The Wind Powered Sail-less Boat

Tom, If the rotor is optimised as a prop for the top speed case, it means pitch_angle is much higher near hub than at the tip, do you agree ?
So how can you adjust variable pitch prop so that blade elements near tip are producing torque trying to slow down angular speed indicating positive pitch angle relative to rotor plane, so that blade element near hub has a lot higher pitch_angle and then claim that part near hub is producing torque trying to increase revs ?
Or did I somehow managed to misread that part in bold ?

 

OK, Rick. I've even found a video: http://www.flixxy.com/sailing-yacht-research.htm

Clearly, it's too long since I engaged my brain cells, and it's too late at night...

 

It is a common problem. Many engage in an opinion before engaging their mind here. Some have dug holes so deep they simply cannot allow themselves to think clearly on the issue. It took me about 6 hours to work out the physics before I properly grasped it.

Funny thing is that I cannot see any real merit in this particularly for a boat because it requires a very large prop for any manned boat. A hydrofoil designed for operation in high wind might do something interesting.

Rick W

 

... but I like the idea of the step-by-step series of slides. Please don't cut that off just because I've seen the light. Technical writing and explaining things are hobbies of mine, so I like seeing them done well, especially for counter-intuitive subjects.

 

My gut feel (yes, I know how useless gut feel is - I once had a manager who said 'See that tripe hanging up behind my desk? Those are the guts of the last lot of people who came offering me "gut feel" as justification for doing something') was that if it worked it would need a huge prop, which would bring its own problems. Good to see you corroborate that, but it's an interesting concept all the same.

 

And why would that be the case ???
And what do you mean by enough ? Really any movement forward at all forces prop to turn the right way as mechanically transmission doesn't allow anything else to happen. Do you expect a transmission failure or why do you make such a claim ?
Do you realise the airflow against the blades are along the axis at the beginning of cart movement and blades almost perpendicular to that near tips where tangential force could create any significant torque. The blades are compleately stalled and aero drag is aligned with flow meaning almost directly forward. Due to stalled flow lift is neglible if blades are also near perpendicular to flow. If using variable pitch prop, blades can even be rotated to produce torque to same direction that wheel are turning them.

Momentum yes, absolutely so, but who says it gets more energy ? It gets more linear power only by using more rotational power. The total power extracted including both linear & rotational doesn't have to change, but the result is dependent on IRF you are making your analyses. You haven't specified that, which significantly increases misunderstandings, and has a risk of changing IRF in the middle without you even noticing doing so.
Can I assume you are using IRF related to inertial observer moving with same speed as the cart currently has, but as being a inertial observer doesn't accelerate unlike the cart ?
That would be good since then the total power doesn't have to change by providing rotational by the shaft to get more momentum. In ground IRF the power is incresing, but if it's more dificult to understand why, then use the other IRF instead to avoid that problem.

Absolutely not so. The spinnaker can definately not reverse airflow unlike a propellor does, at best spinnaker can only stop most of the flow, and some just goes around the spin. If you are talking about symmetrical spin while going ddw course, are you ?
And if so why ? As it's not doing same as prop blade which is producing mostly lift at that point, with very small drag component, while the spin only has drag and near zero lift.

So your make some wierd assumptions, and from that you should conclude your assumptions were incorrect, but instead you make conclusions about the case that others have suggested having nothing to do with your wrong assumptions.
Do you know how proof by induction works in mathematics ?
If so, why don't you try something similar towards this analyses, and first make assumption it works, and if no contradictions were found, then the assumption must be correct. That's how it works in mathematics, why wouldn't it work here as well ?

 

OK. You might be able to critique the presentation so it becomes immediately obvious to those who have trouble with it.

You need to answer the two questions posed with Slide 1 - honestly. If they provide difficulty then tell me the sticking point.

Rick W

 

By the way you need to envision a vehicle having something like bicycle wheels and very large prop that is turning quite slow. The numbers I did relate to a 4m diameter prop and I think it was at 20rpm. A prop this size can get 75% efficiency under these conditions. So the gearing from the motor would be a large ratio contributing to the poor efficiency of the motor/transmission/prop combination. Also it is difficult to get hold of little motors with better than 80% efficiency. However some of the model plane outrunner motors can get up around 90%.

Rick W

 

If you can accomplish that I will see that you're nominated for the Nobel prize in teaching. I mean no disrespect for your approach. I just think "immediately obvious for those that have trouble with it" is an unimaginably high bar.

 

Even after I see the thing working something bothered me and finally I realized what it is.

On the treadmill everything works just like claimed but it is not at all the same as the video trial with the cart. On the treadmill, the following wind is always the same speed relative to the cart except for momentary variations when the cart moves forward or back a bit. On the road trial, the following wind speed relative to the cart is reduced directly mile for mile as the cart speeds up. When the cart is rolling at the same speed as the following wind, the wind speed relative to the cart is zero.

So the question is obvious. How does the tread mill test prove the theory and what does this mean for the theory? There are other questions but they should also be fairly obvious.

What am I missing?

 

There is no wind over the treadmill. The cart is operating at near zero apparent wind or slight head wind on the treadmill . The road is moving. So conditions relative to the cart are identical in both cases.

Sit on the cart on the treadmill- You see the road going away behind you. You do not see much wind just a very slight breeze from the in front.

Sit on the cart on the roadway- You see the road going away behind you. You do not see much wind just a very slight breeze from the in front.

So you have to see both situations as the cart sees them not as a bystander watching from afar. The cart sees exactly the same conditions in both cases.

If you really have a desire to understand it then I can take you through the four slides I prepared in the same way I have started with chabrenas.

Rick W.

 

It proves that crat can exceed windspeed by accelerating forward if already very close to that speed, it's not suppose to prove self starting at all.

http://www.youtube.com/watch?v=9zw2FJfBte8
See the other video on this link with a rotating wheel to see proof for selfstarting and accelerating to ddwfttw condition and maintaining that condition . That video is same as cart in outside having increasing true wind initially both before & after beginning to move related to ground and then truewind staying almost the same, only very slowly slowing down at the time craft passes wind speed.
Talking about the video here in which the cart has only one wheel on the rotating disk and a person starting to accelerate the wheel by han from the spokes during the test. No other forms of energy source present like electric motors. That person stops adding angularspeed to the disk well before cart accheaves windspeed related to the disk. Meaning before the cart is at rest related to the room.

 

Excuse me Rick but apparently I really don't see something here that should be very simple.
Perhaps I have been looking at a video that is different from the one you are talking about? Perhaps I am mixing two different videos. One big problem is that this discussion is showing up on so many different forums that it is difficult to follow the argument.

I removed some stuff here that was confusing.

 

My responses to Slide 1 questions:

1. Yes.
2. I believe so, but would have trouble showing you rigorously why I do.

20Kg is approximately the weight of hold baggage I'm allowed to take on a long distance flight, so this machine is a bit more than knee-high not counting the top of the airscrew. 9 Watts seems a reasonable estimate for moving it at 1 m/sec against air resistance and transmission losses, but I have no hard evidence to back up that assertion. i.e. I have no rigorous way of deciding whether the 9N in the diagram is realistic, using my experience rather than searching for someone else's experimental results.

 

The drag on the cart is actually high. For calculating bike power I use this site as a good reference:
http://www.kreuzotter.de/english/espeed.htm
The Crr for a bike or trike ranges from .003 to .005 so the drag at 1m/s for a 20kg bike would be much less than 9N. Even at 4m/s it is much less than 9N.

The prop needs to be very large and rotate quite slow. I might have to redraw this model to give perspective. The sort of vehicle required is shown in the attached picture only the blade of my cart would be around twice the diameter shown on that vehicle because the air velocity is so slow. The friction numbers I have used would enable the cart to be manned so heavier than 20kg. It would be using racing cycle tyres on a smooth concrete or bitumen surface.

I have also attached Slide 2. The questions are:
1. Will the vehicle just accelerate up to steady state speed of 4m/s under the influence of the 3m/s tail wind assuming the rolling drag and slight windage remains at 9N.
2. If you agree with question 1, confirm that the power supplied by the wind for this to occur is 27W.

Rick W