Merged DDWFTTW in a “Real” Wind

[ThinAirDesigns]

GPS supplies only position. Speed is calculated from the rate of change of that position.

Wrong.

GPSats don't supply position at all (how could they for everyone?). They supply time and Sat ID. Position is calculated from that and speed from any change in that.

Of course we already know you haven't a clue regarding GPS so there is no surprise here.

JB

 

[Dave_46]

<snip>
I told you that only NALSA will see the evidence, not you...
<snip>

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

These two posts don't sit well together.

 

[humber]

Wrong.

GPSats don't supply position at all (how could they for everyone?). They supply time and Sat ID. Position is calculated from that and speed from any change in that.

What a pathetic attempt to try an claw back from the hole you are most definitely within. It's called the Global Positioning System, and not the Guilty Parser's Safehaven, and you can spare me the information you gained from the box. And via the methods that you have trivially described, the satellites do indeed supply position to the receiver, 'coz it don't no.
Holder of the 60 degree ddw record.

ETA: Don't bother. I will raise it with NALSA.

Here's another for the collection of way-too-obviously not-ddw carts. There were not many that you could choose from, were there?

 

[humber]

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

You do that, and listen for the echo.

 

[drewid]

Maybe if I shout in your ear..

 

[69dodge]

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?

There's also a power which is the torque required to spin the propeller times the angular speed of the propeller. What's that? I assume it's the same thing as engine power?

 

[Modified]

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.

Yes, and error in position corresponds to error in direction. I suppose max direction error for two points is approximately arctan(2*max_position_error/(speed * time_interval)) when speed * time_interval is significantly higher than max_position_error, ignoring the errors in the time interval, which are too small to be of concern. If speed * time_interval is less than max_position_error, then the max direction error is 180 degrees.

Though it's hard to tell, as always, I think you are arguing that since the direction readings when not moving were all over the place, that the gps was not working correctly. If that is your argument, then you are wrong. You may also be arguing that a tornado powered up the bb before launch. If neither of those is your argument, then what exactly is it? Aside from introducing yet another simple concept that you don't understand, I don't see what you're trying to accomplish.

 

[Llyricist]

I am so confused...

Are there three different powers here, then? Shaft power, engine power, and thrust power?

Yes

Or are shaft power and engine power the same thing?

They would be, if there were no aerodynamic losses at the prop.

The engine power is the shaft power required for a perfect (and non existent) propeller.

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?

The 600 watts was the shaft power, the efficiency is the real life efficiency of a prop, defined as thrust power / shaft power.

So the 312 Watts was thrust power, which is defined as thrust force X speed through the air.

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

117 W is the aerodynamic and angular losses at the propeller. 483 W is the power required by a perfect propeller of the specified size, at the specified airspeed to produce the specified thrust with no aerodynamic or angular losses.

And as I have said, since those formulas are based on 100% transfer of energy and it is from those formulas the change in velocity of the air is derived, and it is from that change in velocity that the KE loss of the air is calculated, then when doing the energy calculations, you have to account for those real life losses somewhere.

I chose to do it using the difference between the "real life" shaft power and the perfect prop shaft power which is the "Engine Power" derived from those formulas.

 

[Llyricist]

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.

If you use 483 Watts it would be 64.5%. As I said, I work the equations backwards from thrust to derive the Engine Power

 

[Llyricist]

There's also a power which is the torque required to spin the propeller times the angular speed of the propeller. What's that? I assume it's the same thing as engine power?

No, that would be the shaft power.

 

[ThinAirDesigns]

What a pathetic attempt to try an claw back from the hole you are most definitely within.

You could have just admitted you were wrong -- everyone knows it anyway.

And via the methods that you have trivially described, the satellites do indeed supply position to the receiver

Wrong.

The satellites have no idea where the reciever is so it's IMPOSSIBLE for them to "supply position to the reciever". Position is calculated at the receiver just as speed it.

JB

 

[69dodge]

They would be, if there were no aerodynamic losses at the prop.

The engine power is the shaft power required for a perfect (and non existent) propeller.

By "perfect propeller", you don't mean a propeller whose efficiency is 100%, which is totally impossible, but rather a propeller whose efficiency is that given (implicitly) by equation (5), which is only somewhat impossible. Correct?

The 600 watts was the shaft power, the efficiency is the real life efficiency of a prop, defined as thrust power / shaft power.

So the 312 Watts was thrust power, which is defined as thrust force X speed through the air.

117 W is the aerodynamic and angular losses at the propeller. 483 W is the power required by a perfect propeller of the specified size, at the specified airspeed to produce the specified thrust with no aerodynamic or angular losses.

And as I have said, since those formulas are based on 100% transfer of energy and it is from those formulas the change in velocity of the air is derived, and it is from that change in velocity that the KE loss of the air is calculated, then when doing the energy calculations, you have to account for those real life losses somewhere.

I chose to do it using the difference between the "real life" shaft power and the perfect prop shaft power which is the "Engine Power" derived from those formulas.

Thanks. This is all very helpful.

 

[69dodge]

If you use 483 Watts it would be 64.5%.

I see. Yes, that's right.

 

[Llyricist]

By "perfect propeller", you don't mean a propeller whose efficiency is 100%, which is totally impossible, but rather a propeller whose efficiency is that given (implicitly) by equation (5), which is only somewhat impossible. Correct?

Sort of, by perfect I mean 100% transfer of energy between the propeller's surfaces and air, which is also impossible. But that does not correspond with 100% transfer of power from shaft to thrust.

Thanks. This is all very helpful.

Glad to help.

 

[humber]

Yes, and error in position corresponds to error in direction. I suppose max direction error for two points is approximately arctan(2*max_position_error/(speed * time_interval)) when speed * time_interval is significantly higher than max_position_error, ignoring the errors in the time interval, which are too small to be of concern. If speed * time_interval is less than max_position_error, then the max direction error is 180 degrees.

Though it's hard to tell, as always, I think you are arguing that since the direction readings when not moving were all over the place, that the gps was not working correctly. If that is your argument, then you are wrong. You may also be arguing that a tornado powered up the bb before launch. If neither of those is your argument, then what exactly is it? Aside from introducing yet another simple concept that you don't understand, I don't see what you're trying to accomplish.

You can tell yourself whatever it is that you think I was arguing. OK?

 

[humber]

You could have just admitted you were wrong -- everyone knows it anyway.



Wrong.

The satellites have no idea where the reciever is so it's IMPOSSIBLE for them to "supply position to the reciever". Position is calculated at the receiver just as speed it.

JB

You have been busted, and your record will go.

 

[jduffy77]

You have been busted, and your record will go.

How will anyone know the record has gone? Will there be any visible manifestation of its departure or will it only be in your mind?

 

[drewid]

You can tell yourself whatever it is that you think I was arguing. OK?

Dodge noted.

 

[ThinAirDesigns]

You have been busted, and your record will go.

A: wrong.

B: Yes, dodge noted.

JB

 

[recursive prophet]

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.

.


OOOOK. Now I get it. This is all about honor. I forgot you're a newbie and weren't around when honor came up a couple years ago, way back in the aughts. I always remember Humbersan's proud, defiant words that day.

Family shamed. No honor.

I assure you carteers he sees ya'll with similar equilibrium to that you afford him Ll. If he didn't I'd say a lot of folks had been owned, including me. But I do see your point about having to put in the extra time searching since Humber wouldn't show his hand first. He has posted several charts based on that data though, yes? And remember, this is a forum for skeptics. Evidence held in abeyance based on worthiness might not be very convincing to such.

Would you consider ynot or I Ratant worthy of asking? Perhaps a list of all the unworthy would be helpfull?

ETA: I noted the dodge to Myriad's question also, Humber, while acknowledging it was somewhat loaded. But I am also confused about the exact points you hope to make wrt the data. Given the pragmatic limitations involved, what degree of variation would you accept for constituting directly downwind?