h a l f b a k e r yViva los semi-panaderos!
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
Please log in.
Before you can vote, you need to register.
Please log in or create an account.
|
So. Model jet engines have now reached a very high level
of maturity. For a few thousand pounds, you can buy a
plug-and-play jet engine with a thrust of up to 150kgf, and
a weight of <<30kg. These things typically drink a very
few litres per minute.
Clearly, you can't run a jet engine in
a vacuum. However,
why can you not simply supply oxygen (either as gas from
LOX, or more likely as an aerosol of LOX), mixed if
necessary with nitrogen (since I'm sure the engines are
optimised for regular air)? In the simplest system, the
oxygen would simply be sprayed directly at the intake of
the jet engine. This may not be the most efficient, but on
the other hand it must surely work, since this is effectively
what happens in atmospheric flight.
If fuel consumption is litres per minute, then oxygen
consumption (as LOX) would be a few fold higher - still not
outrageous. Even if nitrogen is needed as a 'filler',
consumption is still OK.
I know there is nothing radically new here, and I also know
that people have tried (with some success) to develop big
advanced hybrid rocket/jet engines.
All I'm saying here is that, given that small efficient jets
are baked, why can't they be turned into rockets by just
spraying LOX at their intakes?
(And yes, I know the expansion ratio at the back end would
be non-ideal, but that's a detail. Also, dynamic jet nozzles
are well-baked and robust.)
Lox on a bagel
http://www.bphope.c...ghters_bagel-an.jpg
.... if lox could kill :-) ha [xenzag, Jan 22 2013]
lox rocket
http://science.hows...rks.com/rocket5.htm
AWW SHUCKS someone else thought of it first. [Brian the Painter, Jan 23 2013]
Nitrous vs oxygen facts
http://www.noswizar...chnical-information
sorry I couldn't find a better link, I'm tires [Brian the Painter, Jan 23 2013]
XCOR "Tea Cart" Engine
http://www.xcor.com..._rocket_engine.html
15lbf N2O/Ethane [Klaatu, Jan 23 2013]
A simple energy pattern that could be added
http://charlessowers.com/sand-shaker
is the flow of how burn components combine complex enough? [wjt, May 17 2019]
[link]
|
| |
Even if you could somehow accomodate the internal shapes for a much lower speed, I imagine you'd end up either having to use the fuel as coolant/motive charge or burn out the engine pretty fast with nothing to soak up the heat except the engine. And given that the LOX is compressed there's no need for a compressor/turbine arrangement. |
|
| |
If you subbed in Ar for the missing N2 you could get some interesting results, given the noble gases' ridiculous thermal properties. Might even lower fuel consumption. |
|
| |
If you feed the LOX in as gas (or, probably,
aerosol; and possibly mixed with nitrogen), then
the engine sees exactly the same as it sees when
flying in atmosphere. |
|
| |
As for not needing a compressor, that applies only
if you can feed the oxygen in above the pressure
inside the engine. Conventional rockets either
have turbopumps, or rely on highly pressurized
fuel/oxidiser tanks which are weighty. |
|
| |
However, I see one possible flaw. Does a regular
jet engine suck in a lot more air than is needed
for combustion? If so, then this is doomed. |
|
| |
I imagine it does, but even if it didn't, in the LOX version you've only got 1.3x the amount of gas you started off with (3O2 + hydrocarbon -> 2H2O + 2CO2), as opposed to 5.3x, to distribute the heat of combustion. |
|
| |
So, in order to keep the engine from melting you need to add more O2 or more fuel to keep the exhaust gas temperature down. |
|
| |
At which point you might as well use compressed air instead of O2... or maybe supplemental water-injection to save space. |
|
| |
//you need to add more O2 or more fuel to keep
the exhaust gas temperature down.// Yes,
probably true. I was thinking LOX plus liquid
nitrogen (which, I guess, is liquid air). |
|
| |
//Is this for space?// Yes. Air-breathing up to
some maximum altitude, then progressively
supplemented with LOX or liquid air. |
|
| |
Main question remains - does a jet engine suck in
a lot more air than it needs for combustion? |
|
| |
Isn't this a Soyuz rocket, with the added complexity and inefficiency of unnecessary turbines? Actually scratch that, a Soyuz probably still has turbines (turbopumps) that do about the same job of fuel/lox delivery, so this is really just a unique rocket engine design. |
|
| |
//Main question remains - does a jet engine suck in a lot more air than it needs for combustion?//
Yes, lots more. Most of it is bypass, which you can do away with, but some extra air is still needed for cooling. |
|
| |
I thought this would be similar to Reentry Fried Chicken (but with cream cheese and lox instead). I'm disappointed. |
|
| |
If you try to spray LOX at the front of a jet engine in space very little of it would make it inside, I am afraid, as there is no sucking in a vacuum. |
|
| |
If it was injected inside where combustion takes place, probably better, but some of the combusted gasses would exit the front of the engine. You would need closeable shutters on the front to prevent this. |
|
| |
If this were for near-space, very high altitude, I think it might work as is. |
|
| |
Would be even better with some capers. |
|
| |
//Yes, lots more. Most of it is bypass// I was
afraid of that. If it's just a cooling question, that's
bad enough. But if the jet uses the extra intaken
air (heated by the combustion) as a major
contributor to thrust, then that's a big problem. |
|
| |
//very little of it would make it inside, I am
afraid, as there is no sucking in a vacuum. //
Also good point. I was assuming that you could
have a chamber in front of the engine (an
extended intake, really) into which you'd pump
oxygen fast enough to maintain the pressure
there at something like atmospheric; then the jet
"thinks" it's operating in normal air. |
|
| |
// is that not the Skylon British spaceplane
wossername...// Yes, and I think the engine is
being designed by Reaction Engines? That's the
big expensive version. I was only wondering why
you can't feed air (or oxygen) to a regular model
jet engine and have it work the same way. Again,
though, the problem comes down to how much
"excess" air a jet eats, beyond that needed for
combustion. |
|
| |
OK, so it turns out that turbojets (as used on
Concorde, and on some high-speed fighters) have
a bypass ratio of 0:1, meaning that all of the air
coming into the engine goes through the
combustion chamber. More fuel efficient
turbofan engines send only some of the air
through the combustion chamber to power the
turbine, which then drives the inlet fans, which
send some air to the combustion chamber but
most of the air around it - in effect, a turbofan is
a turbojet with extra big fans at the front which
provide the bulk of the thrust. |
|
| |
Now, my question is: does a 0:1 bypass ratio
mean that all the oxygen in the incoming air is
consumed in combustion? I.e., does it mean that
these engines eat air stoichiometrically with
respect to fuel? Or does it mean that there's a lot
of surplus air (a very lean mixture), all of which
passes through the combustion chamber? |
|
| |
OK again. So it turns out that only a proportion of
the air entering a turbojet (non-bypass jet engine)
is used in combustion, the rest being 'bulk' which
provides cooling and, by expanding as it absorbs
heat, contributing to some of the thrust. The
highest proportion of air "used" in combustion
seems to be about 25%. |
|
| |
Thus, if we have 1kg of fuel, we will need to feed
it about 4 times the stoichiometric amount of
oxygen. This means roughly (very roughly) 4kg of
oxygen. But we are feeding it air (because the
figures for turbojets are based on air, not oxygen),
so that's about 20kg of air. |
|
| |
So now suppose that we have a model turbojet
engine (I don't know if the currently available
model jets are turbojet or turbofan), weighing
30kg and providing a thrust of 150kg. It's going to
use something on the order of 2kg of fuel and 40kg
of liquid air per minute. Call it 50kg in total per
minute. |
|
| |
This is not great, but remember that the engine
can breathe atmospheric air up to a considerable
altitude. Thus, if we had a gross lift-off weight of
say 100kg (30kg engine, 50kg fuel+liquid air, 20kg
structure and payload), we'd probably start
feeding it liquid air at (I'm guessing) 40,000ft, after
which we'd have one minute of operating time
before the liquid air ran out. (The fuel is only a
minor part of the weight, so we don't need to run
out of that.) |
|
| |
At the start of this minute, we have 150kg force
(1500N) and a mass of around 100kg, giving an
acceleration of A=F/M = 15m/s/s. Towards the
end of the minute, we have a mass reduced to
around 50kg, giving twice that acceleration. But
then there's air resistance (constantly reducing,
and already lowish at 40,000 feet). So let's assume
an average acceleration of 10m/s/s for one
minute... Awwww bugger. That only gives us
600m/s. |
|
| |
I bet there IS a way this is workable. As I said, a kerosene
and lox powered rocket like the soyuz has a lot in common
with a turbojet. You would just be relocating the axial
compressor/turbopump to the front of the combustion
chamber and adding a turbine in the exhaust stream to
drive it. Yes, it would be less efficient than either a rocket
or a jet. But it might be more efficient than having
seperate jets and rockets for high alitude flight. |
|
| |
And at which point do the bagels feature in the idea? |
|
| |
//a kerosene and lox powered rocket like the
soyuz has a lot in common with a turbojet// |
|
| |
Yes, you're right! One question is *why* it would
be less efficient to replace conventional rocket
fuel pumps with the compressor stage of a
turbojet - perhaps it needn't be that much less
efficient and, as you noted, the ability to air-
breathe for much of the flight is an advantage. |
|
| |
Still, I guess we are just converging toward the
Reaction Engines/Skylon concept, i.e. it's not just
a question of squirting liquid air into the intake of
an otherwise off-the-shelf miniature jet engine. |
|
| |
the "why" of it being inefficient is that the engine now has a hole at the front where is doesn't need one. The hole and the motion of the engine through the air delivers air to the turbine under substantial pressure, operating the turbine stationary, or without this source of air pressure substantially derates the output, and in effect makes the design operate rather poorly. |
|
| |
// why can't they be turned into rockets by just spraying LOX at their intakes? // |
|
| |
Apart from the above-mentioned problems, we think it is also useful to point out that the LOX will scavenge heat from its surroundings in a quite vicious way. Pretty soon, everything forward of the combustion chamber will be at -180 C. |
|
| |
Odd things happen to metals at such low temperatures. |
|
| |
Further, you may have noted that every device which employs compressed or liquid oxygen is lavishly provided with cheerful labels that read "USE NO OIL". There is an excellent reason for this. The consequences of ignoring the advice of the aforementioned labels are dramatic, fascinating, and most enjoyable, providing the observer is positioned a sufficiently long way from the object under provocation, and has something substantial behind which to take cover. |
|
| |
Turbojet engines require their bearings to be lubricated. Traditionally, this is by means of oil. Minute traces of oil inevitably escape from the front bearings of the N1 spool into the airflow, where they are entrained and conveyed into the combustion chamber, which is all very fine and splendid and makes no difference to the operation of the engine. |
|
| |
However, an intake compressor which contains a mixture of oil and oxygen , even cold, is liable to something called "compressor blowback" (See above regarding safety distances and hiding behind something solid). |
|
| |
//the engine now has a hole at the front where is
doesn't need one.// Not so. In a true turbojet,
the front of the engine is a compressor -
essentially an axial turbopump delivering oxidiser
(air) to the combustion chamber. This compressor
is being driven by the blades at the exhaust end
of the engine. |
|
| |
In a conventional liquid rocket, there are
turbopumps delivering oxidiser and fuel into the
combustion chamber. These turbopumps are
normally driven by a turbine which is powered by
bleeding off some of the fuel (or the hot
exhaust). |
|
| |
Thus, as [DIYMatt] pointed out, the only real
difference is in the relative arrangements of the
components. |
|
| |
Just add something with a high hydrocarbon content, like
cream cheese, into the mix. That's should make for a
tasty fuel mix. |
|
| |
I must try rocket, next time. Quite fond of rocket. |
|
| |
we could name this new invention the "liquid fuel
rocket" |
|
| |
Or you could use yellow rope as a fuel. Don't eat it
though |
|
| |
Or polybutadiene and nitrous oxide... etc. |
|
| |
good call, nitrous has 3x's the oxygen by volume. |
|
| |
I think your wrong, I shall post a link henceforth. |
|
| |
"Furthermore, oxygen can only be ‘readily’ stored
in a compressed ‘gaseous’ form, without being
stored in a special cryogenic thermos cylinder (a
cylinder within a cylinder with a vacuum between
the two walls) and as a gas it loses the cooling
effect that nitrous offers by being available as a
liquid. Adding the oxidiser as gaseous oxygen
would displace more air than adding nitrous in
liquid form, resulting in a lower total power
capability. In other words; by using nitrous oxide
we can squeeze in more oxygen atoms in a more
beneficial form, containing substantial amounts of
detonation suppressing nitrogen, than would be
the case with gaseous oxygen" |
|
| |
The nitrogen also reacts with one of the combustion
byproducts, from memory. |
|
| |
Liquid oxygen is volatile and highly reactive, unlike
nitrous oxide (which is used as a mild anaesthetic). |
|
| |
I would like to retract my 3x's more oxygen
statement. It does in some circumstances, help put
3x's more in the car; but that wont work in outer
space. |
|
| |
Easier and cheaper just to use a liquid fuel rocket
engine. A turbojet has a lot of heavy parts that a
rocket doesn't need.On a small-scale rocket, you
could do away with the need for fuel/oxydizer pumps
simply by pressurizing the tanks. If you wanted a
high-altitude, near-space engine, say for altitudes
around 80-100,000 ft, borrow an idea from the SR-71
and bypass the compressor turbines for ramjet mode. |
|
| |
N2O's not bad: 2:1 ratio of filler:oxidant compared to air's 4:1, and a BP of -80C. |
|
| |
NO2 looks interesting for a rocket oxidiser: BP of 21C. |
|
| |
//do away with the need for fuel/oxydizer pumps
simply by pressurizing the tanks.// That's used for
small liquid rockets; the problem, though, is that
the entire fuel/oxidiser storage and piping system
has to be able to withstand whatever pressure you
have in the combustion chamber. |
|
| |
Re: cooling using bypass air. Liquid oxygen is quite
good at cooling things. |
|
| |
I understand that lots of rockets use liquid oxygen and/or hydrogen, and before combustion it's piped around the parts of the engine to keep them within their thermal tolerance. This solves both problems at once.
It does however make for quite a complicated system - they're not just spraying liquid oxygen in and hoping for the best. |
|
| |
Amazing number of rocket scientists we have on
here. |
|
| |
Since when do we need those pesky "qualifications" for the
bakery? |
|
| |
//not just spraying liquid oxygen in and hoping for
the best.// |
|
| |
No, but there are rockets which use excess fuel or
oxidiser to form a boundary layer to protect the
nozzle, rather than using liquid cooling. They're not
hoping for the best - they have the fluid dynamics
pretty closely worked out. But it's less efficient (for
a large rocket) than active nozzle cooling and
stoichiometric combustion. |
|
| |
// whatever pressure you have in the combustion chamber // |
|
| |
Very approximately, the pressure on the top of the combustion
chamber will be at least equal to the product of the overall mass
of the rocket and its acceleration. |
|
| |
// NO2 looks interesting for a rocket oxidiser // |
|
| |
It's no more difficult to use HNO3, which technique is WKTE. |
|
| |
//Amazing number of rocket scientists we have on here.// |
|
| |
Well, hey - it's not brain surgery. |
|
| |
Yes, except that when a tank of NO2 explodes
everybody laughs. When a tank of nitric acid
explodes, not so much. |
|
| |
More like rocket surgery, I should think. |
|
| |
I am thinking about 40,000 feet and an air-thirsty
jet. The jet gets only the air entering the front
end. At altitude there is less air. Maybe the front
end could have a telescoping cone. The cone would
telescope out (or back in on descent) to maintain
the same air resistance at altitude as at sea level
and by doing so ensure the same amount of gas was
pushed into the engine. This might allow the jet to
operate at even higher altitudes. |
|
| |
Aren't you just describing the SR-71? |
|
| |
There's the two orders of magnitude difference in power between an SR-71 engine and a Space Shuttle solid booster... of course on the bright side there's only one order of magnitude power:weight difference. |
|
| |
well, you'd need about 200 SR-71 engines to sub in for the 2 SSSB engines, and they'd weigh 10 times as much. |
|
| |
Okay, having picked a seed out of my teeth, scramjets are supposed to be about the same as a rocket (when they get operational) in those metrics. |
|
| |
I think the original idea behind this (ie, take an
existing cheap technology and adapt it simply for
spaceflight) is dead, alas. I don't doubt, though,
that the concept of an engine that transitions from
turbojet to ramjet to rocket is doable - that's how
the Reaction Engines machine works. But it's
definitely rocket science. |
|
| |
I wouldn't say "dead", so much as it'd be a niche application. I think you'd have to optimize heavily for one or the other method. Maybe for a LEO application it'd be happiest as a jet engine that could do rocket somewhat inefficiently, while geosynch, t'other way'round. |
|
| |
The Idea "Supercharged Ramjet" (yup that's my horn I'm blowing) is similar in concept: a ramjet that features an electric compressor section that tucks away into the cone when not in use: probably hideously inefficient while operating at sub-ramjet speeds, but enables an aircraft that operates at ramjet speeds to get there and back without having a completely separate engine. |
|
| |
I like the 'supercharged ramjet' idea. But in that
case why not drive the supercharger from a fan on
the back end? In which case it becomes a
turbojet. Then the inlet and outlet blades would
either retract or feather when it reached ramjet
speeds. |
|
| |
More broadly, though, someone mentioned using
a regular(ish) jet engine as the first stage of a
conventional rocket, and I quite like that. Given
the thrust-to-weight ratios of jets (and I'm
thinking here of the so-called model jet engines;
the big buggers are even better), I think they'd
make a pretty good first stage. |
|
| |
Motorjets were used on a few aircraft 60'ish years ago: jet engines which compressor is full-time IC-engine driven instead of exhaust-turbine driven. I just changed the aircraft mission parameters to one exclusively operating in the ramjet speed-range, using the "supercharger" just to get up enough speed for the ramjet to operate without help. I'm pretty sure (for halfbaked purposes anyways) that it could be stowed in the diffuser (nosecone) of a ramjet so wouldn't really affect ramjet operations. |
|
| |
But jet engines' p:w really pales in comparison with rocket engines' (Wikipedia: "power to weight ratio", last table on the page). |
|
| |
//jet engines' p:w really pales in comparison with
rocket engines'// |
|
| |
Wow - it certainly does. However, power isn't the
only consideration. Especially for a rocket (or a jet
climbing vertically), fuel consumption is a huge
factor, since most of the launch mass is typically
fuel (and oxidiser, in the case of a rocket). |
|
| |
I think it's a matter of "can't be arsed": a turbojet will get you to a maximum of 2,500mph at 20mi altitude... if you want to get to 200mi altitude you need to be going 17,500mph to be in orbit, 50x the KE and 100x the PE. The ISS is at 250mi altitude. |
|
| |
I know, but I was thinking about small launchers. 20
miles up gets you above 99% of the atmosphere, and
atmospheric drag is a very, very major factor for
small launchers. |
|
| |
Sure, look at SpaceShip One. |
|
| |
By which I mean SS1 is a rocket that uses a turbojet launch platform. If you actually could combine a turbojet and a rocket then it could be much smaller than the combined two vehicles, but certainly bigger than the SS1 if for no other reason than fuel. |
|
| |
//but certainly bigger than the SS1 if for no other
reason than fuel.// |
|
| |
That depends a great deal on payload. For a
ground-launched rocket, the lower mass limit is
quite high, because as you get smaller air
resistance dominates. |
|
| |
But if you're launching at 20-30km, things scale
pretty nicely. |
|
| |
Rockoons are an attractive option for very low
mass rockets. What I'm wondering is whether a
jet first stage (with the advantage of predictable
performance and use of atmospheric oxidiser) isn't
an equally viable option for very low mass rockets.
You've got the disadvantage of cost compared to a
balloon, but you've got a modest advantage in
terms of starting velocity for the rocket, and also
in terms of guidability of the first stage. |
|
| |
Well that's the Rutan design, innit. Fly a jet up to x feet and release the rocket. |
|
| |
Actually I think the real advantage of a jet first stage would be that you wouldn't have to fart around with a rocket engine which has an atmospheric bell: go straight to the space rocket motor design. Maybe: is 20mi rare enough to use a vacuum bell ? |
|
| |
On the save-weight note, perhaps LOx could be made on the way up. |
|
| |
Ramjets are lightweight (compared to turbojets) and operate at a much higher speed. It could be launched from a (relatively) short rocket or railgun sled to get up fast enough for the rj to kick in. Or from a B58, which was designed to fly with a weapons pod that's bigger than the SS1 (albeit wingless). |
|
| |
Ramjets are already launched with the aid of a booster
rocket. The problem is, the Air Force keeps launching
them, and they keep blowin' up before they get to top
speed. |
|
| |
//perhaps LOx could be made on the way up. // |
|
| |
This idea is a good one, you can think about it like a full-
flow staged-combustion rocket. You run ALL of the LOX and
kerosene propellant through one of those, the older kind
you only transfer a fraction of fuel in the turbopumps itself.
Even in the full-flow variant there is a much smaller volume
of oxidizer being pressurized. A jet turbine is an upscaled
gas turbopump used on hot gas instead of cryogenic fuels.
There is a certain amount of conversion required in order to
get a rocket turbopump to stuff the same quantity of
atmosphere into it as your typical jet turbofan engine. It
needs to be bigger in order to support the volumes
atmospheric air is at. Impellers are swapped with fans
packed with blades. One approach to the air problem being
pursued is an oxygen pre-cooler, which runs liquid hydrogen
fuel alongside the input air, which attempts to liquify
oxygen and flood the turbopump inlet, which is still not
going to approach the efficiency of a tank full of LOX sitting
ready, even if you do get free oxidizer for the first minute
or two of flight. And why? Why bother? Why not just build
two engines dedicated to burning two different oxidizers,
air and LOX. The thrust-to-weight problem is what we're
really trying to solve. |
|
| |
I think the better plan here is to abandon the turbine
completely and figure out how to blast a rocket engine
through a tube and get some sort of venturi effect, burning
additional fuel in the afterburner while it's within the
atmosphere. That's what the SR-71 was and that's what
current hypersonic research aircraft consist of. You'd just
add an additional "pure-rocket" mode where the air-
breathing parts get out of the way, I think in most
incarnations this strap-on air-breathing engine would be a
staged "booster" rocket that lands on it's own once it's job is
complete. If you built this it would quickly adapt to become
a more efficient platform, perhaps using a cluster of 4 large
rocketjet engines at the base instead of rocket nozzles. |
|
| |
Or, why not just build a jet turbine that uses LOX to "boost"
it's performance, maybe you can double the thrust-to-
weight ratio at atmospheric pressure over a conventional
turbine. |
|
| |
I think the best shot at improving propulsion is going to be
some sort of electronic acceleration, it's already 10 times
more efficient, now it just needs to be a few orders of
magnitude more powerful, perhaps by using a nuclear
reaction. We know that nuclear reactions are going to be
the best payoff, it's anyone's guess why it's out of reach to
civilization. A beam of energy from a ground station is
staring us in the face. This is the "light-rail" of space
transportation. This method has already been tested and
proven to work, it just needs higher beam energies. You
could theoretically provide as much or more energy to a
point-source than with the nuclear idea. |
|
| |
I think you'd be better off putting the lox on your
bagel and putting your burned fuel through a nozzle.
Accelerating it to supersonic speeds will improve
efficiency. |
|
| |
So, I just revisited this idea. |
|
| |
It turns out that Big Jet Engines have an air:fuel ratio of
about 33:1, meaning that 33kg of air (which is quite a lot,
volume-wise) goes through for every kg of fuel burned. |
|
| |
I'm assuming that the larger model jet engines have vaguely
similar ratios. |
|
| |
On that basis, a model jet engine producing 22kg of thrust
and burning 10g/s of fuel should need about 330g/s of air.
That means that if the structure (including the engine)
weighs 10kg, we should be able to carry enough liquid air
for 30 seconds of full-power running, for an all-up weight of
about 20kg. |
|
| |
So. We sling our jet-rocket under a balloon and get it up to
about 30km (the practical limit for a hydrogen balloon).
Then we open the taps and point the thing upwards. |
|
| |
Now, to begin with, we have a vehicle mass of 20kg and a
thrust of 22kg, for a net upward force of 2kg, or 20N.
Hence, since acceleration=force/mass, we accelerate
upward at a measly 1m/s^2. However, after 10 seconds,
we've lost 3.3kg of air (and 100g of fuel) so our all-up
weight is now 16.6kg, and our net upward force is 5.4kg or
54N. Doing the a=f/m now gives us about 3m/s2. After 20
seconds, net upward force is 88N, mass is 13.2kg,
acceleration is about 7m/s2. After 30s, we're out of air, and
net upward force is 12kg (120N) for a 10kg machine, for a
final acceleration of 12m/s2. |
|
| |
By my reckoning, that means our final velocity at the end of
the burn is going to be around 170m/s. I used to be able to
do all the integrals and differentials, but now I can't, so I'm
going to take a stab and say the average velocity over the
30s will be 50m/s, giving us an altitude (above our launch
point of 30km) of... oh, bollocks. 1.5km. |
|
| |
OK, back to the drawing app. |
|
| |
OK, some serious spreading of sheets shows me that the
maximum attainable altitude above launch is about 3.5km.
This is not good, people. We need to change physics. |
|
| |
We can't change physics, just find those natural quirks and anomalies that can be usefully scaled. |
|
| |
Are we using all of nature's dimensions to maximise the design of getting into orbit? What I'm try to say is, is burn really understood to the nth dimension? |
|
| |
//is burn really understood// By me? Nope. |
|
| |
I think some of the earlier annotations were more on track -
namely that a jet engine fed with bottled air is basically a
rocket, in which the jet's compressor blades replace the
turbopumps of a conventional rocket. |
|
| |
Even more so for me. I just try to imagine what it is like in the reaction. So many questions. What is the photon density, what is spacetime like at the reaction scale, what happens to the electromagnetic field and electrons what are the motions and shape patterns of all constituents. All possible dimensions happening in the reaction chamber. There may be a natural quirk there. |
|
| |
It doesn't seem to me just about stoichiometry and energy ignition level like in a very complex Bunsen burner. |
|
| |
So, I found a model jet engine that gives 157kgf of thrust.
That'll get you to 41km above launch height, using 3.5kg fuel
and 115.5kg bottled air, if you keep the total weight apart
from the engine itself down to about 6kg. |
|
| |
//jet engine fed with bottled air is basically a rocket//
I would say it's more "jet engine with MASSIVE afterburner". |
|
| |
// use cryogenic propellants for jet engine powered
model aircraft // |
|
| |
What could possibly go wrong? Bun. |
|
| |
The efficiency benefit of a jet engine vs a rocket is
that the oxidizer is provided by atmospheric air and
is not carried on the vehicle. If you've got a tank of
LOX on your aircraft, might as well use a ramjet
instead of a jet turbine. An on-board camera may be
advisable as it may be difficult to see (much less
control) from ground level. |
|
| |
To get into really half-baked territory, find a way to
burn atmosphere as fuel. |
|
| |
Thinking nature is quite strange and quirky, X rays from scotch tape. What are the chances that there are conditions that are right, in a jet engine, to undo an atom's nucleus giving an unmeasured performance boost. In the scale and complexity of reaction this rare one off would never be measured. |
|
| |
If it can't be measured, it can't be selected for. |
|
| |
My questions of the stoichiometry is of the level of particle physics, energy vectors, best combining motions of oxidisers, fuel. Best environmental change. Just don't spray them together and hope most are at optimum. |
|
| |
//What are the chances that there are conditions that are
right, in a jet engine, to undo an atom's nucleus// Well, less
than 1e-23. |
|
| |
//Well, less than 1e-23.// If nature has taught us anything, there's always a way of zig-zagging up the mountain rather than going straight up. Did the Russian's, in the 1950's discover or predict sticky tape Xrays? |
|
| |
2.035011444×10^28 'molecules' of Jet fuel.( approx Jet-5, Jet-9in jet fighter) |
|
| |