sounds good okay first of all while we
start by you getting just a brief
description of what laminar flow is it's
an interesting question to give a brief
description in essence what we're trying
to do is control the boundary layer so
that it looks a lot like a simple
simple-minded way it would be if you
looked at a car that was in a smoke
tunnel and you see the commercials on TV
and you see the smoke waves going over
the car and they're nice and smooth and
then later on they burst and they become
a big bubble the laminar flow part is a
place where they're smooth where the air
actually flows over the wing in a very
smooth manner you know in a low drag
configuration in a more efficient way
it's all air foils have some laminar and
have some turbulent flow on them in the
area where it's laminar it's basically
the more efficient portion of the
airfoil another common phenomenon that
people can relate to laminar flow would
be a cigarette smoke it's the portion of
the cigarette smoke that comes off of
the cigarette real straight and smooth
and tightly wound and then later on it
bursts and there's this big smoke spot
in the middle of or smoke ball in the
middle of off of the cigarette that's
the turbulent section the straight piece
is where the laminar flow is so it's the
tightly wound well organized smooth air
for airflow that you're talking about
when you say laminar versus turbulent
associated with supersonic well probably
the biggest difference in supersonic
laminar flow is that is the airfoils and
the wings tend to be more highly swept
and that the leading edges are you know
and the order of 35 to 70 degrees swept
back from a 90 degree angle and
typically a subsonic laminar flow
airfoil doesn't have quite that much
sweep and the sweep actually makes the
airfoil it makes it more difficult to
maintain laminar flow because you have a
component of inbound air or an air
molecule that's coming towards the swept
wing part of it goes straight back but
part of it goes out towards the wingtip
and that's called cross flow and cross
flow is the phenomenon that makes
supersonic laminar flow was one of the
phenomenon that makes supersonic laminar
flow more difficult to maintain than
subsonic laminar flow it's much more
much more force a larger forcing
function if you will for supersonic
laminar flow than it is for subsonic
laminar flow there's also another
another concern and it has to do with
the size of a leading edge radius and
the fact that the attachment line or the
place where the pressure actually
separate the molecules actually
separates some go over the top some go
over the bottom that area would be
called the stagnation point or the whole
line of those would be called the
attachment line and that attachment line
controlling exactly where that is on a
swept wing and a supersonic wing is a
little bit more difficult than it is
necessarily on the subsonic wing so
we're again supersonic wings tend to be
swept highly making it much more
difficult to control exactly where the
attachment-line occurs so those are the
two things that make it more difficult
the pressure distribution itself is a
lot more difficult to maintain you in
order to maintain it in a laminar flow
conducive a pressure distribution
conducive to laminar flow you actually
have to shape the airfoil properly and
the shaping of that airfoil is part of
the art and that's of learning how to
how to make supersonic laminar flow work
and it turns out that it needs some
augmentation
subsonic laminar flow can occur does
occur easily relatively easily in the
natural state you can actually maintain
subsonic laminar flow back to fairly
high percentage percentage quartz 35 40
percent quart they've been a number of
experiments where we've done that flight
experiments where we've done that and
they've been you know Windtunnel
experiments with them supersonically
there hasn't been very much research in
it it's we know that we can get laminar
flow to you know an inch or so back now
we're trying to maintain it further aft
and in order to maintain the laminar
flow further aft we have to come up with
some method of augmentation and that's
why we're using suction to actually pull
the boundary layer in essence pull the
boundary layer back down andrey laminar
eyes the boundary layer and hopefully we
can maintain a pressure distribution by
augmenting with suction to keep laminar
flow extending further and further aft
along a wing surface and obviously if
you maintain laminar flow for a larger
distance you can reduce the drag of an
airfoil if you can reduce the drag you
can increase your fuel efficiency if you
can increase your fuel efficiency you
can increase your payload capability and
you know it's just a whole raft of
things that come out of being able to
maintain laminar flow indirectly yes
what we have done thus far with one of
the f-16xl number one which was a
cooperative experiment with Rockwell
International North American aircraft
rockwell and nasa langley and nasa
dryden onto a limited extent actually
NASA Ames was also involved in some of
the computational work that went along
with this we have demonstrated that you
can maintain laminar flow back to
roughly 25 percent coordinates under
certain conditions the next experiment
that we planned for the second airplane
is to maintain laminar flow further aft
back as far as 50 to 60 percent cord so
yes we are doing it stepwise the first
experiment showed us that it was in fact
achievable and in fact it might be a
little easier in certain areas to do
than we anticipated the real world tends
to be a little bit more forgiving it
appears you know from a flight
perspective the real world is more
forgiving than the computational or the
theoretical world says it should be but
we haven't gotten enough of an
understanding as to exactly why we're
able to do what we're doing we know we
can do it now we have to try to figure
out exactly what is the phenomenon that
we're actually able to to control to
make us get laminar flow to 25% cord
meanwhile we want to extend that yes
back to 50 or 60% cord which is a big
driver in the design process for the
high-speed civil transport airplane if
we can achieve when I'm going to flow
that far back we have actually
correlated unit Reynolds numbers to a
large enough number that the theoretical
people and the designers for the
high-speed civil transport have a lot of
confidence that when they scale this up
to the full size vehicle the scaling
will actually be fairly accurate but on
a high-speed civil transport they may
not have laminar flow back to 50 or 60
percent cord but if we can achieve it to
50 to 60 percent cord now we know we
understand the phenomenon well enough to
be able to use it to our advantage on a
high-speed civil transport primary
driver is that it has a configuration
that is close to the configuration that
the high-speed civil transport is right
now on the on the table it looks like
it's going to look like it's a very
small airplane but it has a 70 degree
swept wing and the high-speed civil
transport designs right now appear that
the wing is going to be roughly a 70
degree sweep the cord is not long enough
it's but it was an airplane that was
available with the right sweep angle for
a test section and so that appeared to
be the right place to start
it's the only one of the few airplanes
that are available right now to do that
type of work and that's the other reason
why the airplane was selected it was
actually available back in 85 the Air
Force and General Dynamics parked the
airplanes and said they had no more use
for the airplane and in 88 NASA thought
that they could use an airplane and
meanwhile the Air Force was looking for
somebody to either take it off their
hands or to or the Air Force was going
to destroy
the airplane so we said we've got to use
four we'd like to have the airplane the
airplanes are actually loaned to us they
don't belong to NASA they belong to the
Air Force and they're just on loan to
the to NASA for the duration of the
flight experiment well we actually
collect on the order of 250 to 300
pieces of data telemetry to the ground
we display to our engineers somewhere in
the order of about a hundred and fifty
among the parameters were displaying to
our engineers or the pressures
coefficients of pressure it's actually
the pressure is measured and then we
went into a computer to display in a
pressure distribution format what the
pressure distribution looks like we also
measure and display to our engineers
whether the flow is laminar or turbulent
when we use a thing called a device
called a hot film anemometer or hot film
sensor which in essence is a piece of a
strain gauge bridge and by the way it's
manipulated and can condition the signal
is conditioned we can actually tell
whether we have laminar or turbulent
flow at a specific discreet location
along the wing where these things are
located those are the two primary pieces
of information that we collect we also
collect data on the suction levels how
much suction are we doesn't require to
maintain the laminar flow at those in
under those various conditions and of
course the conditions themselves are
recorded whether what our mock mock
altitude airspeed angle-of-attack angle
of sideslip all of those are recorded
and telemetry to the ground so that the
researchers can tell whether or not we
are on the conditions that we need to
examine whether or not laminar flow
occurs then
first three or four percent granulation
what do you learn from that helps most
of what they have done thus far they're
they're the beginning of the experiment
they're the ones that say well if you
can shape your airfoil this way if you
can if you can build a contour if you
can build an experiment that looks like
this you are most likely going to be
able to get through the hardest part of
the region the hardest part of the
experiment which is to get the leading
edge to be laminar if you can maintain
laminar at the leading edge the rest of
it will probably fall out you may have
to manipulate your experiment just a
little bit but the further are and will
follow so what we really get out of them
is verification of some of the theories
that the design theories for our
experiment so the design starts whether
it's and a lot of times that is the
computational fluid dynamics people
start working on what they think is a
good design then they might fly a small
experiment in one of the tunnels and
when they think they have something that
really is does show promise then we'll
scale it up to an airplane and do a
flight experiment which will be the
in-flight validation of what the wind
tunnel said and what the computational
fluid dynamics work said oftentimes we
don't get to 100% correlation in there
in the data what we get is is some
differences in terms of what we get for
real time our flight data and we take
that turn it back into the computational
fluid dynamics folks or to the wind
tunnel people and say well our data
shows this but our configuration looks
like this why don't you run it again put
it through your tunnel again or put it
through your code and see whether or not
you can figure out what the difference
is between what we got and what you got
in terms of results so there's not
always 100% correlation but we use this
as an iterative process often times they
don't get the same answers we get and
they're convinced that their part is
exactly right so we have to go back and
find out what it is and arcs our piece
of the experiment that might be
different so it's you know it takes a
lot of communication a lot of talking
between the computational fluid dynamics
people and the wind tunnel people and
the flight experiment people and the
applications
people and the instrumentation people
everybody has to talk to everybody in
order to make sure that we really are
doing the experiment we all think we're
doing and and we have had on occasion
some differences of opinion in terms of
what we are doing and what we think
we're doing and what somebody else
thinks for doing so it does it's a
difficult process to keep iterating
everybody's data until we get
correlation their work is what is most
important and what that's a positive
thing because that person is very
enthusiastic about what they're doing
and that's where their heart is but what
I see but it's really funny to talk to
somebody do you know who Bernie Spencer
in Spanish I know the name but I don't
know him personally
he's a wind tunnel guy he did a lot of
testing to rephrase that Bernie we kick
all we need anyway it's I mean it is
that's a tough problem you know the and
we have you know we have our growing
pains trying to correlate a you know
make a flight experiment add the most
value to an overall program like this
because everybody does have their empire
if you will and everybody wants to make
sure that their piece gets gets added
into the equation why it is an important
part of the validation process and
especially when you're dealing with a
phenomenon that we don't understand yet
there are some kinds of technologies
that can be done you know
computationally or in the wind tunnels
but I think we're in an area now where
we don't know enough and we need some
flight data to correlate with and I
think overall the program does recognize
that and everybody involved in the
program recognizes that but flights also
very expensive and that's that's a real
drawback any time
anybody looks at trying to do a flight
experiment they say Who am I we're going
to spend millions of dollars doing this
flight experiment and we could do the
same experiment in a wind tunnel or in a
in the computational world for
considerably less and convincing
everybody that you still need the flight
data is sometimes difficult you know so
when you talk about your computational
people or your wind tunnel people and
you talk about your air applications
maybe your flight applications people
getting a meeting of the minds is the
hardest thing you know getting everybody
to say yes this is the very important
thing for us to do is really difficult
and it hasn't been flawless so far in
this program although we're getting
better we're definitely working hard
harder to make sure we're all part of
the big piece of the piece of the
program and I think it's starting to
show well we have we've collected
sufficient amount of laminar flow or
laminar turbulent transition data and a
significant amount of pressure
distribution data to be able to show
that with minor anomalies we can we
cannot we do understand how the pressure
distribution is has been developed you
know there are some things in the
pressure distribution we don't
understand but we're beginning to
believe that some of that's our
instrumentation measurement technique
rather than it has anything to do with
the phenomenon called supersonic laminar
flow which is good I mean it's what it's
done for us is it's it's improved our
instrumentation technique capability as
well which will make the next experiment
a better experiment in transition where
transition location occurs we have been
able to show that the codes that have
that developed that this airfoil shape
was developed by are not a hundred
percent representative of what really
happens in the real world but they're
close enough there's some things that
some phenomenon that they didn't
anticipate in the code development that
need to be revisited it's on it's fair
to say we did not predict the results we
got you know the computational fluid
then
the Windtunnel results did not predict
the results we got out the first part of
the ship one experiment but they
predicted enough of the information in a
satisfactory manner that we now have
something to do some checks and balances
against as I said earlier now is time
for the CFD folks and for the Windtunnel
folks to go back and look at the
differences between what they thought we
were going to flight test and what we
flight tested and see whether or not
they can we can start correlating the
differences between the two most
importantly I think the flight
experiment has shown that yes you can
get laminar flow and it's not as may not
be as difficult to do under these
circumstances as we anticipated it
wouldn't I mean there was a lot of a lot
of apprehension that we were going to
have to do a lot of provide a lot of
suction for example in order to maintain
laminar flow and we're not providing all
that extraordinary in a really large
amount we're definitely providing
suction but the amount is not as much as
people predicted it would be so we are
starting to show you know that that this
is a handleable problem it's not out of
our out of our capability which is a
very big confidence builder that we can
get from here to there without and
without having to go over the impossible
you know the impossible Ridge first so
basically what we've done so far is just
provide the data to validate what we've
done so you know what the the
theoretical people have done so far and
then that gives them the step the
confidence step they need that they can
go the next you know they can go to the
next level of complexity and start
understanding a little bit more about
you know the difference is the
difference between cross flow and you
know you do the n factor computational
results and those kinds of those kinds
of computational theories that they're
using they're getting enough data to
validate that the theories are valid
theories they just need they need to be
tweaked up and tuned up just a little
bit more
what you need for laminar flow control
and what you're finding to achieve the
best possible results how does that
eventually affect what they need in a
sonic sonic boom area or in the high
lift area their needs are obviously
different yeah their needs are different
and in fact the integration of laminar
flow high left sonic boom or shaping is
going to be a very difficult task
because they don't meet those those at
least those three phenomenon don't meet
at the same place so it's going to be a
compromise everybody is going to have to
say through whatever whatever validation
testing they do I can tolerate this much
detriment to my best performance
condition and still get some gain it's
it's the added value added equation
really more than anything else it's if I
have some laminar flow under certain
circumstances but I give it up during
the approach and landing phase or the
take-off phase if I have a sonic boom
but it's not as offensive as a very
sharp sonic boom and if I have you know
a noise footprint from the Heil you know
because of the high lift phenomenon
that's half of what you know meets the
fa r criteria but it's not the not as
good as I really want it that whole
compromise and that whole integration
issue has not really been addressed yet
it's everybody recognizes we're going to
have to compromise high lift and and
supersonic laminar flow are almost
mutually exclusive for certain parts of
a flight regime but you don't need
supersonic laminar flow when you're
subsonic so maybe it's not that big a
deal you know maybe we can work around
that one and so I think that that we
have to understand the conditions where
supersonic laminar flow occurs we have
to understand the conditions for getting
good high lift performance
characteristics and then once we
understand both of those we can
integrate the requirements for both in
such a way that we don't destroy you
know 75% of the capability in either
case the worst thing you could have is a
poorly integrated airplane one that does
ever
think poorly what we're hoping for is an
airplane that has all the technologies
put together in such a way that we've
maximized you know all the parameters at
the same time and you're not gonna get a
hundred percent of any other what do you
feel like the purpose of all your
research the database will probably be
used for years to come to validate B be
a lot of test case data to validate
development of new computational codes
and and theoretical codes the area we're
dabbling in now supersonic laminar flow
is an area that is is brand-new you know
there was some experiments done in years
gone by there's some x21 criteria that
people believe in there's some work that
was done on a 104 you know back in the I
guess was the early 60s those two
experiments were enough to set establish
some criteria for whether or not
supersonic laminar flow is or laminar
flow and supersonic laminar flow were
achievable what we have done and what we
will be doing through the Excel
experiment besides validating some of
the codes that the high-speed civil
transport is going to use for design
methodology we will actually fill the
database that will allow researchers for
future generation airplanes augment the
designs in other ways not just for the
point design called the high-speed civil
transport but perhaps for some other
vehicles some other more focused more
highly specialized vehicle that could
take advantage of an airfoil or a
pressure distribution development for
another region of flight that maybe we
haven't thought too much about to date
so the database by itself is is going to
be valuable to everybody it's it's
certainly designed to help the
high-speed civil transport but to
understand the phenomenon transition
physics and
and you know attachment-line phenomenon
and that type of thing that's the
importance that's some of the important
data that will come out of this
I mean we've played we've been in the
laminar flow business for well if you
read some of the some accounts we've
been in laminar flow since beginning of
NASA or NACA actually there was some
laminar flow work done in the begin
during the NACA days I personally have
been in the laminar flow business since
1979 and it's been subsonic laminar flow
up till now and there's always new
things to look at there's always the
effect of once you you know you take a
known configuration now you start
varying vary any of the parameters
instead of having 70° sweep let's look
at the effect of 75° sweep instead of
having maximum suction let's look at
less suction instead of having two
degrees angle of attack let's look at
you know three degrees or 1 degree angle
of attack there's a whole raft of
parameters there that that when you're
when you're focused on a vehicle that
has a certain flight regime you tend to
only look within that window and will
collect enough data that you can look at
the effect of changing the various
parameters and use that to validate
other codes for other flight vehicles
both f-16xl airplanes are hangared right
now although Friday we'll be flying the
first airplane again so excel ship ship
one which is the one that we started the
NASA Rockwell North American aircraft
experiment with is going into a phase
we'll call it a phase 2 experimentation
where we are actually trying to document
collect significantly more data on the
suction requirements for laminar flow
phase one was basically can we can we
achieve laminar flow back to you know 25
or 30 percent cord phase 2 is understand
the the suction distribution that's
required to do that
so yes the ship one is in a second phase
where we're collecting another set of
data when that's complete the airplane
in fact will
turned back to transferred back to NASA
Langley where they will begin the high
lift experiment where they will actually
start looking into the configuration
requirements for high left for the
supersonic our high speed Scylla
transport and Dryden in Langley will be
working together on that experiment with
Langley being the lead most of the
flight activity occurring back at
Langley and the modification activity
occurring there we will provide the
support as necessary to get that
airplane in the air back there the
second airplane ship 2 is the
centerpiece of the laminar flow control
phase of the high-speed research program
and that airplane currently is
configured with a passive glove which is
no suction at all it's just a foam and
fiberglass glove on the right wing and
with that we'll be examining
attachment-line criteria pressure
distribution verification since they
predicted that they designed the shape
based on codes and we're going to go out
and see if that shape really is
providing the pressure distribution we
had hoped for transition data where is
laminar flow occurring on a passive
surface that's shaped to be conducive to
laminar flow in a supersonic flight
environment and that's that's probably a
four to six month flight program that we
have planned there and at the term at
the completion of that flight program
that airplane will go back into
modification for the installation of the
big experiment if you will and that's
the one where we'll be putting a glove
suction glove on the airplane it'll go
on the left wing of the airplane it'll
be it'll go roughly back to 50 or 60
percent cord and that one will use
suction to try to maintain laminar flow
that far back these gloves are basically
almost full span for the 70 degrees
swept portion of the wing the wing is
the airplanes claim to fame is it's the
cranked arrow it's got a 70 degree swept
portion and then it bends three-quarters
the way out to the wingtip it bends to a
50 degree sweep and the section inboard
of the 50 degree sweep is where we put
all of the experiments because that's
where our 70 degrees is so the second
airplane will be a very busy airplane
it's we're hoping to collect the entire
database for the high speed civil
transport laminar flow control effort by
the end of fiscal year 95 and of course
we don't have the glove on the airplane
yet so you know we've got a lot of work
ahead of us to try to get it all done it
is on it is on and in fact we're hoping
to have the first flight for that
airplane in that configuration before
the before the end of August and we're
hopeful that it'll actually be the first
or second week of August I will actually
get the first flight with that glove on
the glove itself is of course the skin
is porous it's a piece of titanium sheet
that has 2,500 holes per square inch
laser drilled holes per square inch and
then beneath that is a corrugated
substructure and it's we call it flutes
and basically what it looks like is a
piece of cardboard if you will if you
look at the cardboard corrugations
that's basically what's underneath and
we sucked the air span-wise using a
suction pump that's located in the
fuselage of the airplane we sucked the
air through the hole the porous holes
span-wise and then in this case we're
just dumping it overboard because we
have no use for it in a high-speed civil
transport there may be some use for that
air somewhere else but not in this case
we're not worried about total
integration we're just worried about
determining laminar flow requirements so
when we regulate the suction level what
we really do is reduce the suction pump
pumping capability now we haven't done
any of that yet all we're trying to do
is document how much suction we have
right now for the results we've gotten
right now we have a fast-paced program
here that we may delete some of the some
of the nice-to-have objectives and one
of those things is to look at the effect
of changing the suction level and we we
may run out of time to be able to
do that in which case we'll we'll get
that data on the next experiment that'll
go on the second airplane