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Aerospace Team ONLINE

UPDATE #19 - April 17, 1998

PART 1: Upcoming Chats
PART 2: Contest Entry Deadline Extended
PART 3: Winglet Testing
PART 4: The Beginning of the High Speed Civil Transport simulation
PART 5: Subscribing & Unsubscribing: How to do it


Tuesday, April 21, 10:30 a.m.- 11:30 a.m. Pacific Time:
David Picasso, Deputy Director of Aeronautics.

David knows about all of the Aeronautics programs going on at Ames
Research Center.

Registration information is at
Read his biography prior to joining this chat.

Thursday, April 30, 1:00 p.m.- 2:00 p.m. Pacific Time:
Estela Hernandez, Flight Simulation Engineer

Estela is a flight simulation engineer. She uses math
to build computer models that simulate flying airplanes.
This chat will be in English and Spanish.

Registration information is at
Read her biography prior to joining this chat.

Monday May 4, 1998 9:00 a.m. to 10:00 a.m.
George Kidwell, Deputy Director of R & D Services for Operations,

George is responsible for directing the wind tunnel operations
at Ames Research Center. There are three major national wind tunnel
complexes at Ames, and each involves many skilled people, very large
amounts of electrical power, a lot of high pressure and high
speed air, and the need to run as quickly as possible while still
maintaining safety and data accuracy.

Registration information is at
Read his biography prior to joining this chat.


As you know we are holding two contests: "Draw a Picture of an
Airplane" and "Write an Essay Describing the Airplane You
Would Like to Design",

We have received some wonderful entries to date.  The spring
break schedules caused several people to ask for extensions.
The final deadline is now April 24, 1998. There will be no more

[Editor's Note: Steve Smith is an Aerospace Research Engineer. He spends one third of his time in wind tunnels and two thirds doing computational research. Read his bio at http://quest.arc.nasa.gov/aero/team/smith.html ]


by Steve Smith

February 18, 1998

This project is an effort to resolve a problem with two different
sets of wind tunnel data for the same airplane, using computer flow
simulations of the airplane model inside the tunnel and also flying in
free air.

Last year, I worked on a project to design a new, better winglet
to put on the wing tips of the MD-11 jetliner. I got to test my
winglets on a small wind tunnel model (4.7% scale) of the MD-11
in the Ames 12 foot wind tunnel. At the same time, I tested the
original winglets so I could compare them.

Later on, after the test was over, I got the idea that I should
have tested the model with a standard wingtip ( no winglets) for
comparison. It turned out that a bigger model (7.25% scale) of
the MD-11 was going to be tested soon, so I arranged to make the
comparison of the original winglet with a normal wingtip during
that test. So now, I have one comparison on the small model, and
one comparison on the big model. I want to combine the results so
I can compare everything together. But the wind tunnel effects
on the two models were different, and the comparison doesn't work well
unless I can correct for this size difference.

Effects of model size

When air flows over an object, it can tell how big the object
is by how long it takes to flow past it. To compensate for the
difference in size, you can just make the flow go faster. This
becomes a problem because the speed gets close to the speed of
sound, and the flow is distorted by compressibility effects. It
turns out that you can also compensate for the model size by
changing the air density. The relationship of model size, flow
speed, and density that is used to compare similar flows is called
Reynolds number. Theoretically, the flow over two objects of different
size is the same if the Reynolds number is the same.

Wind tunnel results before corrections

For the two different scale models that were tested, the tunnel
conditions were adjusted so that the Reynolds number and the Mach
number were the same. If the influence of the wind tunnel itself
can be compensated for, both these models should produce the
same force coefficients. Force coefficients are basically the
forces divided by the wing area of the airplane model. It is
customary to compare force coefficients instead of actual forces,
because the basic effect of size (a bigger wing makes more lift) is
compensated for. This correction is not the same as the more subtle effect
of Reynolds number, which affects the details of the fluid motion.
Without the tunnel wall effects corrections, a comparison of lift
and drag characteristics for the two models showed about 20%
difference in drag for the same lift. This is a huge difference!
I hope the wall corrections will compensate enough to make the
results for the two models the same, as they should. We will see!

[Editor's Note: Chris Sweeney is a Flight Simulation Engineer. He works at the Vertical Motion Simulator, the largest one in the world. Read his bio at: http://quest.arc.nasa.gov/aero/team/sweeney.html ]


by Chris Sweeney

February 6, 1998

Our preparations for the two High Speed Civil Transport (HSCT)
simulations have started. This year we will run back-to-back
HSCT simulations beginning on June 1 and running through the end of July.

The first simulation will study how a pilot will interact with the
displays and controls on the flight deck. The second simulation will
study more of the handling quality of the HSCT as well as some more
display issues.

The latest version of the "bare" airframe for the HSCT was just
delivered. It takes up four full binders. This model is called the
"bare" airframe because it does not have any of the computer
controlled flight control system with it yet. The "bare" airframe
shows how the aircraft will react if there were no computers onboard.
It strictly displays the pure aerodynamics of the vehicle. We
will start implementing this "bare" airframe immediately and
receive the flight control system at a later date.

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