The Sanger Concept - the scramjet myth

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."