Merged DDWFTTW in a “Real” Wind

[humber]

The charts I posted last week were from the data I had, and I prepared them last month and sent them to Bob (April 8). And offered them to anyone here that wanted them. I didn't even ask for the full day's data until you started posting crap about it in the last couple days.

I already know of the 4 occasions where the cart stayed within 10 degrees of DDW for 15+ seconds straight, above wind speed, and accelerating. But I am not going to post them unless someone that has any worth asks me to.

So only the cherry picked exceptions? There is way more than you have not noticed about that data, and you will not best me at it.
And now you need to calculate from that, what the windspeed must be...etc....etc...

ETA:
" But I am not going to post them unless someone that has any worth asks me "
Afraid I will knock holes it it?

 

[Llyricist]

So only the cherry picked exceptions? There is way more than you have not noticed about that data, and you will not best me at it.
And now you need to calculate from that, what the windspeed must be...etc....etc...

No, there isn't. But there is probably a lot of irrelevant bs that you are going to post about it, and I'll be here to call you on any shenanigans, like I just did.

 

[Llyricist]

" But I am not going to post them unless someone that has any worth asks me "
Afraid I will knock holes it it?

Nope, just not going to jump through any hoops for you.

 

[spork]

Check out this scam! They totally cherry picked the data. There were lots of times he wasn't even running. Hell - before the race he was sitting down at times!

http://www.youtube.com/watch?v=T6LQcPNs9U4&feature=related

And this is some serious cherry picking. There was not even one single instance when this guy was actually above the bar:
http://www.youtube.com/watch?v=x4yhE5KEPq0


Then there's our friend Richard Jenkins... I know for a fact that he had several runs in which he didn't achieve 126.2 mph!

 

[recursive prophet]

I already know of the 4 occasions where the cart stayed within 10 degrees of DDW for 15+ seconds straight, above wind speed, and accelerating. But I am not going to post them unless someone that has any worth asks me to.

Wow! Are you channeling spork now? He has often taken this exact position. Sounds sort of Catch 22-ish to be honest Ll. All those worthy already accept it and have no interest in seeing what you have, right? So why even mention it? In fact, if Humber is unworthy of seeing your evidence, how can he be worthy of refuting itt? Why bother to respond to him at all? You do know how to put him on ignore, don't you?

 

[spork]

RCP being his brilliant self. He's managed to lay low every time humber tells us no one will see his evidence but NALSA. But it's just plain dirty pool if Lyricist won't produce data for humber! Truly brilliant!

 

[humber]

Check out this scam! They totally cherry picked the data. There were lots of times he wasn't even running. Hell - before the race he was sitting down at times!

http://www.youtube.com/watch?v=T6LQcPNs9U4&feature=related

And this is some serious cherry picking. There was not even one single instance when this guy was actually above the bar:
http://www.youtube.com/watch?v=x4yhE5KEPq0


Then there's our friend Richard Jenkins... I know for a fact that he had several runs in which he didn't achieve 126.2 mph!

A puerile, knee-jerk response, due to the paucity technical resources.
The fact is that you, Spork, did cherry pick, whereas those competitors did not.
Examination of the chart beyond what you posted, shows you could have claimed an even higher speed record, but that would have unmasked something else, wouldn't it?

 

[humber]

RCP being his brilliant self. He's managed to lay low every time humber tells us no one will see his evidence but NALSA. But it's just plain dirty pool if Lyricist won't produce data for humber! Truly brilliant!

Yes, you are in trouble.

 

[69dodge]

The cart's mechanism works like any positive feedback loop, and like any positive feedback loop, it would quickly run down to nothing due to losses, unless there is a source of energy replenishing those losses.

In this case the mechanical losses of the feedback loop amount to 150 J / s. With an additional 117 J / s of aerodynamic losses at the prop, which is the difference between the maximum theoretical efficiency of the prop and the efficiency I chose. (The effective "Engine Power" the thrust I used works out to is 483 W).

Can you explain some more how you arrived at 117 J/s and 483 W?

(Here's your original post describing the situation.)

 

[humber]

Nope, just not going to jump through any hoops for you.

As you like...
Not posting what you think you have, does make you look like a lackey.

 

[Llyricist]

Can you explain some more how you arrived at 117 J/s and 483 W?

(Here's your original post describing the situation.)

basically by trial and error, using the Thrust and Engine Power formulas found here. Which I have conveniently set up in a spread sheet set up just for the purpose of doing all the necessary math after plugging in all the relevant specs.

Basically I make a guess at efficiency and multiply the shaft power by that percentage. Then divide the result by the relative airspeed to get a thrust, then I work it backwards through those formulas.

Then calculate the efficiency between the resultant engine power and thrust power, (which is the maximum theoretical efficiency, with 0 aerodynamic losses) and compare it to what I guessed.

In that case I decided to make the margin 12% for the sake of making it definitely possible, and then I retry until I achieve that difference.

Sounds convoluted and difficult, but it's just a matter of typing a number and clicking a button with the spreadsheet.

I can't explain why, but it is that number (engine power), and not thrust power that accounts for the work done in an energy analysis.

 

[humber]

basically by trial and error, using the Thrust and Engine Power formulas found here. Which I have conveniently set up in a spread sheet set up just for the purpose of doing all the necessary math after plugging in all the relevant specs.

Basically I make a guess at efficiency and multiply the shaft power by that percentage. Then divide the result by the relative airspeed to get a thrust, then I work it backwards through those formulas.

Then calculate the efficiency between the resultant engine power and thrust power, (which is the maximum theoretical efficiency, with 0 aerodynamic losses) and compare it to what I guessed.

In that case I decided to make the margin 12% for the sake of making it definitely possible, and then I retry until I achieve that difference.

Sounds convoluted and difficult, but it's just a matter of typing a number and clicking a button with the spreadsheet.

I can't explain why, but it is that number (engine power), and not thrust power that accounts for the work done in an energy analysis.

Oh, dear...where are those ddw charts?

 

[Llyricist]

Wow! Are you channeling spork now? He has often taken this exact position. Sounds sort of Catch 22-ish to be honest Ll. All those worthy already accept it and have no interest in seeing what you have, right? So why even mention it? In fact, if Humber is unworthy of seeing your evidence, how can he be worthy of refuting itt? Why bother to respond to him at all? You do know how to put him on ignore, don't you?

Why should I post data that he has? I already specified what the data says, i.e. within 10 degrees for 15+ seconds, cart speed above wind speed, and accelerating.

Further, he refused to give timestamp ranges for the data he posted, forcing me to go hunting to discover his subterfuge. So why in heck should I do any work for him?

Sorry but I won't post it because he wants me to, I will if anybody else (except you or hyevpanglostoph) asks.

It has nothing to do with any refutation, it has to do with a lack of honor.

 

[69dodge]

basically by trial and error, using the Thrust and Engine Power formulas found here. Which I have conveniently set up in a spread sheet set up just for the purpose of doing all the necessary math after plugging in all the relevant specs.

Basically I make a guess at efficiency and multiply the shaft power by that percentage. Then divide the result by the relative airspeed to get a thrust, then I work it backwards through those formulas.

Then calculate the efficiency between the resultant engine power and thrust power, (which is the maximum theoretical efficiency, with 0 aerodynamic losses) and compare it to what I guessed.

In that case I decided to make the margin 12% for the sake of making it definitely possible, and then I retry until I achieve that difference.

Sounds convoluted and difficult, but it's just a matter of typing a number and clicking a button with the spreadsheet.

I am so confused...

Are there three different powers here, then? Shaft power, engine power, and thrust power? Or are shaft power and engine power the same thing?

In your earlier post, you mentioned something about 600 W. Which power is that? Then, you multiplied it by an efficiency of 52% to get 312 W. Which power is that?

I can see that 117 W and 483 W add up to 600 W. But I don't understand what any of them represents.

 

[Jack by the hedge]

It is a perfectly closed system, consisting of the kinetic energy of the wind that is processed by the propeller (72 kg moving at 7 m/s) and the 295 kg cart moving at 9 m/s. The ground is the reference frame and contributes no energy as it has none. If you say this is not a closed system then you must show another source of energy other than what I have shown. Hop to it!

This thread can move a long way in a few hours.

The air and cart are not a closed system. The definition of a closed system is one in which external forces are absent (or, like gravity, act perpendicularly to the forces we are considering and so can be ignored).

There is a very obvious external force acting on the cart and that is the reaction force against the ground. Do you deny there is a retarding force acting on the cart from its wheels friction against the ground? How could there be torque to turn the wheels if there were no such force? Would it behave the same if there were no friction? No, of course it wouldn't.

Since there is a force, and the cart moves against this force, then work must be done. Energy must be transferred. Since you insist on only considering the ground frame, we aren't allowed to describe this as the cart speeding up the earth infinitessimally, so from your chosen frame of reference the cart slows down the atmosphere infinitessimally. Happy now?

 

[humber]

Why should I post data that he has? I already specified what the data says, i.e. within 10 degrees for 15+ seconds, cart speed above wind speed, and accelerating.

Further, he refused to give timestamp ranges for the data he posted, forcing me to go hunting to discover his subterfuge. So why in heck should I do any work for him?

Sorry but I won't post it because he wants me to, I will if anybody else (except you or hyevpanglostoph) asks.

It has nothing to do with any refutation, it has to do with a lack of honor.

Sounds fey to me.

 

[Modified]

And that error disappears when in the more difficult case of motion? That did take a long time for you to grasp.

There is no error in direction when not moving, since direction has no meaning in that context. When moving, the max direction error does get lower the faster the speed.

 

[humber]

There is no error in direction when not moving, since direction has no meaning in that context. When moving, the max direction error does get lower the faster the speed.

GPS supplies only position. Speed is calculated from the rate of change of that position. The data is processed once a second, no matter what the speed.
It's not about GPS error.

 

[drewid]

GPS supplies only position. Speed is calculated from the rate of change of that position. The data is processed once a second, no matter what the speed.
It's not about GPS error.

Seriously, read that back to yourself and think about it.

 

[69dodge]

Okay let's take a hypothetical cart weighing 295 kg, and give it the type of efficiency you think is appropriate and push it up to 9 m/s in a 7 m/s tail wind.

Using a crr of .02 (which is about twice that of a car tire on concrete) I'll have a rolling resistance of 57.8 Newtons. (crr * mass * 1G)

Using a Cd of .7 (the same as a Caterham open wheeler) and a frontal area of 2 m², gives a drag force of 3.43 Newtons at the 2 m/s airspeed.
(Fd = .5 * air density (1.225 standard day at sea level) * Cd * Frontal area * airspeed²)

For a total opposing force of 61.23 Newtons.

I'll let a (theoretical at this point) 4.876 meter (16 foot) diameter prop through a drive train that is 80% efficient, add an additional 83.4 Newtons of opposing force. So we have the prop, through the drive train doing negative work on the cart at the rate of 83.4 N * 9 m/s = 750 W.

Since the drive train is only 80% efficient the prop only gains 600 W of power from its negative work. At his level of power and this airspeed the theoretical maximum efficiency for a prop of this size is 64.5%, [...]

How accurate is this number supposed to be?

I get 61.6%.

(Using a power of 600 W and a propeller diameter of 4.8768 m, equation (5) here yields an airspeed of 2.148 m/s for an efficiency of 64.5%, and an airspeed of 1.998 m/s for an efficiency of 61.6%, while the airspeed is supposed to be 2 m/s.)

I guess it's close enough, because you subtract a bunch from it anyway.

I'm mainly posting this just to check whether I'm doing things right.