Half-way point in the test
by Fanny Zuniga
- two weeks to go!
February 12, 1998
Off to a slow start but we're finally rolling. We
are behind and everyone's thinking about how to make up for lost time.
Monday: We have completed 70 runs to check
accuracy, repeatability, sample time for each data point, and agreement
with previous test results. We are done with the checkout phase of the
test! We are finally ready to change the model to the first takeoff configuration
and start doing some research.
On another front, some parts of the minituft imaging
system are broken, including the strobe lights and the lens on the camera.
We are still trying to fix it, but we may just have to give up on the
tuft images for this test.
Tuesday: We had our share of problems today.
We got dumped on by "El Nino"; roads were flooded and making it hard for
people to get to work. So, this morning the model was ready to run, but
we did not have a full crew to run the tunnel. Even the weather is slowing
us down. Then, part of the tunnel controls quit working. We didn't get
to run the tunnel until near lunch. This sort of stuff not only slows
us down, but gets on our nerves. This job can be interesting and frustrating
at the same time.
After lunch tunnel problems and software problems
kept us from running until early evening. Basically, we are in the part
of our test where we think we are getting good data but now are faced
with various mechanical and software problems that keep us from running
the tunnel. We are hoping to start the last phase of test soon. That's
the phase where we should be very productive and get most of our useful
results. When everything is working well, we can accomplish a lot in a
Wednesday: Halfway point of the test - at
least on the calendar! We started with 5 weeks (25 days), minus 2 days
for holidays that occur during our test. That left 23 days. Remember,
we are running two full work shifts each day, so we had a total of 46
work shifts for the entire test. We started late 2 days, that's 42 shifts
total. Those two days cost us 8 percent of our test!!! Including today
we have 24 shifts left for the rest of the test. Then the checkout phase
we just finished took longer than planned, so we're more behind. We did
plan extra time into our schedule for problems (we call this "contingency"
time). But we don't like being this far behind this early, because that
means we've used up most of our contingency time before we really even
We are going to have to really crank it up! We decided
that, starting Thursday we would work two 10-hour shifts (instead of 8-hour
shifts) to make up for some of our lost time. This means day crew runs
from 6:00 am to 4:00 p.m. and night crew runs from then until 2:00 a.m.
the next day. Ouch! We also will run on Saturdays if enough of the crew
volunteer. Ouch, Ouch! The good news is that this will only last a few
weeks, sort of like cramming for a final exam. Another way to make up
for lost time is to extend the test past February 20 if we can get extra
time in the tunnel. This could happen if it's OK with the next test to
use the tunnel. Unfortunately, our model is scheduled for use in another
tunnel (at Langley Research Center in Virginia). So even if we could get
more time in the tunnel, we have to pull the model out after February
24, so we could only get two extra days at the most.
We are really starting to make progress in getting
our research runs made, so let me explain a little more of what were looking
for. Some of the runs we are making right now have involved changing the
angle of the flaps at the front (leading edge) and back (trailing edge)
of the wing. I can't show you pictures of this, but imagine the front
and back of the wing droop downward. We say that the flaps are "deflected."
We basically check dozens of combinations of leading edge and trailing
edge flap deflection. Deflecting the flaps makes the wing act like it
has more curvature. The result is that both Lift and Drag go up, but not
always in the same amounts. We are looking for combinations that work
well for takeoff and landing. For takeoff, since the airplane is trying
to speed up and climb, we want lots of lift without increasing drag too
much. On the other hand, for landing we want to fly as slow as possible;
we need all the Lift we can get. Because we are slowing down and descending
we don't care very much if there is a lot of Drag. So we can look for
a combination of flap deflections that gives us higher Lift than we would
use for takeoff. Not only are we looking at flap deflections, we have
several different shapes or types of flaps to try. This will give us plenty
We also want data with the horizontal tail on and
off. We do this so we can determine the effect the tail has on the model's
aerodynamics. We can then figure out how much the wing is contributing
to the overall Lift.
Thursday: At this point we are making better
progress, but we lost several hours yesterday and again today to software
problems. We are getting nervous about finishing everything, so we are
starting to look for things to cut out of the schedule. We might drop
some of the repeat runs that I described earlier because we have more
confidence in our data and we need to save time. In testing, we are always
trading off speed (number of runs) and risk (confidence in the data quality).
Good news is that we have enough volunteers to run
an 8-hour shift this coming Saturday. That should really help.
Friday: As of this morning we have about 295
runs remaining and 20 shifts left, not including weekends. We have decided
to toss out any runs that were just for imaging the mini tufts since we've
pretty much given up on getting the system to work. Since we are behind
schedule and the balance has been behaving so well, we finally made the
decision to cut most of the repeat runs.
Saturday: There was some excitement this morning.
We thought we had lost a bunch of our model parts. That would really mess
up our test plans. It turned out that all the parts are here. We had one
part labeled incorrectly, which messed up the system we use to identify
all the parts.
We just passed run # 200! We made 21 runs in 8 hours!
Now we're cruising!
|| Taking off the horizontal tail.
|In this second picture, the tail is still connected
to the model by the pressure tubes which you can barely see.
|| This picture shows those pesky mini-tufts. They are
finer than your hair, and look like fuzz on the upper surface of the
wing. When the wind is on, they lay flat and point out the direction
of the airflow. Too bad the system isn't working now so I can't show
you how they will look during the test.(I bet you can imagine that