamics are not a concern at low speeds. A ducted fan would be used. The air flow over the fan would not already have been accelerated as with a vertical fan which would make it less efficient,a propellor or fan needs stationary air to work efficiently. The lift to the hull would be applied through a thrust bearing (by the fan trying to rise ).

I'm not a mechanical engineer, but there are some basic physics objections to your idea.

Any upward force on the boat would derive from the net change in vertical acceleration of the air that the fan draws in. This net change would be close to 0 because although the air is first accelerated downward, it is then accelerated upward by the same amount in order to eliminate the vertical component of motion. So there would be little or no lift on the boat from this effect.

I don't see how this setup is going to be more efficient because of the increased friction and turbulence along that long curving duct. (Removed the argument about accelerating the air because I realized that it isn't true).

That is not to say that your plan might not have other advantages. It might be quieter and less dangerous, for example. But I don't think it is going to increase efficiency or provide any lift.

Or are you using a radial fan? I can't tell from the model. If so, then none of my efficiency arguments apply because the mechanism is so different. But I think an air boat with a radial fan would be cool.

[tom kane]

This is a throw away experiment,so free cheap parts to be used. The fan would be as in image, ventilation tower fans which can be easily change pitch of blades. The lifting force of the fan is not a big issue.but the lifting force of a fan is very substantial. what is wanted is a boat that can traverse very shallow sand bars,mud, reeds, flats for camping such areas. water propeller are useless as are jets which just clog up. Long poles are hard work and a fairly big boat to camp on would be nice.

The fan would only accelerate the air down and compress into the chamber,then exit straight backwards past a venturi area past rudders. The air mass acting on the front wall of the chamber moves the boat forward.

To check the lift potential of previous models I put the models on scales and they all showed a loss of weight somtimes one third of the total weight of the model.

[Dave Gudeman]

(please note that I was wrong in part of my previous comment. I removed that part)

Originally Posted by tom kane

To check the lift potential of previous models I put the models on scales and they all showed a loss of weight somtimes one third of the total weight of the model.

This is interesting, but I still don't think I was wrong in that part of my argument. If the net vertical acceleration of the air is 0, then the net upward force on the model should be 0. Think of it this way: the fan is sucking air down, which tends to push the boat up. But the column of air is then hitting the bottom of the duct and that tends to push the boat down. The upward force and the downward force should both be equal, assuming that the air coming out the back is horizontal.

Maybe the duct in the model is not long enough to make the air flow horizontal and it is still coming out the back of the duct in a slightly downward direction. Or maybe it has to do with creating a low-pressure area above the boat. Now that I think of it, that actually sounds plausible --at least for a model. I don't know how the effect would scale.

I know there are mechanical engineers on this list. I wish one would comment because it is an interesting idea.

So when are you going to scale this up and show us some pictures?

[latestarter]

In terms of efficiency, my feeling is that it will be less efficient as you are missing out on the suction effect of the fan to move the boat forward.

I agreed with Dave G's analysis of the air passing through the boat that the vertical forces should cancel out however ducted fans and variable area tubes can do unusual things. The point about the low pressure area above the boat could be right regarding less weight on the scales.

The big benefit would be if it was an open boat the draught of air past the occupants should be much less than sitting in front of a vertical fan.

PS
when I read the first post, I thought it was another solar concrete sub idea until I saw it was by a senior member with good rep.

[tom kane]

The model works like an inflated ballon when the nozzle is released,pressure on the forward end pushes the ballon forward. I was surprised how well the model moved...considering the weight (which probably is an advantage) around in circles without the rudders,where the real problen lies. But with rudders,water and air control seems good. The air is axial flow and would be improved with finns to even out airflow. There is a small amount of venturi effect at the rear of the duct before air hits the rudders. The option I would prefer to complete is shown in image...which I spent more time reseaching...Everything is improvable. The image shown is not a conventional hovercraft or cushion craft.