58 thoughts on “Don’t Know Much About Thermodynamics”
Cavallero does a poor job of explaining the physics. It’s important to remember that this isn’t a sailboat, and the mechanism of moving downwind and upwind is different from a sailboat.
A car mounted with a wind turbine is transferring energy from the wind to the drive system, using primarily lift on the blades of the airscrew to rotate it, so a car like Ventomobile can drive straight upwind, making us much as 10 MPH against true windspeed of 15 MPH and thus apparent windspeed of 25 MPH.
Likewise, a similar vehicle going straight downwind is experiencing an apparent wind speed and aerodynamic drag of 25 MPH when making 40 MPH in a tailwind with a true wind velocity of 15 MPH. Rolling resistance would be a bit higher at that speed, so 35 mph is more reasonable, but consistent with Cavalllero’s report and still faster than the wind.
It’s true that it wouldn’t be possible to *cruise* downwind at 15 MPH in a 15 MPH tailwind. But you don’t have to. At that speed apparent wind resistance is nill, and the still turning airscrew stores enough energy to keep the vehicle accelerating until the prop is experiencing positive airflow again.
It ought to be intuitive that with this set up it should be possible for the boat to achieve at least some small increment of speed beyond the speed of the current of the water
You also have a reduction of speed due to frictional drag.
Replace the propeller with a sheet of plywood. The wind adds energy and friction reduces energy. When those equalize you have a terminal velocity less than the wind but more than zero.
The propeller spins in the opposite direction to that expected
Why is this important? Because the wind isn’t being used to drive the wheels. The wheels really are being used to drive the prop. The lift caused by the rotating prop is being added to the kinetic energy of the entire vehicle minus the drag energy of the rotating prop. If the lift energy of the prop is greater than the drag energy the vehicle goes faster. The relative wind shouldn’t matter much at all except to get the whole thing started.
Take 2: Imagine a robot sitting next to a moving conveyor belt. The robot extends a wheel to touch the conveyor belt which rotates due to the motion of the conveyor. The wheel is attached to a generator which creates a small amount of electricity, this electricity is then used to drive a motor which moves the robot in the opposite direction from the conveyor belt. How fast can the robot go with such a system? Obviously it should be able to travel at some speed greater than 0, since the motion of the conveyor belt will generate usable power.
Now turn it around, imagine instead that the robot is on the conveyor and it is using its wheel placed on the stationary ground to generate power and pushing itself along in the same direction as the conveyor. It should also be obvious that there’s nothing hinky about this scenario, there is power being extracted and used but no free energy or perpetual motion. The robot should be able to achieve at least *some* speed more than 0.
Now switch from a generator/motor to a direct linkage. And switch from a solid conveyor to a fluid. All that’s required is that a wheel traveling over land be able to generate more power than it takes a propeller to maintain a speed X mph *less* than that in air.
Okay, how about this way to look at it:
You are driving the propeller with the wheels from the car, and the propeller is pushing the car. Assume there is no wind. With any power losses in this system, as there must be, if you start out with the car at some speed X, it will slow down and stop. The forward energy of motion supplied by the propeller to the vehicle will be less than all the energy losses.
However:
If you have a tailwind, the situation is better as far as the propeller goes. Since the apparent headwind for the vehicle is less than the speed relative to the ground, it necessarily takes less energy to spin the propeller than it would if there was no tailwind (i.e. the drag energy of the rotating prop mentiond by Ken). So, assuming the vehicle is going faster than the tailwind, what is going on is that we are using the wheel-propeller linkage to turn the prop in the air, taking advantage of the fact that we need less energy to turn the propeller to generate the energy for forward motion.
Hi, I’m JB. Cavallaro and I are the two primary designer builders of the craft in question.
First off, Cavallaro’s explanation has been quoted, clipped and requoted on so many blogs that it’s no longer complete. It is still *accurate* mind you , but incomplete.
If I tell you that when you hold a microphone in front of a speaker, the speaker drives the mike and the mike drives the speaker and the speaker drives the mike … do you think “perpetual motion”? of course not. It IS a feedback loop, but unplug the amp from the wall and the racket quiets.
The propeller does move the craft which forces the wheels to turn which drives the propeller which moves the craft … … … , but ‘unplug’ the wind and the entire thing rolls to a stop.
Happy to take questions as well.
JB
I’ll try to go back through the posts on the thread and come up with some relevent comments over the next bit, but in the mean time here are a few notes related to the craft.
Basics:
— wind power only … no stored energy is used for acceleration ever
— the spinning rotor is a propeller, not a turbine
— the wheels provide the torque to turn the rotor (always).
— the rotor does not provide the torque to turn the wheels (ever).
— it will take off from a standing start on it’s own.
— initially it is just the bluff drag of the entire device that starts it rolling
— we sometimes push it up to speed to save time during testing
— there’s no “null point’ at windspeed.
— other than the change in relative wind heading, there is no funky transition from below windspeed to above.
— given a rolling surface, it will maintain it’s speed 2-3x above wind speed indefinitely
— subsonic, there is no theoretical limit to it’s top speed, but many practical ones.
— By design, this particular one works best when aimed directly downwind.
— One can be built to go faster than the wind in any direction
— A simple gearing change (or smaller wheels) will cause it to go upwind rather than down
We have many video demonstrations on youtube if this site allows me (a new contributor) to post links – perhaps someone can tell me if this is OK … I don’t want to ‘un-welcome’ myself by doing something uncool.
JB
Doug Jones says:
Using wheels to drive a propeller works, but the “inventor’s” description is inarticulate, to be generous.
-snip-
The idea isn’t new, only the implementation, thus the scare quotes.
*****
To be clear, we’ve never ever claimed to be the inventors of this device and have done extensive research to make sure and give credit where credit is due (see first entry in our project blog: http://www.FasterThanTheWind.org)
—
Doug Jones says:
I have a book about the difference between crank and genius, title not handy at the moment, but in the book (and illustrated on the cover) is a bicycle with a propeller mounted on it, that the builder used to demonstrate traveling downwind at greater than the wind speed.
********
Wow — I would LOVE to have the title of that book. Any chance you could get that for me? Thanks a bunch.
Cavallero does a poor job of explaining the physics. It’s important to remember that this isn’t a sailboat, and the mechanism of moving downwind and upwind is different from a sailboat.
A car mounted with a wind turbine is transferring energy from the wind to the drive system, using primarily lift on the blades of the airscrew to rotate it, so a car like Ventomobile can drive straight upwind, making us much as 10 MPH against true windspeed of 15 MPH and thus apparent windspeed of 25 MPH.
Likewise, a similar vehicle going straight downwind is experiencing an apparent wind speed and aerodynamic drag of 25 MPH when making 40 MPH in a tailwind with a true wind velocity of 15 MPH. Rolling resistance would be a bit higher at that speed, so 35 mph is more reasonable, but consistent with Cavalllero’s report and still faster than the wind.
It’s true that it wouldn’t be possible to *cruise* downwind at 15 MPH in a 15 MPH tailwind. But you don’t have to. At that speed apparent wind resistance is nill, and the still turning airscrew stores enough energy to keep the vehicle accelerating until the prop is experiencing positive airflow again.
It ought to be intuitive that with this set up it should be possible for the boat to achieve at least some small increment of speed beyond the speed of the current of the water
You also have a reduction of speed due to frictional drag.
Replace the propeller with a sheet of plywood. The wind adds energy and friction reduces energy. When those equalize you have a terminal velocity less than the wind but more than zero.
The propeller spins in the opposite direction to that expected
Why is this important? Because the wind isn’t being used to drive the wheels. The wheels really are being used to drive the prop. The lift caused by the rotating prop is being added to the kinetic energy of the entire vehicle minus the drag energy of the rotating prop. If the lift energy of the prop is greater than the drag energy the vehicle goes faster. The relative wind shouldn’t matter much at all except to get the whole thing started.
Take 2: Imagine a robot sitting next to a moving conveyor belt. The robot extends a wheel to touch the conveyor belt which rotates due to the motion of the conveyor. The wheel is attached to a generator which creates a small amount of electricity, this electricity is then used to drive a motor which moves the robot in the opposite direction from the conveyor belt. How fast can the robot go with such a system? Obviously it should be able to travel at some speed greater than 0, since the motion of the conveyor belt will generate usable power.
Now turn it around, imagine instead that the robot is on the conveyor and it is using its wheel placed on the stationary ground to generate power and pushing itself along in the same direction as the conveyor. It should also be obvious that there’s nothing hinky about this scenario, there is power being extracted and used but no free energy or perpetual motion. The robot should be able to achieve at least *some* speed more than 0.
Now switch from a generator/motor to a direct linkage. And switch from a solid conveyor to a fluid. All that’s required is that a wheel traveling over land be able to generate more power than it takes a propeller to maintain a speed X mph *less* than that in air.
Okay, how about this way to look at it:
You are driving the propeller with the wheels from the car, and the propeller is pushing the car. Assume there is no wind. With any power losses in this system, as there must be, if you start out with the car at some speed X, it will slow down and stop. The forward energy of motion supplied by the propeller to the vehicle will be less than all the energy losses.
However:
If you have a tailwind, the situation is better as far as the propeller goes. Since the apparent headwind for the vehicle is less than the speed relative to the ground, it necessarily takes less energy to spin the propeller than it would if there was no tailwind (i.e. the drag energy of the rotating prop mentiond by Ken). So, assuming the vehicle is going faster than the tailwind, what is going on is that we are using the wheel-propeller linkage to turn the prop in the air, taking advantage of the fact that we need less energy to turn the propeller to generate the energy for forward motion.
Hi, I’m JB. Cavallaro and I are the two primary designer builders of the craft in question.
First off, Cavallaro’s explanation has been quoted, clipped and requoted on so many blogs that it’s no longer complete. It is still *accurate* mind you , but incomplete.
If I tell you that when you hold a microphone in front of a speaker, the speaker drives the mike and the mike drives the speaker and the speaker drives the mike … do you think “perpetual motion”? of course not. It IS a feedback loop, but unplug the amp from the wall and the racket quiets.
The propeller does move the craft which forces the wheels to turn which drives the propeller which moves the craft … … … , but ‘unplug’ the wind and the entire thing rolls to a stop.
Happy to take questions as well.
JB
I’ll try to go back through the posts on the thread and come up with some relevent comments over the next bit, but in the mean time here are a few notes related to the craft.
Basics:
— wind power only … no stored energy is used for acceleration ever
— the spinning rotor is a propeller, not a turbine
— the wheels provide the torque to turn the rotor (always).
— the rotor does not provide the torque to turn the wheels (ever).
— it will take off from a standing start on it’s own.
— initially it is just the bluff drag of the entire device that starts it rolling
— we sometimes push it up to speed to save time during testing
— there’s no “null point’ at windspeed.
— other than the change in relative wind heading, there is no funky transition from below windspeed to above.
— given a rolling surface, it will maintain it’s speed 2-3x above wind speed indefinitely
— subsonic, there is no theoretical limit to it’s top speed, but many practical ones.
— By design, this particular one works best when aimed directly downwind.
— One can be built to go faster than the wind in any direction
— A simple gearing change (or smaller wheels) will cause it to go upwind rather than down
We have many video demonstrations on youtube if this site allows me (a new contributor) to post links – perhaps someone can tell me if this is OK … I don’t want to ‘un-welcome’ myself by doing something uncool.
JB
Doug Jones says:
Using wheels to drive a propeller works, but the “inventor’s” description is inarticulate, to be generous.
-snip-
The idea isn’t new, only the implementation, thus the scare quotes.
*****
To be clear, we’ve never ever claimed to be the inventors of this device and have done extensive research to make sure and give credit where credit is due (see first entry in our project blog: http://www.FasterThanTheWind.org)
—
Doug Jones says:
I have a book about the difference between crank and genius, title not handy at the moment, but in the book (and illustrated on the cover) is a bicycle with a propeller mounted on it, that the builder used to demonstrate traveling downwind at greater than the wind speed.
********
Wow — I would LOVE to have the title of that book. Any chance you could get that for me? Thanks a bunch.
JB