Microwave beamed power

zoltan wrote:
I actually don't have to run my engine at high speeds. There is plenty
of data from Navajo and the Bomark ramjet engines. There is of course
friction and drag losses. That is the reason why I would switch to a
rocket mode of operation around mach 6.


Yes, there is plenty of data.
How have you analysed this?
What studies of hypersonic aerodynamics have you done?

How have you proved that it will run at high speeds?
Hundreds of hours of analysis on paper, computer simulation, ...

wrote:
"zoltan" wrote:

...
The big deal is that I can run a ramjet at zero velocity without
oxidizer injection.

One can't help but note, however, that zero velocity is of limited
practical value.

It's really handy if you want to hover, and the engine is light.

Zoltan The big deal is that I can run a ramjet at zero velocity
without
Zoltan oxidizer injection.

Ken One can't help but note, however, that zero velocity is of limited
Ken practical value.

Ian It's really handy if you want to hover, and the engine is light.

If the static thrust is high enough, you might be able to launch
with no additional booster. That saves a bunch of complexity. One
of the troubles with ramjet-boost configurations is that once you have
the high-thrust booster to get the ramjet to flight speed, you are
left with the tradeoff of running the ramjet, briefly, to mach 6, or
just making that booster larger, and dumping the ramjet entirely.

A ramjet that could take off from a dead stop could be the first stage
of a TSTO. But of course, there is the problem that the first stage
design is usually driven by thrust and not by ISP.

Iain McClatchie wrote:
Zoltan The big deal is that I can run a ramjet at zero velocity
without
Zoltan oxidizer injection.

Ken One can't help but note, however, that zero velocity is of limited
Ken practical value.

Ian It's really handy if you want to hover, and the engine is light.

If the static thrust is high enough, you might be able to launch
with no additional booster. That saves a bunch of complexity. One
of the troubles with ramjet-boost configurations is that once you have
the high-thrust booster to get the ramjet to flight speed, you are
left with the tradeoff of running the ramjet, briefly, to mach 6, or
just making that booster larger, and dumping the ramjet entirely.

A ramjet that could take off from a dead stop could be the first stage
of a TSTO. But of course, there is the problem that the first stage
design is usually driven by thrust and not by ISP.

But.
Aerodynamic modelling of supersonic flows is not trivial.
It requires lots and lots of supercomputer time, or lots and lots
of testing, preferrably both.

Pointing at an object on a static test stand giving a certain amount of
thrust, and saying that it will continue to do so at multiple mach
numbers, beyond the current state of the art requires fairly strong
justification.

If it hasn't even been operated at 100km/h, nevermind 1000m/s and no
extensive computer simulation has been done then the claim stretches
credulity to breaking point.

In reply to "A ramjet that could take off from a dead stop could be the
first stage
of a TSTO. But of course, there is the problem that the first stage
design is usually driven by thrust and not by ISP. "
I was just wondering how an air launch a'la Spaceship One/White Knight
might change this scenario since less rocket boost would be required to
get the ramjet up to speed. The ramjet first stage could be recoverable
in a TSTO configuration. Seems doable, but is it worth it? Thoughts?
Steve Mickler

Iain McClatchie wrote:
Zoltan The big deal is that I can run a ramjet at zero velocity
without oxidizer injection.

Ken One can't help but note, however, that zero velocity is of limited
Ken practical value.

Ian It's really handy if you want to hover, and the engine is light.

If the static thrust is high enough, you might be able to launch
with no additional booster. That saves a bunch of complexity. One
of the troubles with ramjet-boost configurations is that once you have
the high-thrust booster to get the ramjet to flight speed, you are
left with the tradeoff of running the ramjet, briefly, to mach 6, or
just making that booster larger, and dumping the ramjet entirely.

A ramjet that could take off from a dead stop could be the first stage
of a TSTO. But of course, there is the problem that the first stage
design is usually driven by thrust and not by ISP.

But.
Aerodynamic modelling of supersonic flows is not trivial.
It requires lots and lots of supercomputer time, or lots and lots
of testing, preferrably both.

Pointing at an object on a static test stand giving a certain amount of
thrust, and saying that it will continue to do so at multiple mach
numbers, beyond the current state of the art requires fairly strong
justification.

If it hasn't even been operated at 100km/h, nevermind 1000m/s and no
extensive computer simulation has been done then the claim stretches
credulity to breaking point.

And that's not even going into the whole issue of mass ratio of existing
stages to get to 2Km/s, which isn't really bad.

Even with adding an extra 200m/s or so of fuel to support navigating back to
base (1Km/s maybe with the top stage off) and VTOL isn't horribly heavy.

(Reposted, as my first attempt does not seem to have made it)

Ian But.

Oh yeah, you're right. Zoltan's flamethrower is a really cool home
hack, but he doesn't appear committed to converting it into a real
first stage.

Ramjets as first stages are just dumb. First, there is the air
breather's burden. But lately I've been thinking about another aspect.

In order to combine the incoming oxygen with the fuel you have carried,
you will have to match their speeds. Unless you are building a rocket
and not a ramjet, that means accelerating the incoming oxygen to
vehicle speed.

So what's the difference between accelerating it while in flight versus
accelerating it in a tank?

A: In flight, you don't have to carry the tank, nor lift off with it
fully loaded. You do, however, have to accelerate 4 times as much
nitrogen.

In some sense, the Isp of an airbreather looks good at low speeds
because it's just postponing the acceleration of most of the oxidizer,
to a point later on in the flight when getting energy is less efficient.

The navaho and bomark ramjets had an Isp of 1800 at mach 3. The fastest
flight achieved by navaho was around mach 6.

zoltan wrote:

The navaho and bomark ramjets had an Isp of 1800 at mach 3.
The fastest flight achieved by navaho was around mach 6.

Do you have a reference for this? That would be extraordinary if
true.

Jim Davis

"zoltan" :

The navaho and bomark ramjets had an Isp of 1800 at mach 3. The fastest
flight achieved by navaho was around mach 6.

Have you got an URL pointing to such? And by the way what was the thrust to
drag ratio? If it is near 1::1 then you spend alot of time fighting drag
while trying to get up to speed.

Earl Colby Pottinger

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