Low Drag Propulsion System

[Thunderhead19]

I am interested in developing a low drag propulsion system for very high-speed craft that uses rotating cylinders (configured much like the tires on a car). My intent is to use the boundary layer to provide thrust. Yes, I do realize that this either means I need very high surface area and quite high roatation speed to get a thick enough boundary layer do acomplish anything, but I think it would be acheivable. I've seen this somewhere before though, and I can't remember. Has anyone else seen this type of system???

Originally Posted by Thunderhead19

I am interested in developing a low drag propulsion system for very high-speed craft that uses rotating cylinders (configured much like the tires on a car). My intent is to use the boundary layer to provide thrust. Yes, I do realize that this either means I need very high surface area and quite high roatation speed to get a thick enough boundary layer do acomplish anything, but I think it would be acheivable. I've seen this somewhere before though, and I can't remember. Has anyone else seen this type of system???

You might want to do some research on the Tesla Turbine. It uses the principles that you are talking about. He also used the same designs to make pumps

[Tim B]

Check out Brunel's experiment between screw propeller and paddle-wheel. Consider now the high performance powercraft (class 1 offshore - surface piercing props) and the high-power commercial craft (many using waterjets). The common feature being a propeller of some type. Yes, a rotating cylinder in a fluid will produce a force, but it is unlikely to do it as efficiently as a propeller. The major advance of the water-jet over the marine prop was the reduction in cavitation, as the speed was higher, and the pitch lower, thus preventing to a large extent cavitiation. Also, because the water is in a rigid tube, and is itself incompressible, that reduces the chance.

Don't get me wrong, I'm not trying to put a damper on you're enthusiasm, but this is not a simple area, and the waterjet is efficient for more reasons than I have mentioned. So the question becomes, is it a revolutionary system, or a revolution in an existing system's efficiency?

If for instance, there is a correlation between propeller pitch and speed (but we don't want it to cavitate when we slam the throttle open) then perhaps that systems control and blade optimisation would be a possible way to go. Perhaps even using sensory equipment on the blades to detect cavitation, and reduce pitch/speed accordingly.

Just an idea.

Tim B

[Thunderhead19]

I did look at water jets, but my only issue with them was that (obviously) the intake has to be immersed I am hoping to get the hull an inch or more above the water surface. The Tesla turbine info that I got was encouraging, but a little suspicios, with claims of efficiency in the 90% range. I have seen SNOWMOBILES recently racing on a lake in about 3 feet of water, supported only by dynamic lift and propelled by their usual caterpiller track.

I have seen SNOWMOBILES recently racing on a lake in about 3 feet of water, supported only by dynamic lift and propelled by their usual caterpiller track.

It is true that snowmobiles can successfully sustain high speeds over water, but only after bringing themselves up to speed on land. Those races usually start on shore, or in very shallow water, where tread-to-ground energy transfer is much more efficient, and allows for high accelerations. If you were somehow to start the snowmobile in open water( i.e. with floats) and launched it, it would take so long to accelerate up to a speed that would dynamically support it, that you would definitely sink. As you said, you would need immense cylinders, or cylinders with large paddles, and then you get into the same problem with cavitation.

I thought I had seen a story about an inventor earlier this year who came up with a virtually cavitation free screw drive, but I can't find it. In the mean time check this out
http://www.olds.com.au/marine/maximi...cy/Default.htm

I hope this helped,
-Dom
www.idfuel.com

[danmarine]

Originally Posted by Thunderhead19

I did look at water jets, but my only issue with them was that (obviously) the intake has to be immersed I am hoping to get the hull an inch or more above the water surface. The Tesla turbine info that I got was encouraging, but a little suspicios, with claims of efficiency in the 90% range. I have seen SNOWMOBILES recently racing on a lake in about 3 feet of water, supported only by dynamic lift and propelled by their usual caterpiller track.

I think you are looking at a boat close to a hovercraft. Search around related websites for surface-effect vehicles and ground-effect craft, these rely on air-lubrication under the hull to get their speed. Its become a fine line between hovercraft and aircraft now days and you may find the "hoverhawk" an interesting read. In relation to your caterpiller track concept I know some hovercraft use a centrifugal fan for thrust, this would be spinning in the right direction and with some refinement the idea may just work. Snowmobile engine/gearbox set-up is often used on hovercraft for the air-cooling and variable speed. Try www.4wings.com as this guy seems to know alot about such things and is very helpfull as well.
Good luck and hope to hear more,
Dan