NALSA insisted on 3 wind-vanes and anemometer that were calibrated and certified. MetOne instruments was good enough to donate these units to the cause - complete with calibration certificates.
Afraid not. Certification is not calibration. The accuracy of vanes and anemometers depends on the installation and use. The proximity of obstacles etc.
From NASLA
"Accurate wind measurements are
difficult to make, given fluctuations in wind speed and direction over time and position. To resolve any reasonable doubts, the TAD team
developed an effective and sophisticated system for measuring the wind field. Wind speed measurements from the craft itself were
not used, as the TAD team had previously identified a roughly 1 mph favorable bias in wind speed measured at the front of the craft. The two stationary weather stations were used as secondary instruments. "
Developed a sophisticated instrument package. A borrowed Met One vanes? I mean, did you at least
unpack it yourself?
1) If the vane were on the cart, there would be no need to calculate the true wind. Only the deviation of the vane and cart, which would be visible.
That is; when ddw, the vane will be along the line of the cart, and that is all you need to know. Putting the vane on a CV means that the true wind must be calculated, and introduces tracking errors between the CV and the cart.
The vane would provide visual evidence of ddw for NALSA,
and for the video recording.
NALSA:
The true wind speed and direction were calculated from the vector sum of the speed, heading and apparent wind of the chase vehicle and the
speed and heading of the craft. There is
some increase in measurement uncertainty from 'subtracting large numbers' effects. It is the feeling of the observers and
TAD team that this uncertainty increase is not excessive and is an appropriate tradeoff for the advantages of taking measurements in closer proximity to the craft while avoiding the confounding effects of the large propeller.
How did you justify all those disadvantages to NALSA, on the basis of a small 1mph bias which could be easily calibrate out? What was the basis for the intelligentsia at "TAD" to think it was an appropriate "tradeoff"?
There are many problems with putting vanes on moving cars, but on the constantly accelerating CV, that is very bad news indeed.
When and object is moved through a fluid, it takes on added mass because of the laminar flow and that
Like this: Added mass = ma in the right pane.
Believe it or not, wind vanes have a specific design-dependent L/D ratio, and the force added by the acceleration of the added mass, makes a mess of that, and calibration goes out of the window. Not all vanes are "the same"
The general result will be to suppress the true wind in favour of the accelerating apparent wind. The wind direction readings will certainly be lower than shown, and averaging is a
real boner.
2) There is
nothing on the cart to tell you if you were going ddw.
No tell tale.
GPS will not tell you of the wind direction. The chart shows you following a
fixed heading, with no attempt
at all to follow the shifting wind shown by the black line of your chart.
3) Given the access you have to sport measurement tools. Then why didn't you use telemetry from the CV to the cart? That would inform you immediately of the wind direction. It would be quite easy to replace the GPS display with a wind direction indicator.
4) The vanes from MetOne are designed for fixed use, and to meet NIST standards of 10 minute averages, and not 10 seconds. To meet the standards, the station must withstand heavy winds, and that limits the performance of the vane to the point where they are not suitable for instantaneous readings. What did MetOne say about putting a vane on the cart?
In addition to the numerous hand-held GPS receivers, we also used a number of carrier-phase GPS units that we developed for use in race cars. They're accurate to 2 cm.
They are not certified tools in any way, and the 2cm is sales brochure fodder.
They are not "accurate to 2cm", but use RTK. That is a Doppler method, which allows the static
position relative to the position obtained by the coarse-acquisition code sent from the satellite for use in domestic receivers, so limited by that.
The hand-held GT31 uses a new receiver chip from SiRF. That employs several patented methods, as well as undisclosed proprietary techniques, particularly around the FFT analysis. They will be more accurate than those dated and Rube Goldberg race-car units. Electronics moves fast.
When in motion, the Doppler shift reading is hard to maintain. Tracking depends many things including signal level, carrier noise and the PLL transient response, and must undergo some processing for HDOP etc.
The final result is derived by FFT analysis of the data stream, and will be no more accurate than 0.1m/s.
That may be adequate for speed, but not to measure small changes in acceleration, because or the error margin, and the 1 second update rate.
RTK
"By progressively delaying the local copy more and more, the two ( Doppler) signals will eventually line up properly. That delay is the time needed for the signal to reach the receiver, and from this the distance from the satellite can be calculated. The accuracy of the resulting range measurement is generally a function of the ability of the receiver's electronics to accurately compare the two signals. In general receivers are able to align the signals to about 1% of one bit-width.[1] For instance, the coarse-acquisition (C/A) code sent on the GPS system sends a bit every 0.98 microsecond, so a receiver is accurate to 0.01 microsecond, or about 3 metres in terms of distance."
You also have the receivers spaced apart and in line. The mentioned 2cm comes from the GPS carrier wavelength, so the antennas should be within that distance, or they will not read the same. They will be influenced by turning of the cart, in the same way that your hand moves faster then your elbow when waved. Where you not aware of that?
The GT31 has an internal patch antenna ( below the display), and should be placed back-to back, so that the antennas are as close as possible. Given that you have 3 on the cart, how did you know which was the reference device? Were you consistent in the selection of that device?
I'd say this "sailing club" knows their stuff.
I would say that the glove fits the hand.
They spent an awful lot of time working out the rules for this category, and they were quite thorough with the inspection of the vehicle and observation of the trials (or "trails" to humber).
With little basis other than "we feel that" and "in the view of".
But, you kept them away from public gaze, so that humber could not see bias or technical errors.
The "awful lot of time" seems to also include ad-hoc changes right up to the trial. The regulations are dated. "Revision 3 July 2010"
That suggest that the relationship of judge and contestant may not be as disinterested or impartial as would be expected.
A trail of trial trash.
