Sailing downwind faster than the wind

[spork]

I expect that you already know that your vehicle can travel directly into the wind.
Gear down the turbine as much as is needed to drive the wheels AGAINST the wind force on the turbine.
Measure a few speeds.
That will impress the Yacht Club.

Indeed. That will work, but not very efficiently. Our prop has a "prop" shape rather than a "turbine" shape. This means the trailing edge will become the leading edge by doing as you suggest. It will work, but it could be made to work quite well if we swap out the prop blades for turbine blades. We're thinking about doing exactly that to see if we can't do better than 1X wind speed going directly into the wind.

 

[eyytee]

Our prop has a "prop" shape rather than a "turbine" shape. This means the trailing edge will become the leading edge by doing as you suggest.

Can't you rotate the blade by 180° from the setting you have in mind here ?

 

[spork]

Our prop has a "prop" shape rather than a "turbine" shape. This means the trailing edge will become the leading edge by doing as you suggest.

Can't you rotate the blade by 180° from the setting you have in mind here ?

Yes, you can rotate it 180, but the pitch remains the same and now the camber is on the wrong side.

 

[Mee_n_Mac]

Our prop has a "prop" shape rather than a "turbine" shape. This means the trailing edge will become the leading edge by doing as you suggest.

Can't you rotate the blade by 180° from the setting you have in mind here ?

Yes, you can rotate it 180, but the pitch remains the same and now the camber is on the wrong side.

Not to get too far off the OP but how did USA-17 with it's rigid "sail" handle it's similar predicament (ie - port vs starboard tack) ? Were there some cams to change it's camber ? Or ???

 

[spork]

Not to get too far off the OP but how did USA-17 with it's rigid "sail" handle it's similar predicament (ie - port vs starboard tack) ? Were there some cams to change it's camber ? Or ???

I believe it used a symmetrical airfoil and no twist. JB would be more likely to know - he's been following all those boats.

 

[eyytee]

Not to get too far off the OP but how did USA-17 with it's rigid "sail" handle it's similar predicament (ie - port vs starboard tack) ? Were there some cams to change it's camber ? Or ???

I believe it used a symmetrical airfoil and no twist.

It is symmetrical and has two parts to bend the profile one way or the other:

The twist is what I forgot in my earlier statement about using the prop-blade as a turbine-blade. If you do this, at least one of the following three things will be wrong:
1) trailing edge becomes leading edge
2) chamber on the wrong side
3) twist of the blade wrong way around

I guess 1) causes the least trouble and to create a universal blade one would make the edges symetrical?

 

[spork]

It's a big day for downwind vehicles. The story was picked up today by www.wired.com, Popular Science http://www.popsci.com and USA Today.

On Friday we'll be presenting our test plan to NASA to run tests on their runways at Moffett Field.

 

[Woggles]

I just watch this on Discovery channel show called Daily planet. It worked there. They were using streamers to show direction of the wind (which was flowing from the back to the front of the vehicle) Once the machine reached the wind speed the streamers were not flowing, and as the machine picked up speed the streamer flow behind the vehicle. It seems to me it works. I like what he calls the cart. BUC (Big Ugly Cart)

Sorry, can’t link to the show.

 

[spork]

I like what he calls the cart. BUC (Big Ugly Cart)

Before we added the aerodynamic fairings and paint the "official" name was the BUFC (Big Ugly...Cart). We now call it the Blackbird (which we assume our sponsors might prefer).

Sorry, can’t link to the show.

[youtube]http://www.youtube.com/watch?v=LjLPPInzSzI[/youtube]

 

[Woggles]

[quote [youtube]http://www.youtube.com/watch?v=LjLPPInzSzI[/youtube]

 

[spork]

Yes I remember that, it was named after the SR71 Blackbird!

We did think it had a bit of the SR-71 look after adding fairings and black paint, but we were largely alluding to the Greenbird landsailer built by Richard Jenkins (who we recently had the pleasure of meeting - VERY impressive guy).

 

[Woggles]

Did you guy's ever think about taking it out to the salt flats for testing? Did you get your chain drive fixed? I think that's what broke?

 

[spork]

Did you guy's ever think about taking it out to the salt flats for testing? Did you get your chain drive fixed? I think that's what broke?

We have talked about testing on the salt-flats (and every other flat windy surface we can think of). We hope to be testing at Moffett field in about 10 days.

The chain drive (upper chain wheel) has been replaced and reinforced.

 

[Woggles]

Awesome!! Wishing good luck and favorable winds!!!!

 

[MeteorWayne]

I have a question for you guys. Can you give me some information to create a graph?

Say the wind speed is 8 (km/h, m/s, mph....your choice)

I need two pieces of info. Wind speed, and ground speed of the device.

Then wind speed 6, 4, 2, 10, 12 etc.

And here's the tricky part... since the device moves faster than the wind, the device speed should be greater than zero when the wind speed is zero. And then below, there should be a headwind speed when the ground speed of the vehicle finally reaches zero.

Do you have any actual measurements to help fill in my graph?

This is a serious question, appreciate a response from the experimenters.

Thanx, Wayne

 

[eyytee]

And here's the tricky part... since the device moves faster than the wind, the device speed should be greater than zero when the wind speed is zero.

Are you kidding? That would be perpetual motion! :lol:

The maximum theoretical speed of the device is a multiple of the true wind speed:

v_max_theoretical = v_true_wind / (1 - vehicle_advance_ratio)

If v_true_wind = 0 then v_max_theoretical = 0

You can choose vehicle_advance_ratio freely, and make v_max_theoretical very big, but in reality the vehicle will never quite achieve it, due to losses. The actual real maximal speed depends on efficiency.

 

[MeteorWayne]

All I'm asking for is actual experimental results.

Is that an unreasonable request?

I don't care much about theory, since what of what you propose doesn't pass that without concerns either.

Do you have any actual experimental results that could shed light on this?

 

[MeteorWayne]

And here's the tricky part... since the device moves faster than the wind, the device speed should be greater than zero when the wind speed is zero.

Are you kidding? That would be perpetual motion! :lol:

I don't understand why that conflicts with the title of the thread:

Sailing downwind faster than the wind. If the wind speed is zero, according to what you have said, the speed should be greater than zero...or at wind speed .000001, the ground speed should be higher.

All I'm asking for is some experimental data.

 

[eyytee]

I don't care much about theory, since what of what you propose doesn't pass that without concerns either.

And the concerns are?

And here's the tricky part... since the device moves faster than the wind, the device speed should be greater than zero when the wind speed is zero.

Are you kidding? That would be perpetual motion! :lol:

I don't understand why that conflicts with the title of the thread:

Sailing downwind faster than the wind.

You don't understand why assuming "no wind" conflicts with talking about "downwind"? What would be the downwind direction? Anyway, I didn't make up the title, but you are a mod. If you think it is misleading you can add "for wind speed > 0"

If the wind speed is zero, according to what you have said, the speed should be greater than zero.

No, what I said was the exact opposite:

If v_true_wind = 0 then v_max_theoretical = 0

All I'm asking for is some experimental data.

http://www.fasterthanthewind.org/2010/0 ... graph.html

 

[RCP]

I'm quite curious to see what you make of the readings eyytee posted a link to, MW. Also, I assume you've seen the videos of the 16g cart advancing on the treadmill? How would you explain this? spork has often stated his original prop cart on a TM is an actual instance of DDWFTTW. If you disagree, what do you see happening wrt it advancing on the belt?

 

[spork]

MW, the title of the thread suggests that it's possible to sail directly downwind faster than the wind - and that's what we've demonstrated. It doesn't suggest that this can be done in any wind at all or no wind, or with any configuration of any random mechanism. We simply say that it IS possible to make a vehicle that can be powered by the wind and travel directly downwind faster than the wind - steady state. And that's what our vehicle does in a fairly broad window of wind conditions. Would it go faster than the wind in a hurricane - no - it would explode.

It will however go 100 times the wind speed in no wind.

 

[eyytee]

It will however go 100 times the wind speed in no wind.

And that in any direction!

 

[spork]

It will however go 100 times the wind speed in no wind.

And that in any direction!

As long as it's downwind. :mrgreen:

 

[RCP]

There is a tentative-nature permitting-date now for the NALSA test; July 1 or second. Wayne and other skeptics should make their predictions soon as to the results. For in days we shall have far more verification for the claims of the last 2 years than has ever been presented. Or not. :twisted:

 

[ThinAirDesigns]

Two days of NALSA testing now complete.

NALSA has data sets showing peak speeds of over 3.5x and what we believe to be the best 10 second average of 3.48x.

This does not mean that NALSA will be ratifying a record for that particular run -- there are a host of requirements to be met (wind can't switch directions during run, etc.) before a run becomes NALSA valid.

We are becoming more and more confident that NALSA could ratify a record that is greater than 3x the speed of the wind.