Downwind Faster than the Wind - Successful Run by manned cart

[spork]

Spork: ""one of my team" ain't ME"

But you clearly state:

Spork: "It is. So far I've Bogarted the driver's seat. JB is pretty keen on keeping a close eye on various aspects of the cart from the chase vehicle. But he will undoubtely take a spin soon."

Sounds like a team to me.

Yes it's a team. That doesn't mean JB is me. I'm beginning to think this may be even more difficult than I anticipated.

 

[no_way]

This giant tidbit of wrongness is why halfway's ddwfttw vehicle could never exceed windspeed and why he thinks our prop is the wrong shape.

The only relevent difference between the blade on BMWO as it reaches at 2x WS (downwind vmg) and the blade on the BUFC at 2x WS (vehicle on DDW path) is the radius of the circle.

A: in a sailboat, it's impossible to achieve downwind VMGs of > 1.0 without the airfoil operating as a propeller (adding energy to the wind wrt to the airfoil).

B: in a sailboat (while reaching DW with VMGs < WS) one *can* use the sail as a turbine (removing energy from the wind wrt the airfoil), but even in the simplest modern sailboat the sail used properly is acting as a propeller when reaching.

C: let's be clear, there's not some 'magical' setting that only the 'pros' know that has the sail working as a prop when reaching -- *everyone* that learns the craft in it's basic form sets the sail this way.

D: as spork once said "if the other guy doesn't reach using a sail setting where the sail is acting as a propeller, I want to race him for money."

JB

I think that a claim a sail can be said to work as a blade of a propellor can be correct, given a suitable definition of what exactly working like a blade of a propellor means.
I'm sure that if a fast sailboat sails upcurrent on a river in a calm day, the sail must do work on the air.
I'm not too sure if doing work on the air means the same as doing work on the wind or not, it's just too fuzzy use of word wind to be sure about the semantics.

But saying:
1) a blade of the propellor does work on the air in IRF of the prop or the cart
is not the same thing as claiming:
2) a blade of the propellor does work on the air in IRF of the blade of the prop. !!!

And claiming:
3) a sail does work on the air in IRF of the sail
is much closer to the latter claim 2) than the former claim 1), and that's quite a big difference.
1) is evidently correct, but that doesn't automatically indicate that 2) and 3) are too.
It depends if adding a component of velocity that increases a component of airspeed in certain direction means doing work on the air while speed of air isn't increased, and thus while work is done in some direction, more negative work is done in some other direction at the same time, thust total work done is negative. Or does doing negative work mean that work is done, since word positive is not mentioned ?
I guess such semantics can be used, but it can also be said that doing negative work on the air means air is doing work on the blade instead.

It's clear thogh, that lift deflects the flow, while drag slows the flow down, and there is always drag when there is lift and even if there is no lift. Thus air slows down relative to the airfoil, but not necessarily relative to the cart.

 

[RAI]

Tacking down wind.

For pity's sake don't resurrect that one or we'll have another 100 posts going round in ever-decreasing circles!

Ah! My favourite topic!

 

[RAI]

Not exactly what we would build -- likely we would go with twin props and their profile wouldn't look like those, but enough to give you an idea. We call this one the BBFC.

Hmmm... looks like too much structural complexity to me.

However, I can see the sense in using two props to equalise the torque induced pressure on the wheels. Would you go for side by side (separated or phased) or concentric?

 

[no_way]

Ubergeekian: "that despite the flow of air being changed, no work is being done on the air"

If I put a 4x8 sheet of plywood on the pontoon now, and fix it with a brace against the wind, but slightly angled, is it doing work on the wind?

Or are you going to change the reference again and say the world bumped into the wind. As your proofs only seem to work from one reference point.

Since you didn't define any IRF in your post #411, how could IRF be changed ?

Not at all, it (the IRF) would only be introduced the first time, as your claim ...NEVER ... on the air missed any mention of IRF.

And the work done on an object is force acting on the object dot the distance the object is moved. That distance is dependent on IRF and thus so is the work done on that object.
The total work done by the force is however IRF invariant, because the work done on the object + work done on the thing doing the work on the object by the reaction force remains the same regardless of chosen IRF.

 

[spork]

Almost certainly side-by-side. This gives you the max disk area - which gives the max efficiency. Twin counter-rotating props (in any configuration) also eliminates precession issues.

 

[RAI]

Almost certainly side-by-side. This gives you the max disk area - which gives the max efficiency. Twin counter-rotating props (in any configuration) also eliminates precession issues.

That will make a pretty wide machine, maybe four wheels then?

 

[halfway]

Ubergeekian: "The reference to minimum angle of attack is meaningless"

So are YOU saying that a symmetric aerofoil that has the apparent wind directly in line with the chord still produces lift?
If so, which way up does it occur? Does it toss a coin to find out?

Any foil has an angle of attack that creates zero lift. You can, by forcing air through a prop, make this occur. This is an abnormal use of a round thing with blades.

----
Ubergeekian: "action and reaction are equal and ..."

They are forces. I think most reading this will grasp the issue quite clearly, that the sheet of plywood does not have a nuclear reactor inside supplying energy. Or any other hidden source. So the air was moved without adding energy from any other source. Therefore a sail (a piece of cloth) can move air without adding energy from another source. If while it moves it, there is lift created (like normal sails do) you can take advantage of that lift assuming it has a component in the direction you want to go.

----

ThinAirDesigns:
"let's be clear, there's not some 'magical' setting that only the 'pros' know that has the sail working as a prop when reaching"

OK, so IS it working as a prop when going to windward?
If NO exactly what angle does it suddenly not work as a prop. Or are there two overlapping methods that fade between.

As I said earlier. A sail is a sail. It has no knowledge of the water. It just plays with the air molecules that arrive near its surface. It has no idea which way the water is going. Therefore it can not choose how to "work" in a different way in different situations if the apparent wind is the same.


----

Thinairdesigns, Spork:

On your invitation I went back and tried to find posts from before the big cart projects. I turned up a references to the "hang gliding buddy" proof. That is the exact explanation I have for the concept. However, he has far more variables, as my proof just assumes 45 degree tracks/helix and a known aerofoil spot values. Just enough to prove it as oppose to optimize it. But the conditions still hold. The date of the post was Jan 2009. However just after, you post the Mark Drela analysis, that is the cause of the problems and the energy prop pushing issues. How can you go from a correct proof to the wrong one and then never mention poor "buddy" ever again. His brief life of fame and honour lasted 16 minutes.

8 hours later they were back to props blowing air: "It always act as a simple propeller."

It then suddenly reappears in Jan 2010 on Talk Rational as "TADs analysis" (minutes after Mark Drela missive is posted again).

But then the argument degrades, rapidly with derision of people who want to understand how, as opposed to just believing.

Sadly in 34 minutes it falls back to:

"Yeah, that whole "the energy comes from slowing down the air relative to the ground" explanation is so "spooky'."

Then Humber starts up again. Sadly he missed the only explanation that could possibly have helped his situation.

I want to meet the "hang gliding buddy" and see if he can also see that the force to overcome the friction is actually the difference of the two vectors. His equations clearly state that it is, but does he see that the individual forces could be quite large. Much larger than the force to overcome friction. I bet the cart would have been different.

(The only issue I have with the "buddy" explanation is that he waits for the "no wind" case to introduce the tan(Ф) = (SC-SW) / (SC/G) term. This should have been a little earlier as it is key to the apparent wind angle)

----

Spork: "Yes it's a team. That doesn't mean JB is me."

I really refer to concepts, that you seem to both support. If however there is any division in the ranks of the team, could you make it clear so that we know which points you disagree on.

----

Thinairdesigns, Spork, Ubergeekian:

Random work definitions:

"The transfer of energy from one physical system to another, especially the transfer of energy to a body by the application of a force that moves the body in the direction of the force. It is calculated as the product of the force and the distance through which the body moves and is expressed in joules, ergs, and foot-pounds."

"The transference of energy that is produced by the motion of the point of application of a force and is measured by multiplying the force and the displacement of its point of application in the line of action"

"Physics means for energy transfer: the transfer of energy, measured as the product of the force applied to a body and the distance moved by that body in the direction of the force."

"Work. The amount of energy transferred to or from a body or system as a result of forces acting upon the body, causing displacement of the body or parts of it."


Since the plywood does not get colder, has no hidden energy source, does not move, fall, or anything, it supplies no energy, therefore there is no energy transferred. It is the air that supplies the energy. That energy in a turbine goes into rotating the shaft, in a sail it produces lift. In a turbine the desired output is rotational but in a prop sail the desired output is axial. In a turbine you constrain the axial movement and in a prop sail you constrain the rotational movement.

It does not "suck" or "blow". Now I have real work to do.

 

[ThinAirDesigns]

That will make a pretty wide machine, maybe four wheels then?

Very wide. We would likely stick with three wheels though.

JB

 

[ThinAirDesigns]

Yes it's a team. That doesn't mean JB is me. I'm beginning to think this may be even more difficult than I anticipated.

Yes, Halfway has a very Humberesque feel for logic, doesn't he. LOL

JB

 

[RAI]

Very wide. We would likely stick with three wheels though.

Tricycles can trip over. However, I can see the problems associated with steering two widely separated front wheels. Nevertheless, with two separated propellers, putting the pilot's weight in the middle above (or even below) the rear driving axle might be a trade worth looking at.

 

[Pierrome]

Balloon Test

Spork and JB:

Excuse me if this has been mentioned before and I have missed it. One test the sceptics seem to think is important is the release of a free floating balloon which gets left behind as the cart exceeds windspeed, apparently the telltales are not enough for them.
I wonder if you have plans to demonstrate in this way later?

 

[snowleopard]

A most amazing display of sense and nonsense!!

Any foil has an angle of attack that creates zero lift. You can, by forcing air through a prop, make this occur.

Perfectly correct, but then....
----

I think most reading this will grasp the issue quite clearly, that the sheet of plywood does not have a nuclear reactor inside supplying energy. Or any other hidden source. So the air was moved without adding energy from any other source. Therefore a sail (a piece of cloth) can move air without adding energy from another source.

Now we are into perpetual motion!

The energy required to produce the change in velocity of the wind doesn't come from nowhere, it comes from the reaction with the Earth which is microscopically accelerated in the opposite direction to the acceleration applied to the wind.

A sail is a sail. It has no knowledge of the water. It just plays with the air molecules that arrive near its surface. It has no idea which way the water is going.

Unless there is a medium to stop the sail drifting off downwind it can't sail. That medium may be tyres on a road or water flowing over a foil. In a boat, water flowing over the keel is essential so, regardless of any anthropomorphic 'knowing about the water' it can't work without an appropriate water flow.

Then Humber starts up again. Sadly he missed the only explanation that could possibly have helped his situation.

Oops, wrong forum[/QUOTE]

 

[halfway]

snowleopard: "The energy required to produce the change in velocity of the wind doesn't come from nowhere, it comes from the reaction with the Earth which is microscopically accelerated in the opposite direction to the acceleration applied to the wind."

SL come on, I already put that one to rest by originally saying:

"Or are you going to change the reference again and say the world bumped into the wind."


Just for SL I will restate the problem. Imagine a close box with fan, fixed to the floor, rotating the air inside the box. Now I add the sheet of plywood fixed to the box floor.

The plywood moves the air. Does it do work?

No energy is transferred in the steady state from the plywood to the air. The air is getting its energy from the fan. The air is giving up its energy to the box walls and the fan blades and the plywood. The energy supplied into the box to drive the fan comes out as heat from the box walls. But at no time does the plywood supply any energy to cause work to be done.

 

[no_way]

A most amazing display of sense and nonsense!!

Any foil has an angle of attack that creates zero lift. You can, by forcing air through a prop, make this occur.

Perfectly correct, but then....

Only if air is forced through the rotorplane by something else than the prop itself at just the right speed !

Now we are into perpetual motion!

The energy required to produce the change in velocity of the wind doesn't come from nowhere, it comes from the reaction with the Earth which is microscopically accelerated in the opposite direction to the acceleration applied to the wind.

Or from from the air if kinetic energy of the earth remains the same during time intervall in question in IRF used in the analyses.
That can be the case when direction of motion of earth is reversed, but speed remains the same, while velocity of earth does not.
In that case air slows down releasing the kinetic energy that is converted to losses by the cart + any increase of KE of the cart.

 

[halfway]

snowleopard: "In a boat, water flowing over the keel is essential so, regardless of any anthropomorphic 'knowing about the water' it can't work without an appropriate water flow."

Yes it can. I tonne of concrete on the bottom of the mast and put it in the above box with the piece of plywood.

It will still act like a sail and produces a force. There is no requirement for water or wheels. The cloth has no idea that its mast was stuck into a 1 tonne block of concrete and hidden in a close boxed specially built for SL. It still does the same job. It is a sail and only has "eyes" for the apparent wind.

Just happens that in SL's special box the apparent wind is the same as the real wind.

 

[halfway]

no_way: "Only if air is forced through the rotorplane by something else than the prop itself at just the right speed !"

Thank you. If you go back to how this started you will find that the "something else" was a yellow canvas-covered plane in a gravity dive. At just the right point the air forced through the rotorplane will be enough.

The end result was not so nice though!

 

[no_way]

snowleopard: "The energy required to produce the change in velocity of the wind doesn't come from nowhere, it comes from the reaction with the Earth which is microscopically accelerated in the opposite direction to the acceleration applied to the wind."

SL come on, I already put that one to rest by originally saying:

"Or are you going to change the reference again and say the world bumped into the wind."

Then please adress my post #425 on the subject regarding your statement in your post #411 :

A sail NEVER does work on the wind.

And point out what IRF is supposed to be used and where it is defined.

 

[halfway]

no_way: "in your post #411 "

I am confused it was first brought up in post 417. Sadly when you reply all the numbers go away. There is also a time delay on new members that makes your posts arrive a bit late. But as for references, the hint was that I took the plywood off the boat onto the pontoon and fixed it there. Observer and plywood and fixing on a common base. The earth surface seems to be a default reference in most conversations that are mechanical in nature. But then you might have thought it was a floating pontoon when in fact it is lodged well and truly in the mud.
.


"And point out what IRF is supposed to be used and where it is defined. "

I'll take the concrete block in the above example. Or the box, or the stand for the fan. You choose.


(There is actually one way a sail does work on the wind and that is when a boat recovers from a knock down. During the rise it is giving energy to the system. Just like a prop. But I assume that situation is not part of this discussion)

 

[no_way]

no_way: "in your post #411 "

I am confused it was first brought up in post 417. Sadly when you reply all the numbers go away.

Highlight the adress of the site beforehand + press ctrl+c then press ctrl+T and click with your mouse on the appropriate place and then press ctrl+V AND after all of those are done, then reply to any post.

That way post numbers don't go away at all.
In post #417 you wrote :

Ubergeekian: "that despite the flow of air being changed, no work is being done on the air"
Or are you going to change the reference again and say ...

If it was first brough up in that post, why are you suggesting/proposing Ubergeekian has already changed RF, how could he possibly have done that before the post where it was first brought up ???

Quite clearly, it was discussed before that in post #411 or possibly before that, but that's not clear as quote-function was not used to include links to previous posts, so it's not possible to know what is starting a new side issue and what is continuing on some older one !

There is also a time delay on new members that makes your posts arrive a bit late. But as for references, the hint was ...

"And point out what IRF is supposed to be used and where it is defined. "

I'll take the concrete block in the above example. Or the box, or the stand for the fan. You choose.

All of those posted long after you suggested an attempt was made of changing the IRF.

The earth surface seems to be a default reference in most conversations that are mechanical in nature.

Have to disagree on that. That's just asking for trouble.

In general props are not analysed in IRF of the ground, but IRF of free stream air. That uncommon use of IRF is changing the numbers for props from those usually assumed, like "propulsive"_efficiency going easily well over 100% if defined as normal without corrections.
As a result in IRF of ground: (F dot v_cart ) / (shaft power) > 100% quite easily, because power_in is: (sum of shaft power and that coming from the air in ground IRF).
Obviously that will never happen in IRF of free stream air unless talking about pmm.

And wheels either IRF of ground or RF of cart if that RF is inertial.
However changing IRF during the analyses is usually a bad idea easily leading to errors, so defining IRF to be used becomes quite necessary for carts under discussion.
Just assuming IRF of ground is quite baseless, as this is a boating forum and sailingboats are quite often analysed in IRF of the boat itself under static conditions (=steady state)