Directly Downwind Faster than the Wind on Discovery Channel

[00bean00]

There is something stupider than the Internet?! :P

[technolope]

PhD in Aerospace Engineering here, and it took me a little while to grok this, but I can see now how this is possible. The key to figuring it out (for me) was to recognize that this will only work on a vehicle for which there is significant friction with the ground. When the car is moving faster than the wind, the wind isn't pushing the car forward, the wheels are. But the wheels get power from the (relative) headwind.

[piratewoodleg]

@technolope

No, the wheels are not pushing the car forward, but braking, while turning the prop which creates more thrust than they brake.

The wheels cannot get the power from the (relative) headwind (via a turbine). That turbine would push the air forward, and thus accelerate the (true) tailwind. It would generate more true wind. To harvest wind energy , you have to slow down the true wind. Here that means: push the air backward with a propeller, turned by the wheels.

[technolope]

@piratewoodleg

You are totally right. I had my concept correct, but got my result wrong. In all regimes, the prop turns the same direction; but at start-up, power goes from prop to wheels, and at super-wind, power goes from wheels to prop. Top speed should be determined by energy conversion efficiencies and optimized by gearing. This is a wonderfully counterintuitive thought experiment.

[piratewoodleg]

@technolope

Your idea of using turbine-mode below windspeed, and switching to prop-mode later is correct, and would improve the initial acceleration. But they didn't use it (to make it even more counterintuitive).

On this specifical vehicle the power NEVER goes from the prop to the wheels via the transmission. The wheels ALWAYS turn the prop. Even at start up the prop rotates opposite to torque from the air, and according to the torque from wheels:

watch?v=5CcgmpBGSCI

watch?v=EEuAqq8FINw

[technolope]

@piratewoodleg I thought I was commenting under your comment. I must be doing something wrong.

[honestjohnnfld]

@piratewoodleg

You are wrong. Works in a windmill boat, faster than wind down wind.

This is an old principle and was first brought to light in the late 1960s early 1970s in a Marine Architect paper in Boston, MA.

My efforts were in a senior design paper at UW-Madison in mid 1980s. Got in Capital Times, front page for my scheme, The Prairie Schooner. Built a 10 foot dia 3-blade prop and tested it.

Bravo to Steve Calavarro ( sp. )

John Archibald ( leadminer@qwest.net )

Northfield, MN

[piratewoodleg]

@honestjohnnfld

Hi John,

The wheels turn the prop. The rotor cannot work as a turbine (or windmill) above wind-speed directly DOWNwind for two reasons:

1) It would accelerate the true wind instead of slowing it down to extract wind energy

2) They have ratchet hubs, that prevent the rotor from turning the wheels

Maybe you mean the directly UPwind case? There the rotor is a turbine(windmill) and can go faster than wind too. Rick Cavallaro will try it this summer.

[eurogoldexchange]

Sailing boats have been going faster than the wind for centuries.

[subductionzone]

@eurogoldexchange Not directly downwind. They have to tack back and forth with the wind. This vehicle goes DIRECTLY Downwind Faster Than The Wind.

[eurogoldexchange]

@subductionzone

One could argue that as the propellor blades turn they have to have a 'half wind' angle to get traction..

[piratewoodleg]

@eurogoldexchange

Yes that is the trick: Just the "sails" a tacking here, not the entire yacht.

[DrifterToo]

The narration is abysmal. The narrator get's the explanation backward several time.

This is a consequence of hiring for looks rather than education or intelligence.

But such a program ought to have knowledgeable advisors; where are they?

[JHO1138]

Rick is bitter, as you can tell ... he's also lying. That "internet forum" was very polite to him, trying to engage him in intelligent debate on the subject, until he got very, very nasty. His theory doesn't hold up to scrutiny, and he couldn't handle the criticisms. He signed onto the forum expecting dumb sheep, and got mad when he found clever foxes :)

[piratewoodleg]

@JHO1138

As far I can tell you are bitter, probably because you are one of the "geniuses" who claimed that it was impossible.

[JHO1138]

@piratewoodleg

LOL ... no, merely a witness to the trainwreck

[piratewoodleg]

@JHO1138

The "trainwreck" just set an official world record, sailing directly downwind at 2.8x windspeed. The North American Land Sailing Association (NALSA) has it on their website.

[JHO1138]

@piratewoodleg

Correction, they have the submission report on their website. It's not an official record yet.

And "the trainwreck" refers to the forum thread. That thread is dead in the water, I don't think it'll be setting any wind speed records soon LOLOLOLOLOLOL

[piratewoodleg]

@JHO1138

The record IS OFFICIAL.

Quote from NALSAs page:

"The Blackbird, piloted by Rick Cavallaro sailed directly downwind at 27.7 mph in a sustained 10 mph wind, setting a record for ratio of boat speed to true wind speed of nearly 2.8."

With your reading comprehension problems, it is no wonder the forum-thread didn't go well.

[JHO1138]

@piratewoodleg

Well, perhaps. But is that a real World Record, or a North American Land Sailing Association record?

I admit I did come here to take the piss, but it was primarily because of your bad behavior on that forum thread (which, by the way, I did not actually participate in, only observed).

[to be continued]

[JHO1138]

[continued]

People were disputing your theories, and you took it very personally and behaved quite childishly, eventually crossing the line and CALLING ONE OF THE FORUM MEMBERS ON THE PHONE AT HIS HOME TO HARASS HIM, which is of course a HUGE no-no.

My advice to you is stop being so defensive in internet threads like this, and just let the science speak for itself. If it is sound, that should be enough. Go on TV, that's usually enough to convince the proles. Good luck!

[piratewoodleg]

@JHO1138

Again: I'm not one of the builders.

But it looks like "their theories" (or rather basic school physics) are valid. So the people who insulted them as "cranks" deserved to be insulted back.

Science has spoken on this over 40 ago. Some reality deniers just don't get it, and they never will. No matter how many experiments are made, they will say "But is it not official yet" and other nonsense, that helps them to save their face.

[piratewoodleg]

@JHO1138

You mean: "Is that a real 100m world record, or just an Olympic Committee record?" LOL

And I have no idea what you mean by "your bad behavior". I'm not one of the builders.