Merged DDWFTTW in a “Real” Wind

[Llyricist]

I hope you are not serious! Wind power is usually associated with wind turbines, not propellers (cough) and the turbines are designed to orient themselves so they are facing directly into the wind. That being the case, it is not necessary to consider RMS wind direction. But if you think it is ludicrous to consider it when the turbine, or in this case the propeller (chuckle) is not always aligned with the wind, than you are quite mistaken. In the case of varying wind direction, the wind power density depends as much on RMS wind direction as it does on velocity and the velocity in varying wind conditions is also calculated as an RMS value. Do you think only two people in the world advocate RMS wind calculations? Then which one of those two wrote this research paper?

http://www.gsmt.noao.edu/studies/wind_tests4/wprv_all.htm

Again, that measurement has nothing to do with direction, but pressure.

Furthermore, a propeller is the antithesis to a turbine. Think about that for a moment. If the turbine works best when it is aligned with the wind direction, doesn't that indicate the propeller will work worst when similarly aligned? I think it is obvious that if a propeller is used to gather wind energy, it will do it best when it is not aligned with the wind direction. It only requires common sense to see that, but I'm sure I can find some supporting mathematics as well.

wrong on all counts, a propeller works best when the angle of attack of the blades is optimized all the way around their arc, that can only happen when the disk is normal to the air stream. Anything else and each blade will have either higher or lower angles of attack in the crosswind portions of their arc.

 

[humber]

Actually, I do have a way of knowing that. It is the figure they used, I know that because I got the same results they did when I used it.

And the formula is?

It has nothing at all to do with what GPS was used, it has to do with using the same convention for all the data.

Try again.

Give a time reference, in my data it's 264.4 @ Time reference: 588967.4

No, but that's interesting.
And the vane at 599922.8?

The measured change was .07973 MPH from 588967.8 to 588968 I don't know where your baseline is, so without the time reference, your 40th and 41st may be different.

That's only the difference. What about the anemometer response time?

The actual change may be different by some small amount but is irrelevant.

Yes...sure.

 

[humber]

Again, that measurement has nothing to do with direction, but pressure.


wrong on all counts, a propeller works best when the angle of attack of the blades is optimized all the way around their arc, that can only happen when the disk is normal to the air stream. Anything else and each blade will have either higher or lower angles of attack in the crosswind portions of their arc.

Give it up.

 

[Llyricist]

And the formula is?

I'm not going to hold your hand all the way through it. You seemed to be having trouble either obtaining the offset or figuring it out after several weeks of having the data, so I decided to help you out a little with a number I figured out within 24 hours.

 

[humber]

What's the opposite of facing directly into the wind? Facing perpendicular to the wind, or standing with one's back to the wind?

Where are TAD and Spork? They've got some explaining to do.

 

[Llyricist]

Give it up.

nope.

 

[humber]

I'm not going to hold your hand all the way through it. You seemed to be having trouble either obtaining the offset or figuring it out after several weeks of having the data, so I decided to help you out a little with a number I figured out within 24 hours.

Right, you don't have it.

You "figured it out" in 24hrs, but RMS is a mystery to you. Indeed.

 

[Llyricist]

Again, that measurement has nothing to do with direction, but pressure.


wrong on all counts, a propeller works best when the angle of attack of the blades is optimized all the way around their arc, that can only happen when the disk is normal to the air stream. Anything else and each blade will have either higher or lower angles of attack in the crosswind portions of their arc.

Not to mention decreasing efficiency with the added torsional load on the shaft bearings, bad enough to have the gradient already doing that.

 

[humber]

Not to mention decreasing efficiency with the added torsional load on the shaft bearings, bad enough to have the gradient already doing that.

And the widget modulates the thrust capacitor.

 

[Llyricist]

Right, you don't have it.

You "figured it out" in 24hrs, but RMS is a mystery to you. Indeed.

RMS is not a mystery to me, it is a largely arbitrary method of averaging magnitudes that was widely adopted by those in the electronics field because it yields higher values than the mean of absolute values would. Others have taken to using it for the very same reason.

 

[humber]

RMS is not a mystery to me, it is a largely arbitrary method of averaging magnitudes that was widely adopted by those in the electronics field because it yields higher values than the mean of absolute values would. Others have taken to using it for the very same reason.

But you don't have the method used to calculate the true wind, nor how to allow for transient response etc...etc.
The data at hand is enough to show the cart is not ddw, and the posted data is not RMS.
"largely arbitrary" "because it yields a higher value"
Good grief.
Where are Spork and JB?
It's their responsibility to support their data.

 

[Jack by the hedge]

RMS is not a mystery to me, it is a largely arbitrary method of averaging magnitudes that was widely adopted by those in the electronics field because it yields higher values than the mean of absolute values would. Others have taken to using it for the very same reason.

Funny*, but in defence of electronics engineers, RMS is used in particular circumstances where it gives useful results, rather than "higher values".
The power into a resistive load from a cyclic waveform, P_average = V_rms * I_rms

*I do presume you knew all this.

 

[Llyricist]

"because it yields a higher value"
Good grief.
Where are Spork and JB. It's their responsibility to support their data.

good grief indeed, yeah there is more of a justification in the case of electronics.

When you can show how the power of the wind increases with the square of its relative direction you just might have a point. But velocity polars of actual sail craft do not support such a relationship.

 

[Llyricist]

Funny*, but in defence of electronics engineers, RMS is used in particular circumstances where it gives useful results, rather than "higher values".
The power into a resistive load from a cyclic waveform, P_average = V_rms * I_rms

*I do presume you knew all this.

yep, just needling.

 

[Llyricist]

But you don't have the method used to calculate the true wind, nor how to allow for transient response etc...etc.

yeah, the 650 lb cart is going to respond faster to transients than a few ounce anemometer.

Interestingly, the acceleration varies right along with the measured wind speed, but hardly at all to changes in direction of less than 20 degrees.

 

[A.T.]

Check my diagram. It shows the theoretical max speed (no loses), realistic speed (with loses) and initial acceleration, as functions of the vehicle advance ratio.

[qimg]http://i54.tinypic.com/2gv0kew.png[/qimg]

Can you say something about how you calculated the realistic speed with losses?

You assume some coefficients for hull aero drag, rolling drag, airfoil lift/drag and the areas (airfoil, frontal hull). That gives you the net force as function of velocity. The maximal velocity is the one where that net force is zero.

 

[profpangloss]

What's the opposite of facing directly into the wind? Facing perpendicular to the wind, or standing with one's back to the wind?

The opposite way to use the propeller as a turbine would be to allow it to turn in the opposite direction. That would give you the best power performance from the wind energy as I believe IRatant's videos have shown. Using a propeller to collect wind energy is dumb. I can think of few things dumber. The more directly it faces into the wind stream, the greater tendency it will have to turbine, working against the wind sail force on the cart. I mean, really, you can't see that? The further off of the direct wind stream, the less it will try to turbine. It is just a matter of finding the optimum angle off of DDW to get the best performance, but the best performance will always be worse than if you just use it as a turbine, not a propeller (LOL) This can be easily proved, and I think IRatant has already shown this convincingly. Jeez, just common sense should help you to understand this!

 

[profpangloss]

RMS is not a mystery to me, it is a largely arbitrary method of averaging magnitudes that was widely adopted by those in the electronics field because it yields higher values than the mean of absolute values would. Others have taken to using it for the very same reason.

WHAT? Holy (censored)! Yeah I think RMS is definitely a mystery to you. I don't need to add anything to what you said! LOL

 

[Llyricist]

WHAT? Holy (censored)! Yeah I think RMS is definitely a mystery to you. I don't need to add anything to what you said! LOL

Keep reading.

 

[A.T.]

Interestingly, the acceleration varies right along with the measured wind speed, but hardly at all to changes in direction of less than 20 degrees.

Aren't the adjustments of the propeller pitch the main reason for variations in acceleration?