Hi John,
Those "little vertical fins" are called winglets. Here's a quick history on the concept.
The initial concept dates back to 1897, when English engineer Frederick W. Lanchester patented wing end-plates as a method for controlling wingtip vortices. In 1905, the Wright brothers used a concept they called "blinkers" on the canard of their Flyer III and later, on their Wright Model A aircraft. In 1910 they installed "side curtains" and modified blinkers on their production Wright Model B aircraft, to improve its stability. In the United States Scottish born engineer William E. Somerville patented the first functional winglets in 1910. Somerville installed the devices on his early biplane and monoplane designs.
Dr. Sighard Hoerner was a pioneer in the field, having written a technical paper published in 1952 that called for drooped wingtips whose pointed rear tips focused the resulting wingtip vortex away from the upper wing surface. Drooped wingtips are often called "Hoerner tips" in his honor. Gliders and light aircraft have made use of Hoerner tips for many years.
Hoerner's concept was further developed by Richard T. Whitcomb, an engineer at NASA's Langley Research Center, in response to the sharp increase in the cost of fuel after the 1973 oil crisis. Whitcomb's designs were flight-tested in 1979–80 by a joint NASA/Air Force team, using a KC-135 Stratotanker based at the Dryden Flight Research Center.
Even before NASA did flight testing on winglets, Burt Rutan incorporated them in his innovative Rutan VariEze homebuilt aircraft design, which made its first flight with winglets on May 21, 1975. The VariEze pioneered glass-reinforced plastic composite construction in homebuilt aircraft, which simplified fabrication of the winglets. He reduced the resulting drag penalty by assigning double duty to the winglets; they also serve as vertical stabilizers and rudders in his canard, pusher configuration aircraft....
I wanted to mention Rutan's contributions. During the 1970's, my father and I spent a reasonable amount of time in Burt's shop in Mojave as he was developing many of his "revolutionary" ideas. So, as a teenager, I was privy to numerous engineering discussions while he vetted various concepts with aeronautical engineers and rocket scientists like my father and others. So I've known why and how winglets work for 35 years, and I was pretty jazzed when Boeing added them to their airliners almost ten years later.
Here's a brief description of what winglets actually do.
The upward angle (or cant) of the winglet, its inward or outward angle (or toe), as well as its size and shape are critical for correct performance and are unique in each application. The wingtip vortex, which rotates around from below the wing, strikes the cambered surface of the winglet, generating a force that angles inward and slightly forward, analogous to a sailboat sailing close hauled. The winglet converts some of the otherwise-wasted energy in the wingtip vortex to an apparent thrust.
So, from what I know about props, they don't generate a significant tip vortex. Notice that we don't see winglets on aircraft propellers, wind turbines or similar devices that have had billions of dollars of research thrown at them to make them more efficient.
What we do know is that props can be more efficient if they are put inside a duct (like ducted fans). With very tight tolerances, the duct kind of acts like a stationary endplate for the propeller blades. So one would believe that ducting a boat propeller might increase the efficiency of the drive. That brings us to Kort nozzles.
The Kort nozzle is a shrouded, ducted propeller assembly for marine propulsion. The hydrodynamic design of the shroud, which is shaped like a foil, offers advantages for certain conditions over bare propellers. Kort nozzles or ducted propellers can be significantly more efficient than unducted propellers at low speeds, producing greater thrust in a smaller package. Tugboats are the most common application for Kort nozzles as highly loaded propellers on slow moving vessels benefit the most. The additional shrouding adds drag, however, and Kort nozzles lose their advantage over propellers at about ten knots (18.5 km/h)
There are number of after-market ducts that can be added to the drive legs of outboard motors, but they haven't really delivered on the theoretical improvments on boats like ours.
Now that you have a little more background on your general concept, you can start making a few prototypes and collecting some data on whether or not the concept actually helps in the scale that we're dealing with. Even though I don't think that this will produce a siginficant breakthrough, I'm personally interested to see how well your prototypes will work.
Keep us posted.
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, "John Green" <v_2jgree@...> wrote:
>
> This might be a good idea, or a load of garbage, so bear with me.
> As a child growing up in the fifties, I found out that if I bent the
> outer edges of paper plane wings up, it gave more lift, to the point
> that it forced them to lop, rather than allowing level flight.
> So, I was interested to see that, a few years ago, aircaft designers had
> finally caught up with my technology.
> There are now little vertical fins sticking up at the ends of airplane
> wings.
>
> Now, say this was used on a prop.
> The prop gets designed with a very high aspect ratio, so that it pushes
> water back efficiently, rather than creating a water 'cylinder' that is
> rotating.
> The pitch is minimal for the same reason.
> The water motion is created more by the airfoil (waterfoil, aquafoil?)
> section of the prop, than an angled pitch.
> And at the ends of the prop are little fins facing forwards.
>
> Now, take the same thinking, and apply it to regen, and the pitch used
> is then at 90 degrees to the previous idea.
> The fins then point 'sideways'.
> The idea is, it has minimal drag through the water, yet turns OK using
> aerodynamic lift as the means, rather than pitch.
> Remember, you read about it here first!
>
> John
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