Wind Power Vehicle Traveling Down Wind Faster Than The Wind

yn3

There was and still is a hot debate on the matter of a wind power car that travels down the wind faster than the wind. As a part of larger interest in the subject I put the theory for this case, it can be found in my website
https://sites.google.com/site/yedidianeumeier/
I welcome your comments

mheslep

There are several past threads on the subject containing thousands of posts:
http://www.physicsforums.com/showthr...highlight=wind
http://www.physicsforums.com/showthr...hlight=DDWFTTW
http://www.physicsforums.com/showthr...hlight=DDWFTTW

yn3

"There are several past threads on the subject containing thousands of posts" Indeed so, and all the previous threads are closed, at list one of them because of improper language. My experience with published theory on this subject suggest that I can contribute to the matter. I hope that this thread will remain civil and to the point. I am welcoming your feedback.

rcgldr

The most recent thread includes links to videos of a working full scale (human pilot) model that accomplished about 28 mph speed with a 10 mph tail wind:

http://www.physicsforums.com/showthread.php?t=390801

Videos of this model before the outer skin was added can be seen here:

http://www.youtube.com/user/TraderTurok

Some sailcraft, such as a "Skeeter" ice boat, when tacking downwind (at an angle, not directly downwind), can also achieve a net downwind speed greater than the wind.

yn3

Thanks, you are right I am very familiar with Rick blackbird. NALSA actually ratified a 2.8X speed record on his behalf, you can see it in http://www.nalsa.org/index.htm
Note that unlike sail car, prop-turbine wind car does not tack the wind and thus a race of these cars could take place on a regular closed loop race track. I intend to develop the theory for all direction car and hopefully build one myself.

Curl

Anyone with a half-decent brain can ponder this question for a few minutes and realize that YES, it is possible to make a vehicle go faster than the wind, directly down the wind, solely on wind power.

It is also possible to go directly against the wind, but this one is even easier to figure out.

yn3

Well, the "half-decent brain can ponder this question for a few minutes and realize that YES" seems at that point like Columbus egg. I personally communicated with two distinguished professors, one of which share the Nobel Prize with Al Gore and is currently advising the president on energy matters, the other one run a blog about physics where he explained why it cannot be done. Both admitted to me that now they are confused, they don't know how it can be explained. Now, leave this aside and proceed to ask the following. To move with (down) the wind the car uses a propeller driven by the wheels, to move upwind one needs a wind turbine the shaft of which drives the wheels. How fast can this car go? Now, what happens if you go in an angle to the wind? Is there an angle where the propeller is inefficient and the turbine likewise so that it is so to say a blind spot to the car, meaning an angle it cannot drive or is it a point of overlapping manning both propeller and turbine are effective, if so what is the maximum velocity at this angle? All this can be readily answered, however it will take me a bit more than few minutes to put the equations run the simulation type it neatly and post it.

mheslep

That of course is the the highly political Peace prize, and not for physics or the other sciences.

Academic

Well, I guess I don't have half-decent brain power because I thought about for a few minutes and couldn't come up with it. Damn my less than half decent brain...

yn3

"That of course is the the highly political Peace prize, and not for physics or the other sciences. " Indeed so but the guy, according to his bio is
Professor of Nuclear Engineering and Ph.D (1998) & MA (1986) Harvard University (Physics),
AB (1984) Cornell University (Physics)
The AB is in his bio it may be a typo for BA but you see my point.

"Damn my less than half decent brain" Can I offer you half of mine? My wife says my brain is full of useless physics and otherwise useless historical knowledge.

To the point, humor and gossip is always great but what about discussing the all direction car?

rcgldr

> Angle to wind ...

Once at a significant angle, a standard sail setup would be better. In a DDWFTTW vehicle, the ground force opposes the forward motion of the vehicle, because that force is used by the wheels to drive the propeller. In a sailcraft, except for drag or rolling resistance, the ground force is perpendicular to the forward motion of the sailcraft, and consumes no energy, and this would be a better setup when moving at an angle to the wind.

yn3

"Once at an angle, a standard sail setup would be better" This is a qualitative statement. What angle do you have in mind 1deg? 10 degrees? However, let's wait and see what other thinks.

A.T.

In terms of wind-speed-multiple there is no particular limit in either direction. It just depends on efficiency.

in terms speed relative to the air, there are practical limits related to the gas properties. I doubt the sound barrier could be broken.

in terms speed relative to the ground there the speed of light limit

The blind spot for faster than wind would be at 90°. But with cyclic pitch control propeller/turbine ranges would overlap.

rcgldr

The top class ice boats, called Skeeters, would out perform the DDWFTTW Blackbird, given sufficient room to tach at an angle to the wind (30 to 40 degrees). Based on information about the Skeeter in this pdf file:

http://www.nalsa.org/Articles/Cetus/...ance-Cetus.pdf

I calculated that a Skeeter's downwind component of speed was 3.36x wind speed in an 18 mph wind (over 60.6 mph downwind component while at taching at 30 degrees offset from wind). The ratio would be higher in a 10 mph wind due to less aerodynamic drag from the apparent headwind. See post # 28 in this thread:

http://www.physicsforums.com/showthread.php?t=283813

mender

There were runs as high as 3.48x WS but were not used for the record because they were borderline. The team wanted an absolutely indisputable run for the initial record.

The purpose of establishing the record was more about proof of DDW travel by a recognized independent authority than the highest number achievable - I'm sure that others will go for the big numbers in years to come.

yn3

Surprise surprise: That is if my calculations are true, and rest assure that I am and will double checking them for a while.
The propeller wind car can do extremely well in side winds. Assuming that the propeller shaft can be rotated sideways, (which is not possible in the current ThinAirDesigns car), a car that can do 3XW down the wind can do more than 4XW with 90 degrees wind, the propeller will be swayed about 70 degrees sideways to 20 degrees off the wind. Moreover, the calculations show that even with the fix front thrust propeller, the aforementioned car capable of 3XW down the wind will do still better than 2XW at 45 degrees to the wind. This part of my calculation should be able to be confirmed or rejected by the experience of ThiAirDesigns, I am sure that they took some runs with angle to the wind. mender what say you?

ThinAirDesign

We never ran the vehicle in anger in full 45 cross, but we have data showing ~2.5x in sustained 30-40 cross.

JB