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Aerospace Team ONLINE

UPDATE #13 - February 27, 1998

PART 1: Upcoming Chats
PART 2: Contests Announced
PART 3: Computer Simulation of the MD-11 Models
PART 4: On a roll! - One more week
PART 5: Subscribing & Unsubscribing: How to do it


UPCOMING CHATS

Tuesday, March 3, 1:00 p.m.- 2:00 p.m. Pacific Time: Fanny Zuniga,
Aerospace Engineer will chat in English and Spanish.
Registration available NOW at
http://quest.arc.nasa.gov/chat/prj_won/fz.03-03-98
Fanny is currently testing a model of the High Speed Civil
Transport in the 12' Pressure Tunnel at Ames. Read her biography
http://quest.arc.nasa.gov/aero/team/zuniga.html
and journals prior to joining this chat.
http://quest.arc.nasa.gov/aero/events/test.html

Tuesday, March 10, 9:00 a.m. Pacific Time: Frank Quinto,
Wind Tunnel Test Engineer. Registration information at
http://quest.arc.nasa.gov/aero/chats/#chatting
Prior to joining the chat please read his bio at:
http://quest.arc.nasa.gov/aero/team/quinto.html

Wednesday, March 11, 10:00 a.m. Pacific Time: Christopher J. "Gus" Loria
(Major, USMC) NASA Astronaut Candidate (Pilot). Gus is flying the Vertical
Motion Simulator the world's largest simulator.  He will be flying the
latest simulation of the shuttle orbitor.
Read his bio at http://www.jsc.nasa.gov/Bios/htmlbios/loria.html

CONTESTS ANNOUNCED

The Drawing and Essay Contests are now online.
Please visit the events page for the details,
http://quest.arc.nasa.gov/aero/events/

We hope you will participate in these easy and fun activities. All entries
will be posted on the Aerospace Team Online site.  From that angle,
everyone is a winner.  Prizes will be awarded to the best entries!!

[Editor's Note: Steve Smith is an aerospace research engineer. Read his bio at http://quest.arc.nasa.gov/aero/team/smith.html ]

COMPUTER SIMULATION OF THE MD-11 MODELS

by Steve Smith

First, I needed to get the geometry of the wind tunnel test section and the geometry of the MD-11 model into a form that the computer simulation can use. I used a type of CAD program to create a "surface panel" definition of the model and the wind tunnel. This took me about 3 weeks. I actually needed to do this step six times, because I wanted to simulate the model installation in the wind tunnel at three different angles of attack, and there are two different model sizes.

Next, I ran a simulation of the flow through the empty tunnel to ''calibrate'' it - to make sure the flow speed in the test section was the same as the flow speed in free air. Results: I put a flow sampling point in the test section model, and the velocity at this point was 0.972 times the free stream velocity. Since lift and drag forces are proportional to the square of the velocity, V2, I need to adjust the forces inside the tunnel in my computer simulation by dividing by 0.946.

December 19, 1997
I sent off the three computer runs for the 4.7% scale model inside the wind tunnel, at angles of attack of 0, 5, and 8 degrees.

December 22, 1997
I got two of the computer runs back today. The third one is still running. I submitted the three runs for the 7.25% model.

December 23, 1997
I got two cases back today. Merry Christmas

December 29, 1997
The Cray computer is down today for maintenance

January 2, 1998
I got the remaining two cases back. I submitted the last 3 cases, just the basic MD-11 model in free air at the same three angles of attack.

January 3, 1998
I got all the computer results back today.

Determining the corrections to apply to the data

I made an Excel spreadsheet with all my computer results of lift and drag coefficient. The first correction I did was to adjust all the lift and drag coefficients from the models in the tunnel for the empty tunnel calibration, by dividing by 0.946. Next, for each angle of attack, I subtracted the result from the free-air computation from the result in the tunnel, so I now have the ''delta-lift'' and ''delta-drag'' caused by the wind tunnel at each angle of attack.

January 6, 1998
Today I used a curve-fit routine to find the quadratic parabola that fits through the three data points for each model at the three angles of attack. I ended up with four parabolas, one each for the ''delta-lift'' and ''delta-drag'' for the two models. I arranged to have the actual wind tunnel results for the two models sent over to me from the wind tunnel data group. There are actually mountains of data - I just got the data for the cruise configuration (flaps retracted and elevators set for cruise) with the standard winglets. I put these data into the Excel spreadsheet.

January 7, 1998
Today I actually applied the quadratic curve-fits of my tunnel corrections to the actual wind tunnel data. At each model angle of attack that was tested, I just evaluate the quadratic equation for the delta-lift and delta-drag and add these to the lift and drag coefficients for the model. After doing this for both models, I am ready to compare the lift and drag characteristics of the two models again. Remember they should now be the same if my corrections properly compensate for the wind tunnel effects.

Well, the results still show about 8% difference in drag at the same lift. It looks like my corrections have compensated for some of the differences, but not all. The 8% difference is really big, considering that the models were basically the same, just different size. There must be some more complicated effect that my computer model doesn't account for. I'm going to have to think about this for a while.


[Editor's Note: Fanny is the Project Manager for an upcoming test of a future supersonic airliner. She has written several journals about the preparations for this test. See them online with pictures at http://quest.arc.nasa.gov/aero/events/test.html ]

ON A ROLL! - ONE MORE WEEK

by Fanny Zuniga

We are settling into a routine here, and making great progress on our
test.  We made our 400th run late this week.  Things have really calmed
down, so I'll just give you some highlights of the week.  Our day team and
night team are competing to see who makes more runs in the tunnel.  The
crews are also competing to see who can make the quickest model changes.
Its like we are having some Wind Tunnel Olympics going on here!

We can see the light at the end of the tunnel.  The end of the test means
we all get a much needed rest. Meanwhile, it seems that now we could keep
the model for an extra week if we need it.  And, the next test to use this
tunnel can give us a few extra days if we really need it.   But, by the
end of the week we caught up with our planned run schedule so we may not
need extra time back after all.  So, everyone is asking "When will this
test  end?"   We are feeling a bit less pressure and are confident that
we'll complete almost everything we had planned.

This also means we should get to do some of the interesting stuff we
planned for the end (stuff we'd skip if we hadn't caught up).   For
example, on Thursday, we decided we could set up the model deformation
system I described a few weeks ago.  So we removed the mini tufts from
some of the left hand wing, painted the the wing black to cut down glare,
then applied reflective targets over that.  By Friday we started making
some runs to capture the video images that are used to calculate how our
wing bends and twists under high loads.   As another example, if we keep
making this great progress we  should have time to use the Pressure
Sensitive Paint (PSP) I talked about.  So we are refining our
preliminary plans for using PSP and really working out the details of when
to paint, when to install cameras, and when to make the runs.  And we
still hope to just squeeze in the oil flow studies after the PSP runs.

We have also been able to do some of the things that we really wanted to
do but that weren't the highest priority. We were able to study the
effects of the model "skidding".  This helps make sure the airplane will
be controllable in flight.  For this, instead of just tilting the model's
nose up and down (angle of attack), we also swung the model's nose to the
left and right. We also stuck some model wheels on to see how they effect
the aerodynamic forces during takeoff and landing.  We also got to test
how effective the horizontal tail is. The tail is the primary way that the
pilot controls the speed of the airplane, so we tilted the tail up and
down for a bunch of runs to make sure it could control the airplane.

We have had the usual list of small problems.  For example, we use wax
to fill in holes where screws hold the flaps on the wing.  We had some
trouble keeping the wax from blowing off the model.  We also had a small
piece of the model come off during one of the runs.  A big piece flying
down the tunnel is a test team's worst nightmare because it can damage the
tunnel.    Since it was a small aluminum
part, it wasn't a big deal.  A bigger piece, or harder metal, might have
damaged the giant fan that pushes the air around. Finally, remember those
accelerometers we use to measure the model's angle of attack (a very
important thing to know)?  Also remember I said we double up on
instruments when we can?   Good thing we did!  The main one we were using
quit working properly, but we were able to keep on testing using the
backup.

When everything is working well, here is a typical sequence of activities:
We look at our run schedule and decided what we want to run next. Usually
we follow our original run schedule, but we can make changes based on what
we've learned about the airplane.  If we are running behind, we can skip
over something that is less important. Next, we tell the shift engineer
what we want to do. He/she opens up the wind tunnel and the mechanics
change the model to the next configuration.  When the tunnel is finally
closed up, several different conditions (like airspeed) are run. For each
run we tilt the model through several angles of attack.  As soon as
signals start coming in, technicians process the data and send it to us to
look at.  We plot it up on our computers, check to make sure it looks OK,
and use the information to answer our research questions and to help us
plan the next set of runs.


We do the things that are fastest the most often, like change angle of
attack (the tunnel controllers do this in 2 seconds).  The things that
take a long time, mainly changing the model configuration, we try to do
less often.   Some example, our Olympic Tail Changing Team take the tail
off in 5 minutes once the tunnel is stopped and the test section
is open.  Changing flap angles, however, means taking out a lot of screws,
changing the flap angle, and putting all the screws back in - maybe one
and a half hours.    We generally try to sequence our list of runs in this
order: for each type of flap we go through all the flap angles. For each
flap angle we run with the tail on and off.  For each of these
configurations we get data for all the angles of attack and airspeeds we
want. Finally we put on a new flap type and repeat the whole sequence.
Once we make a model change, we want to get all the data on that
configuration.  We don't want to have to change the model back to the same
configuration later just to get one more piece of information.  That's
why we spend so much time in the beginning of the test making sure
everything is working properly. Once we move on, we want to be confident
that we won't have to back up.   One exception to this pattern is flow
visualization studies which we save until the end of the test because they
take so much time.  Sometimes this means we have to go back to a
configuration we tested earlier.


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