Downwind Faster than the Wind - Successful Run by manned cart

Tommyrot:

Good point. I had not noticed that they had again forgotten to counter the real argument as to the validity, in their eyes, of the "buddy" proof. Is the "buddy" still correct in their view now? It still exists on the site labelled Tad's analysis.


I love the last line of the proof:
"If you made it to here, we should start a club. People like us need friends too."
 
halfway said:
Tommyrot: You quote "ignorant". That would imply I used that word. In the post in question it does not occur. A similar word does, but I take the alteration to show that you do understand the difference.

An "ignorant person" is an insult, "your ignorance" is a description of the current state of play.

Just to quote a completely unreliable source:

"Ignorance is where someone or something is uninformed. This should not be confused with being unintelligent, as one's level of intelligence and level of education or general awareness are not the same. The word "Ignorant" is an adjective describing a person in the state of being unaware. The term may be used specifically (e.g. "One can be an expert in math, and totally ignorant of history.") or generally (e.g. "an ignorant person.") -- although the second use is used less as a descriptive and more as an imprecise personal insult"
Click to expand...


So it can be used as a personal insult, thank you. :)

I understand the meaning rather better than you give me credit for. Like you, I have kept many facts about myself secret.
Here is one for you. My school was founded not long after Columbus discovered the West Indies.
 
Halfway said:
A blindingly simple issue is the difference between a yacht and your cart. Wind is produced by nature. It comes in gusts. In a yacht the gusts are catered for by a lateral heel that de-powers the system. This is not just a rubber band, or chain tensioner, taking up slack, it a serious reduction of air cross section and keel effectiveness. It takes excess energy and creates a potential energy store (righting moment) that smoothes out the gust energy without wasting it all. (Think about the relative wind while recovering). This is completely missing in your cart. You could have easily added the equivalent feature if you had designed the pylon and prop correctly.
Click to expand...

As far as I understand it, this storage of energy would contravene the NALSA rules.

" 2. The yacht shall have no stored energy other than for instrumentation, i.e. small batteries for speedometers or GPSs. Energy shall not be accumulated by pumps or generators driven by the wheels, ground, wind or sun or any other source. All controls on the yacht will be operated directly by the pilot with out consumption of stored energy (other than the pilots breakfast)."

I forgive you for your ignorance. :)
 
Tommyrot: "Like you, I have kept many facts about myself secret."

I do not keep secrets. In fact I blab quite easily. I just don't fill out data online for others to use. I do not normally comment, as I can not normally assume to be around to answer again. But I do read, mostly after the discussion has finished, so it is pointless adding anything.

There is also the case of "all men (and women) are equal". In the internet world everyone CAN start off equal. It is a wonderful leveller initially. But then someone always wants to play the role of the life long expert!


tommyrot: "this storage of energy would contravene the NALSA rules"

Are you telling me that no one lifts a wheel during a race (or has a flexible rig). That is the same as "righting moment" in a boat. It is the bit before that is more of the issue. The bit about going with the gusts to reduce the maximum forces. The small energy just helps you to recover with a better apparent wind since the knock down will have slowed the hull.
 
Tommyrot said:
As far as I understand it, this storage of energy would contravene the NALSA rules.

" 2. The yacht shall have no stored energy other than for instrumentation, i.e. small batteries for speedometers or GPSs. Energy shall not be accumulated by pumps or generators driven by the wheels, ground, wind or sun or any other source. All controls on the yacht will be operated directly by the pilot with out consumption of stored energy (other than the pilots breakfast)."
Click to expand...

This is actually one of the things we have discussed at length with NALSA. They recognize that their current rules don't fit will with this new class and are in the process of producing a new and more relevent set.

It's quite likely that the new NALSA rules for our class will not address directly whether a ddwfft vehicle can *accumulate* energy (pretty hard not to accumulate KE as you go faster), or even the *use* of stored energy (pretty hard not to use stored energy if the wind lulls for a second and the vehicle briefly coasts), but will state that stored energy cannot be used to *accelerate* the vehicle.

JB
 
Last edited:
halfway said:
I do not keep secrets. In fact I blab quite easily. I just don't fill out data online for others to use. I do not normally comment, as I can not normally assume to be around to answer again. But I do read, mostly after the discussion has finished, so it is pointless adding anything.
Click to expand...

You've been asked questions about yourself which you have chosen not to answer.


halfway said:
Are you telling me that no one lifts a wheel during a race (or has a flexible rig). That is the same as "righting moment" in a boat. It is the bit before that is more of the issue. The bit about going with the gusts to reduce the maximum forces. The small energy just helps you to recover with a better apparent wind since the knock down will have slowed the hull.
Click to expand...

No, I am quoting NALSA's rules about stored energy.
You hinted at a system designed to store energy.

To give advice on design, you have to understand the rules that the design must fit. You obviously didn't.
 
Last edited:
Tommyrot: "You hinted at a system designed to store energy"

I actually imagined a damper and a big elastic band.

Tommyrot: "You've been asked questions about yourself which you have chosen not to answer."

I think we are still in the internet? I hope so. I could not cope if real life had reduced itself to black and white dots on a flat screen. Get me out!

Tommyrot: "you have to understand the rules that the design must fit"

That suggestion was an engineering survival issue. How to put it into a "legal" design is another. But since other wheeled carts have energy storage, like wheels that can be lifted, and wheels that have mass and rotate, and even sheets that can be let go, then pulled in, the solutions are not hard.
 
Last edited:
halfway said:
I actually imagined a damper and a big elastic band.


.
Click to expand...

So you didn't take into account the rules governing the record attempt. For someone who goes into minute detail regarding most subjects, you seem to have missed the blindingly obvious.
You were unfairly criticizing the cart, which had to be built within the rules.

As for "Not keeping secrets", you were asked, you decided not to answer. I see little difference.
 
halfway said:
I said "The earth surface seems to be a default reference in most conversations that are mechanical in nature. "

Did I say, prop analysis or yacht analysis. NO. I said mechanical.
Is a piece of plywood a prop? No, neither is it a yacht.
Click to expand...
A yacht is a mechanical system, so is the cart, so is an airplane or a powerboat or a spaceshuttle. Not all of them has a default reference frame, and those that might have it might not be Rf of earth.
halfway said:
As you seem to confirm, later in your post, each type of system does have its default situation. So it seems your answer has proven the point. There is an assumed default in different situations.
Click to expand...
No, not all have assumed IRF, and certainly might have different RF in different context, or not at all in some context while having such in other context. I certainly not do confirm.
halfway said:
(The time delay issue is due to your posts popping up much later than posts created after you. This system has a time warp issue where answers appear sometimes before the question. Maybe you should apply your frames to this software)
Click to expand...
Does that word before in above refers to time or instead of which one is above the other in the thread on the screen ?
Either way, I don't think answer can be before the question. How could anyone answer the question before seeing the question ?
That doesn't make sense regardless of any time dalay, no matter how long.

What a time delay causes, is that new posts appear in the middle of a thread later on.

Your comment on changing RF came later than the post you replied to and is located below the original post. Nothing to do with time delays. Neither of those was a post of mine. Read the #417 again to see what you actually said.
 
Last edited:
I am a bit down cast by the lack of technical (sailing) discussion. Warning I might not be around to follow up.

Imagine Oracle doing a VMG of exactly the wind speed at its sail mid effective point. Assume it is on a 45 degree gybe angle to keep it simple.
Its apparent wind is therefore exactly 45 degrees to the bow. Which is 90 degrees to the, start to finish, direct course line. Definition of "in front"
can be assumed to be half a boat length.

(Q0. SL: did I muck up again with directions.)

Q1. Where do you have to be, to experience the "old" air of Oracle when sailing?

Q2. Do you accept that the air in front of Oracle's bow is unaffected by Oracle behind?
Since those air atoms are rushing away from the bow at the same rate as the bow is progressing down the direct line course.

This is essentially the nub of the "it can not be done argument"
But we do not worry about those atoms. The ones we care about are the ones Oracle encounters with the sail.
These have a 45 degree track over the bow. These are deflected and lift is produced.

Q3. If you think the air in front IS affected then exactly how far does it extend? What is the mechanism to change it? Since it is moving into new "sideway" air all the time.

Q4. So IF there is no pressure difference or forward effect at any racing significant distance; how can Oracle make a pressure difference behind it. That would require it to generate air from nothing. Or to carry behind it a extra dense piece of air. Do they let off a few life vests as they start the race?

Q5. When a wing is in a wind tunnel and a slight attack angle is created, does all the wind head straight down to the bottom of the tunnel and leave a vacuum at the top?

No, the "old" air interacts with the passing air and after a certain length continues along normally. There is a difference of pressure behind the wing (from above/below) that equalizes. The resultant flow is slower, and expands out its effect until it hits the wind tunnel roof and floor.

Q6. If Q5 is wrong and the air does just slow in an ever greater triangle; where is the same triangle around Oracle? (Same as Q1)

----

Imagine 100 Oracles racing. All next to each other, on a perfect start line. They all get up speed to the above situation; wind 45 degree to the bow.
Now the ones across wind, in the "old" wind, are getting less energetic wind. So to be in the same situation they must be slower. Slightly behind.

Q7. So after the 50th boat where is all the energy for the 51st coming from?

----

So now go back to "Cylinder world". Two islands either end, and the side of the bean can being the ocean. Now set off the 100 Oracles around the can evenly from the windward can end to the leeward end. All going the same spiral.

Q8. So if there is a problem with the 100 Oracles in a line; how does that problem translate to Cylinder world? There is no boat with clean air!

----

Now move to, the prop on the cart issue. At a cart speed of around the wind speed the air in the prop is all "stale". So the drag will make it start to rotate at the speed of the prop. So the apparent wind disappears.

Q9. Whoops! I just proved it can not be done. What did I miss?

----

My only explanation is that the prop never sees "stale" air. Since one assumption from the start was invalid. I assumed that the wind speed was the mid point of the sail only.

But in reality the wind speed is a graduation from zero at the ground and rising as you get further up. So at any one time the top of the prop could be in different air than the bottom of the prop. So at no time is the whole prop running in stale air.

Also the prop will impart a lossy "outward" flow, so new air will arrive from the centre and progress outwards.

Also the cart can NOT always be exactly in line with the wind. Wind is turbulent. So there will be a net sideway "refreshing" of the air.

As soon as the wind speed is exceeded by the whole prop all the air is being refreshed. The prop never encounters the same air molecule twice.

Q10. Now what is wrong with all that? I will NOT accept any answer that contains an equation referencing air flow over a aerofoil. Only real life observations and data from wind tunnel tests on aerofoils or sails. Stream lines, smoke or pressure observations away from the surfaces are OK. It has to be real life. No mathematical models.

----


Q12. So what tactics should be used to overtake Oracle?

Q13. And better still, what tactics should be used to overtake a cart going at the speed of the wind?
 
halfway said:
Q2. Do you accept that the air in front of Oracle's bow is unaffected by Oracle behind?
Since those air atoms are rushing away from the bow at the same rate as the bow is progressing down the direct line course.
Click to expand...

No. Disturbances in the flow pattern caused by the sail are transmitted by pressure and propagate at the speed of sound. Unless Oracle is doing (or exceeding) Mach 1, its presence will affect the air in all directions.

Since your further questions appear to depend on this massive misunderstanding, I see no point in addressing them.
 
Ubergeekian: "Disturbances in the flow pattern caused by the sail are transmitted by pressure and propagate at the speed of sound"

Now that begs the question? What is the pressure distribution?

For a sail and a wing?

I also defined "in front". I then said it again with the term "any racing significant distance".
 
I really need to get to Q13. The pressure "sideline" was just to get to the far field (but not infinity) effects.

Q13 might have a significant implication to cart racing? Assuming identical carts?
 
We spent Saturday with the folks from the Discovery channel. They're doing a segment on the downwind cart for a Canadian program called "The Daily Planet". It won't air in the U.S. but I hope to be able to post the video after it airs in Canada.

In the meantime, we've been hard at work adding aerodynamic components to the vehicle since we were hitting higher speeds than we initially anticipated. We also slapped a coat of paint and our sponsors' logos on it just in time for the Discovery channel crew.

With the new slightly less ugly look, we felt it deserved a name change from BUFC (big ugly…cart) to "Blackbird".

We're working with NALSA to establish the new records category for this class of vehicle - and we hope to be taking a shot at the new record in the coming weeks. There are still some more improvements to be made, but we're beginning to be optimistic about an official record of 3X wind speed or more - directly downwind.

As always, you can follow our progress at www.fasterthanthewind.org

attachment.php



attachment.php
 
Looks cool! Give the guy cockpit canopy though! (one way, reflective material would look nice, and give some protection from the prop)

(Which would win in a tug-of-war between a DDWFTTW cart and a Direct-Upwind cart?)

MD
 
spork said:
We spent Saturday with the folks from the Discovery channel. They're doing a segment on the downwind cart for a Canadian program called "The Daily Planet". It won't air in the U.S. but I hope to be able to post the video after it airs in Canada.
Click to expand...

I'll bet there's one thing you won't be able to do, film or no film - get H & H to admit they were wrong!
 
You must log in or register to reply here.

Share this page

Top