The Wind Powered Sail-less Boat

no doubt wind shear is the main driver
but
although my bet is they crunched a lot of numbers before they decided to make the wings and connecting surfaces x thick
thing is if you look through, there is a video of the plane breaking
not surprising since complex orbital mechanics is a mind bender it may have been forgotten in the calculations
and if I remember calculating the induced or excess hyperbolic velocity is a problem taught in diffy Q not even sure they had that in vector analysis
top end of math kids
the theoretical physics and electrical engineering folks all took it
but not sure the basic structural engineer is required to take it
not even sure a aeronautics engineer would have taken it
its not a class for a week of heart
and frankly
Ive forgotten virtually all of it
but
it will add some to the energy of the system
its one reason there is a turn involved in dynamic soaring
other than the obvious
sooooo
Im out
thanks for the entertainment
was great
B

 

The glider needs to have a side force in order to "get thrust" from the wind, that is going much slower than the glider. I guess at that point the side force comes from acceleration due to turning, but in the beginning it must have started with gravity. With that 500 J/kg you can achieve a initial speed of ~30 m/s. How many loops you need to get that 160 m/s?

How much does the speed (kinetic energy) change during each loop. I guess the speed is at maximum just before diving into boundary layer and at minimum before getting back to high wind.

Joakim

 

The attached diagram shows what happens in DS.

 

Downwind Faster Than the Wind

Here's an interesting video about this:

http://www.boingboing.net/2008/12/12/downwind-faster-than-1.html

Don't be put off - stay with it - its not for children!

 

Windmaster, The debate has raged and Rick & a few admitted to a hoax but I am still confused as I have limited theoretical training and failed in advanced maths so I stick to computing - which is just "talking in another language"...

If the mythbusters get to play with this concept - do please post on BD.net - in "Drivel" if busted and a link there if "plausible" It could keep many of us occupied and entertained for a looooong time... Thanks...

 

Hello all.

I can see that I'm late to this party, but thought I would weigh in anyway.

I'm JB and I'm the guy you see in the MythBuster's Challenge video. My partner and I have built over 10 of these DDWFTTW carts and demonstrated them many times.

In spite of the humor of Rick's last posts here, there is no hoax. There is no CGI. There is not string pulling the cart. There is no perpetual motion. There is only long used traditional sailing principles wrapped in a clever, unfamiliar and unintuitive package.

The packaging truly allows the vehicle to travel directly downwind, faster than the wind, powered only by the wind, steady state.

I can offer the math. I can offer analogies. I can offer explanations from simple to complex. Happy to answer any questions.

It's real, it does what we say it does and it can be demonstrated upon request. We present it not as something useful (it's really not), but as a physics brainteaser that confounds some pretty bright people.

We are currently in the design/build process of a ride-along vehicle with which we will be attempting to exceed the downwind velocity of the wind by more than 2x, all while traveling DDW. As the windspeed gets exceeded by such a multiple, it make people look more and more silly when they say it can't even be equaled, let alone exceeded.

Fire away.

JB

PS: Nice to see Mark Drela here -- you're reputation precedes you (courtesy of JJcotes and many, many others -- and of course your work)

 

hehe - welcome JB,

If you have gone through the thread you'll know that its a tough crowd here to convince.

And what the heck does a tredmil prove?

 

Yeah, I've read the thread, but since I have a device sitting here on my desk that goes DDWFTTW upon demand I don't usually let the tough crowds get to me. I even manage to get through to one or two now and then.

I'm hoping that many of the more vocal critics from previously in the thread -- Guillermo, clmanges, 3dyachts, et al, will return for some good exchanges.

Well, for starters it proves 3dyachts wrong in his claim that the craft is running at an angle to the wind -- but then 3dyachts gets a lot of his claims wrong. Take this one for example:

3dyachts:

At no time during DDWFTTW operation does that spinny pinwheely thing on the cart act as a turbine -- only as a plain jane prop.

JB

 

well start singin cause the class is seated and anxiously awaiting something
we're just not sure what yet

as Reorge would say

fool me once
cant get fooled again

 

Hi JB

Hello

I think you are being over-modest to say DWFTTW does not have any application. So many "discoveries" in the past have not had any obvious use, but in the fullness of time they have proved to be very useful. This could be such a case.

I've spent the last few days enjoying the controversy in the other forums.

A ride-along version would go some way to silencing the critics, however, from what I have seen elsewhere, there are some who will not or cannot, believe what to many seems obviously possible.

There have been similar objections to the premise that a boat can sail directly into the wind, and I built a ride-on version to demonstrate it - (it can be seen on Youtube under "windmill driven boat"). This was a few years ago, but I still find people on some forums denying the possibility.

Usually, for the sake of a quiet life, I don't choose to dispute it with them!

 

Hi Boston.

To start, may we stipulate that craft with traditional sailing rigs regularly achieve downwind VMGs (velocity made good) significantly greater than 1.0 while on ~45d broad reach?

Ice-boats and land-yachts regularly achieve downwind VMGs of greater than 3x and there are many sailboats that can also break the 1.0 barrier though not to the same extreme due to obviously greater hull drag.

A way to visualize the above is to imagine a ice-boat racing a free floating balloon. A start point is defined on the upwind side of the lake with a finish point a few miles directly downwind. As the sailing craft crosses the start point on a steady state 45d broad reach, the neutral bouyancy balloon is released into the air. The balloon takes the shortest and direct path to the finish point while the ice-boat will make the longer angled path. At the halfway point, the ice-boat will jibe and take aim at the finish point. The result of the race leaves the balloon cryin' for it's mommy.

The fact that these craft can beat the speed of the balloon and the wind by more than 3x puts lie to the "perpetual motion" and "where's the energy coming from" arguments regarding DWFTTW. Once past that, it's a straightforward engineering problem -- how can we build a device whose sails trace a traditional path and yet allow the chassis to go DDWFTTW.

JB

 

Hi Windmaster. Though it's easily done and has been done many times, including by you, I understand just a tiny bit where people think it can't be done in a boat. What amazes me even more is that people believe a turbine powered device *on land* can't drive directly upwind. Following is a link to a Physics Prof who states that straight upwind can't be done.

http://blog.dotphys.net/2008/12/physics-and-directly-downwind-faster-than-the-wind-dwfttw-vehicles/

This was one of my comments to him regarding the "straight upwind" issue:

JB

 

I'd like to throw another point out for stipulation: The definitional difference between a 'turbine' and a 'prop'.

In their conventional form (constrained to a shaft) both a turbine and a prop can be considered a spinning disk of sorts. I present that the difference between the two simply involves the direction of the flow through the disk -- the flow through the disk of a turbine is from a region of high pressure to a region of low. The flow through the disk of a prop is a forced one from low pressure to high.

Is that a definition folks here can live with?

JB

 

Welcome to Boatdesign JB
Indeed your reputation preceeds you. I congratulate you on your efforts with the carts. I really hope Mythbusters picks it up and applies some decent funds to it.

I am glad you weighed in although have some concern that it an unnecessary diversion from your experiments. You are dealing with a tough crowd here. The worst type of skeptics with closed minds and not a smudge of maths ability among many of them. As you can see I simply gave up and made a joke of it. I found the thread was polluted with nonsense so hopefully you can breathe some fresh air into it.

I will look forward to your full scale vehicle. The physics will benefit the scale up because the prop gets into better Re# but it is going to need to be quite large to do what you want. The downwind prop has to be much larger than the upwind turbine. To get a single person boat to work I needed a monstrous prop but the land vehicle does not have quite so much drag.

My offer still stands to help you with the prop design if you require it. Maybe Mark Drella will chime in and assist.

You are a glutton for punishment if you try to convince people here without them actually seeing it or having some world renown sceptic like the Mythbusters demonstrating it. Generally a waste of time. Better off just building it and showing a video of it in operation. This will occupy them for many months while they try to debunk your demonstration. We have skeptics here who are convinced the Earth is flat and man has never walked on the moon. So grasping something as complex as sailing DDWFTTW is impossible for them.

Rick W

 

Thanks Rick

Thanks again. A MythBusters episode would be fun to see. We're crossing our fingers.

Right now the plan is ~15ft diameter, but that's open to input.

The prop is absolutely key and I welcome any assistance.

One thing I've learned in the last couple months is that there isn't any demonstration that I could ever film that would convince some people. Some folks could get run over by a device going 2x the wind and they would still get up and claim it "impossible".

Best wishes.

JB