Proposals for air breathing hypersonic craft. II
Robert Clark
relative velocity to the craft to eliminate the problem of the ram
drag created by ingesting and slowing down the surrounding air for
combustion:
From: Robert Clark
Date: Thurs, May 6 2004 9:12 pm
Email: rgregorycl...@yahoo.com (Robert Clark)
Groups: sci.astro, sci.space.policy, sci.physics, sci.mech.fluids,
sci.engr.mech
Subject: Proposals for air breathing hypersonic craft. I
http://groups.google.com/group/sci.astro/browse_frm/thread/45dfd18abf58f307/
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.
DARPA and Johns Hopkins' Applied Physics Laboratory are already
investigating a partial version of this idea at lower velocities:
New Powerplant Key To Missile Demonstrator
By Stanley W. Kandebo/Aviation Week & Space Technology
September 3, 2002
"APL's dual combustion ramjet is yet another way to obtain hypersonic
speeds. In this powerplant, supersonic air ingested through one inlet
is slowed to subsonic speeds, mixed with a conventional hydrocarbon
fuel in a fuel-rich environment and ignited, as in a ramjet. To break
through the ramjet's operating speed limitations, though, the expanding
combustion products are then mixed with supersonic air entering through
a second inlet and are more completely burned in a supersonic
combustor. According to APL researchers, the DCR has an operating
threshold of about Mach 3, and a maximum operating speed of about Mach
6.5."
http://www.aviationnow.com/avnow/news/channel_awst_story.jsp?view=story&id=news/mdcrj0903.xml
I shall argue that the method of not slowing the incoming air at all
but accelerating the fuel up to the relative air speed will result in a
marked improvement in fuel efficiency. Specifically, the exponential
increases in fuel according to velocity given by the rocket equation
will no longer be needed.
Let X be the mass of the rocket with fuel, v the rocket velocity, r
the ratio of air to fuel in mass, and e the nominal exhaust velocity of
combusting still air with still fuel.
For this method to work I will assume that the force produced by the
combustion of the air with the fuel can be fully communicated to the
craft. To derive the thrust equation take the craft including the fuel
to be a closed system and the air to be outside the system and take the
rest frame to be the Earth, or likewise the still air.
Now if we did not combust the ejected fuel with the air then by
momentum conservation we would have:
(X + dX)(v + dv) + 0(-dX) = Xv
In the first term on the left we add dX to X because dX is negative
since the mass is decreasing as fuel is consumed. So the first term
represents the mass of the rocket less the ejected fuel times the
increased velocity of the rocket. In the second term we are multiplying
the velocity with respect to ground of the ejected fuel times the mass
of the fuel ejected. Since we are ejecting the fuel at a speed to stay
at zero relative velocity to air, i.e., to the ground, this velocity
here is 0. The negative sign in front of dX again is because dX is
negative so -dX is the positive mass of the fuel.
This equation expanded out is Xv + Xdv+ vdX + dXdv = Xv. So the change
in momentum is Xdv + vdX + dXdv = 0, and the rate of change of momentum
is:
0 = Xdv/dt + vdX/dt + (dXdv)/dt = Xdv/dt + vdX/dt , because the term
with two differentials dXdv vanishes as dt ---> 0.
Now when we do combust the fuel with the air, then the rate of change
in momentum of the system is the force on the craft due to the
combustion of the air and fuel. This is the thrust produced by this
combustion which equals mass flow rate, air + fuel, times the nominal
exhaust velocity of the combustion of still air and still fuel:
Xdv/dt + vdX/dt = -ed(rX+X)/dt = -e(r+1)dX/dt , where the minus sign
comes from dX being negative.
Let c = e(r+1). Then the equation becomes Xdv/dt + (c + v)dX/dt = 0,
which is equivalent to:
d[(c +v)X]/dt = 0
This has solution (c + v)X = constant. Let X0 be the initial mass and
v0 the initial speed of the rocket. Then the solution is (c +v)X = (c +
v0)X0.
Therefore X0/X = (c + v)/(c + v0), i.e., the mass ratio of the fully
fueled rocket to the empty rocket is just a linear function of ending
velocity.
(II.) There are a couple of problems with this idea. First, you have
to accelerate the fuel up to the velocity of the craft which can be up
to 8 km/sec to reach orbit. Secondly, we shall see communicating the
full thrust of the combustion to the craft is no easy matter. Actually
I think probably only some portion of this thrust will wind up being
applied to the craft, call it a fraction given by f. Then the
calculation will carry through similarly to as before so the final
equation will be (fc + v)X = (fc + v0)X0.
For accelerating the fuel, the DARPA/APL method is to combust a fuel
rich mixture first using subsonic combustion which results in
uncombusted fuel in the exhaust moving at the exhaust speed. However,
even if you used the highest exhaust speed for chemical rockets of 4500
m/s this still would not be fast enough.
So my suggested method is to use the idea of using high temperature
atomic hydrogen stored on board:
From: Robert Clark
Date: Tues, Jun 13 2006 3:44 am
Email: "Robert Clark" <rgregorycl...@yahoo.com>
Groups: sci.astro, sci.space.policy, sci.physics, sci.chem, sci.energy
Subject: Storing atomic hydrogen propellant at high temperature.
http://groups.google.com/group/sci.astro/msg/f41d7a2c95826eee
The Accelerated Fuel Combustion method since the fuel requirements are
so low would be ideal for the stored atomic hydrogen since the high
temperature, high pressure tanks to hold the atomic hydrogen could be
minimized in size. Atomic hydrogen propulsion can also have ISP up to
1600 sec, which means the exhaust velocity can be up to about 16,000
m/s.
How much fuel would be required? Hydrogen/LOX engines can have exhaust
speeds of 4500 m/s. However, this is by using liquid oxygen oxidizer
which results in high flame temperatures and using high pressures in
the combustion chamber. Using ambient oxygen from air that also
contains 80% nitrogen that does not contribute to the combustion and
using incoming air that is not compressed as with typical (sc)ramjet
methods would result in significant reduction in performance. Let's
suppose the exhaust speed for still air, fuel is 2000 m/s. At
stoichiometric mixture ratio of 8 to 1 oxygen to hydrogen and 5 times
the total mass of air as the mass of oxygen this gives r = 8*5 = 40 and
c = e(r + 1) = 2000*41 = 82,000 m/s.
If you wanted to reach 8000 m/s from 0 initial velocity the equation
would be X0/X = (c + v)/(c + v0) = (82,000 + 8,000)/82,000 = 1.098.
This means less than 10% of the empty rocket mass would have to be
carried as fuel. This compares to typical rocket fuel loads that are
several times larger than the mass of the empty rocket.
(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. Pulsed combustion for hypersonic craft is
being researched with Pulsed Detonation Engine (PDE) propulsion for
craft:
PDE Faq.
http://www.innssi.com/pde01.htm
The idea is to carry out detonations many times a second to result in
smooth propulsion. The key distinction of PDE propulsion is that the
combustion is through detonations rather than through simple burning
(deflagration.) A benefit of this that the combustion can take place
orders of magnitude faster than with simple burning.
The technical problems with PDE though still have not been worked out.
I believe though am far from certain that the Accelerated Fuel
Combustion method will not require PDE to work.
(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
Bret Cahill
> speeds. In this powerplant, supersonic air ingested through one inlet
> is slowed to subsonic speeds, mixed with a conventional hydrocarbon
> fuel in a fuel-rich environment and ignited, as in a ramjet. To break
> through the ramjet's operating speed limitations, though, the expanding
> combustion products are then mixed with supersonic air entering through
> a second inlet and are more completely burned in a supersonic
> combustor.
Interesting. Could this be done in three or more stages?
. . .
> I shall argue that the method of not slowing the incoming air at all
> but accelerating the fuel up to the relative air speed will result in a
> marked improvement in fuel efficiency.
Ever look at the P-V diagrams for an internal combustion engine without
compression?
Bret Cahill
dlzc1 D:cox T:net@nospam.com N:dlzc D:aol T:com (dlzc)
"Bret Cahill" <BretC...@aol.com> wrote in message
news:1150608845.2...@h76g2000cwa.googlegroups.com...
>> "APL's dual combustion ramjet is yet another way to
>> obtain hypersonic speeds. In this powerplant,
>> supersonic air ingested through one inlet is slowed
>> to subsonic speeds, mixed with a conventional
>> hydrocarbon fuel in a fuel-rich environment and ignited,
>> as in a ramjet. To break through the ramjet's operating
>> speed limitations, though, the expanding combustion
>> products are then mixed with supersonic air entering
>> through a second inlet and are more completely
>> burned in a supersonic combustor.
>
> Interesting. Could this be done in three or more stages?
What are we going to do when:
- the water vapor at high altitiude breaks the "oxides of
nitrogen" cycle of ozone production, and
- these engines consume the very oxygen that ozone is made from?
How low do you want the ozone layer to have to form?
One-offs is not a problem, but for commerce...
David A. Smith
Bret Cahill
> - the water vapor at high altitiude breaks the "oxides of
> nitrogen" cycle of ozone production, and
> - these engines consume the very oxygen that ozone is made from?
These are just special mission craft. It's not like all 8 billion
people on the planet will have to buzz around in them 24/7.
Bret Cahill
Bret Cahill
> fuel cooled combustor panels, while at the same time raising the
> temperature of the liquid JP fuel and partially cracking it to greatly
> speed up kinetic rates.
If the hydrocarbon fuel was only partially burned in several stages
maybe liquid H2 cooling could be reduced or eliminated altogether.
Bret Cahill
Bret Cahill
craft which can be up
< to 8 km/sec to reach orbit.
If you are planning on using a nozzle that will require a pressure of
millions of psi.
Bret Cahill
Willia...@gmail.com
you ejected the fuel behind the vehicle - perhaps using electrostatics,
or some sort of detonation process - so that the speed of the ejected
fuel relative to the air was below that needed to sustain combustion,
and then detonated the air/fuel mixture outside the vehicle in a well
defined region - and well defined shape - using a laser or particle
beam - and rode the resulting shaped shock wave?
Willia...@gmail.com
Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:
> On 18 Jun 2006 11:59:14 -0700, in sci.engr.mech Willia...@gmail.com
> wrote:
>
> >Well, what if you dispense with slowing the air down altogether?
>
Ejecting the fuel at a speed that brings its relative velocity down to
a reasonable speed relative to the movement of the air.
>
> > If you ejected the fuel behind the vehicle - perhaps using electrostatics,
> >or some sort of detonation process - so that the speed of the ejected
> >fuel relative to the air was below that needed to sustain combustion,
>
> What the heck are you thinking about here? What actual physical processes
> are you envisioning?
Detonating a fuel air mixture external to the craft as in a fuel-air
explosive and somehow making use of a portion of the shockwave that
results to propel the craft - and if you're lucky, using a portion of
the shockwave's energy to eject your next round of fuel.
>
> >and then detonated the air/fuel mixture outside the vehicle in a well
> >defined region - and well defined shape - using a laser or particle
> >beam - and rode the resulting shaped shock wave?
>
> Again just how have you mixed the air and the fuel ?
Explosively
> Without mixing you
> have no combustible or detonable mixture.
In an air-fuel explosive you have two explosions. One to detonate the
fuel and spread it into a cloud. The second, to detonate the cloud.
You could do that here. You could eject a plastic bottle of fuel from
a gun, with one explosion bringing it to rest in the air behind the
aircraft, detonate the bottle with a second explosion spreading the
fuel into an air-fuel mixture, then detonating the air-fuel mixture to
create a shock wave. The shock wave propels the vehicle.
> You just can squirt fuel out the
> back and burn/detonate it.
> --
Well, you have to be careful with the details, but if you can use a
air-fuel bomb to smash a tank on the ground, it seems to me you might
have a shot in creating an air-fuel mixture behind a hypersonic
aircraft that has a shot at propelling the aircraft.
> Ed Ruf (Use...@EdwardG.Ruf.com)
Willia...@gmail.com
Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:
> E-MAIL IN SIG!)" <egruf_...@cox.net> wrote:
>
>
> >have no combustible or detonable mixture. You just
> CAN"T
> > squirt fuel out theback and burn/detonate it.
>
> --
> Ed Ruf (Use...@EdwardG.Ruf.com)
I agree. But you can eject fuel in a bottle, with one explosion,
spread fuel with a second explosion, into an air-fuel explosive
mixture, and detonate it with a third explosion. You can then ride the
resulting shock wave.
This is the crudest way to achieve this result. A cooler way would be
to electrostatically eject the fuel from a large number of small
nozzles (think inkjet printer type surface facing rearward) and then
detonate the resulting cloud with some sort of electrostatic discharge.
Of course, when I say eject this out of the back of the aircraft,
that's one approach without tubes or channels of any sort. Another
approach would be to create some sort of tube or channel, that didn't
even try to slow the ram air down - a tube or channel that diverged
would actually speed the flow in the channel or tube up when operating
at supersonic speed.
Anyway, eject the propellant into the stream with a speed that brought
the propellant to a low speed relative to the moving air, and then,
spread it, and detonate it when it was at the right air/fuel mix, and
ride the resulting shock wave.
Careful design might even use the high stagnation temp to create a
detonation wave and hold it by controlling channel or tube width with
length. Likely such a device would have to change shape with speed.
But a channel equipped with flaps that ejected droplets from behind
them, might be workable.
For gasoline vapor, the explosive range is from 1.3 to 6.0% vapor to
air, and for methane this range is 5 to 15%. Many parameters contribute
to the potential shock from a vapor cloud explosion, including the mass
and type of material released, the strength of ignition source, the
nature of the release event (e.g., turbulent jet release), and
turbulence induced in the cloud (e.g., from ambient obstructions).
Based on the known properties of flammable substances and explosives,
it is possible to use conservative assumptions and calculate the
maximum distance at which an overpressure or heat effect of concern can
be detected. Distances for potential impacts could be derived using the
following calculation method [described in Flammable Gases and Liquids
and Their Hazards]:
D = C x (nE)^1/3
where D is the distance in meters to a 1 psi overpressure; C is a
constant for damages associated with 1 psi overpressures or 0.15, n is
a yield factor of the vapor cloud explosion derived from the mechanical
yield of the combustion and is assumed to be 10 percent (or 0.1) and E
is the energy content of the explosive part of the cloud in Joules. E
can be calculated from the mass of substance in kilograms times the
heat of combustion (hc) in Joules per kilogram as follows:
E = mass x hc
Combining these two equations gives:
D = 0.15 x (0.1 x mass x hc)^1/3
Vapor cloud explosion modeling historically has been subject to large
uncertainties resulting from inadequate understanding of effects.
According to current single-degree of freedom models, blast
damage/injury can be represented by Pressure-Impulse (P-I) diagrams,
which include the effects of overpressure, dynamic pressure, impulse,
and pulse duration. The peak overpressure and duration are used to
calculate the impulse from shock waves.
Aviation fuel has 43 MJ/kg at a reasonable altitude air has a density
of about 0.4 kg/m3 (1/3 sea level density) and at 2% density - the
vapor would possess 0.008 kg/m3 - and would release about 344 kJ per
m3.
This of course is all stationary - and at Mach 5 for example, at 10,000
m ( a little over 30,000 ft) that speed is 1,500 m/sec. So, each
SQUARE meter sees 1,500 cubic meters of air flow through it every
second ON AVERAGE. So, that's a power of 516 Megawatts per square
meter and a fuel consumption of 12 kg per second. Kerosene masses 0.81
kg/Liter so this is equal to 9.72 liters per second per square meter.
Now, the power needed to eject 12 kg per second at a speed of 1,500
m/sec is;
12 * 1,500^2 = 27 MW.
Around 5% of the total energy released by the fuel/air explosion.
So, this appears very doable.
Now, lets talk about the resulting shockwave.
http://en.wikipedia.org/wiki/Shockwave
http://www.aerodyn.org/HighSpeed/waves.html
If the fuel is stationary in the air, and evenly spread by a spreading
explosion or equivalent, the shockwave radiates in all directions far
from the explosion - at the speed of sound. A series of explosions
like this would create a resulting shockwave whose angle relative to
the flow would have an angle equal to;
angle = arc-cos(1/M)
and since in this case we said M was 5 then the angle is 78.46 degrees.
So, if a ring of propellant were detonated behind an aircraft body with
a conical rear surface with an opening angle of 22 degrees - part of
the shock made by the exploding ring of fuel air would compress the
back of the aircraft body propelling it forward - the same way pressing
your fingers together on the back of a slippery pumpkin seed propels it
forward at many times the closing velocity of your fingers.
Willia...@gmail.com
Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:
> wrote:
>
> >
> >Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:
> >> On 18 Jun 2006 11:59:14 -0700, in sci.engr.mech Willia...@gmail.com
> >> wrote:
> >>
> >> >Well, what if you dispense with slowing the air down altogether?
> >>
> >> And just how to you intend to mix the fuel and air?
> >
> >Ejecting the fuel at a speed that brings its relative velocity down to
> >a reasonable speed relative to the movement of the air.
>
Here's a reference
http://www.fas.org/man/dod-101/sys/dumb/fae.htm
In its simplest implementation you have a bottle of fuel equipped with
a couple of fireworks. Say a 2 liter bottle of kerosene. That masses
about 1.62 kg, and contains about 70 MJ of energy. It will detonate if
brought to between 2% and 6% of the air mass and detonated.
Now air masses around 1.2 kg per m3 near the surface and drops to about
0.4 kg per m3 at 10,000 m altitude - 30,000 ft- so you could run a
detonation if you had a spreader explosion that spread the 2 liter
bottle across a volume of say 40 cubic meters of space. That's a
sphere around 4 meters across. Once you've got your air fuel spread
across this volume, you then have a second firework that detonates it.
So, the sequence is rather simple.
You throw a bottle of kerosene out the back of a fast moving aircraft,
so that it comes to rest relative to the air. You then detonate a
spreading explosion that spreads it to the appropriate air-fuel mix
ratios. Then you detonate a second explosion that detonates the air
fuel mix. If you did things right, the resulting shockwave will impact
some sort of propulsive surface that will produce thrust from the
explosion.
>
>
> >> Again just how have you mixed the air and the fuel ?
> >
> >Explosive
> Baloney.
Why do you say that? Fireworks have routinely been used to create
air-fuel mixes in thermobaric weapons. Absolutely no reason they
cannot be used here.
> You haven't said how you actually intend to mix the air with the
> fuel.
Well the air surrounds the aircraft, you toss a bottle of fuel out the
aircraft in a way that brings it to rest in that airstream, you then
detonate the bottle to spread it to the right air-fuel ratio, and then
you detonate the cloud of air fuel to create a shockwave - you then
catch the shock wave to provide propulsive force.
> How about giving us some mixing correlation you have in mind of
> trying to implement?
Sure. Kerosene explodes at air/fuel mass ratios from 2% to 6% - so a
two liter bottle would need to be spread across a sphere about 4 meters
in diameter - and then detonated with a second explosion. Think of a
4th of July firework.
Of course we don't need to use two liter bottles. We could use vitamin
capsule sized bottles or five gallon gas tank bottles - or anything in
between.
Since this is a half-baked notion, there's no reason we couldn't eject
droplets at a speed that brought them to rest in the airstream with a
large number of ejectors, and then detonated them at the right spot
near the aircraft's surface with a spark or something.
> >Well, you have to be careful with the details, but if you can use a
> >air-fuel bomb to smash a tank on the ground, it seems to me you might
> >have a shot in creating an air-fuel mixture behind a hypersonic
> >aircraft that has a shot at propelling the aircraft.
>
> Conjecture.
That a shock wave can push something? A pretty reasonable conjecture I
must say.
> That's mixing at zero velocity.
That's the whole point. If you can't figure out how to do something
one way, do it a way you CAN figure out. Bringing the fuel to rest
relative to the air does that.
> 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.
> The airflow has
> orders of magnitude more kinetic energy in it.
Now you're just spouting words. You missed the essential feature of
what I've described.
>The laws of physics don't
> work that way.
Not the way YOU describe - no. Because you missed a rather simple
point. The fuel and air are sitting still while the aircraft is
zipping by. lol.
> Let's see the mathematics behind your concept.
What mathematics would you need exactly? Its really rather simple.
You eject the fuel so that it is stationary in the air, you spread it
if need be to get to the right air/fuel ratio, and then you detonate
the mix - creating a shock wave. The shock wave moves at sound speed,
so that means a series of these spherical shock waves will have a Mach
Cone whose angle is equal to the ACOS(1/M) - if you insist on math.
lol.
A tapering tail cone would pick up the shock cone of a successive
detonation of rings of fuel around the aircraft in this way, and
produce thrust. Just as swept wings reduce the effective velocity
across the chord, so too does a tapered propulsive surface reduce the
effective velocity of the aircraft so that it can interact efficiently
with the shockwave. Think of squeezing a pumpkin seed between your
fingers. The seed's speed when it exits your grasp, is several times
the closing speed between your finger and thumb! lol.
> --
> Ed Ruf (Use...@EdwardG.Ruf.com)
Willia...@gmail.com
Ed Ruf (REPLY to E-MAIL IN SIG!) wrote:
> 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.
>
> 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?
> 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.
> 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.
>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.
redneckj
"Ed Ruf (REPLY to E-MAIL IN SIG!)" <egruf_...@cox.net> wrote in message
news:1dhb92dm49b2gqvrm...@4ax.com...
> On 18 Jun 2006 14:10:04 -0700, in sci.engr.mech Willia...@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.
>
> powered vehicles at Mach 7 and 10. Just what have you done?
>
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.
> 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 (Use...@EdwardG.Ruf.com)
Robert Clark
> ...
>
> (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
Henry Spencer
Robert Clark <rgrego...@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. | he...@spsystems.net
Robert Clark
> <rgrego...@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.
>
> --
> Ed Ruf (Use...@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
Bret Cahill
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
rgrego...@yahoo.com
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:
> 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
==========================================================
pete
(REPLY to E-MAIL IN SIG!)" <egruf_...@cox.net> sez:
` On 19 Jun 2006 20:29:20 -0700, in sci.engr.mech "Robert Clark"
` <rgrego...@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.
Willia...@gmail.com
Ed Ruf wrote:
> On Mon, 19 Jun 2006 01:02:58 GMT, in sci.engr.mech "redneckj"
> <redn...@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
>
> 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.
Robert Clark
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:
> ...
> 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
rgrego...@yahoo.com
accelerated rearward plus the thrust from the combustion of this fuel
with the still air.
However, this creates problems with communicating the thrust due to
combustion with the rocket since the air is flowing freely, actually
still, so is outside the rocket "system".
Question: if the air is made to flow in a circle or for example in a
helical path, does this air now become part of the rocket system? Does
momentum imparted to this air also become transmitted to the rocket? If
so, this may provide a means to impart most or all of the thrust
produced from combustion to the rocket.
A key question though is would this create the same type of heating
problems as when the air is decelerated from hypersonic speed? Though
the air is not decelerated, it is being accelerated in moving in a
curved path.
Bob Clark
Robert Clark wrote:
> ...