> From: Robert
> a scram jet engine would not require anywhere
> near as much propellant/fuel as a the shuttle

Neither would flying unicorns, but then again they do not exist either.

Scramjets are currently seen, at best, as sustainer engines for hypersonic
missiles. Possible something that can be fitted to a ramjet which helps the
engine exceed its normal flight envelope; just like an after burner helps a
turbofan exceed its envelope. A lot of engineers believe fundimental limits
of fluid dynamics mean they will *never* get better than that. They are the
air breathing equivolent of ion engines. At present no one can even guess
how to increase the thust to meaningful amounts.

I did not 'miss what you were saying'. I am saying that the kind of high
performance scramjets you are talking about are completely mythical at best,
and against the laws of physics at worst.

John

i have to disagree. I've seen the indications that they have existed
since the 70's at least. they may not be that powerful, but they
still have the 'sustainer engine' capacity, that you refer to. that
is sufficent to get them from high altitude (10000 feet) at mach 2 in
to near outer space.

one thing ive always wondered about. is they say the airflow has to
be mach 2. what if the fuel was injected at mach 2.

--- In spacesettlers@yahoogroups.com, "ANTIcarrot"
wrote:
>
> > From: Robert
> > a scram jet engine would not require anywhere
> > near as much propellant/fuel as a the shuttle
>
> Neither would flying unicorns, but then again they do not exist
either.
>
> Scramjets are currently seen, at best, as sustainer engines for
hypersonic
> missiles. Possible something that can be fitted to a ramjet which
helps the
> engine exceed its normal flight envelope; just like an after burner
helps a
> turbofan exceed its envelope. A lot of engineers believe
fundimental limits
> of fluid dynamics mean they will *never* get better than that. They
are the
> air breathing equivolent of ion engines. At present no one can even
guess
> how to increase the thust to meaningful amounts.
>
> I did not 'miss what you were saying'. I am saying that the kind of
high
> performance scramjets you are talking about are completely mythical
at best,
> and against the laws of physics at worst.
>
> John
>
simplicity and ease of use." - PC Magazine

> From: Robert
> they (scramjets)
> still have the 'sustainer engine' capacity, that you refer to. that
> is sufficent to get them from high altitude (10000 feet) at mach 2 in
> to near outer space.

Please try reading up about a subject before you post. In this case:
sustainer engine. Once you learn what one is, you might realise how
nonsensecle the above statement is.

John

what ever you read, i know what i have seen. IF i told you of some of
it, id be risking jail. lets just say that if nasa could not do it,
the USAF could. hydrogen fusion packs quite a punch.

--- In spacesettlers@yahoogroups.com, "ANTIcarrot"
wrote:

On 08/06/06, Robert wrote:
> i have to disagree. I've seen the indications that they have existed
> since the 70's at least. they may not be that powerful, but they
> still have the 'sustainer engine' capacity, that you refer to.

They have ridiculously low thrust/weight ratio (2!), and they usually melt.

> that
> is sufficent to get them from high altitude (10000 feet) at mach 2 in
> to near outer space.

Mach 7-9 has been used so far.

> one thing ive always wondered about. is they say the airflow has to
> be mach 2.

Nope. Mach ~5 minimum on scramjets; in practice more like mach 7-8 is minimum.

Some designs may be able to run as ramjets then progressively
reconfigure themselves in flight into scramjets, in theory, then you
would be about to go mach 2.0 - mach 17 (ish).

But there's huge problems; and you'd still have to get to mach 2.0 and
from mach 17 to mach 25 (orbital speed) somehow (i.e. rocket!) Going
faster than mach 17 seems to be off the table at the moment (details
of the hydrogen combustion rates do not seem to support higher speeds
than that).

> what if the fuel was injected at mach 2.

It's not the fuel, it's the airflow through the engine that has to be
supersonic. Injecting fuel at supersonic speeds is called a ducted
rocket.

Personally I think the high supersonic designs have more legs
(Skylon)- you run atmospheric using precooled turbojets until you
reach about mach 5.5 and high altitude, then do a rocket burn for
orbit. That seems to be doable, single stage, with reasonable payload.
The precooler was the most challenging part, but that's been demoed
now.

Scramjets don't even look like they can achieve single stage to orbit
at the moment.

--
-Ian Woollard

"Gravity is just a theory. We shouldn't be teaching it to children as
if were fact."
"The NSA would like to remind everyone to call their mothers this
Sunday. They need to calibrate their system."