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UPDATE #14 - March 6, 1998

PART 1: Upcoming Chat
PART 2: Asking Experts Questions by Email
PART 3: How a Computer Simulation Works
PART 4: Final week - We're done ! ! ! !
PART 5: Subscribing & Unsubscribing: How to do it


UPCOMING CHATS

The chat Tuesday, March 10, 9:00 a.m. Pacific Time: Frank Quinto,
Wind Tunnel Test Engineer has been cancelled due to Frank's 
work schedule.

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 orbiter. Registration information is at
http://quest.arc.nasa.gov/aero/chats/#chatting
Read his bio at http://www.jsc.nasa.gov/Bios/htmlbios/loria.html

Thursday, March 19, 11:00 a.m.- 12:00 p.m. Pacific Time: 
Jason Hill, Flight Simulator Technician Jason is responsible 
for maintaining two of NASA's flight simulators. Registration 
information is at
http://quest.arc.nasa.gov/aero/chats/#chatting

Read his biography prior to joining this chat.
http://quest.arc.nasa.gov/aero/team/hill.html

Tuesday, March 24, 10:00 a.m.- 11:00 a.m. Pacific Time: 
Stephen Jaeger, Aeroacoustics Engineer 
Stephen develops tools for measuring aircraft noise. He also conducts
acoustics research on wind tunnel models of supersonic jets, airliners and
aircraft engines. Registration information is at
http://quest.arc.nasa.gov/aero/chats/#chatting

Read his biography prior to joining this chat.
http://quest.arc.nasa.gov/aero/team/jaeger.html



ASKING EXPERTS QUESTIONS BY EMAIL

I get lots of notes from people that say "My class would 
like to have an engineer all to ourselves for email 
exchange."  Well unfortunately there just isn't a practical 
way to give you each your own engineer but we think we've 
got the next best thing and we hope you'll take advantage
of it.  K-12 students and teachers can email questions to engineers,
scientists and support staff. This interaction will be supported by
a "Smart Filter" which protects the professional from Internet
overload by acting as a buffer. The actual email addresses of these
experts will remain unlisted. Also, repetitive questions will be
answered from an accumulating database of replies; thus the
valued interaction with the experts will be saved for original
questions.

We believe that the email Q&A service is a good compliment to
the bios, Field Journals, Web chats and other materials. Students 
have an opportunity to follow-up on any Aerospace Team Online
information, or they can pursue their own lines of interest.

For the logistics and tips on asking good questions visit:
http://quest.arc.nasa.gov/aero/question/ask.html

The Aerospace Team members have already answered about 
100 questions and their answers a very thoughtful and
informative. You'll learn a lot by visiting the archive
of questions at http://quest.arc.nasa.gov/aero/question/


[Editor's Note: Chris Sweeney is a flight simulation engineer. Read his bio at http://quest.arc.nasa.gov/aero/team/sweeney.html ]

HOW A COMPUTER SIMULATION WORKS

by Chris Sweeney 

October 28, 1997 

A computer simulation of an aircraft is based upon the mathematics and
physics of aerodynamics and flight, converted into computer code. The
accuracy and realism of the simulation is only as good as the mathematical
equations which describe the aircraft. The better the model description,
the better the pilot will like the simulation. 

A computer simulation works by calculating all of the equations of the
aircraft as fast as it can. One pass through all of the equations is
called one cycle. The faster the computer can cycle through the equations,
the better the simulator will "fly." The computers we use now can cycle
through the equations once every 0.01 seconds or 10 milliseconds.
This is a 100 Hertz frequency or 100 cycles per second. 

At the beginning of the cycle, the computer reads the pilot's inputs from
the control stick, the rudder pedals, the throttles, and any other device
the pilot may be touching. These commands are sent to the flight control
system equations to calculate how these pilot commands should deflect the
control surfaces of the airplane like the elevators, the ailerons, the
rudder, the flaps, and the engine. These surface positions are used by the
aerodynamic equations to calculate the aerodynamic forces exerted on the
aircraft due to the deflections of the control surfaces and the speed of
the plane. The throttle position is used by the engine model equations to
determine how much thrust is being generated by the engines. 

The aircraft model uses equations of motion to move the motion system and
to move the aircraft over the computer-generated ground. From physics, we
know F=M*A (force equals mass times acceleration). We divide the
mass of the aircraft by the forces (aerodynamic, engine, and gear) acting
on the airplane to calculate an acceleration. We mathematically integrate
the acceleration to get the aircraft velocity and integrate the velocity
to get the aircraft position. We send an acceleration command to the
motion system which moves the cab to generate an acceleration the pilot
can feel. We send the position of the aircraft to the visual system to
update the visual display so the pilot sees the plane moving down the
runway or moving through the air. 

The pilots respond to the feel of the motion and what they see out the
window by moving the controls, and the whole process begins again.
 

[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 ]

FINAL WEEK - WE'RE DONE ! ! ! !

by Fanny Zuniga
  
March 3, 1998

This test of the Supersonic Transport model is done!   We all worked hard
and got a lot done in our five weeks in the wind tunnel.  The last week we
started looking forward to the end of the test because testing is hard
work.  I get so focused on a project like this, that I have to adjust to a
more normal life after that focus goes away.  Ending any long, challenging
project feels a little funny.  Even though a big project is tough, and
you're glad to see it end, working towards a goal with a team of people is
really rewarding too.

The last week of our test had a different feel than the rest of the test.
The knowledge that we had accomplished most of our objectives took a lot
of pressure and stress off of everyone.  We started the week by wrapping
up aerodynamic loads testing.  This included testing other "control
surfaces".  I mentioned that we tested the horizontal tail to see how well
it would control the airplane's speed.  This week we tested the the other
main control surfaces - the rudder and ailerons.  We want to know how well
they control the skidding and rolling of the airplane.

Then the focus turned toward getting some detailed information about our
favorite model configurations.  Getting this extra information, flow
visualization for example, is slow work so it is reserved for only the
best model configurations.  We started with model deformation. Checkout
data from last week looked like it was working well.  So we made
some runs this week to get wing bending information.  As I mentioned in my
fourth journal, this data helps us remove the effect of wing bending and
twisting from the aerodynamic data we have collected.  Basically, wing
deformation is an undesired effect.  So we measure it and then we can
subtract its effect from the lift and drag data.

Preparing the model for painting with Pressure Sensitive Paint (PSP) began
Wednesday afternoon.  We changed the model configuration to one of our
favorites and cleaned the right-hand wing.  The painting team spent the 
rest of the night putting on a base coat of paint.  They had problems
getting the paint to stick to the model, so it took until after midnight
to finish.  They also put reference marks on the wing, measured their
location, and finally went home.  Measuring the location of those marks is
a tricky business, as you can see in the picture below.  Why so tricky?
The wings are curved so we can't just lay a ruler on it to locate a point.

The actual pressure sensitive part of the paint was sprayed on Thursday
morning and the PSP system was finally ready to go by Thursday afternoon.
We then spent the rest of Thursday and Friday getting PSP images (see
picture below).

In testing, we always have to be planning and working ahead.  We were told
we could have Monday to finish up.  So, while PSP runs were going on, we
were getting some colored oil ready for the final study of our test.
First we mixed the colored dye into the oil.  We used 30 grade motor oil
(nothing fancy here) and mixed in a bunch of color to get it to the right
thickness.  We painted a sample and experimented with different ways to
put it on.  We were looking forward to having some fun on Monday!

We started off with oil flow first thing Monday morning.  We tried to get
the right amount of oil on the wings to get a good picture of the flow.
We tried little drops, big drops, blobs, and stripes of oil.   We got lots
of different effects this way as you can see in the pictures.  What we are
looking for is places where the flow doesn't go straight back on the wing.
We also want to see if there are places where the air flow "separates" off
the surface of the wing.  As you can see, the airflow on the wing is very
complicated.  These pictures will help us understand why some types (or
positions) of the wing flaps worked better than others.

At 8:00 Monday night we made the decision to shut down the tunnel and pull
the model out.  We had finished our last run - just over 500 runs!    We
had the model out of the tunnel by midnight.

This was a great test and had great people on it.  Now we can go home and
get some much deserved rest.  All of the out-of-town research staff from
Boeing and elsewhere are heading home.  The model is being put into its
crate and shipped immediately to the model makers in Virginia.  They are
waiting for it to get it ready for the next test.  The balance will also
be packed up and shipped out to Langley Research Center, another NASA
center, to be re-calibrated and inspected.  The next model to use this
tunnel is downstairs undergoing final preparations.  It gets
installed on Wednesday and then another test team will call the control
room home for a while.

Now that we're out of the tunnel, I'll be busy for the next few weeks
wrapping things up.  I'll tell you about some of that in a week or two in
my last journal entry

SUBSCRIBING & UNSUBSCRIBING: HOW TO DO IT!
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