The Wind Powered Sail-less Boat

Perfect example of still not engaging.

JB

 

My apologies. In the future we'll try and be better about producing specific analyses to meet the demands of those that refuse to communicate with us.

 

Where do you guys find time? I have only today gotten engaged in this issue and have come full circle after finally seeing a key issue resolved for me by Rick.

Rest easy that Guillermo is a gentleman and not trying to rattle anyone's cage. Maybe being Spanish makes him a little excitable. Probably it's the spicy food.

 

This seems to be a great topic for off season banter. Of course it is possible to sail DDW faster than the wind.

A Friend asked me to post this from a thread on the subject on SA:

Link

Cheers.

R

 

Windage would kill it. If huge wheels were a good idea you would see them being used on boats now. I have also seen the idea of buoyant tubular tracks. This reduces the windage of course. However these things need to be engineered to be weightless and frictionless to match what you can do with a CF hull.

I have considered a 7.2m long model boat (I have a spare hull with 230mm beam this long). Essentially a mono hull with wide set outriggers just on the water level. Would need to weigh less than 30kg. Prop would need to be around the 4m mark. The turbine say 0.6m diameter. It would be able to achieve DDWFTTW in wind speed range 3 to 5m/s. Maybe even higher wind as well but I gave up on considering it further when the size of the prop sinks in.

To get a manned boat DDWFTTW the prop gets up over 12m mark. That is a massive prop to prove a point. Let em demonstrate it with a land vehicle. The proportions are better.

Rick W

 

DDWFTTW.
Cart with air rotor and wheels in an steady wind.


A) Rotor acting as a turbine moving the wheels:

When departuring from an stand still position, the cart begins to accelerate because of the action of the wind, by two means: one is by transmitting the wind energy to the wheels from the rotor (acting as a turbine) and so using the floor reaction on them and the other one due to the drag on the whole apparatus. It keeps on accelerating till it reaches the equilibrium, this is when the energy applied to the cart is equal to its kinetic energy plus the lost energy, whatever they are.

Let’s consider propulsion force due to drag negligible, for the sake of argument, and so all changes of movement being caused only by the wind energy transmitted via the turning rotor to the wheels.

Let me remark there’s no more place where to extract energy than the one usable from the wind at any given moment. This is absolutely clear. On the other hand, the force of the floor at the contact point with the wheels is just a reaction to the turning movement of the wheels induced by the transmitting belt, from the rotor where wind is transmitting its energy to the cart.

The blades of the rotor may indeed go 'faster than the wind' in their turning (tangential speed for a given section). That's equivalent to the sails of the iceboats. But downwind for the sections of the blades is not the direction of movement of the cart, but are the helicoids resultant of composing tangential movement and the advance of the cart. We need an angle of incidence of the profile (section) with this downwind direction, to create lift. The first problem that arises is that this stablishes a limit to the reachable speed of the cart as the blades’ pitch has to match the target speed of the cart, which cannot be surpased once such pitch is fixed. Tricky.

Ice boats speed increases up to a certain angle of incidence of the real wind and then it begins to quickly decrease when it reaches a certain angle from the stern, as always in sailing. The sails do not produce anymore enough lift and the iceboat slows down to eventually an speed close (but lower) to that of the wind speed. The same happens to the blades of the rotor in their 'downwind' way. When the cart approaches wind speed the net resultant of wind acting on the cart diminishes and so the component of the 'real' wind the blades perceive, thus diminishing their lift. We can think of having two 'real' winds here: one the proper real wind, and the other the resultant wind the blades perceive (real wind speed less movement of the cart), which is the one to be composed with the tangential movement due to the spinning of the rotor, to get the final apparent wind on the blades. So the blades begin to slow down in their turning and so transmitting each time less power to the wheels which slows down the cart, probably very quickly except for inertial considerations. This is congruent with the fact that the usable energy from wind over the whole system also decreases when the cart approaches the wind speed.

So the cart can never reach the wind speed, except for, perhaps, possible 'fluctuations' under and above wind speed due to inertial considerations.


B) Rotor acting as a propeller moved by the wheels:

When departuring from an stand still position, the cart begins to accelerate only by transmitting the wind energy to the cart by simple drag on its structure and the not turning rotor blades, or then slowly doing it against the wind. When the speed builds up, let’s admit the total drag of the cart’s structure and rotating rotor (remember: against the wind from the very beginning) is powerful enough to evercome the natural tendency of the rotor to turn the other way round as it should because of the wind acting on the ‘reversed’ blades (*).

In such scenario the rotor will be able to extract more energy from the wind that reaches the rotor’s disc (against when it's not turning), by slowing down and/or diverting a bigger amount of wind by the now quickly turning blades, so getting more momentum (energy) from it. At the limit we could, theoretically, totally stop or then divert outwards of the rotor disc the whole of the incoming wind and transfer all of its forward energy to the cart, if there were no loses.

In this case the rotor is acting like if it were an spinnaker and the reachable speed can never exceed that of the wind, except for some possible inertial fluctuations, as mentioned before.

So, if I'm not wrong this cart thing cannot go faster than the wind whichever the rotor moves the wheels or the wheels move the rotor.

To prove the contrary, away from all doubt, is easy: Run the cart in a well controlled open air scenario, or then the wind tunnel I proposed some posts ago; do it for an statistically significative number of times, properly register all required data (among other wind shifts if in open air) and posts results here.


(*) In fact I think this cannot happen and cart probably will never speed up enough by itself, unless ‘convinced’ to do so.

 

Guillermo
I take back what I said earlier - you should eat your hat. It might do you some good.

You are talking about a DDWFTTW cart and turbine again. WRONG. You need to eat your hat to get the message. IT IS ALWAYS A PROPELLER AS LONG AS THE DDWFTTW CART IS MOVING.

If it is a turbine you have an upwind cart going against the wind with the turbine powering the wheels.

I guess we could all accept your poorly put, confusing explanation that it cannot happen and the 20 or so who actually appreciate the science involved just accept your superior understanding of all things physical and agree with you to save the aggravation.

Rick W.

 

Rick, by changing the gearing you can make a downwind cart in which the turbine is turning the wheels. But it's a particularly uninteresting case in my opinion, and will never reach the wind speed. From a power generation point of view this case is (slightly) interesting in that it is the same as that of the prop configuration at 1/2 the wind speed downwind.

But to be sure, this has nothing to do with understanding the prop cart with fixed pitch blades that self-starts and achieves steady-state DDWFTTW.

 

I agree but it requires two changes, not just a ratio change.

To get the turbine cart to go downwind you need to do 2 things. Change gear RATIO so the blades have mechanical advantage and also switch the direction of the turbine so it is facing the wind direction from behind. In these circumstances it cannot exceed windspeed as you point out.

Rick W

 

spork
Have you started to build a cart suitable for manned operation yet?

Rick W

 

If you apply this logic to a propeller driven boat then it will never exceed the speed of the current as it will lose all thrust once the prop stops working like a spinnaker. Likewise an airplane can never exceed wind speed as it will have zero thrust once you lose the spinnaker affect of the prop.

This is utter nonsense.


Rick W

 

Actually, Guillermo, the propeller is functioning as a PROPELLER, not just as a spinnaker...by functioning as an aircraft propeller does in a tailwind, it diverts & resists the tailwind first, but it eventually develops enough turning speed to create thrust by pushing air behind it at velocity, instead of merely stagnating it. This is how the DDWFTTW cart can achieve faster-than-the-wind speeds using a propeller driven by the wheels.

If you re-read my earlier post explaining this, it should shed a lot of light on this for you.

 

I put this in the highest possible category of wishful thinking.

In post #6 on this thread Tom Speer clearly described the operation of a DDWFTTW cart referring to it being propelled by a propeller driven from the wheels. At post #542 Guillermo finally acknowledged we were talking about a propeller and not a turbine. But now he is reverting to the turbine. (Actually you have to admire Tom for not getting sucked into the nonsense here that goes on as scientific discussion. I have learnt my lesson.)

I expect in maybe 1000 plus more posts Guillermo might come to learn how a propeller works. I have the honest view he does not read what others post.

He never identifies any flaw in the science or logic offered by others just dreams up his own convoluted and illogical reasoning to say it cannot happen. He is the ultimate flat earther - his view of the world is the only right one. All others are stupid.

Good Luck Rob.

Rick W

 

According ONLY to what goes on in this thread, I'd be pretty tempted to agree with you, but I HAVE seen some of Guillermo's posts in other threads that prove him to be very intelligent. Therefore, I am still holding on to the hope that he'll extend me the same respect & re-read my posts describing the propeller operation...for now at least.

 

The gear change I had in mind is to not only change the magnitude but also the sign of the gearing. This will do the job, but you're right that it will be horribly innefficient if you don't use the appropriate blades (the camber is still toward the front of the cart, but the pitch should be reversed - in which case you don't have to change the sign of the gearing - so I guess we're back to what you said - never mind )

We have been woefully slack on that front. We need to get started so we can have it ready for the steady summer winds around here.

There's some truth to this, but he can't even begin to hold a candle to the clown we have on the JREF forum.