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  #616  
Old 01-15-2009, 03:59 PM
Guest625101138 Guest625101138 is offline
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Quote:
Originally Posted by tom28571 View Post
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.
Tom
To be clear on the treadmill I have attached a link to Goodman's video;
http://www.ayrs.org/MOV05703.mpg

Here his cart is operating on an inclined treadmill. The propeller is driven by the wheels rolling on the running treadmill. The cart is able to propel itself up the treadmill. There is no external fan.

To change the reference frame to the cart operating on a roadway with a tail wind you simply need to consider yourself sitting on the cart as I explained above to realise the treadmill in still air is the same as a roadway with a tailwind.

Rick W
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  #617  
Old 01-15-2009, 07:27 PM
tom28571 tom28571 is offline
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Quote:
Originally Posted by Rick Willoughby View Post
Tom
To be clear on the treadmill I have attached a link to Goodman's video;
http://www.ayrs.org/MOV05703.mpg

Here his cart is operating on an inclined treadmill. The propeller is driven by the wheels rolling on the running treadmill. The cart is able to propel itself up the treadmill. There is no external fan.

To change the reference frame to the cart operating on a roadway with a tail wind you simply need to consider yourself sitting on the cart as I explained above to realise the treadmill in still air is the same as a roadway with a tailwind.

Rick W
I understand these examples very well. Forces driving the cart in both cases are very clear although from different sources..
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  #618  
Old 01-15-2009, 07:48 PM
Guest625101138 Guest625101138 is offline
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Quote:
Originally Posted by tom28571 View Post
I understand these examples very well. Forces driving the cart in both cases are very clear although from different sources..
The force driving the cart in both cases is the same. It is the propeller thrust in the air stream.

The only thing that has changed is the frame of reference for an external observer. If you were sitting on the cart you would see exactly the same condition. Slight airflow from in front and roadway disappearing behind. The propeller produces all the thrust required to overcome the rolling drag on the wheels and the very slight windage from the head wind.

Rick W
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  #619  
Old 01-15-2009, 07:57 PM
InetRoadkill InetRoadkill is offline
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Video looks fishy. Conservation of energy and such.
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  #620  
Old 01-15-2009, 08:22 PM
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Originally Posted by InetRoadkill View Post
Video looks fishy. Conservation of energy and such.
Yes. A lot of people engage in an opinion on this one before engaging their brain and then regret it and wish they could retract it. Some have dug holes so deep without taking the time to understand it that they simply go away to avoid further embarrassment.

Anyone who really understands conservation of energy can work it out quite readily.

Rick W
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  #621  
Old 01-15-2009, 08:28 PM
spork spork is offline
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Quote:
Originally Posted by InetRoadkill View Post
Video looks fishy. Conservation of energy and such.

That's why we posted a set of detailed build videos including all part numbers. It's pretty trivial to build your own and test it yourself.
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  #622  
Old 01-15-2009, 08:35 PM
InetRoadkill InetRoadkill is offline
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Quote:
Originally Posted by Rick Willoughby View Post
Yes. A lot of people engage in an opinion on this one before engaging their brain and then regret it and wish they could retract it. Some have dug holes so deep without taking the time to understand it that they simply go away to avoid further embarrassment.

Anyone who really understands conservation of energy can work it out quite readily.

Rick W
I'm going to assume they didn't do something sleazy like pull it with a hidden string.

That said, I'm thinking the cart is a variation of the wooden helicopter toy. What appears to be happening is that they are building momentum up in the propeller by holding the cart stationery while the wheels spin up the prop. Once sufficient energy is built up, they release the cart and it magically moves against the tide of the treadmill. I noticed the video cuts out rather quickly once the cart starts to move. I doubt the cart was able to move very far since the energy stored in the prop's angular momentum would run dry rather quickly. A clutch in the gear train would be all that was needed to pull this off.
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  #623  
Old 01-15-2009, 08:45 PM
Guest625101138 Guest625101138 is offline
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Quote:
Originally Posted by InetRoadkill View Post
I'm going to assume they didn't do something sleazy like pull it with a hidden string.

That said, I'm thinking the cart is a variation of the wooden helicopter toy. What appears to be happening is that they are building momentum up in the propeller by holding the cart stationery while the wheels spin up the prop. Once sufficient energy is built up, they release the cart and it magically moves against the tide of the treadmill. I noticed the video cuts out rather quickly once the cart starts to move. I doubt the cart was able to move very far since the energy stored in the prop's angular momentum would run dry rather quickly. A clutch in the gear train would be all that was needed to pull this off.
Your starting to dig a hole. You have not given it any real thought yet.

How do you explain this with your theory on angular momentum.
http://www.youtube.com/watch?v=1pSYALWQ-nI

Rick W
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  #624  
Old 01-15-2009, 09:25 PM
InetRoadkill InetRoadkill is offline
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The energy is being supplied by the treadmill. Roll it down the incline with the treadmill stopped and see how far it gets.
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  #625  
Old 01-15-2009, 09:33 PM
spork spork is offline
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Quote:
Originally Posted by InetRoadkill View Post
The energy is being supplied by the treadmill.
Yes - now you're half way there. If it were on the road with a tailwind the energy would be supplied by the wind. If it were in a wind tunnel, the energy would be supplied by a giant electric fan. This isn't supposed to be perpetual motion.

Quote:
Roll it down the incline with the treadmill stopped and see how far it gets.

All the way.
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  #626  
Old 01-15-2009, 09:37 PM
Guest625101138 Guest625101138 is offline
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Quote:
Originally Posted by InetRoadkill View Post
The energy is being supplied by the treadmill. Roll it down the incline with the treadmill stopped and see how far it gets.

OK. So we got past the video being fake!!!

The topic is wind powered sail-less boats. The particular issue being discussed is the ability for a boat or road vehicle to exceed windspeed directy downwind. The answer is of course it can and the vehicle on the treadmill demonstrates this by reversing the frame of reference for an external observer.

It is not perpetual motion. If there is no relative movement between the roadway and the air there is no go.

So what is your point? No one is saying it will roll along the treadmill in the absence of relative movement between air and rolling surface!!!

Rick W
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  #627  
Old 01-15-2009, 10:15 PM
tom28571 tom28571 is offline
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Quote:
Originally Posted by Rick Willoughby View Post
The force driving the cart in both cases is the same. It is the propeller thrust in the air stream.
Rick W
The source on the road is the wind and the source is the treadmill in the other case. Seems like an important distinction to me.
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  #628  
Old 01-15-2009, 10:37 PM
Guest625101138 Guest625101138 is offline
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Quote:
Originally Posted by tom28571 View Post
The source on the road is the wind and the source is the treadmill in the other case. Seems like an important distinction to me.
The reason the vehicle can advance along the treadmill is because the propeller is being driven by the wheels and the propeller is moving air backwards to generate thrust. It is the air thrust that keeps the vehicle advancing along the treadmill. The same propeller thrust moves the vehicle against a tail wind on a roadway.

The reason you see a distinction is that you are still acting as an external observer and concerning yourself with the ultimate source of energy. I agree that there is a difference here but it is immaterial to what the vehicle sees. You have to place yourself on the vehicle to see it from the vehicle perspective. Consider yourself sitting on the vehicle placed on a huge treadmill with trees and all stuck to the treadmill. You will see your visual world passing by and a slight head wind as the propeller drives you along against a tail wind.

Now take the vehicle out on the roadway where there is a tail wind and get it moving at a speed just so there is a slight headwind. You will experience exactly the same things as you did on the massive treadmill. Your visual world will be moving past you and you will experience a slight headwind.

In fact the earth is already moving at a hell of a rate it is just that you cannot stand far enough back to see it unless on a space ship. Just happens the air is moving roughly at the same speed at the earth. What is the ultimate source of the wind energy anyhow? How far back do you want to stand? For this situation you need to plant yourself on the vehicle and look around. Whether on a treadmill in still air or on a roadway with a tail wind your world is the same.

If you are bogged down understanding this then it might help if you work through my 4 slides.

Rick W
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  #629  
Old 01-15-2009, 11:20 PM
spork spork is offline
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Quote:
Originally Posted by Rick Willoughby View Post
I agree that there is a difference here but it is immaterial to what the vehicle sees.
This is one point I don't actually agree with. If you want to say the your treadmill is different from the street in front of your house, I'd agree. But the street in front of my house is different from the street in front of your house also. Beyond the notion of size, materials, etc., operating on the treadmill surface is identical to operating on the road surface. People often act like the treadmill is intended to "simulate" the road and wind. But this isn't the case.

When the vehicle is on the treadmill it IS going directly downwind faster than the wind. It's not a simulation, and there's nothing about doing it on the road that's any better than doing it on the treadmill.

I suspect you actually agree with this Rick, and it's just down to semantics. But I think it's an important point.
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  #630  
Old 01-15-2009, 11:33 PM
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RHough RHough is offline
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42 pages?

Can we all agree that it is possible for a wind driven vehicle to have a VMG downwind higher than the wind speed?

The only mental challenge here is to see how a DDW course can yield a VMG higher than wind speed.

If your DW VMG > TWS vehicle needs to gybe through 90 it travels 140% of the DDW distance. All the blades of the propeller have to do is travel through 140% of the DDW distance that the vehicle travels to have the same basic forces working as a boat gybing through 90.

The single vehicle being two ice boats connected by telescoping frame is very apt. The surface interface, hydrofoil (keel or daggerboard), iceboat runner, road wheel, provides the resistance needed so the sails (or propeller blades) can operate at an angle of attack that produces lift.

If you can do the math to prove that a sail driven vehicle can sail faster than the wind and achieve VMG > TWS, all you have to do is wrap the course and angle the sails need around a hub and you have the propeller. Take the angle of attack and course of the keel and wrap it around a hub and you have the water prop. The resulting water prop, wind prop will have exactly the same operating conditions as the keel and sails of a boat sailing angles DW to achieve DW VMG greater than wind speed.

This is not that tough. Sheesh.
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