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how can we ride 40-50 mph in only 20-25 mph of wind?

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SethP
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Re: my 2 cents

Postby SethP » Fri Jun 09, 2006 1:15 pm

fxeric wrote:not to get off the topic but can you sail directly upwind?
With a typical sailboat or kite, I don't believe sustained travel directly upwind is possible (if you have momentum and turn directly upwind, you'll continue for a short distance, but it won't be sustained).

However, let's say you put a wind-powered electric generator on a boat. Connect that to an electric motor, point directly upwind, and "sail" for as long as there is wind. You could gear the wind rotor directly to a prop as well, and I'm sure there are other designs that can take you directly upwind as well.

Seth

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Klaus (c:E
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Postby Klaus (c:E » Fri Jun 09, 2006 1:29 pm

Hai,

with a vehicle that has a gear it can be done.
It depends on what You call sailing. It has been done with a boat that was driven upwind by a propeller that has been driven ba a propeller type wind energy converter instead of a sail. Click on the picture! It´s a link.
The first time i´ve heard about something like this was at a wind energy conference where there was described a monohull boat utilizing the same propulsion concept.

Edit:
Link was not longer available, so i added three more recent links.
Wind turbine powered sailboat
Windmill Sailboat: Sailing Against the Wind
Pictures of "Revelation II"

Sea You: Klaus (c:E
Last edited by Klaus (c:E on Sat Aug 09, 2008 2:57 pm, edited 1 time in total.

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Postby SethP » Fri Jun 09, 2006 1:52 pm

Good to see that what I conceptualized has been done! Here's a quote from that boat's site: "Unlike a normal sailing craft this vessel makes its' best time sailing straight into a headwind."

I wonder if it can exceed the actual windspeed?

Seth

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Re: my 2 cents

Postby ImagineParadise » Fri Jun 09, 2006 3:07 pm

fxeric wrote:you can't sail downwind faster then true windspeed but you can get downwind faster then windspeed by storing energy from the sail as forward velocity and redirecting it downwind in bursts (can't be done for more then bursts due to drag ,the less drag u have the more effectively u can use the stored energy like in ice boats to get a better vmg)

not to get off the topic but can you sail directly upwind?

fxeric
I just said that!

spork wrote:Even if that could work, wouldn't that be powered partially by the kiter's muscles rather than purely by the wind?
By the muscules? When I say pull, I mean when you cut out more with the boards edging capibilities, basicly fighting the kite a little with leg strength. So...
Its the only way it could work.
Our kites and boards arent that efficient when compaired to something like a wind world breaking speed record by a boat.

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spork
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Postby spork » Fri Jun 09, 2006 3:42 pm

gdorfman wrote:i have reviewed #1, and i believe the sails must be on the top spokes, not the bottom ones. otherwise it will go backwards and upwind.
Nope. All points above the axle are going faster than the cart. All points below the axle are going slower (but in the same direction) as the cart. Go out to the garage and push on the spokes of your bicycle. Push the middle of the spoke below the axle and you'll see that the bike moves in the direction you push, but at twice the speed as your hand moves as you push. This will only work for a few inches as the spoke will quickly cease to be the bottom spoke. Then you have to move to the new bottom spoke and do the same thing.
gdorfman wrote: this is not complicated. are you trying to trick me?
On the contrary. I'm trying every way I know how to make this as clear as possible.
i do not have a yo yo. isn't it just a fixed axel, or is it complicated?


It's no differnt than your bike wheel in this respect. Not complicated.

i guess that you are saying that even though the kite/parachute is flying slower than the object it's fixed to, the lines don't slacken and it doesn't fall down, because the lines are being reeled in. but that entails work and i think breaks the argument. i can winch a car downwind at infinite times the wind speed.

Sorry, now I'm lost.

for 3, i don't understand your "spiralling 45 degree downwind path" do you mean the path of the blades or the actual vehicle?
This is the path of the tips of the blades. By changing the gearing you can change the angle at which they spiral downwind. If you were to construct such a vehicle (which has been done) you'd also want to make the blades variable pitch so you could optimize them as you approached and passed the wind speed.

Image
i still disagree your current example is relevant. upwind is easy...
OK. Let's take it in pieces. If you are floating in a current of 10 knots, but there is 0 knots of true wind, do you agree that you could raise your sails and tack into the apparent wind? Do you agree that you'd reach your destination before the water around you?
can a fast boat in 0 wind and 10kts current, hold it's place in respect to the ground?
I don't think so.

fxeric wrote:you can't sail downwind faster then true windspeed
Really? That's your whole argument? I've posted 5 example of how you can do this in great detail. "No you can't" is your counter argument?
not to get off the topic but can you sail directly upwind?
Of course.
Last edited by spork on Fri Jun 09, 2006 6:37 pm, edited 1 time in total.

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Postby hein » Fri Jun 09, 2006 4:36 pm

Want to go downwind faster than windspeed?

Point a skate board straight down wind.
Get a small fast kite and start looping it in
the power zone while you ride straight down
wind. I'll bet you can exceed windspeed.

You'll have losses from drag/friction so when
they balance out the pull of the kite then you
will stop accelerating.

-Hein

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Postby spork » Fri Jun 09, 2006 5:37 pm

Hein, I've been thinking about your approach of looping the kite while riding a skateboard straight downwind. I'm having trouble with this approach since there is no direct connection between your downwind speed and the kite's "forward" speed. When the rider reaches true wind-speed downwind I think we run into problems. I realize the kite could still have relative wind over it, but I think this implies that someone could stand on solid ground on a day with no wind and loop the kite continuously. Granted, this might require some starting condition, but even so, I don't think that is possible. Help me out here.

RC

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Postby hein » Fri Jun 09, 2006 5:52 pm

I think you might need to have some controlled
braking to keep from outrunning and stalling the
kite. Keeping the system in balance while you
reach the limit of it's capability will be where
some tweaking might be necessary.

I do think you will be able to outrun the wind.
Perhaps only a little. -But I could be wrong.
Maybe it's not sustainable. I understand your
argument and I'm not sure I have an answer.

-Hein

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Postby kitebored » Fri Jun 09, 2006 6:43 pm

spork, where do you kite in the bay?


enjoying your posts.... i agree with the yoyo, but it's a transient condition that runs out when the string runs out.

About the wagon spokes, as far as practicality, wouldn't you end up gearing a rigid sail(wing) to rotate through a series of angles with respect to the wheel's rotation? Seems possible, but not unless someone lays down their $100K.


As far as the kitelooping skateboard, this I do believe is a perpetual motion machine. It will work, but only with a zero drag kite, and only to the limit of the windspeed.

Every one of spork's concepts involves using the wind to create a force, and using gears or levers to cantilever that force into a weaker, but farther moving (hence faster) push. The stationary object (ground or water) provides the pivot for the cantilever system.

With the skateboard, there is no stationary reference point, so the theoretical limit would be to match windspeed.

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Postby gdorfman » Fri Jun 09, 2006 7:26 pm

I did my empirical test on the spokes. I had visualized that top/bottom mattered for forward/reverse, but it’s actually front half/rear half. Anywhere you push on the spokes in front of the axel will make it go forward. This would be a good test question somewhere. Anyways, I agree with you. If you only put temporary sails in the bottom forward quarter of the wheel, these will still be in a tailwind when the rest of the bike is in a headwind and keep pushing it. Pretty cool.

I will need to skip the yo yo one since I can’t try it or visualize it perfectly.

For 3, yes my point was that the pitch would need to change as the vessel’s apparent wind direction would change. I had earlier used the inability to sail upwind as a proof against some of these, but you are right that with a prop you could actually go upwind—so I don’t see that as a stop against progress once the vessel hits a headwind. However, it would need to generate significant speed from that (small at first) headwind, and I don’t know how feasible that is.

We agree about the current. My point was that it’s very easy to make upwind progress faster than the current—but that does not show you can stay stationary or make progress downwind relative to ground (which is the topic and which you wrote you agree on). But actually, we are saying that it is possible to do that—with an iceboat probably in regards to VMG, and one of your contraptions for a dead downwind course.

I don’t think the kite looping works because you will hit a headwind which disrupts it, even if they are looping very fast. This is the point I made originally—I think it’s true for all conventional wind vehicles. But it seems like with a rigid, tunable prop you actually could continue accelerating in a headwind, so you probably could go directly downwind faster than the wind.

I still think that the encapsulated, reframed ice boats is the most conceptually elegant of all these contraptions…


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