CASES99: PropVanes Messages: 5 Entries..

General:

There was one prop failure noted during CASES99 (probably due to rain)
which caused a loss of most data from 15m on the 58m tower between
28 Sep and 9 Oct.  Station 5 lost data due to S-bus cable problems (I think)
which were fixed 4 Oct.

Wind directions from the tower appear not to have been
very accurate.  However, the boom angles were shot twice and differed by only
37 minutes at worst.

Wind directions from sites 1-6 were better behaved, with differences typically
less than 3 degrees.  Site 3 was the worst, with directions consistently about
3 degrees counterclockwise from the average of the rest.  It is possible that
this difference is real (since it was close to a gully).  [Though it was 
site 2's boom angle that was different by 3 degrees during the two shoots -- 
see next entry.]

Sensors:
ASTER props on 58m tower
PAM props on PAMs

Logged problems:
28 Sep 16Z: 15m starts reading 0 much of the time, probably associated with
            a strong rain event -- fixed 9 Oct 16 UTC.
9 Oct 16Z:  15m vane bent back to straight by hand.

Wind direction up the tower:

For most of October, there were constant differences between the props
at different levels of up to 10 degrees, probably caused either by incorrect 
boom angles being entered and/or shot.  The ASTER vanes are easy to bend
(as noted on 9 Oct), but I would expect this to cause a wind-speed dependence
on the direction differences, which isn't obvious to me in the data.

There was a change in this bias on 17 Oct at 45m and 26 Oct at 15m.  The
reason is not known.  The attached plot shows this behavior.

Inspection of the wind direction plots indicate that the wind direction does not change monotonically with height for the tower.

The prop at 15m (W0002) has been reading nearly 0 speeds for quite a while.
I just spent the last hour+ swapping it with spare sensor (W0003).  I
initialized this spare in the trailer with new propeller P56159 with
a pitch of 306, reset the boom alignment (only changed by one count from
what it had initially), and set the boom angle to 97.0 deg.  (I note that
W0002 had 96.7 deg, which is off by 0.3 deg from the boom angles which
were logged.)  I put the old vane in the new sensor.  It bent slightly when
I pulled it into the tower (even when I was watching for this), but I think
I bent it back close to straight.

The speed profile appears to be better now.

The table below provides the prop pitch information
for each propeller vane on the 60 meter tower

prop location	prop s/n	pitch
---------------------------------------------
15 meter	56182		304
25 meter	54606		304
35 meter	54614		304
45 meter	54636		304

  Below are the propeller calbrations for the units used in
CASES99. The propellers on the PAM sensors have a higher pitch
then specified by RMYoung. As a test, one PAM propeller was tested
on an ASTER sensor.The computed pitch was 294. The correct value.
At this time, we are assuming the physical dimensions of the PAM
sensor has an effect on the flow resulting in the higher pitch values.
The raw data can be extracted from the computed data if we decide the
pitch values used are incorrect.
  In some cases, a propeller has already been assigned to a sensor.
This is noted in the table below.
PAM:
propeller	pitch (mm/rev)	sensor
53686		309		355
62082		307		314
44341		309		319
43554		309		245
53678		304		318
53664		307		313
48627		304		315
53665		306

ASTER
propeller	pitch (mm/rev)
56182		304
54614		304
54636		304
56159		306
53560		305
54631		304
56153		306
54606		304