The Wind Powered Sail-less Boat

Say what you like, but I'm with MarkDrela on this one. The energy flow is always extracted from the surface and "spent" by the air propeller. The cart has its own reference frame that it "lives in" and that determines where the energy comes from.

 

You have misinterpreted what I said in post #27. I did not say it was impossible. I was pointing out to Windmaster that it had such a narrow range of application that it was impractical.

I had long ago dismissed it as a curiosity with limited practical application. This came about because I worked out the prop required to achieve DDWFTTW had to be monstrous compared with the turbine required to go directly upwind. In any case I have never felt a mechanically driven system had much merit. The real value comes when you combine the system with energy storage. In this way you can store energy in strong wind rather than just making bigger waves. That energy is put back when the wind dies. I have been developing electric transmissions to that end.

There are many skeptics who lack appreciation of the physics involved to work it out and continue to believe it is impossible despite numerous explations and demonstrations. They will believe any drivel that supports their view of the world per my joke at post #205. I simply got fed up trying to educate the uneducatable. You can see the ones who quickly jumped at the opportunity to verify their ignorance without any attempt to discredit my nonsense about April fool, battery powered and gel in level guages. How gullible are they and how lacking in scientific enquiry but it does prove my point that they view it is impossible and have completely closed minds. You have to have an open mind to learn and there are a number here beyond learning. You can choose where you want to place yourself.

Rick W

 

The thread starter started two threads on this topic and has never returned since making those posts so how they have evolved will not bother DuncanRox as he has never bothered to return. I guess he found inspiration elsewhere or got enough out of the first response.

I previously put an end to it at page 14 post #205 as I knew some simply lacked the understanding to work it out and would grasp at any straw that supported their ignorance. Everyone was happy with that until JB realised the hoax I had pulled and called me on it. He could not leave well enough alone.

Rick W.

 

Sure thing, Lee, sure thing. You have a picture in your head of how it works (which I think is mostly right) and a catch phrase that you think describes that picture.

Nobody else on the planet seems to think your catch phrase describes anything, but you've spent 10s of thousands of words and hundreds of posts on sailinganarchy trying to justify your catch phrase (I assume -- I have just skimmed occasionally)

Why don't you stop trying to torture the language to mean what you want, and accept that you don't get to decide what words mean?

Oh, right, because you're insane.

Carry on!

 

Well, I had not been paying close enough attention to see that DuncanRox had never even bothered to reply, or post a thank you. Aside from that, however, would it not still be prudent to create a new thread for Direct Upwind/DDWFTTW discussion. Obviously (by the number of posts in here, at least) it is of keen interest to a good number of members in this forum. Why not give it its own "home" or "frame of reference" if you will.

cheers!

 

Dwfttw

I agree.

"Downwind faster than the wind" should certainly have its own thread.

Perhaps in the new thread a mood of tolerance might prevail where "fools" are suffered gladly.

I have been building wind-turbine boats that go directly upwind for a number of years, both models and fullsize and there has always been a certain proportion of people who cannot believe that even this is possible, let alone going downwind faster than the wind (powered only by the wind). In fact, going directly upwind proves that downwind faster than the wind IS possible.

DWFTTW is really no big deal, in fact it seems rather obvious to me, but maybe this is because I have the experience mentioned above and have dealt with this kind of thinking for many years.

The people to whom DWFTTW seems impossible, sincerely believe what they say, because they do not have the ability to turn things around in their heads and see things from a different frame of reference. Having the knowledge that it is "impossible", they seek to justify their belief in any way they can.

I think the role of the DWFTTW believers is to patiently explain to them, and refrain from inferring that they are fools and idiots, or triumphantly poking fun at them when "victory" is claimed.

 

...so does that mean I don't have to hear an "I told you so" now? Since I at first wanted to scream at all of you that your drag ratios would be too high...but now, after reading through most of the posts in this thread, I see that IN THEORY it is quite possible, and believe you that you've accomplished it in real life...though I'm still having a LOT of trouble seeing all of the how...the physics routines in my head don't take very kindly to being forced to change & see how this can work...though they're (very) slowly coming around....

 

I have prepared a little presentation that takes you through the steps required to grasp the concept of the cart in what I hope is very easy to understand.

The numbers provided are all realistic for a large scale RC cart weighing about 20kg. Something that would carry a person would need more power as friction is likely to be higher. The losses I have indicated are also realistic.

Rick W

 

That's a fine theory. And in fact many of us have spent countless hours doing just that for anyone that is curious or skeptical. But I have a hard time showing that type of patience with folks that start out with insults toward us. Perhaps that's my own failing - in fact I'm sure it is - but I'm too old and crusty to change or apologize for who I am.

 

Also, what's the story with the JeeLerry claiming he's on the same page with Drela in claiming the energy ALWAYS comes from the ground and is "spent" by the propeller!? I'm pretty sure that's not what Drela said. In fact I think it was pretty much the opposite. Whether the ground does the work or the wind does the work is entirely dependent on the frame chosen for the analysis.

 

http://www.boatdesign.net/forums/pr...wnwind-faster-than-wind-25527.html#post246631

As no one else seemed to be taking the initiative.

Rick W

 

so...if I'm reading correctly (between the lines, that is)...you're stating that DDWFTTW vehicles will reach faster than wind speeds, but only a certain speed above wind speed...depending on wind/ground speed, and efficiency factors. Beyond that point, acceleration will cease because there is no "other" power to fuel further acceleration?

(and no magical, mystical energy being harvested from the ground either...unless lightning hits nearby...lol )

 

The multiple of windspeed achievable will be limited by the overall efficiency of the system or the gearing. With variable ratio transmission you can probably get close to the best result for a fixed prop size that is large enough to get you going.

It may be that the highest speed possible for a given wind condition would be achieved with a vehicle that needed to be towed up to a certain speed before the prop developed the necessary power to overcome the drag.

Conventional sails have the ability to be flattened to improve their lift to drag at high velocity. The thickness of a propeller is fixed so you are stuck with moving the blades through the air. At high speed they will work at low angle of attack but you are still dragging a thick blade through the air. If you opt for smaller, thinner blades then these will not develop efficient thrust at low speed.

So that is the long answer. In short you are correct. The vehicle cannot keep accelerating. There will be a point where the thrust and drag are balanced. If it has variable gearing then you can keep inching it up to a delicate balance. It would be possible to go too far and then the speed drops quickly until you adjust the gearing.

One other possible limit is wheel slip. If the friction is too low and the wheels start slipping then this is, in effect, reducing the efficiency of the overall system. So you want a good surface. This situation is not an issue for a boat because the turbine has to be drawn through the water although capsize is a possibility.

Rick W

 

It's also interesting to note that with any fixed gear ratio the vehicle has a theoretical top speed relative to wind speed. Even with no drag, induced losses, or transmission losses, it would not continue to accelerate indefinitely. It's true that with variable gearing there is no theoretical top end if you could build infinitely efficient props, transmissions, etc.

 

Thanks for your efforts Mark.
I think your analysis doesn't answer what I'm asking for as you've done a 'fixed photo' analysis at a DDWFFTW situation, asuming it happens. Then you explain the sharing of energies in that situation. But this analysis does not explain how Fnet is possible, in other words how do you arrive to the DDWFTTW situation.

All the best.