[ Rabi/Ames - 2
- 11:02:19 ]
RE: [Susan/NASAChatHost] Welcome
Rabi, It's great to have your here today!
It is nice to be here --- I look forward to some interesting questions.
[ Rabi/Ames - 4
- 11:04:29 ]
RE: [Susan/NASAChatHost] In your
journal you mentioned pressure sensitive paint. It sounded like you have
made some progress there.
Yes, this was a relatively new application for us and it worked great!
[ Rabi/Ames - 6
- 11:07:17 ]
RE: [Susan/NASAChatHost] Can you
say some more about that, it seemed to work better at low speeds now.
Yes, this technique has worked really well at high speeds in the past
-- this was the first time that we got good results at low speeds.
[ Rabi/Ames - 8
- 11:11:41 ]
RE: [Susan/NASAChatHost] How about
your sportsball research, are you getting any results yet?
The ongoing sportsball research is with tennis balls --- the group has
shot many high-speed videos of tennis players in action and these are
currently being studied. The main interest in in studying the flight paths
and bounce properties of tennis balls.
[ Rabi/Ames - 10
- 11:16:03 ]
RE: [Susan/NASAChatHost] Have
you test sports balls in the wind tunnel
I have tested cricket (a game played in England) balls in a wind tunnel.
We are also planning to test tennis balls in a wind tunnel here at NASA
[ Rabi/Ames - 11
- 11:17:56 ]
Amongst the sportsball that we are familiar with, cricket balls, baseballs
and golf balls have received the most scientific attention over the years.
[ Rabi/Ames - 12
- 11:19:32 ]
Wind tunnel testing is not particularly easy with sportsballs since, in
most cases, the ball spins during flight and this is not easy to achieve
in wind tunnels without affecting the air flow around them.
[ Rabi/Ames - 16
- 11:22:06 ]
RE: [Susan/NASAChatHost] So how
do you test them?
Well, typically we can project spinning balls through a wind tunnel or
hold it on fine wires attached to motors which spin them up.
[ Rabi/Ames - 17
- 11:24:43 ]
RE: [Jason-AndersonElemSchool] Mr. Mehta, how long does it
take to test a model using the pressure test? What is the average pressure
that the models can stand?
The time it takes for the pressure measurements depends on how many parameters
you are intertested in. For example, with a typical wing, you mat want
to measure the pressures at several speeds and angles of attack (wing
attitude relative to the flow). For each point, we take several images
lasting 2 to 3 minutes. Lower pressure are good for the technique ---
more light emission.
[ Jason-AndersonElemSchool - 18 - 11:25:48
Dr. Mehta, what would you say have been the major differences between
your life in Nairobi and the United States? Do you think you will ever
go back to Nairobi?
[ Rabi/Ames - 20
- 11:28:21 ]
LIfe in Nairobi was excellent --- great weather (it lies on the equator)
and lots to do in your spare time. I was also fortunate enough to be born
in a household which could afford some luxuries. Life out here is quite
different --- we are way ahead technologically, but we work a lot harder
and we are rewarded adequately.
[ Rabi/Ames - 21
- 11:29:57 ]
RE: [Jason-AndersonElemSchool] Do you know about how much
pressure something can take before you test it, or do you have to wait
until the test to find out? Thanks for answering my last question.
I have a feeling you are asking about the maximum pressures a model can
stand -- there are several calculations performed by engineers before
the model is tested.
[ Rabi/Ames - 22
- 11:31:01 ]
RE: [Jason-AndersonElemSchool] Dr. Mehta, what would you
say have been the major differences between your life in Nairobi and the
United States? Do you think you will ever go back to Nairobi?
I don't think I will ever go back to Kenya to live there, but I would
love to take my son (15 years old), just to show him where and how I grew
[ Rabi/Ames - 25
- 11:35:00 ]
RE: [Susan/NASAChatHost] I can
imagine that the pitted of the surface of the golf ball catches air and
generates lift, is that how a cricket ball works?
No, the basic aerodynamic principles are somewhat different for the two
balls. The overall roughness on a spinning golf ball helps to reduce drag
and generate lift. On a cricket ball, the two halves are joined together
by lines of stitching and these can be used to generate a sideways force.
[ Rabi/Ames - 26
- 11:36:33 ]
RE: [Sarah-AndersonElemSchool] Can you study how a ball bounces
in a wind tunnel
Yes, you could, but that would not be all that useful. the wind tunnel
is really suited for measuring aerodynamic forces on the ball --- the
wind tunnel could be useful for studying effects of cross winds, for example.
[ Rabi/Ames - 29
- 11:39:00 ]
RE: [Sarah-AndersonElemSchool] Do you play cricket? I saw
it on TV it looks like baseball but different. I play softball.
That is great -- I play softball too. Cricket has many similarities to
baseball, but there are some distinct differences as you point out ---
you may want to check out a web page on cricket for more information---
I played cricket all my life until a few years ago.
[ Sarah-AndersonElemSchool - 31 - 11:41:40
Cool! Thanks for your answer do you know the url of a cricket page?
[ Rabi/Ames - 32
- 11:41:43 ]
RE: [Patti/CJHS] Could you tell us a little more about the
applications of the testing you're doing on pressure sensitive paint?
Sure. Just to give you a bit of background, one of the more important
properties that one wants to measure in a wind tunnel test is the distribution
of the pressures on the surface --- these give the forces on the model.
The paint is great because it is relatively easy and costs less than other
conventional techniques. We mainly test airplane models with this technique,
but a couple of weeks ago, we applied it to a van.
[ Rabi/Ames - 33
- 11:43:39 ]
RE: [Jason-AndersonElemSchool] Mr. Mehta, How does the stitching
work to generate sideways force, did people figure this out when they
designed the ball?
Good question. No, the stitching appeared through a historical accident,
I think. The earlier players soon found out that if you can release the
ball with the seam angled than the two halves of the ball are affected
differently by the airflow and this generates a pressure difference and
hence a side force.
[ Rabi/Ames - 34
- 11:45:04 ]
RE: [Sarah-AndersonElemSchool] Cool! Thanks for your answer
do you know the url of a cricket page?
No, I do not off-hand, but if you e-mail this question to us, I will make
sure that you get some web addresses. You may also want to just type keyword
"cricket" on one of the engines such as "Yahoo".
[ Sarah-AndersonElemSchool - 36 - 11:46:45
[ Rabi/Ames - 37
- 11:47:54 ]
RE: [Jason-AndersonElemSchool] Mr. Mehta, Thanks for the
answer, is that side force like a curve ball in baseball?
Yes, Jason, the side force (or the mechanisms responsible for generating
it) are very similar. It also turns out that the side force magnitude
is about the same so that you get about the same amount of movement.
[ Rabi/Ames - 39
- 11:51:04 ]
RE: [Sarah-AndersonElemSchool] We were talking about building
a wind tunnel. Can you make one with a fan and a box?
You you sure can. Again, if you e-mail this question, I will send you
details of an article (on the web) which shows you how to make a simple
[ Sarah-AndersonElemSchool - 42 - 11:52:52
Ok I will
[ Rabi/Ames - 43
- 11:53:50 ]
RE: [Patti/CJHS] Do you do any of the ball studies as part
of NASA? Is there a NASA application?
Not really. As you can imagine, sportsball aerodynamics is not high on
NASA's priority list! The tennis ball project I keep tallking about is
actually conducted by a private company --- I am just helping them with
it. Of course, one of the hopes is that young children would become more
intertested in aerodynamics through this topic.
- 44 - 11:55:20 ]
Great questions kids!
[ Rabi/Ames - 45
- 11:56:00 ]
RE: [Jason-AndersonElemSchool] Mr. Mehta, Thank you is the
fact that the ball is symmetrical important?
Jason, you have been asking some excellent questions -- are you really
in elementary school? The fact that the cricket ball is symmetric about
the seam is very important. By angling the seam, you ensure that only
one side of the ball (or the flow over it) is affected. So apart from
the seam, you want the surface to be identical.
[ Jason-AndersonElemSchool - 47 - 11:58:13
Mr Mehta, Thank you when I don't fold my paper airplanes well they fly
crooked. That's how I figured out the symetry!
[ Rabi/Ames - 48
- 11:59:29 ]
RE: [Sarah-AndersonElemSchool] Do you like research? Do you
like working on projects like a van?
Sarah, your questions are great too --- I wish I had attended your school!
I love research, especially the fact that we are always doing something
new, something no one has done before. Projects like the van are neat
because it gives us the opportunity to learn about the aerodynamics of
vehicles -- more interesting would be racing cars!
- 49 - 11:59:49 ]
Thanks for the great answers Rabi, Kids send in your last questions now
it's time to go!
[ Jason-AndersonElemSchool - 50 - 12:00:51
Thank you Mr. Mehta, Good bye.
[ Sarah-AndersonElemSchool - 51 - 12:01:39
Bye! Thanks, good luck at softball!
[ Rabi/Ames - 52
- 12:01:54 ]
Bye kids, I hope you had a good time and learned something about aerodynamics
in the process.
- 53 - 12:02:35 ]
Thanks Rabi and kids, I've learned a lot!