April 25, 2000
QuestChat with Steve Smith
Aerospace Research Engineer
NASA Ames Research Center, Moffett Field, CA
- 2 - 05:40:47 ]
Hello! Today's Aerospace Team Online QuestChat with aerospace research engineer
Steve Smith will begin at 10 am, PDT (1 pm, EDT). Be sure to check out Steve's
bio BEFORE coming to the chat room: http://quest.arc.nasa.gov/aero/team/smith.html
-- We look forward to chatting with you!
- 7 - 09:09:29 ]
RE: [Sue] Hi Sandy! We're logging
on to make sure we've got a good connection. We're looking forward to
today's chat. I've got 12 middle school students studying aeronautics
with me today.
Hi Sue! Looks like you've got a good connection right now! We are really
looking forward to chatting with you and your 12 students today :-) "See
you" in about 45 minutes...
- 8 - 09:30:58 ]
[ Sue - 9 - 09:38:34 ]
- 11 - 09:47:12 ]
EVERYONE: I am holding all of your questions in my "moderator's chat room"
until the chat officially begins in about 10 minutes. You won't see them
until I post them so you don't need to keep resending them.
- 12 - 10:02:54 ]
Ok Everyone, Steve is here and ready to take your questions :-)
- 15 - 10:05:30 ]
RE: [Cindy] I read in your bio that
you are building your own powered airplane. What will the finished product
HI Cindy, Well, its a 2-seat airplane, with a low wing, and its what we
call a tail-dragger: it has two main landing gear and a tail wheel. the
seating arrangment is tandem, front and back seats. It has a 25-foot wingspan,
and it will have a maximum weight of 1850 lbs.
- 16 - 10:07:01 ]
RE: [Njuguna] Hallo Steve, Being
a little bit more specific, IF you were planning a helicopter blade design
project including testing in the wind tunnel, what budget would you work
with, an approximation. Thanks!
Well, it depends on if you just want to test a blade section, or a complete
rotor system. A simple blade test might cost about $100,000, but a full
rotor test could cost several million dollars!
- 20 - 10:13:29 ]
RE: [Sue] Tell us more about wing
design. We know that you have researched some advanced wing designs. We're
building gliders, and the kids have been experimenting with various shapes.
What shape do you think offers the most promise?
There are classical theoretical results that show that an elliptical wing
planform is best. Modern refinements show that a good wing planform is
to have a half-ellipse with the trailing edge straight. This shape gives
the best spanwise distribution of lift. Of course not many "real" airplanes
are built that way, because it is expensive to build a curved planform
shape, and for most purposes, a straight, tapered wing works almost as
well. But for hand-launch gliders, the half elipse really works well.
- 21 - 10:16:13 ]
RE: [Sue] Followup question about
wing design: What works better, wings that encompass the entire fuselage,
or wings more like the standard commercial design? Which gives the longest
glide time? How necessary are rudders?
I'm not sure what you mean by "encompass the fuselage" please explain.
The vertical fin, (which the rudder is a moving control surface on) is
really important for directional stability, so if gusts or turbulence
hits the airplane, it will always straighten out and fly straight ahead.
The rudder is a control for yawing, to help turn the airplane, in combination
with the aileron controls on the wing, which are roll controls. The pilot
uses the rudder and the ailerons together to make a smooth banking turn.
- 23 - 10:19:44 ]
RE: [Njuguna] Hallo Steve, Waht is
you biggest challenge in you career and what would you advice an aspiring
aeronautical engineer outside the USA who fancy Nasa?
Wow, thats a hard question! I guess my biggest technical challenge was
to do all the research to finish my PhD degree while also working on regular
projects. But there are other kinds of challenges at work - things like
getting ideas for projects approved. Sometimes the research that I think
is important is not what the leaders want us to do. So I have to find
things that are within the research areas we are supposed to focus on.
This is frustrating and challenging. Aeronautics research isn't very well
funded right now, so its hard to give advise about being an aeronautica
engineer. The best we hope for is that the business cycles will come around
again, and aeronautics research will be better funded.
- 26 - 10:22:44 ]
RE: [Sarang] Hello Sir,first i would
like to ask you is that besides the Einstein's equation ,why it is not
possible practically to build a spacecraft that will exceed or equate
the speed of light?
Hmmm, this is not a field I'm an expert on, but I know that according
to modern theory, objects that go very fast, almost to the speed of light,
seem to act as if they are heavier, so it takes more and more power. In
the limit, at the speed of light, it takes infinite power because the
object acts infinately heavy. So, the only things that can go the speed
of light are actually weightless - they have zero mass.....
- 29 - 10:29:30 ]
RE: [Sue] The kids want to know:
What do you think careers in aeronautics will look like in the future?
How do you envision them changing?
WEll, as I said to Njuguna, I hope the business cycles come around and
there is better funding for research. I think there will be two big changes
in the way aeronautical research works in the future. 1st, on the way
we work...computers are still getting faster, and we are getting better
and better at simulating flow over airplanes with the computer. So the
trend is definately to use the computer simulation more in design, and
use the wind tunnel for final validation and to explore the things the
computer can't do. At the same time, computers let us share information
easier, so there is a whole new field of how to have designers collaborate
better. Another thing that is changing is more competition from other
airplane companies in other countries. To stay competitive, we will need
to design airplanes that not only perform well, but are easier and faster
to build, so our companies are more profitable. A big change in the future
will come when we don't have enough fossil fuels left to power our whole
civilization, but especially aircraft. There are not realy very good alternatives
for powering airplanes. So there will be research on propulsion using
alternate fuels, and also the related research of what the airplanes should
be shaped like to work with those fuels. Example: Hydrogen fuel must be
stored in a huge tank, so how can you shape the airplane to store the
fuel it needs?
- 32 - 10:32:53 ]
RE: [Sarang] Sir,what are the opportuinties
for a research are open for a an aerospace engineer?
Well, right now, not very many opportunities in aeronautics. Hopefully
that will change soon. New types of materials for building airplanes,
and new manufacturing methods to assemble them faster, and easier to maintain.
Those are areas where people are doing a lot. Another area with a lot
of opportunity is in the area of air traffic control.. We are working
on better ways of managing the air traffic around airports and also criss-crossing
the country going every which way, without running into each other. We
need better tracking information, and then help from computers on how
to organize the traffic flow. So those are some new areas.
- 33 - 10:39:11 ]
RE: [Sue] Hi Steve--The "encompassing
wing" the kids are referring to are like on the B2 stealth bomber, where
the wing is attached to the full length of the fuselage. How is this an
advantage/disadvantage in terms of gliding characteristics?
Oh, I see, like a flying wing.....That type of airplane has two main advantages.
First, if you can carry the payload in the wings, spread out sideways,
the wing structure can be much lighter, because it doesn't have the bending
stress from having all the weight in the middle, and all the lift in the
wings. By putting more weight out in the wings, it cancels the bending
moment from the lift. The other advantage is that it doesn't have the
drag and weight from the fuselage. But the disadvantage is that without
a horizontal tail to provide stability and control, the wing itself can
not be designed to be as efficient. There are trade-offs on the wing shape
to make it stable, and to make the wing controls work to control the airplane.
I helped design a foot-launched sailplane like a hang glider, called the
SWIFT. There is one on display at the aviation museum in San Carlos, CA.
For gliders, it still works out that it is better to have a fuselage,
mostly to provide a place to put the horizontal tail. The other thing
about making a flying wing airplane, is if you want to put people in it,
and have them sit in the wings, You find out how thick the wings have
to be to make room for the passengers to stand up. So you end up designing
a really HUGE airplane. It would be nice if people were smaller!
- 36 - 10:42:56 ]
RE: [njuguna] What would you say
about the pricing of costs in Nasa research centres let say, AMES as compared
to other centres in Europe like the DNW?
This is an iteresting question. In the past, NASA, as part of the government,
has done work to help american companies, without charging much money.
This was to help keep american companies more profitable, and more competitive
in the world economy. But this is changing. We at NASA are now supposed
to charge the real costs for what our research costs. This has 2 problems.
One is we are not very good at figuring out how much it costs, because
we didn't used to keep track. Also the companies are not used to having
to pay so much - because they used to get the benefits of our research
much cheaper. So now, the companies are trying to decide how much they
can afford to spend on our research, and how much they can do by themselves.
This is another reason why aeronautics research is not funded very well
right now. I think the problem will work itself out.
- 37 - 10:44:34 ]
EVERYONE: We have about 20 minutes left in today's chat with Steve. When
it's over please let us know how we've done by filling out the short chat
survey at: http://quest.arc.nasa.gov/qchats/qchat-surveys
- 38 - 10:45:13 ]
RE: [Sue] Amy wants to know: Did
the magazines and books you read as a kid influence your research and
WEll, I had several books on history of aviation. I used to study those
a lot. I especially liked the fighter planes of world war II. I also read
Aviation Week because my father brought it home from work. But when I
was a kid, my main interest was birds. I wanted to be a biologist. It
wasn't until high school that I found how much I like building and designing
things, and How exciting it is for me to figure out how things work.
[ Sue - 39 - 10:47:50 ]
Wow! Thanks for the great response. Looks like we have our next design
- 42 - 10:48:37 ]
RE: [Sarang] what are the shapes
of the wings of the aircrafts you design in order to get min. air resistance
as well as speed?
Well, the wing shape really depends on what the purpose for the airplane
is. Gliders have very long, slender wings, we call that "high aspect ratio"
so that the drag that comes from making lift is very small. But those
wings are too heavy for some airplanes, and not very maneuverable. A maneuverable
airplane, like for airshows, or a fighter plane, has much shorter, stubby
wings. The drag is higher, but they need the short wings for maneuverability,
so thats what you call a design trade-off. Commercial jetliners are designed
to fly about 85% of the speed of sound, and at this speed, the wings must
have sweepback to keep the compressibility drag small. But they also have
pretty high aspect ratio, so low drag from lift too.
[ Sue - 44 - 10:51:28 ]
We appreciate the time you took to be on-line with us today. This is our
first on-line chat; it was exciting to be able to ask questions of a real
expert! Your answers have been very helpful--thanks for encouraging this
group of potential aeronautical engineers!
- 45 - 10:51:52 ]
RE: [Sue] Malorie wants to know:
If you had unlimited funding, what project would you most want to research??
Wow, what a great question. I guess my favorite projects are trying to
do better design optimization with the computer, so we need to get good
flow simulations, and connect them with special procedures that change
the design and see if it works better in the simulation.. There are lots
of design constraints that come into the problem - like making sure it
takes off on a certain length runway, and making sure it can fly safely
if one engine stops, and making sure it can fly to the desired destination
with some reserve fuel left over. We call this design synthesis. Thats
- 46 - 10:52:24 ]
EVERYONE: THere are only 10 minutes left in the chat today... Don't forget
to fill out our short survey when the chat is over: http://quest.arc.nasa.gov/qchats/qchat-surveys
- 47 - 10:53:20 ]
RE: [Sue] We appreciate the time
you took to be on-line with us today. This is our first on-line chat;
it was exciting to be able to ask questions of a real expert! Your answers
have been very helpful--thanks for encouraging this group of potential
Sue: You and your students asked some awesome questions! Thank you for
participating today -- it's obvious you did your homework before coming
to the chat! Hope you can join us again for another chat soon!
- 49 - 10:54:10 ]
RE: [njuguna] With a total of about
nine JSF test flights accidents, would you attribute the failure with
anything to do with the complicated aircraft desing involved and do you
think this is something that can be sorted out by R&D, paticularly the
windtunnel tests? Thanks!
Hmmm, I don't know much about these. I do know that it is a very complicated
airplane, one of the biggest challenges is flying the airplane unstable.
The natural design, and the center of gravity are made to make the airplane
more maneuverable, but it is not stable by itself. A sophisticated computer
controller has many sensors about the motion of the airplane, and provides
artificial stability. If anything goes wrong with the computer or the
sensors, it will probably crash.
- 51 - 10:55:36 ]
EVERYONE: Please don't send anymore questions and Steve will do his best
to the answer the remaining few...
- 52 - 10:57:44 ]
RE: [njuguna] Steve, I am quite concerned
about the funding of R&D, does this reflect the future of aviation? A
few months ago, the Deputy President, Lockeed Martin mentioned that the
Engineers that aviation is focusing on are IT specialists with interest
in Aviation, what does this mean to you?
Well, right now, everyone is excited about information technology, but
not really sure what the best thing to do with it. Our web chat is a good
example - we couldn't do this a few years ago. Its a great idea to be
able to communicate so easily. But, how do we translate that into doing
engineering more easily? Better? its really hard to say....but thats what
everyone is interested in right now. So, to combine them, we need engineers
that understand the potential of what could be done, and then, when they
get an idea, they can develop it and share it with the new IT. but its
still not clear how that will figure into design....
- 53 - 11:00:11 ]
RE: [Sue] So, your last answer gave
us another question: It seems that larger area on wings is good for gliders
that need lots of lift, whereas smaller wings give more maneuverability.
What size tail (in relation to the wing size) makes for the longest glide
distance on a glider? Does the size matter much?
Yes, you want the horizontal tail to be big enough to do its job, but
not any bigger, since it would be extra drag and weight. a good rule of
thumb is 15 to 20 percent of wing area. Many newer gliders for radio control
and hand launch are making smaller tails, but using a longer fuselage,
so the tail effectiveness is still good, but with a very small tail. Of
course, it is important to make the fuselage very light....they are using
carbon fiber tubes that are made for kites.
- 54 - 11:00:52 ]
Ok Everyone, it's time to let Steve get back to work today! Thank you
so much for participating today! You really asked some great questions!
We hope you can come back and join us for another chat next week. Check
out our chat schedule at: http://quest.arc.nasa.gov/common/events
- 55 - 11:05:16 ]
RE: [Sarang] Sir,what are the speeds
of the fastest of aircrafts that are available on the earth?and what about
Well, the fastest airplanes go about Mach 3, or 3 times the speed of sound.
it is possible to go about mach 5, but so far, there has not been a good
reason to do that since it wastes a lot of fuel. Spacecraft go much faster.
Without air resistance, you can go really fast. I think the space shuttle
in orbit goes about 20,000 miles per hour. maybe a little less. But its
really fast. It would be interesting to figure out how fast a geosynchonous
satalite must go to stay in one spot over the earth.... But unfortunately,
spacecraft speed is limited by how much fuel you can get up there, which
takes bigger booster rockets. Maybe if we stored fuel in a tank up there
with several trips, we could get enough fuel to go very fast, like half
the speed of light or so - but even at that incredible speed, it would
take a long time to reach the nearest star. So I don't know if we will
do it anytime soon.
- 58 - 11:13:28 ]
RE: [Sarang] Sir, have you ever designed
the hypersonic aircrafts?and are they built with some other technology
than that of an ordinary aircraft?
Actually, yes, I've been helping on a hypersonic design for a reusable
space plane. My part has been to make it fly well at low speeds too. This
is hard because the requirements for hypersonic flight are so different,
its hard to make the same shape fly slow. The space shuttle is actually
a really smart design!
- 59 - 11:16:45 ]
RE: [Sarang] Sir,what are the possibilities
in near future that our spacecrafts would explore our galaxy ,although
a natural speed limit is given by time?
But unfortunately, spacecraft speed is limited by how much fuel you can
get up there, which takes bigger booster rockets. Maybe if we stored fuel
in a tank up there with several trips, we could get enough fuel to go
very fast, like half the speed of light or so - but even at that incredible
speed, it would take a long time to reach the nearest star. So I don't
know if we will do it anytime soon.
- 61 - 11:20:43 ]
Thanks everyone for coming, and thanks to Sandy for organizing this!