OT. DDWFTTW YES NO

The obfuscation keyword is "spurts" :-) ...Jim Thompson

-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

Phoenix, AZ, a city noted for many civic-oriented inventions such as automated garbage collection, has added a new tool to its Fire Department safety equipment... addressing problems with accidents involving so-called Smart Cars: A Hydraulically Assisted Spatula.

OK, so take out spurts. Is your answer no? And don't obfuscate your answer! MikeK

Looks OK to me.

John

• -- Just as soon as you learn how to properly place this delimiter.

MikeK "Jim Thomps>

OK, so take out spurts. Is your answer no? And don't obfuscate your answer! MikeK

...Jim Thompson

On a sunny day (Thu, 5 Aug 2010 09:47:28 -0500) it happened "amdx" wrote in :

No.

The thought experiment goes like this: Say you travel at wind speed. Then there is zero wind. The guy agreed you cannot start with zero wind, QED. There would have to be a wind speed *variation* to get you past that point, PAST that point it reduces to going against the wind, and that is possible (railroad thing). So without a changing wind speed you can never go past wind speed. My view anyways, is not electronics challenging enough? ;-)

JB was being so annoyingly coy about answering questions that I lost interest--which may have been part of his intention, I don't know. Then he started trading insults with the usual suspects, sinking into abject trolldom. However, since you ask, let's do the analysis, which isn't difficult (it's a high school problem again).

First let's formulate it a bit more crisply, so as to eliminate irrelevancies.

Imagine a propeller driven car with wheel generators, going downwind at exactly the wind speed V. The additional drag force due to air resistance is zero at that point, and so can be ignored for our purposes.

If it is possible for the thrust to exceed the drag at this condition, the car can accelerate downwind, i.e. it will go downwind faster than the wind.

Let's change to the co-moving frame of reference, as if we were sitting on the car. Exactly equivalently, imagine the vehicle standing stationary on a dynamometer (with a motor running the dyno).

In that frame of reference, the work available from perfectly efficient generators on the wheels is

dW/dt = V*F,

where F is the drag force on the wheels.

If the prop is pushing out a mass M of air per second at velocity V_2 with respect to the car, this provides a force of MV_2 and requires power

P = (M/2)(V_2)**2.

In order for the car not to lose velocity, the force provided by the fan must equal or exceed the drag force on the wheels, so for the boundary case we can write force balance and energy balance equations:

MV_2 = F (1)

(M/2)(V_2)**2 = FV (2)

Dividing (2) by (1), we get

(1/2) V_2 = V,

so for both force and energy to balance, the air velocity from the prop (with respect to the car) has to be exactly twice the car's speed on the ground. That means that (seen from the ground) the exhaust air leaving the prop is going the opposite direction from the wind, at exactly the same speed.

By increasing M slightly and decreasing V_2 by the same proportion, we can get the same force for less energy, i.e. the drag force on the wheels can be less than the propulsive force of the prop, at the point where the car is running at the speed of the wind, so at that point it can in principle accelerate downwind.

So it looks like yes, it's possible in principle to go faster than the wind, assuming very high efficiencies. Slightly reduced efficiencies will require more reaction mass at lower velocity, but won't render it impossible in principle.

This isn't the same as the thought experiment, because of the speed difference between the ground and the wind, which the thought experiment ignored.

I'm no more fond of the trollish JB than I was before, but even trolls can be right sometimes (in this case apparently without being able to explain why in a coherent manner).

Cheers

Phil Hobbs

Ok, now what is your answer. And don't think I didn't see the obfuscation :-) -- MikeK

nd

"Believers?"

Can you explain any physical mechanism whereby any wind-powered vehicle could outrun the wind that's powering it? (skateboarding down a 20% grade doesn't count!)

Or are we talking about going sideways, or tacking upwind, which are entirely different phenomena?

Thanks, Rich

"Believers?"

Can you explain any physical mechanism whereby any wind-powered vehicle could outrun the wind that's powering it? (skateboarding down a 20% grade doesn't count!)

Or are we talking about going sideways, or tacking upwind, which are entirely different phenomena?

Thanks, Rich Directly Down Wind Faster Than The Wind (OLG) OLG ( On Level Ground ) \ MikeK

Spurt... discontinuous. ...Jim Thompson

Yes, it works.

Tim

-- Deep Friar: a very philosophical monk. Website:

nd

I saw the video and an analysis at a different site that explained it quite well. The explanations given on SED were worthless, however.

Spurt... disingenuousness.

MikeK

So far with my yes vote, 5 ya, 2 nay and one obfuscation. MikeK

Sorry that you're having trouble understanding. Larkin actual mentioned this once, but it didn't meet his "intensity of bloviation" criteria ;-) ...Jim Thompson

Paraphrasing Larkin "The Bloviator" Larkin:

"If you dump all the energy from the wind into another object, and do it efficiently, momentum is not conserved."

It's a hand-waving subterfuge. Can anyone show me a working case? Referral to flakes' websites _does_not_suffice_. ...Jim Thompson

eK

The linked video shows a working case. The linked landsailing which sanctioned and confirmed the tests and results site is not flaky. The linked news articles include a clear analysis of why and how it works.

I hardly expect you to admit you are wrong, however.

Just heard about the true "perpetuum mobile": Charitable-Remainder Trust... benefit a charity, get tax credits, buy untaxable insurance to provide for your children... and stick it to Obama ;-) ...Jim Thompson

The math is pretty simple. You can get more power from the wheels than the prop needs to push the car. Even an MIT grad should be able to understand that.

John