Novel Propeller propulsion, going faster downwind than the wind

[Dave_S]

The prop is always pushing against the true wind.

Originally Posted by TrentePieds

1) Assume the vehicule has a Right Hand Prop in the sense we seafarers use that term, and that that prop is to harvest power from the wind in order to transmit that power to the wheels of the vehicle in order to drive it in the direction the wind blows, e.g. in a South wind the vehicle is desired to move north.

2) Now contemplate the vehicle from above, with the true wind coming at the prop at 90ºs

3) I don't have my scanner or a drafting program handy here, so clumsy words will have to do.

4) There can be no dispute that the ANGLE OF INCIDENCE of the prop will have to be such that the leading edge of the of the aerofoil that is the crosssection of the blade is “east of south”, and the trailing edge “west of north”. Twist can be ignored for the moment. If so, as long as there is apparent wind from the south, the propeller will rotate clockwise and harvest some power, though increasingly less as the apparent wind drops off.

5) Some people here are positing that at ZERO apparent wind, the vehicle will pass through a “transition zone” where the prop, rather than harvesting power from the wind and using it to drive the wheels, will be driven by the wheels and take over the propulsion of the vehicle by imparting that power to the medium in which it operates, viz the air in the manner that an aeroplane is driven.

6) If that were so, then, given no change in the direction of rotation of the prop, the ANGLE OF INCIDENCE of the blades would have to be such that the leading edge of the blades would be east of north and the trailing edge west of south, i.e. a CHANGE OF PITCH is required.

7) Nowhere do the tricksters in the video indicate that a CHANGE OF PITCH takes place.

8) In any event, nowhere do they mention that a their prop DRIVING the wheels of the vehicle cannot absorb from the medium in which it works 100% of the energy available to it in that medium. In wind turbine design the amount of energy that can be harvested from the wind has a limit. It is 59%.of the energy in the “tube of wind” having as its cross sectional area the swept area of the prop. This limit is called “Betz's Limit” in honour of the man who determined it. For a DRIVEN prop operating in water and driving a displacement hull, we talk of “slip” and we reckon it as 50% because we don't have a good objective way of determining what it really is.

9) Contemplating now a DRIVEN prop (which our prop would be once through the transmission zone, PROVIDED the change of pitch had taken place), the prop cannot transmit to the medium in which it operates 100% of the energy required to rotate it at some RPM (any RPM). There is Betz's Limit again!

10) ERGO: The video is entertaining precisely because it's utter codswallop!

The fundamental rule of modern life is that if “it” is on YouTube, then “it” is suspect unless "it" is corroborated by a competent, disinterested party. Whether it is physics or National Affairs is immaterial in that regard.

Cheers

TP

[Corvidae]

I think the next stage of this challenge is a car that flaps opposing sails tied to the wheels, and a sailboat that does the same, but tied to articulated keel fins. Let's face it, rotary motion is easy mode, we need to bring this to the next level.

[RaymondR]

This "power from the wind" fascination that western peoples appear to have defies all logic.

The Brits have installed something like 11,000 wind turbines. That's hard to believe but it, and the other statistics quoted herein, come from a newspaper article written by a usually reliable source.

In theory they can produce 25,000 megawatts of electrical power which should be sufficient to supply 100% of Britain's power usage of about 22,000 megawatts overnight and 30,000 - 35,000 megawatts during the day, and average which increases to about 45,000 megawatts in winter.

On a good windy day the windmills produce around 13,000 megawatts, or about half requirements however it's summertime in Britain and there is a dearth of "good windy days".

But, one would suppose that with that massive an investment surely that's an aberration. Nope unfortunately not and in spite of the public being assured that the wind is always blowing somewhere what as been production during say a week or more of fairly calm summer days. Try 60 -70 megawatts.

Fortunately for the British public, and unlike the government of the state of South Australia, they have not yet demolished all their coal fired and nuclear power stations and they were able to import power from Europe but hey there's still time for the wind power cult to disseminate more myths on the efficacy of wind power and induce the government to a frenzy of conventional power station wrecking and remedy this situation.

[TrentePieds]

Props never "push". Like any other airfoil , e.g. an aeroplane's wing, they create a low pressure area on the "upper" (the most curved side) of the airfoil. They do that ONLY if the ANGLE OF ATTACK (NOT the same as the ANGLE OF INCIDENCE) is appropriate for the particular shape pf the airfoil. Some foils, namely "fat" ones are tolerant of variation in Angle of Attack. "Thin" ones are not.

Many, many years ago, NACA (not NASA) did a great amount of work defining and specifying the shapes of airfoils. Here is a link to NACA:

https://en.wikipedia.org/wiki/Nation...or_Aeronautics

Any attempt to understand why aircraft (and bumblebees) can fly and why propellers, nautical AND aeronautical, work, must begin with a contemplation of the work done by NACA.

There is wisdom also in reading "Der Vogelflug als Grundlage der Fliegekunst" by Otto Lilienthal. Here is a link:

https://www.amazon.de/Vogelflug-als-.../dp/3980902382

TrentePieds

[RaymondR]

Originally Posted by TrentePieds

Props never "push". Like any other airfoil , e.g. an aeroplane's wing, they create a low pressure area on the "upper" (the most curved side) of the airfoil. They do that ONLY if the ANGLE OF ATTACK (NOT the same as the ANGLE OF INCIDENCE) is appropriate for the particular shape pf the airfoil. Some foils, namely "fat" ones are tolerant of variation in Angle of Attack. "Thin" ones are not.

Many, many years ago, NACA (not NASA) did a great amount of work defining and specifying the shapes of airfoils. Here is a link to NACA:

https://en.wikipedia.org/wiki/Nation...or_Aeronautics

Any attempt to understand why aircraft (and bumblebees) can fly and why propellers, nautical AND aeronautical, work, must begin with a contemplation of the work done by NACA.

There is wisdom also in reading "Der Vogelflug als Grundlage der Fliegekunst" by Otto Lilienthal. Here is a link:

https://www.amazon.de/Vogelflug-als-.../dp/3980902382

TrentePieds

Nah, if that was the case jets would not fly, they don't have propellers.

It's all Izaac again. Accelerating a mass of air aftwards propels the plane forward. Everything else is secondary to the acceleration F=ma prop or jet driven.

You folks do realize that if Boris reads this thread he'll be mandating that wind propelled cars must replace IC propelled ones by 2030.

[CyKlop]

For naysayers who want a rigorous analysis, here’s one about the http://www.ijsrp.org/research-paper-...srp-p16135.pdf

Here’s another from Denmark

https://backend.orbit.dtu.dk/ws/port...19/2009_28.pdf

[barryglewis]

Looked at the 2 pdfs but couldn't make sense of them, but I'm approaching my dotage so perhaps that's my bad. But, Could we have an analysis which explains how the energy is extracted from the wind to propel the car faster than the apparent wind? (With the true wind dead astern).
The propeller is pushing the boat driven by the wheels and the boat is going faster than the true wind, so there is an apparent wind from ahead , how is that wind giving up energy to the car so as to maintain its forward speed?

[RaymondR]

Originally Posted by barryglewis

Looked at the 2 pdfs but couldn't make sense of them, but I'm approaching my dotage so perhaps that's my bad. But, Could we have an analysis which explains how the energy is extracted from the wind to propel the car faster than the apparent wind? (With the true wind dead astern).
The propeller is pushing the boat driven by the wheels and the boat is going faster than the true wind, so there is an apparent wind from ahead , how is that wind giving up energy to the car so as to maintain its forward speed?

It cannot. You might be able to extract and store sufficient energy to accelerate the vehicle beyond the wind speed but when the energy is consumed the vehicle will decelerate to below the winds velocity.

[Dave_S]

Originally Posted by barryglewis

Looked at the 2 pdfs but couldn't make sense of them, but I'm approaching my dotage so perhaps that's my bad. But, Could we have an analysis which explains how the energy is extracted from the wind to propel the car faster than the apparent wind? (With the true wind dead astern).
The propeller is pushing the boat driven by the wheels and the boat is going faster than the true wind, so there is an apparent wind from ahead , how is that wind giving up energy to the car so as to maintain its forward speed?

If there is 10 knots of breeze and the vehicle is traveling DDW. The breeze is either pushing at speeds below TWS or reducing drag once the apparent wind turns.

With the above advantages and the propellers effort increasing at a greater rate than the change in apparent wind speed.

And with the continuous apparent air flow and angle of attack experienced by the rotating blades it is not limited by the wind speed.

[zstine]

Originally Posted by barryglewis

Looked at the 2 pdfs but couldn't make sense of them, but I'm approaching my dotage so perhaps that's my bad. But, Could we have an analysis which explains how the energy is extracted from the wind to propel the car faster than the apparent wind? (With the true wind dead astern).
The propeller is pushing the boat driven by the wheels and the boat is going faster than the true wind, so there is an apparent wind from ahead , how is that wind giving up energy to the car so as to maintain its forward speed?

don't look at it as extracting energy from the wind. Think of it from a drag and force point of view (force balance). When the car matches the wind speed, there is no apparent wind, no drag except the friction in the wheels and drive mechanism. The propeller is providing a force forward, which due to gearing is greater than the force to drive the propeller applied from the wheels to the ground (like anything with mechanical advantage). the law is conservation of energy, not conservation of force. the wheels are spinning faster than the propeller, geared down. So if you assumed identical shaft torque, then the propeller would use less energy than the faster wheels are providing and the car would accelerate.

[CatNewBee]

Originally Posted by jbinbi

Tell me you have a PhD in Physics, specifically in aero or hydro dynamics and I will believe what you say.



This isn't about a sail. I think everyone agrees that Aw = Tw + Bs (vectors). If your boat is going 5mph directly into a 5mph wind, there is 10mph of apparent wind. If you are doing the same DDW, you have 0 mph of apparent wind. For a sailboat, this last scenario doesn't work with sails.



However, this experiment uses a propeller. So if I could mount a 500' propeller (wind turbine) on my car, and in 5mph of breeze it can generate 500hp, are you saying I can only go 5mph?

No, you won't even move. Because the mast and propeller will be quite heavy.

As soon as you start moving downwind your 500hp will decline quickly, at 2.5kn you will likely have then only SQRT(500hp) = 22hp because there are only 2.5kn wind left. once you reach 3.75kn, only 1/4 of the wind is availlable, providing only 4.7hp.

at some point all power will be gone by the friction before you even reach wind speed (no power, but friction, that slows you down).

[waterman46]

Originally Posted by barryglewis

Looked at the 2 pdfs but couldn't make sense of them, but I'm approaching my dotage so perhaps that's my bad. But, Could we have an analysis which explains how the energy is extracted from the wind to propel the car faster than the apparent wind? (With the true wind dead astern).
The propeller is pushing the boat driven by the wheels and the boat is going faster than the true wind, so there is an apparent wind from ahead , how is that wind giving up energy to the car so as to maintain its forward speed?

The mathematical analysis of thrust and drag of a prop or wind turbine is way beyond me, but it's not hard to see how it works on a qualitative basis.


Let's say it's a right hand prop - viewed from astern and with the prop not rotating, a blade at top of the prop would have it's right hand edge forward of it's left hand edge. To go faster DDW than true wind, apparent wind will be dead ahead. With apparent wind from dead ahead, the prop will act as a power generator - it will be forced to rotate clockwise as air is deflected to the left from that top blade.


OK, make the blades large- lots of power generated from the rotation of apparent wind into the prop. Now send all that power to the wheels through nearly loss-less gear train. Key here is the gear ratio. The wheels will receive that power and if the gearing is correct, it will apply the power to force the vehicle forward.

Remember you could get a huge amount of power by increasing the prop size. It's up to the gear ratio to correctly transmit that power at an RPM appropriate for acceleration of the vehicle.

I think the gear ratio has to be carefully designed so that the power from the prop rotation will apply slightly more forward torque at the wheels relative to the apparent wind speed. Too high a gear ratio and the prop, without a pitch adjustment, would stall. Too low a gear ratio and the vehicle would not accelerate.

[waterman46]

Originally Posted by CyKlop

For naysayers who want a rigorous analysis, here’s one about the http://www.ijsrp.org/research-paper-...srp-p16135.pdf

Here’s another from Denmark

https://backend.orbit.dtu.dk/ws/port...19/2009_28.pdf

Thanks for those links.

For those who read the first paper, the authors use the term "thrust" in a way that took me a while to understand. I thought the usual definition of propeller thrust would be the forward force produced by a propeller of an airplane driven by an external power source. After more thought, it seems to me the authors use the term "propeller thrust" to refer to power output by the propeller acting as a wind turbine, not as a propeller.

[JoeRobertJr]

Originally Posted by waterman46

The mathematical analysis of thrust and drag of a prop or wind turbine is way beyond me, but it's not hard to see how it works on a qualitative basis.


Let's say it's a right hand prop - viewed from astern and with the prop not rotating, a blade at top of the prop would have it's right hand edge forward of it's left hand edge. To go faster DDW than true wind, apparent wind will be dead ahead. With apparent wind from dead ahead, the prop will act as a power generator - it will be forced to rotate clockwise as air is deflected to the left from that top blade.


OK, make the blades large- lots of power generated from the rotation of apparent wind into the prop. Now send all that power to the wheels through nearly loss-less gear train. Key here is the gear ratio. The wheels will receive that power and if the gearing is correct, it will apply the power to force the vehicle forward.

Remember you could get a huge amount of power by increasing the prop size. It's up to the gear ratio to correctly transmit that power at an RPM appropriate for acceleration of the vehicle.

I think the gear ratio has to be carefully designed so that the power from the prop rotation will apply slightly more forward torque at the wheels relative to the apparent wind speed. Too high a gear ratio and the prop, without a pitch adjustment, would stall. Too low a gear ratio and the vehicle would not accelerate.

The prop on this car is never acting as a generator. It is the propulsion, pushing on the air. The video of the model on the treadmill helped clear this up for me.

[trifan]

If it could be adapted for water, that is.

https://www.yahoo.com/news/youtuber-...120100405.html


Be sure to watch the youtube video which explains it all.