PELTI Flight Report for RF03, 11 July 2000

   The objective of this flight was to vary the parameters that control the
LTI's performance to see how the efficiency varies with these things.  We
used sea salt as the test aerosol (The day was nearly a minimum in dust
concentration.) by flying at 60 m most of the time.  The flight was conducted
to the east and slightly north of St. Croix.

   We made the LTI {isokinetic/superisokinetic/subisokinetic},
{turbulent/laminar}, and varied the suction percentage that controls both the
enhancement and the losses in tubing bends.  For each leg there was setup time
to get the flows adjusted and the LTI software running, followed by the
10-minute period in which APS data was collected, and then a few minutes in
which the hot-film anemometer probe was used to profile the flow at the rear
of the porous diffuser. 

[Note:  The most reliable information on whether the LTI was isokinetic,
laminar, etc. is on the DU computer, to which I don't have access.  When that
data is available, we will produce a table listing times for various inlet
conditions, APS integrations, and filter exposures so that other data - such
as FSSP output - can be averaged over precisely those same times.  The times
noted below for each condition are from the APS, which was usually not started
until the flow had been stabilized.  If seconds are given, the time should be
an accurate picture of the stable segment. -BJH]

   No filters were exposed on the 15 minute legs, as there was insufficient
time to get meaningful samples.  TAS was not operational on this flight, as
we lacked some parts.


UTC
16:41   Takeoff

16:42 to
16:53   Sounding up to 2400 m (Roughly ENE)
        about 700 m cloud base, about 1600 m tops

16:53 to
17:03   Level at 2400 m - LTI Flow/Pressure-drop check

17:03:40 to
17:17:30   Sounding down to 60 m in the MBL 
           Turned East and remained at 60 m

Isokinetic LTI with various target sample flows to test enhancement. 
17:17   35 lpm - Min bend velocity, Laminar, FSSP flow off
17:37   70 lpm - Laminar, FSSP on again
17:57   95 lpm - Laminar
18:13   Turned to West, still 60 m
18:16   160 lpm - Barely turbulent

18:31 to
19:10   120 lpm - Barely laminar, Max bend velocity

18:31 to
19:10   Filters exposed

18:47 to
19:10   Good APS data (sample flow too high during first part of leg)

19:15   Turned to East, still 60 m
19:22   190 lpm -Turbulent

Subisokinetic (by about 13%)
19:42 to
20:27   120 lpm - Barely laminar

19:47 to
20:27   Filter exposure

19:57   Penetrated a rain shaft 
20:27   180 Turn to West, still at 60 m

Superisokinetic (by about 20%)
20:39:02  120 lpm - Barely laminar

Isokinetic
20:55   214 lpm - Turbulent

20:55 to
21:20   Filter exposure

21:22 to
21:32   Common-inlet APS and Neph calibration

21:32:30 to
21:43:15   Sounding up to 2400 m

21:43 to
21:46   Level at 2400 m

21:46   Descent and Return to STX
21:54   Landed at STX


Notes:

Some Teflon and Nuclepore filters broke.  We are awaiting backings to support
them on future flights.  Chemical data shows LTI to be more efficient than the
other inlets.

The DU LFE sample flows sometimes disagreed with those from serial UH
TFMs.  This could introduce extra uncertainty into how closely we could set
isokinetic flow.

There may be a leak behind the internal FSSP-300 that allows flow when
the FSSP valve is closed.  The flowmeter also needs to be re-calibrated or
exchanged for another.  The cabin 300 seems to show larger concentrations
above 3-4 micrometers than the wing-mounted 300.  To assure that this
observations is not due to calibration differences, we will exchange 300
positions on each flight. 

The APS behind the NASA inlet was replaced before this flight; it behaved
strangely and will be replaced by the one that had been removed.  NASA's
APS data will not be considered valid for this flight.


Commentary:

   This was a successful flight for testing the LTI under a variety of
conditions in sea salt.  It would have been desirable to have higher salt
concentrations, but the statistics of the APSs and FSSPs look satisfactory,
certainly up to 7 micrometers.  It still takes quite a while to get all the
sample and suction flows stabilized, resulting in the shortening of the time
available for collecting data.  Automating the LTI flow control to achieve
isokinetic and laminar conditions would enable a much more efficient use of
flight hours in subsequent programs.  Is the double-peak structure behind the
LTI real or an artifact of enhancement and plumbing losses?  It is clear that
the LTI admits more large particles than the other inlets under laminar flow
conditions and even when somewhat turbulent.  It is not clear, however, how
much enhancement is occurring (in flight the different conditions didn't seem
to make much difference, so their impact is subtle).  At high turbulence,
however, the LTI produces APS distributions that look very much like those
from the other inlets. We still need TAS and APS data to address the issue
of ambient/LTI differences.

Barry Huebert
17 July 2000