Airboat with Horizontal Fan

Unless I missed it, no one mentioned the old air hockey game, lots of low pressure holes and the puck glides along with almost friction free movement.
This idea is the same but with the power and air flow is on board, the hockey puck could have had it's own air system and operated on a solid and flat table.
I think the power needed might be less than most would think.

As for patent protection, anyone can patent it, but could not prevent someone else from building and selling the same product. (just my thinking)

Floating things on air is easy, but as speed increases, the volume needed becomes quite large.
As a slow speed floater on a quite lake, I think it looks good.

Hope this is not too much for my first post.

Ron

 

Might work on a very smooth surface, but over the ground or over rough water that's probably not going to cut it. You need skirts or some type of extension down into the water, and once you do that it is just the pressure that is doing the work, so the flat plate with the holes isn't necessary. Interesting though in that it might have some advantages, but I can't quite put my finger on what it would do for you. Also remember that the weight of the air hockey puck is low, so the pressure loading on the bottom of the puck is almost nothing. To support some real weight is going to take more pressure and flow. It's another example, like a model airplane, where spectacular performance can be obtained in the subscale model and when you scale it up to the real world reality bites you in the rear end.

 

Mass and pressure but don't forget surface area as an important variable.

-Tom

 

All parts I need are readily available,(free for a period of time), available new or secondhand. Take one 8m ally barge or smaller max 2.5m wide for road transport.weight 500kg. Fit outboard on rear, install 260 HP diesel all soft rubber mounted,positioned for centre of gravity preferably nose down attitude at outboard idle speed. Install fan tower ( with gates for steering control.No air rudders needed, and fan.

You have an air propelled boat.?? built in modules. When you have finished with bits and pieces sell of on Trademe.

Problems.. being able to have a fan of sufficient diameter to absorb 260 HP diesel motor.It might be too wide to transport on the road.

 

Pressure is directly related to mass and area, or to put it another way, if you know the mass and the pressure you want, the area falls out...

 

If you look at typical aircraft propellers, the tip speed is close to mach 1.0 and the diameter is set by the disk loading. A typical aircraft prop for a 250 hp airplane is about 78 inches in diameter. You would turn that prop at about 2100 to 2500 rpm. So you can probably barely fit a prop with the area you need if you are going to move it on the road. There are also airboat props that are made for low speed thrust and have a lot more area at the blade root. Walker and Whirlwind are just two manufacturers that have composite props that are designed specifically for low speed thrust.

One area that may be an issue is the fact that you want to use a diesel engine. Aircraft props (and probably all propellers) have big issues with torsional shaft pulses. Props that do not have controllable pitch, or don't have adjustable pitch are probably fine, but you want and need a low prop pitch to get propulsive efficiency and that may not be available in a fixed pitch one piece prop. The problem with a diesel engine is that the combustion pulses are much stronger and that basically puts a lot of acceleration into the prop. The net result is that you beat the heck out of the blade attachment. Pilots check the tightness of the prop hub during preflight inspection by rocking the blades and making sure they aren't getting loose with age. This problem is more prevelent in four cylinder engines than it is for sixes, for obvious reasons. The two prop manufacturers I mentioned are selling composite props and they are probably a lot better in that regard than an aluminum prop. Either way you would want to keep a flywheel on the engine, as opposed to letting the prop be the flywheel, and there is a weight penalty for that, but I don't think that it would be smart to go without it.

 

All I can do is to use maximum HP available to move the maximum amount of air at the maximum speed and pressure possible through the air tower,and hope I can maintain momentum in the direction I want to go. The wind must be in my favour somtime. I will have a talk to King Neptune next week at the seaside.

I spent a lot of time during the ww2 years playing about Gruman Avengers,Lockheed Hudsons,Harvards,Kittyhawks etc., pinching parts and annoying maintenance staff and getting rides across the airfield. I appreciate what you are saying. I have tried to cover as much new developments materials for fans as possible.
Anything that will absorb vibration and noise must be an advantage. I would not want to lift a fan of and replace it for transport. I like to just get in the water quick and move of with little work as possible. Thank`s.

 

We could build an airboat with a horizontal fan like in the image for test purposes only. Note the wide area of water disterbance.

 

Experiments I have done over Christmas with the model modified, show that an airboat with a horizontal fan creates a Cyclone above the fan which probably accounts for the power to push the boat forward,in effect a powerful captured Tornado. Cyclones are vertical in nature whether they be in air or water. This does not happen with a vertical fan on an airboat.
The model airboat with a vertical fan shown would not even go forward or turn, turning the fan for directional control.

 

Tom,
Interesting proposal here, my question is, where do you see this 'boat'(assuming it went to production) in the market, Im certainly no expert here but IMHO there are too many questions about the design, I see it that the air would efectively have to dogleg to give any appreciable drive,
Have you made any calculations for full scale?
At full size I dont see that the design would work, (as it may on your little model) however if you went to fine precision engineering then possibly make it work but I belive you would be working on the level (and experience) of industry experts. perhaps on Formula 1 levels.
I am prepared to accept that this would work, I dont see that it does right now.

 

Personally I am not interested in the problems of commercial production or producing a high efficiency propulsion for boats,but a propulsion that will take a boat anywhere reasonable for exploring or transporting people reasonably quietly.
Any boatie who has sat in a boat drifting with the wind over shallows and sand bars would appreciate the experience, and it is not necessarily slow or without power.
The change of direction of the airflow in the air tower is a necessary part of the propulsion drive to provide a surface for the incoming compressed air flow to push against. You could calculate the thrust by multiplying the forward surface area available by the atmospheric pressure plus any increased pressure supplied by the horizontal fan

What I would be creating is a captured cyclone or Tornado as created in Nature, revolving as in Nature in a horizontal plane, not like a conventional airboat,trying to work in a verticle plane.
As with trying to make something fly you just need to overcome gravity plus a little more for success.
I would not invest large sums myself on such a doughtful project but the necessary experimental work can be done very low cost if you are not paying so-called experts to carry out the work.

 

Ok Tom,
I take your point, high performance isnt your aim, a nice day out on the water is more your mark, fair enough.
From what Ive read here I understand that your aim is a hybrid between ahovercraft and a jet drive, the downward cushion to lift you out of the water, and the rearward diversion of air for propulsion, would that be correct?
For me this would throw up more questions, what is the design for 'boat'? I mean in regards lateral stability, I would assume you are aiming for something along the lines of a flattie,
Have you calculated for a boat at full size, I apreciate that your small model may work but myself, in your small model, I dont see the full sized craft, and this is where I lose the direction, I dont see it working at full size, as you say from readily available parts, I cant see how, as you belive you could, you can get a craft much more than maybe 4-6' in lenght to take on the caracteristics you require, I would assume you are aiming for something more like 15-20' in length or maybe more, this is why I say I belive it possible could if you had the resources of a formula one team to design/construct your vessel.
Would it not require a significant amount of speed to become anything near efficient, If it were to work, I dont belive it would at low speed.
I feel that you are overdesigning your brief, I belive it has been more complicated than necesary. if your out for a gentle day on the water, would a mast and sail not be a better option, and possibly more fun (depending on your preferance of course) and lastly does the volume of the drive also not relate to what is driving your propeller aswell?
Please belive me I am not trying to be sarcastic here, I just see LOTS of traps to fall into, I applaud you for your efforts, However Im not convinced (Im sorry)
Also I apologise If you have clarified these points before and I have missed it.
Regards
Sam

 

Some fundamental laws of physics that might help understand "efficiency":

Any time you change the direction of a mass flow you lose energy as heat in turning the flow around the bend. A horizontal (vertical axis) fan changes the mass flow direction twice - the horizontal component of the inlet flow (due to forward velocity) is turned through an angle into the fan inlet, the fan radial flow velocity is turned through another angle to produce a net aft facing mass flow. Both of these turns reduce the fan efficiency over a properly sized and pitched, horizontal axis, axial flow fan or prop configuration.

For low speed propulsion a high mass flow with a flow velocity just greater than the velocity of the vessel will give the best overall efficiency. For an airboat this translates to a large prop diameter, running at as low a tip velocity as practical (for low noise). Anything that decreases the outlet area will act as an accelerating duct to some degree and may increase thrust, but this will be traded against the additional losses incurred from the drag of the duct plus the duct losses.

Jeremy

 

The free vortex ("Tornado") you have observed is simply a sign telling us that your fan is operating with a higher pressure than it is designed for, which results in a lower flow than optimum. This in turn means that there are major losses in the inlet, which cause a secondary flow, which is manifested in the inlet vortex.

So, it is not a new phantom discovery, it is just showing a lousy fan efficiency, which is one of the obvious drawbacks of your experiment; some of the other are touched upon by Jeremy H.

 

I appreciate the comments being made and I definately take no offence to any comments, but all of the suggestions seem to be a repeat of past comments, it won`t work.. but it does (just as a waterjet works by changing the direction of the waterflow into the low air preassure envoroment) and is ideal for pushing a craft around through shallow or obstructed waterways. I did say that and outboard or trimmable drive would be used in deep clear water as a main propulsion. I don`t think that making a craft look elegant or stream lined is important but useful work for the purpose is. A conventional airboat would not be of any use because of all the disadvantages.