RE: [Paddlewise] lift and efficiency: D

 -----Original Message-----
From: Robert C. Cline [mailto:rcline_at_onramp.net]
Sent: Tuesday, August 04, 1998 8:59 AM
To: K. Whilden; paddlewise
Subject: Re: [Paddlewise] lift and efficiency: D


Kevin wrote:

>Ok, now lets talk about lift... but first lets talk about drag. The
>paddler is pulling backwards on the paddle (force vector points towards
>the stern). The resistance of the water (drag) on the paddle resists   that
>pull (force vector points towards the bow). The drag force vector is
>slightly smaller than the paddler force vector, which is another way to
>think about efficiency. The difference in the size of the vectors
>represents the energy that is lost due to turbulence and the slippage of
>the paddle through the water. When lift is generated due to laminar   flow,
>the size of the resistance vector is slightly increased because the lift
>vector points in the same direction as the drag vector. Even if further
>calculations were to show that the lift generated by Greenland paddles
>really is insignificant, efficiency is probably still increased because
>there is a lot less turbulence created by the laminar flow. And note,
>modern, non-wing paddles can significantly reduce turbulence by slicing
>the paddle outwards away from the kayak, just like racers and greenland
>paddlers.
>
>Well, the concepts above are quite clear to me, but I wonder how clear   it
>is to the readers. I suppose I could put it down on a web page, with   force
>vector diagrams, and with maybe even a bonus picture of me waving my
>hands.  Anyhow, I hope my definitions make sense, and maybe clear up a
>little confusion.

What is clear to Kevin is clear as mud to me.  If Drag were less than the
force...then the paddle is moving through the water.  I guess the laminar
flow is on the power face and the turbulent flow is on the other face...   ??
But if that were true, then lift would be created on the underside of the
wing.

Lift...  Lift on a wing is created because there is a greater greater
distance on the upper surface of the wing between the leading edge and   the
trailing edge of the wing.  Isn't this called the airfoil... corrolated
with "hydrofoil?"

What is a "wing paddle?" John Winters speaks of low-aspect ratio... what   is
that?

I'm having a difficult time with this discussion not knowing the
vocabulary. I've looked for ads for a "wing paddle" but haven't seen any.
Perhaps that refers to the asymetrical design??  I'm reaching here.

Thanks

Robert


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I was similarly confused several years ago when George Gronseth first
wrote about Greenland paddles having lift. Since Greenland paddles are
symmetrical in section, they obviously can't have the kind of lift
generated by air moving over the top of an airplane wing.

However, lift is created when there is a difference in pressure between
opposite sides of an object regardless of the means used to create that
pressure difference. (John, correct me if I am wrong about this.) Despite   
the word, the direction of lift does not have to be up. You can also
create lift by moving an inclined object through a fluid. A prime example   
is holding your hand outside a moving vehicle and tilting it so the wind
moves it up. Other examples are when you scull your kayak paddle either
on or under the surface of the water, or support yourself with a sweep
stroke, or roll using a sweep or screw roll. I think this is the kind of
lift most people are referring to with regard to Greenland and other
paddles.

If I understand them correctly, wing paddles are an exception in that
they *are* shaped like airplane wings in section, and generate forward
lift in the same way. However, they are specialized paddles used mostly
for racing, and since they do not perform as well as standard paddles
for bracing and rolling, they are rarely stocked by recreational paddling   
shops. I think I have seen only one ad for them in Sea Kayaker.

Chuck Holst  
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