Proposals for air breathing hypersonic craft. I
Robert Clark
oxidizer at hypersonic speeds is the drag involved. There is
apparently a maximum speed that "air breathers" according to this
constraint can achieve: less than orbital velocity. The air hitting
the intakes at hypersonic speeds causes a tremendous amount of drag:
From: Steven Pietrobon (steven@****.UniSA.Edu.Au)
Subject: Liquid Air Cycle Rocket Equation
Newsgroups: sci.space.tech
Date: 1994-12-19 13:31:55 PST
http://groups.google.com/groups?th=2c2a527376d72620
I was thinking then about ways you could get surrounding air that is
at the speed of the craft. It occurred to me possibly you could use
the boundary layer. This is the layer of air that sticks to the
aircraft as it flies so is moving along with the craft at the same
speed. Usually you want to get rid of this because of the drag it
causes. But if it's going to be there anyway, moving along with the
craft, why not use it to provide the oxidizer for the craft?
I saw there is research ongoing that involves sucking in this air in
the boundary layer but only for drag reduction purposes, a method
known as "boundary layer control" or "laminar flow control":
Boundary Layer Control.
http://aerodyn.org/Drag/blc.html
Such research is ongoing even for supersonic craft:
F-16XL Laminar Flow Research Aircraft.
http://www.dfrc.nasa.gov/Newsroom/FactSheets/FS-023-DFRC.html
Then perhaps these already available systems can be adapted to
provide air for the engines. A problem is the boundary layer is quite
thin so you might need to use quite large wings or lifting body to get
sufficient air for the engines. This could wind up producing just as
much drag as what you are trying to get rid of. Another problem is
that according to this web page at low density conditions the boundary
layer air may not be moving at the same speed as the craft:
Hypersonic Waveriders - Flow Characteristics.
Low Density Flow:
http://www.aerospaceweb.org/design/waverider/flow.shtml
Bob Clark
johnhare
"Robert Clark" <rgrego...@yahoo.com> wrote in message
news:832ea96d.04050...@posting.google.com...
> I've read that the main problem from using the surrounding air as
> oxidizer at hypersonic speeds is the drag involved. There is
> apparently a maximum speed that "air breathers" according to this
> constraint can achieve: less than orbital velocity. The air hitting
> the intakes at hypersonic speeds causes a tremendous amount of drag:
>
The mass of the ABE* system is far in excess of the rocket engines
required to get the same performance. This weight is dead mass for
most of the acceleration profile of any rational spacecraft.
The second most serious problem with fast ABEs is thermal. At
anything Mach 3 and above, serious effort must be put into keeping
the vehicle temperature down. spending many minutes in the Mach
3-7 range guarantees a major TPS requirement for any vehicle.
The specific problems with sucking the boundary layer in are
that this is the hottest air available at any Mach number, which
leads to serious engine thermal problems. The air has not been
compressed by an intake, which means that the air at the engine
face is 2 to 50 times less dense than it could be, which translates
directly in engine thrust 2 to 50 times less than with an efficient
intake. And that the thermal cycle is narrow with less temperature
differential available to drive the turbine cycle.
If you are refering to a ram cycle, then the lack of intake compression
makes the engine nonfunctional with no pressure differential available
through the nozzle.
*ABE=air breathing engine
Uncle Al
>
> I've read that the main problem from using the surrounding air as
> oxidizer at hypersonic speeds is the drag involved. There is
> apparently a maximum speed that "air breathers" according to this
> constraint can achieve: less than orbital velocity. The air hitting
> the intakes at hypersonic speeds causes a tremendous amount of drag:
>
> From: Steven Pietrobon (steven@****.UniSA.Edu.Au)
> Subject: Liquid Air Cycle Rocket Equation
> Newsgroups: sci.space.tech
> Date: 1994-12-19 13:31:55 PST
> http://groups.google.com/groups?th=2c2a527376d72620
Look at the SR-71 Blackbird's engine intakes. Those big cones
occluding the apertures provided 64% of the plane's full-throttle
thrust ("Skunk Works," Ben Rich). A more important problem in
hypersonic engines is time interval. Traveling at Mach 6-10, how long
does the combustion mixture stay in the engine vs. reaction kinetics?
The working fluid isn't in the engine long enough to react.
Burning hydrogen barely pulls it off. Hydrocarbons don't have the
kinetics. One supposes 1,2-dinitroethylene or trimethylaluminum might
be interesting if low-efficiency fuels. Would you like to snuggle
next to 50,000 lbs of either with the airframe skin glowing dull red
from air friction?
> I was thinking then about ways you could get surrounding air that is
> at the speed of the craft. It occurred to me possibly you could use
> the boundary layer. This is the layer of air that sticks to the
> aircraft as it flies so is moving along with the craft at the same
> speed.
[snip]
Do you have any Fermi idea how much air the engine will be
inhaling/second? Each SR-71 engine inlet at Mach 3 inhaled 100,000
ft^3/sec of air. How thick is your boundary area? What is its area?
> A problem is the boundary layer is quite
> thin so you might need to use quite large wings or lifting body to get
> sufficient air for the engines. This could wind up producing just as
> much drag as what you are trying to get rid of. Another problem is
> that according to this web page at low density conditions the boundary
> layer air may not be moving at the same speed as the craft:
[snip]
Why are you sweating the small stuff?
--
Uncle Al
http://www.mazepath.com/uncleal/qz.pdf
http://www.mazepath.com/uncleal/eotvos.htm
(Do something naughty to physics)
TMG
Uncle Al wrote:
<snip>
> Burning hydrogen barely pulls it off. Hydrocarbons don't have the
> kinetics. One supposes 1,2-dinitroethylene or trimethylaluminum might
> be interesting if low-efficiency fuels. Would you like to snuggle
> next to 50,000 lbs of either with the airframe skin glowing dull red
> from air friction?
OR as scary - breathing it as it spills out on the tarmac - the SR-71
leaks like a sieve until it gets up to speed and temp. But a stunningly
beautiful machine.
Bill Vajk
Uncle Al wrote:
> Look at the SR-71 Blackbird's engine intakes.
snip
Michael Varney
"Bill Vajk" <bill9...@hotmailDITCHTHIS.com> wrote in message
news:BKCdnY7To_X...@comcast.com...
>
>
> Uncle Al wrote:
>
> > Look at the SR-71 Blackbird's engine intakes.
>
> snip
What is your point, Vacuous?
Gregory L. Hansen
Uncle Al <Uncl...@hate.spam.net> wrote:
>Robert Clark wrote:
>>
>> I've read that the main problem from using the surrounding air as
>> oxidizer at hypersonic speeds is the drag involved. There is
>> apparently a maximum speed that "air breathers" according to this
>> constraint can achieve: less than orbital velocity. The air hitting
>> the intakes at hypersonic speeds causes a tremendous amount of drag:
>>
>> From: Steven Pietrobon (steven@****.UniSA.Edu.Au)
>> Subject: Liquid Air Cycle Rocket Equation
>> Newsgroups: sci.space.tech
>> Date: 1994-12-19 13:31:55 PST
>> http://groups.google.com/groups?th=2c2a527376d72620
>
>Look at the SR-71 Blackbird's engine intakes. Those big cones
>occluding the apertures provided 64% of the plane's full-throttle
>thrust ("Skunk Works," Ben Rich). A more important problem in
>hypersonic engines is time interval. Traveling at Mach 6-10, how long
>does the combustion mixture stay in the engine vs. reaction kinetics?
>The working fluid isn't in the engine long enough to react.
>
>Burning hydrogen barely pulls it off. Hydrocarbons don't have the
>kinetics. One supposes 1,2-dinitroethylene or trimethylaluminum might
>be interesting if low-efficiency fuels. Would you like to snuggle
>next to 50,000 lbs of either with the airframe skin glowing dull red
>from air friction?
I thought the problem with hydrocarbons in a SCRAM jet was that the air
is hot enough that they don't burn at all -- they dissociate, and cool
the air.
--
"Let us learn to dream, gentlemen, then perhaps we shall find the
truth... But let us beware of publishing our dreams before they have been
put to the proof by the waking understanding." -- Friedrich August Kekulé
Mary Shafer
wrote:
> Look at the SR-71 Blackbird's engine intakes. Those big cones
> occluding the apertures provided 64% of the plane's full-throttle
> thrust ("Skunk Works," Ben Rich).
Er, not exactly. The compression from the inlets (not just the
spikes) produces subsequent expansion which produces thrust, but only
when the rest of the engine is working and the airplane is moving. If
the airplane is sitting still on the ground, the engines can still
make thrust but the inlets can't.
> > I was thinking then about ways you could get surrounding air that is
> > at the speed of the craft. It occurred to me possibly you could use
> > the boundary layer. This is the layer of air that sticks to the
> > aircraft as it flies so is moving along with the craft at the same
> > speed.
> [snip]
>
> Do you have any Fermi idea how much air the engine will be
> inhaling/second? Each SR-71 engine inlet at Mach 3 inhaled 100,000
> ft^3/sec of air. How thick is your boundary area? What is its area?
The boundary layer is up to a foot thick, maybe thicker, and it's the
size of the vehicle, less any areas of turbulent flow. For example,
the boundary layer on the upper surface of the wing of a Mach 2
fighter is over two inches thick at low altitudes.
Actually you want to take in still air for the maximum delta in
energy, so that the inlet can extract as much as possible. That means
your inlet needs to see the free stream, not the boundary layer.
You'll notice that the SR-71 inlets are well in front of the leading
edge of the wing, although they are behind the bow shock (but you have
to keep the bow shock off the wing or you get shock impingement and
localized heating).
Even old-fashioned aircraft like the F-4 didn't use the boundary
layer. If you look at one, you'll see that the inlet is separated
from the fuselage and there's a boundary layer splitter plate there.
Mary
--
Mary Shafer Retired aerospace research engineer
mil...@qnet.com
Mary Shafer
That's just low-volatiles kerosene. It won't ignite. We never
bothered to do anything about the spillage out on the ramp and
taxiways. We just let it evaporate. In fact, we'd even operate motor
vehicles in the vicinity, to the point of driving through the JP-7.
The TEA/TEB didn't leak out. Not only does it ignite the JP-7, it
bursts into flame in contact with air. It's dangerous, unlike JP-7.
We had an SR-71 on display at the EDW Open House and it was dripping
fuel, sitting out in the hot sun. Some guy from the Air Force saw
that and got excited. He'd called the Fire Department, even. He had
a hard time believing us when we told him it wasn't a hazard and that
we didn't need the Fire Department at all. I'm not sure he really
believed it until the Fire Chief confirmed it, in fact. I can't blame
him, but it was kind of funny.
Rand Simberg
Shafer <mil...@qnet.com> made the phosphor on my monitor glow in such
a way as to indicate that:
>We had an SR-71 on display at the EDW Open House and it was dripping
>fuel, sitting out in the hot sun. Some guy from the Air Force saw
>that and got excited. He'd called the Fire Department, even. He had
>a hard time believing us when we told him it wasn't a hazard and that
>we didn't need the Fire Department at all. I'm not sure he really
>believed it until the Fire Chief confirmed it, in fact. I can't blame
>him, but it was kind of funny.
I've been told that the SOP among SR-71ers was to make sure that there
were puddles before taking taxiing. If there weren't, you had
forgetten to tank up.
Uncle Al
Thanks for the technical readout. The civilian literature is
marginalized for reasons good and proper.
Mark Fergerson
> On Thu, 06 May 2004 19:08:27 -0700, Uncle Al <Uncl...@hate.spam.net>
> wrote:
>
>
>>Look at the SR-71 Blackbird's engine intakes. Those big cones
>>occluding the apertures provided 64% of the plane's full-throttle
>>thrust ("Skunk Works," Ben Rich).
>
>
> Er, not exactly. The compression from the inlets (not just the
> spikes) produces subsequent expansion which produces thrust, but only
> when the rest of the engine is working and the airplane is moving. If
> the airplane is sitting still on the ground, the engines can still
> make thrust but the inlets can't.
They can't get full throttle _at cruise altitude_ thrust
on the ground. Getting the thing to take off without JATO or
RATO was a major accomplishment. Those afterburners aren't
for show.
>>> I was thinking then about ways you could get surrounding air that is
>>>at the speed of the craft. It occurred to me possibly you could use
>>>the boundary layer. This is the layer of air that sticks to the
>>>aircraft as it flies so is moving along with the craft at the same
>>>speed.
>>
>>[snip]
>>
>>Do you have any Fermi idea how much air the engine will be
>>inhaling/second? Each SR-71 engine inlet at Mach 3 inhaled 100,000
>>ft^3/sec of air. How thick is your boundary area? What is its area?
>
>
> The boundary layer is up to a foot thick, maybe thicker, and it's the
> size of the vehicle, less any areas of turbulent flow. For example,
> the boundary layer on the upper surface of the wing of a Mach 2
> fighter is over two inches thick at low altitudes.
>
> Actually you want to take in still air for the maximum delta in
> energy, so that the inlet can extract as much as possible. That means
> your inlet needs to see the free stream, not the boundary layer.
> You'll notice that the SR-71 inlets are well in front of the leading
> edge of the wing, although they are behind the bow shock (but you have
> to keep the bow shock off the wing or you get shock impingement and
> localized heating).
That's why the OP needs to look into Aerospike designs,
where the concept of "boundary layer" becomes interesting.
> Even old-fashioned aircraft like the F-4 didn't use the boundary
> layer. If you look at one, you'll see that the inlet is separated
> from the fuselage and there's a boundary layer splitter plate there.
Most of its descendants do too.
Mark L. Fergerson
Bill Vajk
snip
> Even old-fashioned aircraft like the F-4 didn't use the boundary
> layer.
The reports I read about a captured Egyptian MIG in the
late 1960's had some timeframe relevant interesting
revelations regarding boundary layer issues in the
engine ducting. It started a major rethink of the
way we subsequently did business.
johnhare
"Uncle Al" <Uncl...@hate.spam.net> wrote in message
news:409BB46C...@hate.spam.net...
> Mary Shafer wrote:
> > Even old-fashioned aircraft like the F-4 didn't use the boundary
> > layer. If you look at one, you'll see that the inlet is separated
> > from the fuselage and there's a boundary layer splitter plate there.
>
> Thanks for the technical readout. The civilian literature is
> marginalized for reasons good and proper.
>
> --
J. Seddon and E.L. Goldsmith
Richard Henry
"Mary Shafer" <mil...@qnet.com> wrote in message
news:5fan90t1avr5tnovp...@4ax.com...
Which moves in and out depending on Mach no. and has many small holes
drilled in it to reduce turbulence. Airframe mechanics were forbidden to
paint the drilled area.
jeff findley
>
> Mary Shafer wrote:
> >
> > The boundary layer is up to a foot thick, maybe thicker, and it's the
> > size of the vehicle, less any areas of turbulent flow. For example,
> > the boundary layer on the upper surface of the wing of a Mach 2
> > fighter is over two inches thick at low altitudes.
> >
> > Actually you want to take in still air for the maximum delta in
> > energy, so that the inlet can extract as much as possible. That means
> > your inlet needs to see the free stream, not the boundary layer.
> > You'll notice that the SR-71 inlets are well in front of the leading
> > edge of the wing, although they are behind the bow shock (but you have
> > to keep the bow shock off the wing or you get shock impingement and
> > localized heating).
> >
> > Even old-fashioned aircraft like the F-4 didn't use the boundary
> > layer. If you look at one, you'll see that the inlet is separated
> > from the fuselage and there's a boundary layer splitter plate there.
>
> Thanks for the technical readout. The civilian literature is
> marginalized for reasons good and proper.
Mary hasn't posted anything here that you couldn't figure out by
hiring an aerospace engineer with a major in aerodynamics. I don't
have a major or minor in aerodynamics, but the few classes I took
included figuring out the angle of a bow shock at a certain Mach
number. From this data and the top view of a drawing of an SR-71, you
could figure out how fast an SR-71 could go before the bow shock hit
the engines.
Here is a web site with that three view drawings:
http://www.dfrc.nasa.gov/Gallery/Graphics/SR-71/
Same thing with boundary layer thickness. It's a simple thing to
calculate. The thing that's hard is to figure out where the flow goes
turbulent.
I really don't think Mary is giving away any secrets here. She
probably can't tell anyone the absolute top speed of an SR-71, but
that's not stopping anyone here from running the numbers and coming up
with a good estimate. The web site I mentioned only gives the Mach 3+
answer. ;-)
Jeff
--
Remove "no" and "spam" from email address to reply.
If it says "This is not spam!", it's surely a lie.
Jake McGuire
> Burning hydrogen barely pulls it off. Hydrocarbons don't have the
> kinetics. One supposes 1,2-dinitroethylene or trimethylaluminum might
> be interesting if low-efficiency fuels.
I think your information on hydrocarbon combustion is out of date.
The Air Force and some of its contractors claim to have run
hydrocarbon-fuelled scramjets in wind tunnels; plenty of press
releases are out there online. It's possible that the press releases
are deceptive, and it's possible that they won't have competitive
performance in the first or second generation, but it looks like at a
basic level, they work.
http://www.afrlhorizons.com/Briefs/Dec01/PR0102.html
... and plenty of others if you search appropriately.
-jake
Mary Shafer
wrote:
> Mary hasn't posted anything here that you couldn't figure out by
> hiring an aerospace engineer with a major in aerodynamics. I don't
> have a major or minor in aerodynamics, but the few classes I took
> included figuring out the angle of a bow shock at a certain Mach
> number. From this data and the top view of a drawing of an SR-71, you
> could figure out how fast an SR-71 could go before the bow shock hit
> the engines.
It's really quite simple once you decide what the bow shock is doing
on that ogival nose.
> Here is a web site with that three view drawings:
>
> http://www.dfrc.nasa.gov/Gallery/Graphics/SR-71/
>
> Same thing with boundary layer thickness. It's a simple thing to
> calculate. The thing that's hard is to figure out where the flow goes
> turbulent.
>
> I really don't think Mary is giving away any secrets here.
Mary can't. She doesn't know any about the SR-71, having only come
onto the program at Dryden, which started after it was declassified.
> She
> probably can't tell anyone the absolute top speed of an SR-71, but
> that's not stopping anyone here from running the numbers and coming up
> with a good estimate. The web site I mentioned only gives the Mach 3+
> answer. ;-)
Sure she can. It's Mach 3.5. Dave Lednicer worked it out a few years
ago. Any faster and the bow shock starts burning holes in the leading
edge of the outboard wings.
That's a cruise maximum. It's possible to do a very quick dash to
such a speed, but it can't be sustained. It is said (meaning I've
heard this and read this but am not guaranteeing it's true) that a
Blackbird did a dash to Mach 3.5 during the initial testing.
Greg D. Moore (Strider)
"jeff findley" <jeff.f...@sdrc.com> wrote in message
news:yz9brl0...@sgipd572.net.plm.eds.com...
> Uncle Al <Uncl...@hate.spam.net> writes:
> Mary hasn't posted anything here that you couldn't figure out by
> hiring an aerospace engineer with a major in aerodynamics. I don't
> have a major or minor in aerodynamics, but the few classes I took
> included figuring out the angle of a bow shock at a certain Mach
> number. From this data and the top view of a drawing of an SR-71, you
> could figure out how fast an SR-71 could go before the bow shock hit
> the engines.
Ayup, years ago amidst a debate I saw someone do a detailed analysis of the
top speed of an SR-71 just based on known data (i.e. size, shape, engine
location) and concluded that the bow shock would be a problem before I think
it was Mach 4. Of course the folks claiming it could do Mach 4+, etc didn't
want to let this get in the way of their beliefs.
Uncle Al
DONT ATTRIBUTE THAT STATEMENT TO UNCLE AL! It is libel as stated.
The puke who ran the thread doesn't know how to use his newsreader.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!
Eric Pederson
One key element in this article is that the fuel, JP7, is used to cool the
structure and is with this additional heat is broken down into simpler
molecules. IIRC Steam + CH4 is how most of the H2 used today is produced.
It is this mix of hot H2, CH4, etc. that goes into the engine. It is
likely that the H2's and maybe the CH4's are the only things with time
to react in the motor.
Ed Ruf
<"Zeric.a.pedersonZ"@ZboeingZ.comZ deZ to respond> wrote:
>One key element in this article is that the fuel, JP7, is used to cool the
>structure and is with this additional heat is broken down into simpler
>molecules. IIRC Steam + CH4 is how most of the H2 used today is produced.
>It is this mix of hot H2, CH4, etc. that goes into the engine. It is
>likely that the H2's and maybe the CH4's are the only things with time
>to react in the motor.
The JP-7 is not broken down this far, especially at the low end speeds of
Mach 3.5-4. In fact at the fuel temps associated with thermally balancing
the fuel cooled structure at these flight Mach numbers very little, if any,
cracking of the fuel may occur. A gaseous simulant that has been used for
higher Mach number tests is ethylene, not methane.
________________________________________________________
Ed Ruf Lifetime AMA# 344007 (Use...@EdwardG.Ruf.com)
http://EdwardGRuf.com
Henry Spencer
Richard Henry <rph...@home.com> wrote:
>> Even old-fashioned aircraft like the F-4 didn't use the boundary
>> layer. If you look at one, you'll see that the inlet is separated
>> from the fuselage and there's a boundary layer splitter plate there.
>
>Which moves in and out depending on Mach no. and has many small holes
If memory serves -- references aren't handy -- the holes are actually for
a second level of boundary-layer removal. The splitter plate diverts the
fuselage boundary layer around the intake, and the holes have suction
applied to suck the *plate*'s boundary layer in so it doesn't make trouble
either. (Which could be considered turbulence reduction, sort of.)
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. | he...@spsystems.net
Henry Spencer
Uncle Al <Uncl...@hate.spam.net> wrote:
>> Even old-fashioned aircraft like the F-4 didn't use the boundary
>> layer. If you look at one, you'll see that the inlet is separated
>> from the fuselage and there's a boundary layer splitter plate there.
>
>Thanks for the technical readout. The civilian literature is
>marginalized for reasons good and proper.
As others have noted, the civilian literature is all over these topics,
and has been for many years. Boundary-layer removal, in particular, is
such a glaringly obvious feature of most fuselage-mounted air intakes that
nobody would think there was anything secret about it. (Sneaky ways to do
it, maybe, but not the basic concept and requirement.)
Robert Clark
The idea of using the boundary layer for the oxidizer is similar to
the way insects breathe, which is through their skin. I thought
perhaps it could be for the same reason: opening up their mouths to
breathe while in flight could also result in a great increase in drag.
But of course insects don't fly at supersonic speeds.
However, for the very small insects the air is very viscous. Then the
problem of drag for them is analogous to that of a aircraft flying at
supersonic or hypersonic speed. It is frequently said that insects
couldn't get very big because they use this inefficient breathing
system. It might actually be the reverse: they use this breathing
system because they are so small.
An intriguing hypothesis but there is a problem with it. Amphibians
such as frogs also breathe through their skin. They are not really
small and they don't have to fly. Frogs however do have to swim
through the water. They breathe through their skin even underwater
using the oxygen that diffuses into the water from the atmosphere.
Underwater however the frog is a very unhydrodynamically sculpted
creature. You would have an analogous drag problem if they had to open
that huge maw to breathe.
An additional factor that may be at work is illuminated by this fact:
have you noticed how hard it is to breathe with a high wind in your
face? This may be also have contributed to the insects use of a skin
breathing system. But what of birds? They don't breathe through their
skin. They have a special breathing system they may have especially
evolved to deal with this problem:
Is There More to Bird Flight than Meets the Eye?
http://home1.gte.net/impekabl/Birdflight.html
Bob Clark
rgrego...@yahoo.com (Robert Clark) wrote in message news:<832ea96d.04050...@posting.google.com>...
Brian Whatcott
>Mary hasn't posted anything here that you couldn't figure out by
>hiring an aerospace engineer with a major in aerodynamics. I don't
>have a major or minor in aerodynamics, but the few classes I took
>included figuring out the angle of a bow shock at a certain Mach
>number. From this data and the top view of a drawing of an SR-71, you
>could figure out how fast an SR-71 could go before the bow shock hit
>the engines
>Jeff
I imagine Jeff is alluding to the Mach 7 number for the leaky SR71,
that is available for you to read on the net (with or without an aero
degree)
Brian W
jeff findley
> Sure she can. It's Mach 3.5. Dave Lednicer worked it out a few years
> ago. Any faster and the bow shock starts burning holes in the leading
> edge of the outboard wings.
>
> That's a cruise maximum. It's possible to do a very quick dash to
> such a speed, but it can't be sustained. It is said (meaning I've
> heard this and read this but am not guaranteeing it's true) that a
> Blackbird did a dash to Mach 3.5 during the initial testing.
This is about as "official" as anything I've seen about the
Blackbird's top speed. That is to say, a top speed based on analysis
and hearsay. But coming from you, that's about the best hearsay one
can get about high speed aircraft. ;-)
I'm wondering if we'll ever get an "Official" top speed for the
Blackbird to place in the history books. The "Official" top speed
still seems to be "Mach 3+", as is seen on the web site I mentioned
earlier in this thread.
jeff findley
> I imagine Jeff is alluding to the Mach 7 number for the leaky SR71,
> that is available for you to read on the net (with or without an aero
> degree)
Not at all. I'm referring to the Mach 3.5 number Mary posted. You
can argue a bit about the tenths of a Mach, but certainly the SR-71
runs into trouble before Mach 4. Mach 7 is unthinkable.
Mary Shafer
wrote:
> Mary Shafer <mil...@qnet.com> writes:
> > Sure she can. It's Mach 3.5. Dave Lednicer worked it out a few years
> > ago. Any faster and the bow shock starts burning holes in the leading
> > edge of the outboard wings.
> >
> > That's a cruise maximum. It's possible to do a very quick dash to
> > such a speed, but it can't be sustained. It is said (meaning I've
> > heard this and read this but am not guaranteeing it's true) that a
> > Blackbird did a dash to Mach 3.5 during the initial testing.
>
> This is about as "official" as anything I've seen about the
> Blackbird's top speed. That is to say, a top speed based on analysis
> and hearsay. But coming from you, that's about the best hearsay one
> can get about high speed aircraft. ;-)
>
> I'm wondering if we'll ever get an "Official" top speed for the
> Blackbird to place in the history books. The "Official" top speed
> still seems to be "Mach 3+", as is seen on the web site I mentioned
> earlier in this thread.
No, we can do better. Officially, the USAF flew at a maximum cruise
speed of Mach 3.2. With the squadron commander's permission, max
cruise could be at Mach 3.3. It says so in the Dash 1.
There's also a NASA press release, somewhere, referring to the SR-71
flying at Mach 3.23. That's also official.
And the official speed record set flying from Los Angeles to
Washington is, indeed, official, too.
Now, let's go back and clear something up. The maximum speed isn't
actually set by the configuration (that's just an obvious way to
calculate a maximum Mach without any inside information) but by the
compressor face inlet temperature, CFIT. When the air is slowed down
in the inlet it heats (conservation of energy). The faster it, and
the aircraft, are going, the more it heats. However, the engine has
temperature limits that cannot be exceeded. The temperature at the
front of the engine, the compressor face, must be no higher than 427
degC.
Henry Spencer
jeff findley <jeff.f...@sdrc.com> wrote:
>I'm wondering if we'll ever get an "Official" top speed for the
>Blackbird to place in the history books. The "Official" top speed
>still seems to be "Mach 3+", as is seen on the web site I mentioned
>earlier in this thread.
Of note is <http://www.blackbirds.net/sr71/>, especially its "Blackbird
Myths & Facts" page, <http://www.blackbirds.net/bbirdm&f.html>, which says
that Mach 3.2 is normal maximum, 3.3 is allowed with caution, and 3.5 is
the highest known to have been achieved.
Bear in mind that for a limited-production kludge like the Blackbird,
there may not *be* an official top speed in the sense of "this is the best
the aircraft could ever do", because quite possibly nobody ever had reason
to figure out what that is.
Len
> In article <yz93c68...@sgipd572.net.plm.eds.com>,
> jeff findley <jeff.f...@sdrc.com> wrote:
> >I'm wondering if we'll ever get an "Official" top speed for the
> >Blackbird to place in the history books. The "Official" top speed
> >still seems to be "Mach 3+", as is seen on the web site I mentioned
> >earlier in this thread.
>
> Of note is <http://www.blackbirds.net/sr71/>, especially its "Blackbird
> Myths & Facts" page, <http://www.blackbirds.net/bbirdm&f.html>, which says
> that Mach 3.2 is normal maximum, 3.3 is allowed with caution, and 3.5 is
> the highest known to have been achieved.
>
> Bear in mind that for a limited-production kludge like the Blackbird,
> there may not *be* an official top speed in the sense of "this is the best
> the aircraft could ever do", because quite possibly nobody ever had reason
> to figure out what that is.
Like the mach 8 version of the X-15: designed, built,
but to the best of my knowledge, never flown.
Best regards,
Len (Cormier)
PanAero, Inc.
x...@tour2space.com (change x to len)
http://www.tour2space.com
Robert Clark
intakes. These studies look at still using intakes but partially
burying them in the body/wings to take in the boundary layer air. They
note this results in reduced drag. The reduction in air compression is
overmatched by the drag reduction:
Blended Wing Body Systems Studies:
Boundary Layer Ingestion Inlets With Active Flow Control
http://techreports.larc.nasa.gov/ltrs/PDF/2003/cr/NASA-2003-cr212670.pdf
This report has a nice discussion of the drag induced simply by the
engine intakes, aptly called *ram drag*, and how this subtracts from
the thrust produced by the engines. The purpose of the "boundary layer
ingestion" as it is called is to reduce this ram drag.
The "ram drag" is even more extreme at the speeds at which ram jets
and scram jets operate and so you might want to take in even more
boundary layer air in these cases.
The report also discusses for a low speed commercial transport an
aircraft shape called the "blended wing body". This might be the type
of shape you would want for a hypersonic transport if the air is taken
from the boundary layer over the wings to increase the wing area.
However, following the example in this report it may work simply to
have engine intakes depressed into the body to use large amounts of
boundary layer air.
Bob Clark
Mary Shafer <mil...@qnet.com> wrote in message news:<5fan90t1avr5tnovp...@4ax.com>...
Robert Clark
> The boundary layer is up to a foot thick, maybe thicker, and it's the
> size of the vehicle, less any areas of turbulent flow. For example,
> the boundary layer on the upper surface of the wing of a Mach 2
> fighter is over two inches thick at low altitudes.
>
> Actually you want to take in still air for the maximum delta in
> energy, so that the inlet can extract as much as possible. That means
> your inlet needs to see the free stream, not the boundary layer.
> You'll notice that the SR-71 inlets are well in front of the leading
> edge of the wing, although they are behind the bow shock (but you have
> to keep the bow shock off the wing or you get shock impingement and
> localized heating).
>
>
> Mary
I was wondering about using high-bypass commercial jet engines such
as the
GE90 where most of the thrust comes from the bypass air anyway. Also,
for such engines most of the compression for combustion comes from the
engine turbines. However, how would such subsonic engines as the GE90
work at hypersonic speeds? Keep in mind I'm not thinking of having
these engines exposed in the hypersonic air stream. I want them to be
completely enclosed in the aircraft with the required oxygen being
delivered to them from the boundary layer suction devices.
For such engines most of the compression for combustion comes from
the engine turbines. But most of the air is only minimally compressed,
being sent directly out the back to produce thrust. The portion of air
that is highly compressed for the most part is used for combustion to
drive the turbines. Only ~10% of the thrust is produced by the jet
exhaust in such high bypass engines.
This NASA web article seems to suggest the exit velocity should
exceed the air stream velocity:
General Thrust Equation
"Looking at the thrust equation very carefully, we see that there are
two possible ways to produce high thrust. One way is to make the
engine airflow rate (m dot) as high as possible. As long as the exit
velocity is greater than the free stream, entrance velocity, a high
engine airflow will produce high thrust. This is the design theory
behind propeller aircraft and high-bypass turbofan engines. A large
amount of air is processed each second, but the air velocity is not
changed very much. The other way to produce high thrust is to make the
exit velocity very much greater than the incoming velocity. This is
the design theory behind pure turbojets and turbojets with
afterburners. A moderate amount of airflow is accelerated to a high
velocity in these engines. If the exit velocity becomes very high,
there are other physical processes which become important and affect
the efficiency of the engine."
http://www.grc.nasa.gov/WWW/K-12/airplane/thrsteq.html
But this is due to the ram drag term in the thrust equation isn't it?
With the engines completely enclosed, the situation would be more like
the rocket version of the thrust equation where the ram drag term
disappears. Note that with scramjet engines, the net thrust may only
be as much as 10% of the gross thrust produced by the engines because
of this ram drag term.
I've also seen in other sources that you need low bypass engines and
high velocity thrust at supersonic speeds, but is this largely a
consequence of those engines sucking in air at supersonic speeds? It
seems to me by Newton's 3rd law, low velocity thrust will propel the
craft forward even at hypersonic speeds when that thrust is of
sufficient magnitude as with the GE90 (127,00 lbs. thrust max.),
keeping in mind there is no ram drag term in the scenario I'm
suggesting.
Another possibility would be to use rocket engines such as the shuttle
main engines, with the air taken on board being liquified to use for
the liquid oxygen oxidizer. This is the plan for the Skylon SSTO,
which however still uses standard jet intakes prior to switching to
rockets.
I'm envisioning using the boundary layer suction at the hypersonic
speeds while delivering the oxygen to these rocket engines. This would
have the benefit of eliminating the ram drag term as with rockets
while at the same time having the benefit of not having to carry the
oxidizer on board as with jets.
Bob Clark
johnhare
"Robert Clark" <rgrego...@yahoo.com> wrote in message
news:832ea96d.04051...@posting.google.com...
> There are studies that use boundary layer air for the jet engine
> intakes. These studies look at still using intakes but partially
> burying them in the body/wings to take in the boundary layer air. They
> note this results in reduced drag. The reduction in air compression is
> overmatched by the drag reduction:
>
control to do that. Without the BLI, fuel consumption increased.
> Blended Wing Body Systems Studies:
> Boundary Layer Ingestion Inlets With Active Flow Control
> http://techreports.larc.nasa.gov/ltrs/PDF/2003/cr/NASA-2003-cr212670.pdf
>
I skimmed it. It resembles a lot of papers in that it reaches positive
conclusions
partially by way of assuming several other technologies work in their
favor, though these same support technologies are somehow unavailable
to the standard system. You notice the 42% figure requires changing the
airframe system and adding an effective BLI system, with all supporting
assumptions favorable only to the proposed system.
Other than that, they were having to work to assume a 5% improvement.
> This report has a nice discussion of the drag induced simply by the
> engine intakes, aptly called *ram drag*, and how this subtracts from
> the thrust produced by the engines. The purpose of the "boundary layer
> ingestion" as it is called is to reduce this ram drag.
> The "ram drag" is even more extreme at the speeds at which ram jets
> and scram jets operate and so you might want to take in even more
> boundary layer air in these cases.
>
At ramjet speeds, the intakes provide a compression ratio of ~3 to over
100 to make the cycle work. The boundary layer injestion would not
have sufficient pressure ratio to make the cycle work at those speeds.
Ramjets by definition require ram pressure. This is a very different
animal than the subsonic BWB under discussion in the paper you
referenced.
> The report also discusses for a low speed commercial transport an
> aircraft shape called the "blended wing body". This might be the type
> of shape you would want for a hypersonic transport if the air is taken
> from the boundary layer over the wings to increase the wing area.
> However, following the example in this report it may work simply to
> have engine intakes depressed into the body to use large amounts of
> boundary layer air.
>
Boundary layer injestion is not always bad. For the pure subsonic climb
out of a space ship, the the lighter dry weight and cleaner lines during
the real burn become much more important.
>
> Bob Clark
>
Interesting reference you mentioned. May I suggest you take a bit harder
look at what supersonic intakes are actually required to do? They are
fairly sophisticated bits of hardware for good technical reasons. They
can certainly be improved on. You just might be able to find some on your
own that are better than the ones you read about.
Robert Clark
the fact that they don't have to carry oxidizer.
There is also the problem with air breathers that using scramjets you
still have to carry a rocket for the final step to orbital velocity.
However, this is due to the drag penality that the ram drag term
induces on jet intakes, especially at supersonic and hypersonic
speeds. With boundary layer suction this ram drag term is greatly
reduced and perhaps eliminated. In fact the originally intended
purpose of boundary layer suction was to *reduce* drag, which has been
confirmed experimentally.
You also might be able to use rocket engines as with the Skylon
project with the liquid oxygen oxidizer taken from the air after being
liquified onboard.
There are several approaches to dealing with heating. One is
transpiration cooling which sends a gas or liquid over the wings to
cool them. In fact the method of sending a gas over the wings is
another form of boundary layer control which is known to reduce drag.
However, this method of cooling might not work when you're using
boundary layer suction at the same time.
There are some thermal protection systems now available that use high
temperature materials, for example ultra-high temperature ceramic
tiles which are stable up to perhaps 3600 F and metallic tiles stable
up to 2000 F. Remember the broad surfaces of the wings are not where
the greatest heating occurs, as confirmed by the shuttle. The greatest
heating occurs on the nose cone and on the wing leading edges. On the
broad areas where the boundary layer suction would occur, you could
use the lower temperature materials. These temperatures would be far
less than the temperatures experienced inside scramjet engines.
This proposed SSTO study suggests using currently available high
temperature materials:
Hyperion: an SSTO vision vehicle concept utilizing rocket-based
combined cycle propulsion.
http://www.ssdl.gatech.edu/main/ssdl_paper_archive/aiaa_99-4944.pdf
Bob Clark
"johnhare" <john...@tampabay.rr.com> wrote in message news:<fLBmc.6750$2f6.2...@twister.tampabay.rr.com>...
> "Robert Clark" <rgrego...@yahoo.com> wrote in message
> news:832ea96d.04050...@posting.google.com...
> > I've read that the main problem from using the surrounding air as
> > oxidizer at hypersonic speeds is the drag involved. There is
> > apparently a maximum speed that "air breathers" according to this
> > constraint can achieve: less than orbital velocity. The air hitting
> > the intakes at hypersonic speeds causes a tremendous amount of drag:
> >
> The main problem with air breathing accelerator vehicles is the weight.
> The mass of the ABE* system is far in excess of the rocket engines
> required to get the same performance. This weight is dead mass for
> most of the acceleration profile of any rational spacecraft.
>
> The second most serious problem with fast ABEs is thermal. At
> anything Mach 3 and above, serious effort must be put into keeping
> the vehicle temperature down. spending many minutes in the Mach
> 3-7 range guarantees a major TPS requirement for any vehicle.
>
> The specific problems with sucking the boundary layer in are
> that this is the hottest air available at any Mach number, which
> leads to serious engine thermal problems. The air has not been
> compressed by an intake, which means that the air at the engine
> face is 2 to 50 times less dense than it could be, which translates
> directly in engine thrust 2 to 50 times less than with an efficient
> intake. And that the thermal cycle is narrow with less temperature
> differential available to drive the turbine cycle.
>
> If you are refering to a ram cycle, then the lack of intake compression
> makes the engine nonfunctional with no pressure differential available
> through the nozzle.
>
>
> *ABE=air breathing engine
Robert Clark
> ...
>
> The boundary layer is up to a foot thick, maybe thicker, and it's the
> size of the vehicle, less any areas of turbulent flow. For example,
> the boundary layer on the upper surface of the wing of a Mach 2
> fighter is over two inches thick at low altitudes.
>
This report gives some of the data for the F-16XL supersonic boundary
layer control experiment:
SUMMARY OF TRANSITION RESULTS FROM THE F-16XL-2
SUPERSONIC LAMINAR FLOW CONTROL EXPERIMENT
http://www.dfrc.nasa.gov/DTRS/2000/PDF/H-2410.pdf
Figs. 9 and 11 give the mass flow from the suction system in
proportion to the mass flow of the free stream. I'm trying to
determine how much this suction is in absolute terms.
The data gives the proportion C_q = - m/(r*U) , where m is the mass
flow of suction per unit area, r is the density of the free stream
air, and U is the velocity of the free stream air, see terms defined
on page 1.
Judging by the bar graphs in Figs. 9 and 11, this ratio C_q is about
1/10,000 for the broad areas of the wing (the ratio increases to
1/1000 on the leading edge.) So to determine how much air can be
sucked in by this system, I need to calculate this product r*U then
multiply by 1/10,000 for most of the wing.
U is just the air speed, about Mach 2. But how to calculate r, the
density? The altitude is given in the report as 16.8 km. But since the
air stream is moving supersonically with respect to the aircraft, the
density shouldn't be just the same as the static density at this
altitude. So how do you calculate it?
Bob Clark
Robert Clark
large mass of oxygen to combust with the fuel. For example if you used
the same mass of liquid oxygen, which is quite cold, would you get
the same amount of thrust with a turbojet engine?
For ramjets you get even greater compressions and heating of the air,
but you also need to generate high thrust to overcome the ram drag due
to the high speed. Would you get the same thrust using the cold liquid
oxygen of the same mass?
The same question for scramjets.
Bob Clark
"johnhare" <john...@tampabay.rr.com> wrote in message news:<rszqc.37441$2f6.1...@twister.tampabay.rr.com>...
johnhare
> I wonder if the compressions used in jet engines are just to get a
> large mass of oxygen to combust with the fuel. For example if you used
> the same mass of liquid oxygen, which is quite cold, would you get
> the same amount of thrust with a turbojet engine?
> For ramjets you get even greater compressions and heating of the air,
> but you also need to generate high thrust to overcome the ram drag due
> to the high speed. Would you get the same thrust using the cold liquid
> oxygen of the same mass?
> The same question for scramjets.
>
>
> Bob Clark
If you are going to use liquid oxygen, then you have a rocket engine
and can do your accelerating outside the atmosphere. ABEs must
provide some improvement to a space launch vehicle in order to
justify incorporating them. The more contortions you go through
to make them work, the less likely they are to be worthwhile.
From a pure performance standpoint, you will be better off
comparing the dry mass of various configurations than the gross
mass. On an SSTO in particular, the extra engines, instalation
weight, and thermal management mass during ABE acceleration
must be carried all the way to orbit and back. Doing this to save
$100.00 a ton liquid oxygen is usually a poor trade.
Scramjets, even if successfully developed, are useless for space
transports. Complicated airframe, engine, and thermal cycles
vs normal rocket engines and symetrical tanks and a bit more fuel.
Any researcher getting paid to study scramjets for space transport
should be at least suspected of fraud. What you do on your own
dime is your own business of course.
Richard Henry
> I wonder if the compressions used in jet engines are just to get a
> large mass of oxygen to combust with the fuel. For example if you used
> the same mass of liquid oxygen, which is quite cold, would you get
> the same amount of thrust with a turbojet engine?
> For ramjets you get even greater compressions and heating of the air,
> but you also need to generate high thrust to overcome the ram drag due
> to the high speed. Would you get the same thrust using the cold liquid
> oxygen of the same mass?
> The same question for scramjets.
If you are mixing fuel and oxidizer, both contained in the vehicle, then you
have a rocket, not an air-breathing craft.
Henry Spencer
Robert Clark <rgrego...@yahoo.com> wrote:
> This NASA web article seems to suggest the exit velocity should
> But this is due to the ram drag term in the thrust equation isn't it?
Yes, but you haven't escaped from that term. To run subsonic engines, the
air must enter them at subsonic speed. Decelerating that air to those
speeds *by any means whatsoever* incurs ram drag. Taking the air from the
boundary layer doesn't magically avoid this. You've still got X kg/s of
air whose velocity relative to the vehicle is being reduced by Y m/s
before it enters your engines, and that necessarily and inevitably
transfers X*Y kg*m/s^2 of momentum *somewhere*, almost certainly to the
vehicle.
(It also unloads rather a lot of kinetic energy, some of which will go
into making that air very hot, something turbofan engines do not like.)
>With the engines completely enclosed, the situation would be more like
>the rocket version of the thrust equation where the ram drag term
>disappears.
If the engines were *completely* enclosed, they wouldn't be getting any
air to run on. The air has to come from somewhere. If it's not coming
out of on-board tanks, it has to be acquired from the fast-moving ambient
air. That means its momentum has to go somewhere; you don't get to just
wish it away. This is fundamental, and independent of exactly how the
intake system works.
Robert Clark
relative speed as the free stream air. It has close to zero relative
velocity with respect to the aircraft, depending on how close to the
aircraft surface it is. You'll note the ram drag term is dependent on
this relative velocity. So if the relative velocity for this air is
zero, the ram drag term due to this air will be zero.
This is illuminated by the report I cited:
Blended Wing Body Systems Studies:
Boundary Layer Ingestion Inlets With Active Flow Control
http://techreports.larc.nasa.gov/ltrs/PDF/2003/cr/NASA-2003-cr212670.pdf
On pages 14, 15, according to the PDF file page numbering it says:
"When an engine is buried into the airplane fuselage with BLI inlets,
it will
ingest a portion of the lower energy boundary layer air. Figure 1.4
shows the
velocity profile differences between a conventional freestream mounted
engine and an engine inlet positioned close to the fuselage. The
Boundary Layer Ingestion (BLI) inlet consumes a portion of the lower
energy air near the fuselage and a portion of the freestream air."
"From the ram drag equation presented in figure 1.2, it is apparent
that a large ram drag reduction will be experienced by ingesting the
lower velocity boundary air.
However, this ram drag reduction is partially offset by the pressure
recovery loss. As Figure 1.5 shows, the pressure recovery for a BLI
inlet (97.7%) is poorer than a conventional inlet (99.8%). Thus, the
aircraft performance assessment must include the engine performance
degradation that offsets the ram drag reduction from BLI."
This is also illuminated by the report:
SUMMARY OF TRANSITION RESULTS FROM THE F-16XL-2
SUPERSONIC LAMINAR FLOW CONTROL EXPERIMENT
http://www.dfrc.nasa.gov/DTRS/2000/PDF/H-2410.pdf
It confirms experimentally the drag is *reduced* by the boundary
layer suction system used on the F-16XL.
However, studies on suction-type laminar flow control have noted that
the drag can be increased rather than reduced if the holes in the wing
are too large or if the suction used is too large.
That's why I wanted to find out how much suction air can be brought
in by these systems at the optimal rate, so as to compare this to how
much air the engine intakes normally bring in and to how much ram drag
would be eliminated by removing the intakes.
Bob Clark
he...@spsystems.net (Henry Spencer) wrote in message news:<Hxyuu...@spsystems.net>...
johnhare
> The key fact is that the boundary layer air is not moving at the same
> relative speed as the free stream air. It has close to zero relative
> velocity with respect to the aircraft, depending on how close to the
> aircraft surface it is. You'll note the ram drag term is dependent on
> this relative velocity. So if the relative velocity for this air is
> zero, the ram drag term due to this air will be zero.
>
will not slow to near zero velocity relative from mach? without
applying energy to it in the form of ship drag. The question you
seem to be working on is, "Is the added drag from the intake
more trouble than it is worth?".
Supersonic intake drag is only a fraction of the total ship drag.
For us space types, a rocket allows us to accelerate above
the atmospere with effectively zero drag. Flying in the atmosphere
with or without intakes generates drag. The main question
is whether putting up with the drag at all is worthwhile compared
to getting out of the air completely.
For engine effectiveness at mach 1+, a well designed intake is critical.
It can be fairly said that supersonic flight is the story of intake design
if ABEs are used. A example might illustrate the point.
At some point in supersonic flight, the intake will compress the air by
ten times before it reaches the engine. Your boundary layer injestion
does not. If your engine swallows 1,000 cubic feet of air per second,
then at some altitude your boundary layer unit will get about 20 pounds
of air per second to work with. The same engine behind an effective
intake, gets 1,000 cubic feet per second, that has been compressed
from 10,000 cubic feet per second by the intake. The engine behind
the effective intake has ten times the reaction mass to work with per
second. About 200 pounds This would mean ten times the
thrust per engine mass, minus the intake drag, and intake mass.
The numbers should be run anyway of course. The intake might be
a quarter of the total vehicle drag, and mass as much as the engine itself.
So with your boundary layer injestion, you need three quarters
of the thrust to reach the same acceleration, but you would need
over seven of the same engines to achieve this. You end up
with one intake and one engine vs seven engines, clear win
for the intake inclusion.
A second problem with skipping the intake is the reduced pressure
ratio in the exhaust. If the standard engine has a nozzle pressure
ratio of three, then your boundary layer injestion engine will retain
that ratio of three for thrust. The intake plus engine at the same
mach number considered above will have a pressure ratio of
thirty to ambient. Sombody here has the real numbers, but my
first guess is that thrust per unit of air at the higher ratio will be
more than three times that of the lower pressure ratio exhaust.
Depending on the accuracy of the last paragragh, you could
easily require 21 engines injesting boundary layer air to match
1 engine and 1 intake at whatever mach number gives an intake
compression ratio of ten. Even this does not address the issue
of engine number and performance when intake compression
is 3 or 30 at higher and lower mach numbers.
Henry Spencer
Robert Clark <rgrego...@yahoo.com> wrote:
>The key fact is that the boundary layer air is not moving at the same
Yes, because it has been *decelerated* by interaction with the vehicle.
Suppose there's 1kg of boundary-layer air in the vicinity of your intake
system. You suck that 1kg in. *What replaces it?* Answer: air from the
free stream, which has to decelerate as it moves in. The momentum from
that air has to go somewhere; it can't just disappear. Your boundary
layer has become part of your intake system, and drag induced by air
decelerating as it enters the boundary layer is ram drag on your intake
system.
There may, or may not, be somewhat *less* ram drag with this approach; it
may, in some situations, be a more efficient intake. But the drag won't
entirely go away. The air ultimately comes from the free stream, and it
inherently has to lose most of its momentum somehow as it's taken in.
Robert Clark
through engine intakes seems about right. The actual amount will
depend on aircraft configuration. For example most forms of hypersonic
craft now considered have minimal wings, consisting mostly of a
lifting body. The suction system would have to be along the entire
body in this case.
I saw an estimate that gave the net thrust (equal to: gross thrust -
ram drag) as only 10% of the gross thrust for scramjets. This is from
a passage in "Spacecraft Dynamics" by William E. Wiesel, McGraw-Hill
1989, pg. 213:
"If very high Mach numbers are to be obtained, the incoming airflow
cannot
be slowed down but must be allowed to proceed through the engine
unhindered. This occurs in the scramjet, or supersonically combusting
ramjet. However, this introduces new problems. Since the airflow
through the engine is supersonic, it does not "know" where the engine
is
located since it cannot communicate with the engine walls by pressure
waves. The injected fuel might burn within the engine or several
hundred meters behind the vehicle. In the later case, of course, it
would produce no thrust.
The dynamics of hypersonic flight are much different from those of
rocket flight. A rocket attains high speeds by exiting the atmosphere
quickly and rotating into a horizontal attitude. This completely
eliminates drag after the first two or three minutes of flight. As
an aerospace plane achieves high speeds, the net thrust (the
difference between the thrust and ram drag terms) becomes relatively
small, probubly only about 10% at Mach 10. This does not leave much
margin for external forces Fext. In particular, there cannot be any
extra drag in Fext, so the aerospace plane must be essentially all
inlet seen from its front. A sudden flameout of the engines would
remove the thrust term, but not the ram drag, and the vehicle would
undergo catastrophic deceleration. Combined with a very severe
heating environment, these problems may make achieving a practical
vehicle quite difficult."
I found this quoted in:
From: Andy Haber (an...@hcxio.hdw.csd.harris.com)
Subject: Re: Air Breathing Spaceplanes?
Newsgroups: sci.space.tech
Date: 1996/08/07
http://groups.google.com/groups?&selm=4uadfj$o...@ns.hcsc.com
The book is from 1989. IF this were still the case then you might be
able to get by with simply eliminating the scramjet intakes, and the
associated ram drag, and using entirely the boundary layer air.
However, some more recent refs. suggest the ram drag is not as bad
with more current designs:
UQ researchers signal major advance in flight efficiency
Monday , 26 March 2001
"Up to 40 percent of the drag in an aircraft like a 747 is due to skin
friction," Professor Stalker said. "This technique could allow smaller
engines to go from A to B using less engine thrust, achieving quite a
saving.
"These economies are extremely important in the hypersonics game where
we're developing models for space craft to operate at earth orbital
speeds. We've found skin friction drag on models in hypersonic
aircraft to be at least half the total drag."
http://www.uq.edu.au/news/index.phtml?article=2160
Since NASA has demonstrated in flight positive acceleration at
scramjet speeds, it couldn't be that the ram drag takes up 90% of the
gross thrust with these later models.
In this case what might work is to have a mixed system with both
scramjet intakes and boundary layer suction. If you reduce the amount
of air taken in by the intakes by say 10% thereby reducing ram drag by
that amount, and if the suction method reduces friction drag by say
5%, you could reduce drag by 15%.
Conceivably this could go into the net thrust for the craft. What I
envision is an engine that would work as a scramjet and a turbojet at
the same time(!) The scramjet intake air would be directed around to
bypass turbines to the rear of the engine to be combusted as with a
scramjet, but the boundary layer air would be directed to the turbines
to produce thrust like a usual turbojet engine. The engines of the
SR-71 operated as both a turbojet and as a ramjet so it is possible to
have such combined cycle engine. What would be novel is that both
modes would be operating at the same time.
Bob Clark
"johnhare" <john...@tampabay.rr.com> wrote in message news:<SE%qc.9$0X2....@twister.tampabay.rr.com>...
johnhare
rather than discuss.
"Robert Clark" <rgrego...@yahoo.com> wrote in message
news:832ea96d.04052...@posting.google.com...
> Your estimate of 20lbs. of boundary layer air compared to 200 lbs.
> through engine intakes seems about right. The actual amount will
> depend on aircraft configuration. For example most forms of hypersonic
> craft now considered have minimal wings, consisting mostly of a
> lifting body. The suction system would have to be along the entire
> body in this case.
I am willing to discuss supersonic posibilities. Hypersonic is something
I won't discuss, as I have no polite words for any advocate of such.
You have not addressed the issue of needing more engine.
> I saw an estimate that gave the net thrust (equal to: gross thrust -
> ram drag) as only 10% of the gross thrust for scramjets. This is from
> a passage in "Spacecraft Dynamics" by William E. Wiesel, McGraw-Hill
> 1989, pg. 213:
>
That is understandable, 10 tons of thrust fighting 9 tons of drag, leaving
1 ton of thrust for acceleration. That is why rockets outperform
scramjets in fuel consumption as well as thrust to weight.
Note the last sentences in your quote.
> I found this quoted in:
>
> From: Andy Haber (an...@hcxio.hdw.csd.harris.com)
> Subject: Re: Air Breathing Spaceplanes?
> Newsgroups: sci.space.tech
> Date: 1996/08/07
> http://groups.google.com/groups?&selm=4uadfj$o...@ns.hcsc.com
>
> The book is from 1989. IF this were still the case then you might be
> able to get by with simply eliminating the scramjet intakes, and the
> associated ram drag, and using entirely the boundary layer air.
> However, some more recent refs. suggest the ram drag is not as bad
> with more current designs:
>
> UQ researchers signal major advance in flight efficiency
> Monday , 26 March 2001
> "Up to 40 percent of the drag in an aircraft like a 747 is due to skin
> friction," Professor Stalker said. "This technique could allow smaller
> engines to go from A to B using less engine thrust, achieving quite a
> saving.
A 747 is subsonic. This has nothing to do with your hypersonic
concepts.
> "These economies are extremely important in the hypersonics game where
> we're developing models for space craft to operate at earth orbital
> speeds. We've found skin friction drag on models in hypersonic
> aircraft to be at least half the total drag."
> http://www.uq.edu.au/news/index.phtml?article=2160
I feel the need to repeat that the rocket ship has no drag at the same
velocities, outside the atmosphere.
>
> Since NASA has demonstrated in flight positive acceleration at
> scramjet speeds, it couldn't be that the ram drag takes up 90% of the
> gross thrust with these later models.
Sure it can. They had a whopping 10% of the total thrust for accelerating.
This means that the scamjet would need an Isp of 4,500 just to match
fuel consumption with the hydrogen rocket, or 3,500 for the kerosine
rocket. And consider the difficulty levels, NASA has demonstrated
one time positive acceleration at mach 7 with a scamjet, and not much
of that. This is something thousands of rockets have done with relative
ease. Of course it needed a rocket to get it up to mach 7 in the first
place. BTW, what did that one data point cost them?
> In this case what might work is to have a mixed system with both
> scramjet intakes and boundary layer suction. If you reduce the amount
> of air taken in by the intakes by say 10% thereby reducing ram drag by
> that amount, and if the suction method reduces friction drag by say
> 5%, you could reduce drag by 15%.
What happened to the whole front of the craft being intake already?
There is no intake area available to reduce. Also, you would need
to account for lost thrust.
> Conceivably this could go into the net thrust for the craft. What I
> envision is an engine that would work as a scramjet and a turbojet at
> the same time(!) The scramjet intake air would be directed around to
> bypass turbines to the rear of the engine to be combusted as with a
> scramjet, but the boundary layer air would be directed to the turbines
> to produce thrust like a usual turbojet engine. The engines of the
> SR-71 operated as both a turbojet and as a ramjet so it is possible to
> have such combined cycle engine. What would be novel is that both
> modes would be operating at the same time.
>
Turbojets operate with a temperature differential between the compressor
outlet and the turbine inlet, which is how it expands the air to drive the
system. The boundary layer air at scramjet speeds is already hotter that
the jet can handle. It will melt the compressor. Ramjet dual mode is barely
doable.
May I suggest, "Intake Aerodynamics, Second Edition" by J. Seddon and
E. L. Goldsmith.
One thing that is very important in understanding these various references
is that everybody has an axe to grind, and not all of them are fully honest
in their analysis. Knowing the slant of a given reference is quite usefull
in
weighing it as evidence. My slant is that of an inventor and businessman.
An inventor needs to be able to sort out the bad ideas without throwing
out the good. (My track record is only so so.) A businessman must
make decisions based on whether or not something will make money.
I have apparently invented a new type of air turborocket engine,
usefull subsonic certainly (if it works). Supersonic is very maybe,
dependant on subsonic success, intake performance in cost and mass,
and secondary effects on the ship. Secondaries include extra thermal
loads on the airframe, configuration constrictions, stability effects at
supersonic speeds, and a few other problems that make rockets feel
real attractive above mach 0.8.
Your slant appears to be that you have a concept that you want to push.
You have to be carefull when you push too hard, you might fall off the same
cliff as a poor concept that you're hooked on. And you will miss good
things on the way, like possibly the drag reduction with hydrogen injection.
That info might be usefull.
Robert Clark
>...
That reference should be:
Spaceflight dynamics
William E Wiesel
1989
English Book xii, 323 p. : ill. ; 25 cm.
New York : McGraw-Hill, ; ISBN: 0070701067 :
Bob Clark