Merged DDWFTTW in a “Real” Wind

[humber]

Yes.

Well, also, it's easier to spin the propeller fast enough to get thrust out of it.



Yes, but it's moving over the ground.



The propeller isn't just spinning. It's being spun. The cart is moving over the ground. This turns the wheels, which spin the propeller. It takes some force to turn the wheels, but the thrust provided by the spinning propeller is greater than this force. So the net force is positive.

See my calculations, based on figures provided by spork and by ThinAirDesigns. (These calculations are for the cart moving even faster than the wind.)

Which don't work and are in total disagreement with the measured trial results. The net force on the cart is a near constant 32N*(assuming 640lb is remotely correct) whereas the calculations show a net force that changes with the ratio of cart to wind speed - and is not enough to propel the cart after losses are considered.
* acceleration is nearly constant.

 

[humber]

In both cases we can try to use the power coming from the moving ground...

Voodoo.

Air power at prop = 18mph*61.3lb = 26.4ft/s*61.3lb = 8.0m/s*272N = 2176W =2.92HP
Power at wheel = 28mph*48.11lb = 41ft/s*48.11lb = 12.5m/s*214 = 2675W =3.58HP

The prop both extracts energy from the air to generate the power, to produce the thrust to drive itself, and then some more to run the "generator" at wheel. I have been told that the wind is the energy source.

 

[tobermoryphil]

Voodoo.

Air power at prop = 18mph*61.3lb = 26.4ft/s*61.3lb = 8.0m/s*272N = 2176W =2.92HP
Power at wheel = 28mph*48.11lb = 41ft/s*48.11lb = 12.5m/s*214 = 2675W =3.58HP

The prop both extracts energy from the air to generate the power, to produce the thrust to drive itself, and then some more to run the "generator" at wheel. I have been told that the wind is the energy source.

You have. It is.
One day you might get it, but after two years, I rather doubt that.

 

[humber]

You have. It is.
One day you might get it, but after two years, I rather doubt that.

The numerous inconsistencies are a result of ad-hoc fantasy. The trial data contradicts the theory.

The author of Javaprop, dismisses the notion of the literal airscrew as well as thrust from an air-driven prop.

Anyway his "advance ratio" is defined as follows:
"The velocity of rotation n is given in revolutions per minute, but for the actual calculations, as in the advance ratio v/(nD), n usually means revolutions per seconds."
V is the airspeed and D is diameter, so is a ratio of the turns of the prop to the airspeed: the number of feet traveled per turn, per second in still air.
For example, the cart and prop may move 8m per turn, per second. The motion relative to the air.

Do a "Galilean Transform", and add 10m/s to both the prop and the air, you still get the same number of feet per turn relative to the air, as to the ground, even if the effective advance ratio changes with relative velocity of air and prop.
The theory has different "advance ratios" for the prop and for the cart.

 

[windgrins]

What will they think of next?

I'll go out on a limb and say you're wrong. These folks reported 98.6% efficiency http://www.jhu.edu/news_info/news/home99/aug99/bike.html

I believe our drive was just over 90% - but I KNOW, our cart went 2.8X wind speed. So I don't really care that much what the exact efficiencies were. I guess I'd love to learn our chain drive gave us less than 80% efficiency. That would give us an easy improvement to shatter our own existing record.

Imagine that: A web site that actually supports the point the poster is making quite clearly instead of negating the very point made in the post! Perhaps we should all strive for the concept!

I feel slightly cleaner, already!

Regards,

WindGrins

 

[Subduction Zone]

Some recognised evidence of the cart's weight. Weight can make a lot of difference.
And the prop data for 132rpm?

Javaprop won't work for negative airspeeds, and you have not posted the data for start-up at all. If the theory fails to show that prop thrust is responsible for motion from a standstill, then it must be something else.

That reminds me, they didn't have an official color check either. I mean, it was black sure, but how black was it? Inquiring people want to know. And why didn't they paint it red? Red cars are pulled over by the police more than any other color, so obviously it would have gone faster if it was red.

Hah!! A "black" Blackbird, even more evidence that this was a hoax from the beginning.

 

[Jack by the hedge]

Let's knock this "retreating prop" argument over. All points of the prop are symmetrical about the hub. All points on the prop, move the same distance forwards as the hub. There is at no time any motion other than that.
Think of the prop as a solid disk and it becomes obvious that must be the case.

You are merely confusing yourself by calling it this "retreating prop" argument.

Consider a point on the propeller's arc which is, let's say, midway along the blade's length and vertical to the shaft's centre line. Turn the prop so the leading edge of a blade is on this vertical line. Project a perpendicular point from the leading edge to the propshaft's centre line. Now turn the prop a few degrees so the blade's trailing edge is now on the vertical. Project another perpendicular point onto the propshaft centre line. Is this point further rearward than the first? Yes, it is.

For every point on the surface of the blade as you turned it, the point projected perpendicularly onto the centre line moved consistently backwards.

That is all.

 

[Jack by the hedge]

That reminds me, they didn't have an official color check either. I mean, it was black sure, but how black was it? Inquiring people want to know. And why didn't they paint it red? Red cars are pulled over by the police more than any other color, so obviously it would have gone faster if it was red.

Hah!! A "black" Blackbird, even more evidence that this was a hoax from the beginning.

I really think you're onto something. Did the Blackbird have to submit to a sex test?

It is conventional for any boat, ship or similar craft (surely including land yachts) to be described in the feminine gender. In that case, why is "she" black? Black blackbirds are all male. Female blackbirds are brown. Busted!

 

[EHocking]

Quite an interesting exchange there and I'm sure there are efficiencies to be made to the original design, but what it boils down to is:

...but when it turned out the cart pulled forward on the dyno in all configurations and speed settings, we said screw it and headed for the dry lake.

^^^^ THIS ^^^^

(and then set a record for DDW at 2.8 x WS)

 

[profpangloss]

Quite an interesting exchange there and I'm sure there are efficiencies to be made to the original design, but what it boils down to is:
^^^^ THIS ^^^^

(and then set a record for DDW at 2.8 x WS)

Well, except for the minor detail that the cart was not going DDW, and we don't know what the true Wind Speed was, I guess what you wrote is correct: They were handed a record for something or other, maybe it was an attendance record?

 

[profpangloss]

Imagine that: A web site that actually supports the point the poster is making quite clearly instead of negating the very point made in the post! Perhaps we should all strive for the concept!

I feel slightly cleaner, already!

Regards,

WindGrins

If you think that short chain, Brand new and made to special specifications, perfectly aligned and tensioned, running in a clean lab where even lubricant was not needed, driven by computer controlled electric motors, has anything to say about a 5 + meter long twisted chain, operating out in the open , twisted so it could not possibly have been perfectly aligned and tensioned, with dust and dirt collecting on it, then you are indeed a true member of the Church of Carts, and an apologist for everything spork does. Still feel clean?

 

[ThinAirDesigns]

Meaning that you don't have an official weight, but guessed it.

Wrong.

However there is a post where you claimed NALSA weighed the cart.

Lie.

JB

 

[ThinAirDesigns]

If you think that short chain, Brand new and made to special specifications, perfectly aligned and tensioned, running in a clean lab where even lubricant was not needed, driven by computer controlled electric motors, has anything to say about a 5 + meter long twisted chain, operating out in the open , twisted so it could not possibly have been perfectly aligned and tensioned, with dust and dirt collecting on it, then you are indeed a true member of the Church of Carts, and an apologist for everything spork does. Still feel clean?

Well, except that his link was only presented to prove your blatently misrepresented '*theoretical* straight chain' assertion wrong.

And it did.

If you don't like being 'dirty', do your research better.

JB

 

[profpangloss]

Well, except that his link was only presented to prove your blatently misrepresented '*theoretical* straight chain' assertion wrong.

And it did.

If you don't like being 'dirty', do your research better.

JB

My "blatently misrepresented" what? I wrote " A very short chain that is perfectly aligned can achieve theoretical efficiencies of over 90%."
Now tell me how achieving 98.6% in laboratory conditions, with a brand new made-to-order short chain, perfectly aligned and tensioned, makes my comment "wrong".

While you are at it, please explain how spork's comment that his chain, over 5 meters long, out in the dust and dirt, twisted so it cannot be perfectly aligned and tensioned, with apparently home-made chain tensioners on it, can possibly achieve "90% efficiency" as claimed.

Which one of us is wrong? Be honest, if that is within your capabilities, I know it must be hard!

 

[spork]

[FONT=Verdana, sans-serif]
[FONT=Verdana, sans-serif]If the propeller and air only interact in an equal and opposite manner . . .[/FONT]
[/FONT][FONT=Verdana, sans-serif][/FONT]
[FONT=Verdana, sans-serif]The only advantage a cart travelling at wind speed has over a cart pushed up to the same speed in still air is that it doesn't have a headwind.

Wrong.

Otherwise all other frictional losses are essentially the same for both carts

Wrong.

At wind speed the cart is effectively in still air.

Wrong.

How does a propeller spinning in still air develop extra energy to sustain and increase the cart's speed ONLY from an equal and oposite reaction with that air?

You seem to have gotten it backwards. Ask the question before coming to all your wrong conclusions and telling us we have it all wrong.

 

[A.T.]

Llyricist, I think you are correct. Clearly a symmetrical airfoil can produce lift with a positive angle of attack. But since the airfoil is aligned with the direction of motion of the cart, Without skidding, the total force vector (lift + drag) will always be pointed behind the perpendicular to the pylon-impeding the cart in the direction of travel.

Exactly, the pylons cannot be rotated and are aligned with the wheel track. Your sail boat wouldn't work with the sail aligned with the keel. The keel is aligned with the relative ground velocity and the hull, while a wingsail is aligned with the relative air velocity for optimal AOA and can be rotated relative to the hull.

But here is a fun idea: You can make the keel rotatable too. Think of 3 rotatable hydro foil keels (inverted T). Once the hull is lifted out of the water it experiences only aero drag, which can be minimized by aligning the hull with the relative air velocity just like the wingsail. So at high speed the wingsail is almost aligned with the hull, while just the underwater keels at an angle to the hull. The entire visible boat would look like going sideways, because it would be aligned with the apparent wind, not with the travel direction.

I don't know if someone did this on water, but Bob Dill build his record land yachts like this. See Figure 8 and 9 of this:
http://www.sailingscuttlebutt.com/news/08/tt/bobdill.pdf

Instead of keels he has wheels which are oriented at optimal angle to the hull. Unlike a hydrofoil boat, a land-yacht doesn't have to get to speed to lift the hull out of the surface-medium, so you can fix the non steering wheels at an angle to the hull.

 

[windgrins]

Thanks A.T.

Exactly, the pylons cannot be rotated and are aligned with the wheel track. Your sail boat wouldn't work with the sail aligned with the keel. The keel is aligned with the relative ground velocity and the hull, while a wingsail is aligned with the relative air velocity for optimal AOA and can be rotated relative to the hull.

But here is a fun idea: You can make the keel rotatable too. Think of 3 rotatable hydro foil keels (inverted T). Once the hull is lifted out of the water it experiences only aero drag, which can be minimized by aligning the hull with the relative air velocity just like the wingsail. So at high speed the wingsail is almost aligned with the hull, while just the underwater keels at an angle to the hull. The entire visible boat would look like going sideways, because it would be aligned with the apparent wind, not with the travel direction.

I don't know if someone did this on water, but Bob Dill build his record land yachts like this. See Figure 8 and 9 of this:
http://www.sailingscuttlebutt.com/news/08/tt/bobdill.pdf

Instead of keels he has wheels which are oriented at optimal angle to the hull. Unlike a hydrofoil boat, a land-yacht doesn't have to get to speed to lift the hull out of the surface-medium, so you can the non steering wheels at an angle to the hull.

Thanks A.T.

I don't mind making an honest error every now and then (but try not to make a habit of it.) The exchange with Llyricist, you, Spork, Newbie, etc is what I came here for. I learned a simple lesson by an honest exchange and was persuaded to change my mind. I enjoy education! Especially at the price of these classes!

Regards,

WindGrins

 

[A.T.]

If the propeller and air only interact in an equal and opposite manner . . .

Ynot, as usual you confuse yourself with your inprecise floksy language. What is "manner" here. It's called "force".

The only advantage a cart travelling at wind speed has over a cart pushed up to the same speed in still air is that it doesn't have a headwind.

Less headwind makes a huge difference for a propeller. It allows it to develop more thrust force with the same input shaft power.

How does a propeller spinning in still air develop extra energy to sustain and increase the cart's speed ONLY from an equal and oposite reaction with that air?

The propeller doesn't "develop energy". It uses energy to develop a force. With less headwind that force can be greater for the same input power (energy/time). Then both equal and opposite forces of the interaction with air are greater.

 

[ThinAirDesigns]

My "blatently misrepresented" what? I wrote " A very short chain that is perfectly aligned can achieve theoretical efficiencies of over 90%."
Now tell me how achieving 98.6% in laboratory conditions, with a brand new made-to-order short chain, perfectly aligned and tensioned, makes my comment "wrong".

A: The 98+% is achieved for real, not just in theory (everyone here knows exactly how you meant that.)

B: According to your "theory" of correctness, this statement would also have been just as valid. "... theoretical efficiencies of over 10%".

You're the only one who believes your story.

JB

 

[Llyricist]

Does this mean the numbers show the cart can' get to wind speed? I suspect that is the case but I would like to see some numbers.

No, this means that their are no readily accessible formulas or programs that bother to calculate thrust for the condition of air moving back to front through a propeller.