Two Weeks to Go - Calibrating the
Balance
By Fanny Zuniga
December 31, 1997
Two weeks to go before our test starts. We are busy right through
the holiday getting ready for our test. A lot of work is going into
getting our internal balance ready, so I want to explain some of it
to you. Remember, our balance measures the aerodynamic loads
(like Lift and Drag) on our model. Think of it as a very fancy, and
expensive, bathroom scale that can measure forces in any direction
very accurately.
First I need to explain how a balance works. The balance
is a cylinder 5 inches wide and 18 inches long. Inside
the balance are small metal parts that bend when a load is applied
and send out a small electrical signal. The more it bends, the higher
the voltage output. Fine, except that we have to calibrate the voltage
signal. This is because if you double the load on the balance, you
don't necessarily get twice the voltage out. When the balance is
calibrated, it means that we can say "this many volts means this
many pounds."
To calibrate the balance you have to hold on to one end of the
balance, hang some "known" weight on the other end, and measure
the output voltage. The balance is actually inside
the rectangular metal "block." The block is only there to provide a
convenient way to attach weights to the balance. We attach a red
cart that holds about a ton of metal plates that we can hang from the
balance. We hung up to 12,000 pounds because we expect the model
to generate at least 10,000 pounds of Lift. That's 5 tons!
Are you surprised by how much weight there is?
Thinking about all that weight sure gives you an idea how much Lift our
model can generate in the wind tunnel. Now you know why we had to make
sure the model was so strong.
Now that its calibrated, we've moved the balance into a preparation
room where it can get hooked up to the software that has been
written for this test. It is mounted on the two struts which
will be used to hold the model in the tunnel. Remember, the balance is
inside the metal block. The electrical cable comes out of the
back of the balance. Soon the metal block comes off and the model will be
attached to the balance. When everything is ready, the model,
balance, and these struts will all be carried into the tunnel.
Our software is nearly ready and it has been loaded onto a
computer in the prep room which is just like the computer in the
wind tunnel. One of the next big steps is to make sure our computer
software understands the electrical signals from the balance and that
it uses the balance calibration information correctly. To do this we
will hang some weight off of the balance again to check that the
software program records exactly the right weight. This should
happen next week.
Also this week I'm reviewing the "plan of test" (or run schedule)
and adding detail to this plan. I have to make sure that everyone is
in agreement with the plan and that we make sure we set out our
plan as efficiently as possible. Time in the tunnel is very precious.
We only have five weeks to do everything we want to do including
installation and de-installation so it's critical that we have an
efficient plan.
Finally, this week I am also working on getting some software files
ready for our use during the test. All this needs to be ready so that
we can easily and quickly plot up information about our model as
soon as we get data from the tunnel. Once the test begins, the
researchers will want to look at the data as soon as we get it. This is
important because, no matter how well we plan out this test, we
will have to make some decisions about what we want to test based
on how the model performs.
Well, that's it for this week. Things are getting very hectic and time
is running out before the test begins, only two more weeks to go. I
suspect I'll be working long hours the next couple of weeks. It's
crunch time!!
[Editor's Note: Frank Quinto is a test engineer at
NASA Langley Research Center. He works at the 14 by 22
-foot Subsonic Tunnel there.]
Test Day
by Frank Quinto
Monday, October 13, 1997
It is Day 3 for this test, Dynamic Ground Effects Test on Various
Wing Plan forms. The test started on Saturday, October 11 at 7:00
a.m. Our Facility, the 14- by 22-Foot Subsonic Tunnel, is
temporary operating around-the-clock (24 hours/day, 7 days/week).
Two of the five test engineers on this test have covered the weekend
shifts for this test. I am one of the three engineers that cover the
weekday shifts. This morning is my first day on this test. Even
though I wrote the plan and schedules for this test, I need to read
two days worth of notes to see where we are and where we need to
go. It is especially tough after a long weekend. This past weekend
was my sixteenth annual football get-together with my
"dorm-mates" at Virginia Tech. Tech's football team was victorious
over Boston College, 17-7 - GO HOKIES!!! I am reading the shift
notes and listening to the Test Engineer from the previous shift tell
what they did on their shift and what else is left for us to do on our
shift before we can start the test.
I spent most of the morning determining why some instruments
were not giving the right output. In trouble-shooting this problem,
I normally work from the computer that is getting the information
back to the instrument. As I try to track the problem, I will pass-by
Technicians working on various items for the test. They will update
their progress, so I know what is going on and also write it in the
test log. In the log, I note how the Technicians did certain things or
what the next shift should do or avoid. Communications among the
staff and across the shifts is very, very important. Everyone has to
know what is going on. It is like having a band playing the right
note of a song at the right time. The band uses a song sheet to know
when each note occurs, if they did not have it, they could play
different notes at different times. The Test Plan that I put together
earlier in the month, during my planning days, and the daily test
logs are like that song sheet. I finally track the problem of the
instrument output to an "interface" rack. The connections to power
the instruments and the signal from them was NOT connected. I
make the appropriate connections and now I trace the output from
the rack back to the computer to make sure the output is the same
all the way back to the computer.
In the afternoon, we check the clearance of the model support
system and surrounding cover plates. We move the model down to
the tunnel floor and check the clearance of the support as it goes
below the cover plates. As the model nears the floor, the back part
of the large support structure has a few items that may hit the cover
plates. The Technicians mark the cover plates, so they cut out those
areas. While they are cutting into 1/4 inch aluminum plates, other
Technicians are working on the models to get them ready. In the
meantime, I write in the test log what occurred with the instrument
problem and the cutting of the cover plates. As I am typing, I get a
telephone call from the Test Engineer that will cover the second
shift. He will not be coming in because his daughter went into labor
and is expecting to the deliver her third child, real soon. I called
the other Test Engineer who cover the third shift to see if he could
come in 4 hours earlier and I would work 4 hours more to cover
the second shift. When the third shift Test Engineer comes in, I
update him on what has happened and what else needs to be done.
The end of another test day, one day of over 4000 different day.
Now it's time to go home and relax after a long 12 hour shift!!!
SUBSCRIBING & UNSUBSCRIBING: HOW TO DO IT!
If this is your first message from the updates-aero list, welcome!
To catch up on back issues, please visit the following Internet URL:
http://quest.arc.nasa.gov/aero/updates
To subscribe to the updates-aero mailing list (where this message
came from), send a message to:
listmanager@quest.arc.nasa.gov
In the message body, write only these words:
subscribe updates-aero
CONVERSELY...
To remove your name from the updates-aero mailing list, send a
message to:
listmanager@quest.arc.nasa.gov
In the message body, write only these words:
unsubscribe updates-aero
