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Proposals for air breathing hypersonic craft. II
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Ed Ruf (REPLY to E-MAIL1
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Joined: 03 Dec 2005
Posts: 46

PostPosted: Sun Jun 18, 2006 9:33 pm    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

On 18 Jun 2006 14:10:04 -0700, in sci.engr.mech William.Mook@gmail.com
wrote:

Quote:

Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:

You can't just wave your hands
and extrapolate that to supersonic shear layer mixing.

You're doing that not me. I'm doing something very simple. Eject the
fuel so that it is at rest relative to the air moving around the
vehicle. Then, spread it if need be, and detonate it.

Lets see. I've been part of the group which has flown H2 fueled scramjet
powered vehicles at Mach 7 and 10. Just what have you done?

I've seen and done the homework to accomplish the above. Other than simple
hand waving and saying so and so should work, what exactly have you
actually done?
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)
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William.Mook@gmail.com
science forum addict


Joined: 06 May 2006
Posts: 50

PostPosted: Sun Jun 18, 2006 11:48 pm    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:
Quote:
On 18 Jun 2006 14:10:04 -0700, in sci.engr.mech William.Mook@gmail.com
wrote:


Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:

You can't just wave your hands
and extrapolate that to supersonic shear layer mixing.

You're doing that not me. I'm doing something very simple. Eject the
fuel so that it is at rest relative to the air moving around the
vehicle. Then, spread it if need be, and detonate it.

Lets see. I've been part of the group which has flown H2 fueled scramjet
powered vehicles at Mach 7 and 10. Just what have you done?

lol. Attempting to pull rank so soon? Jesus. You are either a liar
or a fool, but one thing is for certain. You are not being responsive
to the very simple point I am making which assures everyone reading
this you are at core, DISHONEST!

What's my point here? Namely, if you eject a quantity of fuel in a
small bottle with some fireworks from an aircraft so that the bottle is
stationary in the air, and then the fireworks operate to first spread
the fuel and then detonate it, you can produce a shockwave that might
have a propulsive effect.

Obviously others think such a propulsive scheme could be made to work.

http://www.fas.org/irp/mystery/pde.htm

This is a USENET thread with the title Proposals for air breathing
hypersonic craft. CLEARLY this is one proposal that might be made to
work. Why are you so damned focused on discrediting the possibility?


Quote:
I've seen and done the homework to accomplish the above.

Stick to the damn point sir.

If what you say is true then it should be child's play for you to see
what I'm proposing. Why can't you see it? Likely because you're a
damn liar or worse.

Look, I've provided sufficient analysis to be acceptable for any usenet
standard on this topic. Respond to that, don't pull your dick out and
hope everyone looks at that, distracting them from the topic at hand.
Sheez.

Quote:
Other than simple
hand waving and saying so and so should work,

Yep. Handwaving. I admit it. And quite convincing too don't you
think? While you, with all of your supposed superiorty, have provided
absolutely no convincing argument to the contrary. I challenge you to
do it. Prove that one could not toss bottles of fuel out of an
aircraft so that they were stationary in the airstream, and that its
then impossible to spread the fuel and detonate the fuel with attached
fireworks. Or that its impossible to produce propulsive effects from
the resulting shockwaves. Prove any of that. Since you're supposedly
so damn smart.

OH - I noticed you didn't do that. I guess you're not as smart as you
thought you were.

Quote:
what exactly have you
actually done?

Um, stump you obviously.

http://www.fas.org/man/dod-101/sys/dumb/faeanim.gif
http://www.fas.org/man/dod-101/sys/dumb/cbu-72.htm

These things exist, they work, and the technology can obviously be
adapted to the ends I've described. Nothing you have said, or can say,
changes that. Which is why you attempted to pull rank and change the
subject from air breathing hypersonic aircraft to personalities - when
I didn't buy your OBVIOUSLY WRONG references earlier.

Stick to the damn point and keep your small penis out of it! lol.
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redneckj
science forum beginner


Joined: 28 Mar 2005
Posts: 2

PostPosted: Mon Jun 19, 2006 1:02 am    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

"Ed Ruf (REPLY to E-MAIL IN SIG!)" <egruf_usenet2@cox.net> wrote in message
news:1dhb92dm49b2gqvrmpn8gj8o4lp0n6fg5s@4ax.com...
Quote:
On 18 Jun 2006 14:10:04 -0700, in sci.engr.mech William.Mook@gmail.com
wrote:


Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:

You can't just wave your hands
and extrapolate that to supersonic shear layer mixing.

You're doing that not me. I'm doing something very simple. Eject the
fuel so that it is at rest relative to the air moving around the
vehicle. Then, spread it if need be, and detonate it.

Lets see. I've been part of the group which has flown H2 fueled scramjet
powered vehicles at Mach 7 and 10. Just what have you done?

Would it be correct to say that at mach 7, using Mooks concept, you

have well under a millisecond to inject, mix, and detonate the fuel/air
mix? I'm going with 7 feet per millisecond relative velocity of vehicle
to ambient. Btw, I'm against scramjets for acceleration missions.

Quote:
I've seen and done the homework to accomplish the above. Other than simple
hand waving and saying so and so should work, what exactly have you
actually done?
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)
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Robert Clark
science forum Guru Wannabe


Joined: 30 Apr 2005
Posts: 129

PostPosted: Mon Jun 19, 2006 1:18 pm    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

Robert Clark wrote:
Quote:
...

(III.) However, the key problem is how to communicate the thrust of the
combustion, which is taking place in still air, to the craft. The
problem is the fuel is being combusted in still air while the rocket is
moving away at up to 8000 m/s. So even if the combustion products are
moving at 4500 m/s they still can not catch up to the craft to impart
momentum to the vehicle.

...

(a.) First method to communicate thrust to rocket: use the accelerated
fuel to propel a plate rearward to be at the same speed of the fuel/air
mixture and at the front of it. When the fuel air is ignited since the
plate is still with regards to the fuel/air it receives the momentum of
the combustion products moving forwards. You see here it can only
receive a portion of the thrust produced since it does not receive the
momentum of the combustion products moving rearward. At best it could
receive 50% of the thrust produced.
For this to work this "pusher plate" if you will needs to be of a
light material, lighter in fact than the mass of the fuel/air
combusted. Then the momentum imparted to it will give it a velocity
higher than that of the exhaust gases to be a speed at least as high as
the speed of the rocket moving forward. Once it has received the
greatest momentum boost from the expanding combustion gases, it is
allowed to catch to the walls of the rocket or to a stop bumper towards
the front thereby transferring its momentum to the rocket.


This method is analogous to using a gas gun to propel a projectile
forward after the fuel is ignited. Unfortunately, a projectile in a gas
gun can not exceed the velocity of the gas in this scenario:

SHARP.
"No gun projectile can exceed the velocity of the propellant gases in
the barrel. The light gas gun takes advantage of the fact that a lower
molecular weight gas, such as hydrogen, has a higher velocity at a
given temperature than the heavier molecules of conventional gun
propellants."
http://www.astronautix.com/lvs/sharp.htm

So the pusher plate couldn't exceed about 4500 m/s if the gas was
water vapor from hydrogen/oxygen combustion.
However, I found this interesting discussion that suggests theoretical
unsteady expansion can be higher by a factor of 2 than the speed
expected for normal steady combustion:

Gun velocity (Andrew Higgins; Bruce Dunn).
http://yarchive.net/space/exotic/gun_velocity.html

This would be in the range required to match the speed of the rocket
moving forward.

The article suggests though this is rarely reached in practice. Gas
guns are also quite massive to contain the high pressures produced.
This might also make them unsuitable for this purpose.

If however the method of unsteady expansion could be made light
weight, we might also want to use it as the method used for
accelerating the fuel rearward at up to 8000 m/s. This would mean lower
temperatures would be required. I had wondered whether the high
temperatures required for accelerating the fuel, hydrogen say, up 8000
m/s or so would induce the same problems now experienced with scramjets
of sustaining burning at very high temperatures.


Bob Clark
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Ed Ruf (REPLY to E-MAIL1
science forum beginner


Joined: 03 Dec 2005
Posts: 46

PostPosted: Mon Jun 19, 2006 9:32 pm    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

On 19 Jun 2006 06:18:53 -0700, in sci.engr.mech "Robert Clark"
<rgregoryclark@yahoo.com> wrote:


Quote:
If however the method of unsteady expansion could be made light
weight, we might also want to use it as the method used for
accelerating the fuel rearward at up to 8000 m/s. This would mean lower
temperatures would be required. I had wondered whether the high
temperatures required for accelerating the fuel, hydrogen say, up 8000
m/s or so would induce the same problems now experienced with scramjets
of sustaining burning at very high temperatures.

Just what supposed problem are you alluding to here?
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)
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Henry Spencer
science forum beginner


Joined: 04 Jul 2005
Posts: 24

PostPosted: Mon Jun 19, 2006 11:08 pm    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

In article <1150723133.851353.232190@f6g2000cwb.googlegroups.com>,
Robert Clark <rgregoryclark@yahoo.com> wrote:
Quote:
...Unfortunately, a projectile in a gas
gun can not exceed the velocity of the gas...
So the pusher plate couldn't exceed about 4500 m/s if the gas was
water vapor from hydrogen/oxygen combustion.

Careful here, you're confusing two different expansion processes. Guns
and rocket engines are different. Knowing that O2/H2 rocket engines get
gas up to about 4500 m/s maximum tells you nothing about what velocities
O2/H2 guns can reach.

(By the way, quite a bit of the exhaust of an O2/H2 rocket is hydrogen,
not water vapor -- such engines run very fuel-rich. Guns would probably
want to do likewise.)

Quote:
However, I found this interesting discussion that suggests theoretical
unsteady expansion can be higher by a factor of 2 than the speed
expected for normal steady combustion...

Again, you're confusing two different things. Gun projectiles can reach
about 2 times the *initial speed of sound in the gas*, in practice (the
theoretical limit is considerably higher, but that requires an immensely
long frictionless barrel). That has nothing in particular to do with the
gas velocity attained by steady combustion in a rocket engine.

(Rocket exhaust is sonic at the throat, not at the nozzle exit. And for
that matter, the speed of sound at the throat isn't the same as the
initial value in the chamber, because the gas has already expanded and
cooled significantly.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | henry@spsystems.net
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Robert Clark
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Joined: 30 Apr 2005
Posts: 129

PostPosted: Tue Jun 20, 2006 3:29 am    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:
Quote:
On 19 Jun 2006 06:18:53 -0700, in sci.engr.mech "Robert Clark"
rgregoryclark@yahoo.com> wrote:


If however the method of unsteady expansion could be made light
weight, we might also want to use it as the method used for
accelerating the fuel rearward at up to 8000 m/s. This would mean lower
temperatures would be required. I had wondered whether the high
temperatures required for accelerating the fuel, hydrogen say, up 8000
m/s or so would induce the same problems now experienced with scramjets
of sustaining burning at very high temperatures.

Just what supposed problem are you alluding to here?
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)

Slowing down the air from high hypersonic speeds down to low
supersonic speeds, Mach 2 or 3 or so, as with scramjets creates a
tremendous amount of heat. At the high speeds required to reach orbit
it can be several thousands of degres. Temperatures this high are
enough to dissociate the water vapor that would be created with
hydrogen/oxygen combustion.
If the surrounding temperature is already higher than that required to
break apart the resulting compounds then the chemical combination of
the reactants won't take place.
Hydrogen exhaust alone since it's lower molecular weight than water
vapor exhaust requires a lower temperature to reach high exhaust
speeds. Nevertheless, 8000 m/s is quite a high velocity and probably
would require a few thousand degree temperature.



- Bob Clark
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Bret Cahill
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Joined: 05 May 2005
Posts: 480

PostPosted: Tue Jun 20, 2006 4:36 am    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

Issues like these will make test pilot recruiting difficult without
first developing a full size drone.

A Russian rocket scientist was telling me about hypersonic flight
problems when he could hear my mind reel in silence. He then asked,
"it's something to think about isn't it?"

Good conversationalists those Russians.


Bret Cahill
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Robert Clark
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Joined: 30 Apr 2005
Posts: 129

PostPosted: Tue Jun 20, 2006 1:55 pm    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

Henry Spencer wrote:
Quote:
In article <1150723133.851353.232190@f6g2000cwb.googlegroups.com>,
Robert Clark <rgregoryclark@yahoo.com> wrote:
...Unfortunately, a projectile in a gas
gun can not exceed the velocity of the gas...
So the pusher plate couldn't exceed about 4500 m/s if the gas was
water vapor from hydrogen/oxygen combustion.

Careful here, you're confusing two different expansion processes. Guns
and rocket engines are different. Knowing that O2/H2 rocket engines get
gas up to about 4500 m/s maximum tells you nothing about what velocities
O2/H2 guns can reach.

(By the way, quite a bit of the exhaust of an O2/H2 rocket is hydrogen,
not water vapor -- such engines run very fuel-rich. Guns would probably
want to do likewise.)

However, I found this interesting discussion that suggests theoretical
unsteady expansion can be higher by a factor of 2 than the speed
expected for normal steady combustion...

Again, you're confusing two different things. Gun projectiles can reach
about 2 times the *initial speed of sound in the gas*, in practice (the
theoretical limit is considerably higher, but that requires an immensely
long frictionless barrel). That has nothing in particular to do with the
gas velocity attained by steady combustion in a rocket engine.

(Rocket exhaust is sonic at the throat, not at the nozzle exit. And for
that matter, the speed of sound at the throat isn't the same as the
initial value in the chamber, because the gas has already expanded and
cooled significantly.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | henry@spsystems.net

Andrew Higgins who worked on gas guns appears to be saying
specifically the velocity achievable by unsteady expansions is about
twice that for steady combustion from rocket nozzles:

===========================================================
From: Andrew Higgins
Date: Thurs, Dec 16 1999 12:00 am
Email: "Andrew Higgins" <higg...@mecheng.mcgill.ca>
Groups: sci.space.policy
Subject: Re: Deep-undersea gas-gun launchers.
----------
In article <83a84l$...@crl3.crl.com>, gherb...@crl3.crl.com (George
Herbert)
wrote:

Quote:
It's not the speed of sound, it's the gas expansion velocity of
the propellant mix in question (which is roughly Ve or c* in rocket
terms, if you're using the same propellant mix or have the same
products of combustion).

For example... max practical speed for tank guns is a shade under
2,000 m/s (typical is 1,500 to 1,700 m/s). Isp for burning the
propellants in question in a rocket, expanded to vaccum, is around
250s, or 2500 m/s. If you take 1,650 m/s as typical main gun round
muzzle velocity then the gun's operating at a hair under 2/3 of Ve.
There are whole books on the details of internal ballistics leading
to explaining what fraction of Ve a particular designed gun will get.

This is not quite right.

The maximum expansion velocity of gas in a gun is an *unsteady*
expansion,
so the max velocity is different than the maximum expansion velocity in
a
rocket nozzle.

For an unsteady expansion, the maximum velocity is:

Vmax = 2 a0 / (gamma-1)

Where "a0" is the *initial* speed of sound in the gas and "gamma" is
the
ratio of specific heats (gamma = 1.4 for diatomic gases like nitrogen,
hydrogen, etc.). So, the maximum velocity for a hydrogen gas gun is
about 5
times the initial sound speed of the hydrogen propellant. In practice,
gas
guns can rarely reach these speeds; 2 or 3 a0 is a more realistic
limit, due
to friction and other effects.

In steady expansions (such as rocket nozzles), the maximum velocity is:

Vmax = Sqrt[2/(gamma-1)] a0

Vmax = 2.24 a0 (for gamma = 1.4)

Thus, the maximum velocity is only about half the ideal maximum
velocity for
a unsteady expansion.

This fact is why, for example, extremely high speed wind tunnels
(hypersonic
tunnels) use an unsteady expansion to generate the high velocity flow,
such
as shock tubes. A steady, continuous flow wind tunnel would never be
able
to simulate the aerodynamics of orbital re-entry.
--
Andrew J. Higgins Department of Mechanical Eng.
Assistant Professor McGill University
Shock Wave Physics Group Montreal, Quebec CANADA
higg...@mecheng.mcgill.ca
==========================================================
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Ed Ruf
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Joined: 19 Jun 2005
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PostPosted: Tue Jun 20, 2006 3:29 pm    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

On Mon, 19 Jun 2006 01:02:58 GMT, in sci.engr.mech "redneckj"
<redneckj@tampabay.rr.com> wrote:


Quote:
Would it be correct to say that at mach 7, using Mooks concept, you
have well under a millisecond to inject, mix, and detonate the fuel/air
mix? I'm going with 7 feet per millisecond relative velocity of vehicle
to ambient?

For Mach 7 at 100kt I get roughly 7500 ft/sec, so yes that's a decent
number
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Ed Ruf (REPLY to E-MAIL1
science forum beginner


Joined: 03 Dec 2005
Posts: 46

PostPosted: Tue Jun 20, 2006 10:34 pm    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

On 19 Jun 2006 20:29:20 -0700, in sci.engr.mech "Robert Clark"
<rgregoryclark@yahoo.com> wrote:

Quote:
Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:

Just what supposed problem are you alluding to here?

Slowing down the air from high hypersonic speeds down to low
supersonic speeds, Mach 2 or 3 or so, as with scramjets creates a
tremendous amount of heat.

First if you look at the available literature you'll see the inlet throat
Mach numbers are higher than this above Mach 8 or so.

Quote:
At the high speeds required to reach orbit
it can be several thousands of degres. Temperatures this high are
enough to dissociate the water vapor that would be created with
hydrogen/oxygen combustion.
If the surrounding temperature is already higher than that required to
break apart the resulting compounds then the chemical combination of
the reactants won't take place.
Hydrogen exhaust alone since it's lower molecular weight than water
vapor exhaust requires a lower temperature to reach high exhaust
speeds. Nevertheless, 8000 m/s is quite a high velocity and probably
would require a few thousand degree temperature.

The static temperature at the inlet throat is not this high. This is not to
say this isn't a possible issue at the combustor exit at some point, but
this needs to be factored in. However, you have to give up airbreathing at
well below orbital speeds. Even if you could capture enough air you run
into the problem that the amount of energy due to the heat addition becomes
small compared to the total energy of the air resulting in an
insignificant pressure rise due to combustion. A rule of thumb that can be
used to first order is the rule of 89s. The ratio of the heat of combustion
to that of the total airstream goes approximately as 89/M^2. where M is
the flight mach number.

--
Ed Ruf (Usenet2@EdwardG.Ruf.com)
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pete1149
science forum beginner


Joined: 03 Nov 2005
Posts: 11

PostPosted: Wed Jun 21, 2006 1:19 am    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

In sci.space.policy, on Tue, 20 Jun 2006 18:34:40 -0400, "Ed Ruf
(REPLY to E-MAIL IN SIG!)" <egruf_usenet2@cox.net> sez:

` On 19 Jun 2006 20:29:20 -0700, in sci.engr.mech "Robert Clark"
` <rgregoryclark@yahoo.com> wrote:

` >Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:

` >> Just what supposed problem are you alluding to here?

` > Slowing down the air from high hypersonic speeds down to low
` >supersonic speeds, Mach 2 or 3 or so, as with scramjets creates a
` >tremendous amount of heat.

` First if you look at the available literature you'll see the inlet throat
` Mach numbers are higher than this above Mach 8 or so.

` > At the high speeds required to reach orbit
` >it can be several thousands of degres. Temperatures this high are
` >enough to dissociate the water vapor that would be created with
` >hydrogen/oxygen combustion.
` > If the surrounding temperature is already higher than that required to
` >break apart the resulting compounds then the chemical combination of
` >the reactants won't take place.
` > Hydrogen exhaust alone since it's lower molecular weight than water
` >vapor exhaust requires a lower temperature to reach high exhaust
` >speeds. Nevertheless, 8000 m/s is quite a high velocity and probably
` >would require a few thousand degree temperature.

` The static temperature at the inlet throat is not this high. This is not to
` say this isn't a possible issue at the combustor exit at some point, but
` this needs to be factored in. However, you have to give up airbreathing at
` well below orbital speeds. Even if you could capture enough air you run
` into the problem that the amount of energy due to the heat addition becomes
` small compared to the total energy of the air resulting in an
` insignificant pressure rise due to combustion. A rule of thumb that can be
` used to first order is the rule of 89s. The ratio of the heat of combustion
` to that of the total airstream goes approximately as 89/M^2. where M is
` the flight mach number.

I'm trying to wrap my mind around this; a couple of naive questions:

Assume a vehicle travelling at a hypersonic speed, such as the M7-10
you've referred to. Disregarding any geometry issues, ie assume for the
following the vehicle by itself imparts minimal disurbance to the
airstream, and in particular don't worry about any combustion chamber.
If the vehicle were to release an atomized mist of some hydrocarbon
fuel, in substantial volume, but with no attempt to match velocity
with the passing airstream, a) how long (time;distance) before the
fuel has mixed with the air, and slowed to sufficiently matching velocity
that it could sustain combustion?

You talk about the heat of the airstream. I am guessing that this
assumes a model where the fuel mixes with the air approximately
as described above, and the heat comes from the impact of the
gas masses. So, am I understanding the gist of this, if you could
(somehow, magically) launch the fuel at low temperature and high
(matching) velocity from an injector, it would then be able to mix
with the air at a lower local temperature, and thus be able to combust,
as the temperature would be low enough for the combustion products
to exist, however, the required velocity necessary to impart to
the fuel stream would be so large that it would represent a
substantial fraction of the total thrust produced, even if you
capture the energy of combustion?

I am imagining some sort of variable geometry situation, like an
animated summary of the results of a series of simulations for
increasing vehicle velocity, where the length of the vehicle
must steadily increase between the fuel injection point and the
combustion chamber, to the point where it becomes impossible
to sustain structural integrity in an object that has an aspect
ratio like a flagpole...

--
==========================================================================
vincent@triumf[munge].ca Pete Vincent
Disclaimer: all I know I learned from reading Usenet.
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Ed Ruf (REPLY to E-MAIL1
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Posts: 46

PostPosted: Wed Jun 21, 2006 9:19 am    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

On 21 Jun 2006 01:19:15 GMT, in sci.engr.mech vincent@triumfunspam.ca
(pete) wrote:

Quote:
In sci.space.policy, on Tue, 20 Jun 2006 18:34:40 -0400, "Ed Ruf
(REPLY to E-MAIL IN SIG!)" <egruf_usenet2@cox.net> sez:


I'm trying to wrap my mind around this; a couple of naive questions:

Assume a vehicle travelling at a hypersonic speed, such as the M7-10
you've referred to. Disregarding any geometry issues, ie assume for the
following the vehicle by itself imparts minimal disurbance to the
airstream, and in particular don't worry about any combustion chamber.
If the vehicle were to release an atomized mist of some hydrocarbon
fuel, in substantial volume, but with no attempt to match velocity
with the passing airstream, a) how long (time;distance) before the
fuel has mixed with the air, and slowed to sufficiently matching velocity
that it could sustain combustion?

Extremely doubtful for H2, let alone an HC with much slower kinetic rates.
If you look at the very early work in supersonic combustion this is exactly
what was tried, eternal burning. The problem is the static pressure and
temperature of the air are too low, so kinetic rates are slow and the
distance you are trying to mix over is much larger so it is much harder to
mix in short distances as well.


Quote:
You talk about the heat of the airstream. I am guessing that this
assumes a model where the fuel mixes with the air approximately
as described above, and the heat comes from the impact of the
gas masses. So, am I understanding the gist of this, if you could
(somehow, magically) launch the fuel at low temperature and high
(matching) velocity from an injector, it would then be able to mix
with the air at a lower local temperature, and thus be able to combust,
as the temperature would be low enough for the combustion products
to exist, however, the required velocity necessary to impart to
the fuel stream would be so large that it would represent a
substantial fraction of the total thrust produced, even if you
capture the energy of combustion?

Low temperature for the fuel just compounds the kinetics issue. Matching
velocity minimizes shear which is normally used to help mixing. You can't
divorce the physics and just say it mixes. If you are talking about
supersonic injection the static fuel temperature will be quite low as well.

Higher Mach number systems, say above 12 or so tend to talk about the use
of O2 augmentation or even just taking the hot fuel which has been used to
cool vehicle and engine structure and expanding out nozzles aligned with
the flight axis and not trying to mix and burn, just recover as much of the
fuels stream thrust as possible.

Scramjet powered vehicles are an exercise in force accounting where both
the drag and internal thrust are large numbers, but the net thrust being
the difference of the two isn't so large. The low speed range, say Mach 8
and below, have a different optimization than the high speed range. At high
speed, say > M10 loss mitigation becomes an increasingly important part of
the design. Doing this all in a single design is a challenge.
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)
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William.Mook@gmail.com
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Joined: 06 May 2006
Posts: 50

PostPosted: Wed Jun 21, 2006 2:31 pm    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

Ed Ruf wrote:
Quote:
On Mon, 19 Jun 2006 01:02:58 GMT, in sci.engr.mech "redneckj"
redneckj@tampabay.rr.com> wrote:


Would it be correct to say that at mach 7, using Mooks concept, you
have well under a millisecond to inject, mix, and detonate the fuel/air
mix? I'm going with 7 feet per millisecond relative velocity of vehicle
to ambient?

For Mach 7 at 100kt I get roughly 7500 ft/sec, so yes that's a decent
number

Absolutely correct. Except for Mach 7 I get around 7,000 ft/sec but at
30,000 ft altitude. Which is what the earlier post used. Since the
math's easier at 1 ft per millisecond, let's use that altitude. lol
(sound speed changes with altitude and temperature)

So, anything shot into the airstream so that it moves along with the
air would be moving at 1 ft per millisecond. 1/80th of an inch (half a
millimeter) per microsecond.

A tiny fuel-bomb carrying 2 ml fuel would have to be spread across a
sphere 2 feet in diameter by a spreading explosion. The spreading
explosion moves about sound speed, 1/7th the speed of the aircraft.
So, it takes 1 millisecond to spread a 2ml fuel bomblet with an
appropriately small spreading explosion. In that time, the fuel pellet
has moved along the length of the aircraft by 7 feet.

So, if you want to create a shockwave at a certain point around the
aircraft to produce thrust somewhere on its skin, you must spread a 2
ml fuel bomblet 7 feet ahead of that point at this speed.

Of course if you have small bomblets and big aircraft - I believe the
Aurora was purported to be 140 feet long - you have plenty of time to
spread fuel to the correct air/fuel mixture.
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Robert Clark
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Joined: 30 Apr 2005
Posts: 129

PostPosted: Sat Jun 24, 2006 2:25 am    Post subject: Re: Proposals for air breathing hypersonic craft. II Reply with quote

Instead of directly trying to use the thrust from combusting the
accelerated fuel, it may be better to simply use the energy produced
from combustion to heat the fuel that is still onboard to high exhaust
velocity.
The idea is to accelerate the fuel rearward so that it is still with
respect to air. This allows the combustion to easily take place when
the fuel and the air are at zero relative velocity to each other. It
also eliminates the problem of the high temperatures produced by
decelerating hypersonic air preventing the combustion of the fuel with
air.
Now we can use various electrical energy generation methods to produce
electrical power from burning of the fuel. The generator would have to
be lightweight to be carried along rearward with the fuel/air. It would
be connected to the rocket itself by wires.
Several possibilities exist. You could simply use pistons or a turbine
electrical generator driven by the gas expansion produced by
combustion. You could use a Stirling engine or thermoelectric
generators driven by the heat itself. You might even be able to use
fuel cells.
Now we have a simple method of accelerating the fuel rearward. From
the electrical power produced we could use arc thrusters for the
purpose for example. We don't need to use the large power to dissociate
the hydrogen, just sufficient power to heat the hydrogen to the exhaust
velocity to match the velocity of the craft.
This would have to be pulsed propulsion. You could use several
separate generators moving one after another so that the thrust is
produced continuously.
This is probably a method that could be implemented near term.



Bob Clark


Robert Clark wrote:
Quote:
...
Another possibility would be to accelerate the fuel up to the same
velocity of the craft then eject this into the air flow. Call it
Accelerated Fuel Combustion (AFC). Then you would not have to slow down
the air inflow at all for combustion. The problem then would be to be
able to accelerate the fuel up to the maximum velocity of the craft to
reach orbit, about 7.5 to 8 km/sec.
...
(III.) However, the key problem is how to communicate the thrust of the
combustion, which is taking place in still air, to the craft. The
problem is the fuel is being combusted in still air while the rocket is
moving away at up to 8000 m/s. So even if the combustion products are
moving at 4500 m/s they still can not catch up to the craft to impart
momentum to the vehicle.
A couple of proposed solutions. Both of these though require the
combustion to be pulsed.
...
(a.) First method to communicate thrust to rocket: use the accelerated
fuel to propel a plate rearward to be at the same speed of the fuel/air
mixture and at the front of it. When the fuel air is ignited since the
plate is still with regards to the fuel/air it receives the momentum of
the combustion products moving forwards. You see here it can only
receive a portion of the thrust produced since it does not receive the
momentum of the combustion products moving rearward. At best it could
receive 50% of the thrust produced.
For this to work this "pusher plate" if you will needs to be of a
light material, lighter in fact than the mass of the fuel/air
combusted. Then the momentum imparted to it will give it a velocity
higher than that of the exhaust gases to be a speed at least as high as
the speed of the rocket moving forward. Once it has received the
greatest momentum boost from the expanding combustion gases, it is
allowed to catch to the walls of the rocket or to a stop bumper towards
the front thereby transferring its momentum to the rocket.
(b.) Second method to communicate thrust to rocket: use in fact not
only a pusher plate but a full combustion chamber moving rearward at
the same velocity of the fuel/air and containing the fuel/air, with its
nozzle pointing rearward. As with the pusher plate it would need to be
made of a light material to wind up at a higher velocity moving forward
than the exhaust gases. To make it lighter you might only want it to
consist of a front plate and a rear nozzle connected by strong thin
rods to keep the volume of the chamber constant as the combuston gases
expand. The walls of the rocket would then serve as the walls of the
combustion chamber. This method has the advantage that more of the
thrust produced will be transmitted to the rocket.



Bob Clark
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