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Ian Parker
science forum Guru Wannabe

Joined: 15 Jul 2005
Posts: 100

Posted: Wed Jun 21, 2006 8:31 pm    Post subject: Re: Turbo Scram

It is and it isn't. If what you are saying is that the fuel cost of the
Shuttle is small then you are right. If what you are saying is that
energy efficiency is not important you are wrong.

An aircraft is completely recoverable. If you only had a delta V of
6km/s instead of 9 or so the craft could be made considerable simpler
with a fuel tank that could return to Eartyh. This is the critical
factor - NOT the raw fuel cost.
Ken S. Tucker
science forum Guru

Joined: 30 Apr 2005
Posts: 1230

Posted: Wed Jun 21, 2006 6:39 pm    Post subject: Re: Turbo Scram

ianparker2@gmail.com wrote:
 Quote: Rand Simberg wrote: 1) To cruise, use an airbreather Probably true but acceleration and ballistic cruise is also possible. 2) To accelerate, use a rocket NO it ius not energy efficient. Let us suppose we have an exhaust velocity of 4km/s or so. If you are travelling at 4km/s your exhaust is stationary and you have optimum energy efficiency. 8km/s (LEO) represent 32 Megajoules/kg. If you have liqid hydrogen (about 120MJ/kg) you would in theory need about 1/4 of your mass to get into orbit. This assumes 100% efficiency. In fact you would be doing well to get 30-50% mean. At 100% efficiency of course you are accelerating a large mass of air backwards at a few m/s. This is the raw energy situation. If you look at the Shuttle you will find that quite a lot of delta V is at relatively low speeds >1km/s. The Shuttle rises vertically and turns. Chucking mass out at 4km/s for vertical acceleration and turns is quite clealy inefficient. We want to "push" at 1km/s or less. To do this you need an airbreather accelerating a large mass. OK a rocket may be the best way of getting from 2-8km/s but it is certainly not the best way of getting to 2km/s from the ground.

Right on! When I try to explain power transfer ,
I use a Harrier jet compared to a helicopter and

Power = Force x Velocity .

Force = Power / Velocity .

The Force is what you want to lift, and the Velocity
is the speed of the air/exhaust you're using to do it.
Obviously a Harrier needs a lot more Power than a
helicopter and thus has a higher fuel consumption.
Is that what you guys understand too?
Ken
Henry Spencer
science forum beginner

Joined: 04 Jul 2005
Posts: 24

Posted: Wed Jun 21, 2006 5:55 pm    Post subject: Re: Turbo Scram

<ianparker2@gmail.com> wrote:
 Quote: 1) To cruise, use an airbreather Probably true but acceleration and ballistic cruise is also possible.

Only with considerable difficulty. The poor T/W and limited speed range
of airbreathers hurts them badly for acceleration missions.

 Quote: 2) To accelerate, use a rocket NO it ius not energy efficient.

Why does this matter? Energy in the form of chemical fuels is cheap and
lightweight; high-speed airbreathing engines are neither.

 Quote: If you look at the Shuttle you will find that quite a lot of delta V is at relatively low speeds >1km/s. The Shuttle rises vertically and turns. Chucking mass out at 4km/s for vertical acceleration and turns is quite clealy inefficient.

It looks inefficient, but actually the delta-V that goes into the initial
vertical rise is quite modest -- it doesn't last that long. Almost all of
the shuttle's delta-V goes into near-horizontal acceleration at extremely
high altitude.

Anyway, so what? What matters is what it costs, and energy inefficiency
is a very minor component of the cost. Rocket fuel and rocket engineering
are cheap and easy.

Especially since the initial rise isn't that big a fraction of the
delta-V, spending very large amounts of money on making it more efficient
is foolish. Most everyone who has looked at this, and then done an honest
comparison to just using rockets, has concluded (often to their stunned
surprise) that rockets are better -- easier to develop, cheaper to
operate, less constraining.

 Quote: ...OK a rocket may be the best way of getting from 2-8km/s but it is certainly not the best way of getting to 2km/s from the ground.

In practice, other things being equal (e.g., you have to design and
develop either system yourself), it usually is.

 Quote: It would seem that the best launch strategy might be an aircraft tralleing at up to 2 km/s which then returns to base.

If you could buy/rent a big aircraft with that performance -- one that
could carry and release a big payload -- it could be very useful.
*Developing* one, for this purpose alone, simply does not pay for itself.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | henry@spsystems.net
Ian Parker
science forum Guru Wannabe

Joined: 15 Jul 2005
Posts: 100

Posted: Wed Jun 21, 2006 10:45 am    Post subject: Re: Turbo Scram

Bret Cahill wrote:
 Quote: If you look at the Shuttle you will find that quite a lot of delta V is at relatively low speeds >1km/s. The Shuttle rises vertically and turns. Chucking mass out at 4km/s for vertical acceleration and turns is quite clealy inefficient. We want to "push" at 1km/s or less. To do this you need an airbreather accelerating a large mass. A big catapult to get started would save some fuel. If you could drill a big hole through the earth the rocket could take off going down into the ground and thereby get better average propulsion efficiency. Bret Cahill

Not quite - One of tghe main problems is tghat you cannot go fast in
dense atmosphere. An aircraft going at 2km/s would be travelling
horizontally in rareified air. A rocket then has a straight 6km/s delta
V to LEO.

A aircraft would be totally recoverable and not add much to launch
costs, although it would linit heavy indivisible loads. A single 6km/s
stage I am not saying could be easily built but is within the realm of
practicality.
Bret Cahill
science forum Guru

Joined: 05 May 2005
Posts: 480

 Posted: Tue Jun 20, 2006 8:15 pm    Post subject: Re: Turbo Scram < If you look at the Shuttle you will find that quite a lot of delta V is < at relatively low speeds >1km/s. The Shuttle rises vertically and < turns. Chucking mass out at 4km/s for vertical acceleration and turns < is quite clealy inefficient. We want to "push" at 1km/s or less. To do < this you need an airbreather accelerating a large mass. A big catapult to get started would save some fuel. If you could drill a big hole through the earth the rocket could take off going down into the ground and thereby get better average propulsion efficiency. Bret Cahill
Ian Parker
science forum Guru Wannabe

Joined: 15 Jul 2005
Posts: 100

Posted: Tue Jun 20, 2006 10:53 am    Post subject: Re: Turbo Scram

Rand Simberg wrote:

 Quote: 1) To cruise, use an airbreather

Probably true but acceleration and ballistic cruise is also possible.
 Quote: 2) To accelerate, use a rocket

NO it ius not energy efficient. Let us suppose we have an exhaust
velocity of 4km/s or so. If you are travelling at 4km/s your exhaust is
stationary and you have optimum energy efficiency. 8km/s (LEO)
represent 32 Megajoules/kg. If you have liqid hydrogen (about 120MJ/kg)
you would in theory need about 1/4 of your mass to get into orbit. This
assumes 100% efficiency. In fact you would be doing well to get 30-50%
mean. At 100% efficiency of course you are accelerating a large mass of
air backwards at a few m/s. This is the raw energy situation.

If you look at the Shuttle you will find that quite a lot of delta V is
at relatively low speeds >1km/s. The Shuttle rises vertically and
turns. Chucking mass out at 4km/s for vertical acceleration and turns
is quite clealy inefficient. We want to "push" at 1km/s or less. To do
this you need an airbreather accelerating a large mass. OK a rocket may
be the best way of getting from 2-8km/s but it is certainly not the
best way of getting to 2km/s from the ground.

 Quote: 3) To turn, use a wing

Yes.

It would seem that the best launch strategy might be an aircraft
tralleing at up to 2 km/s which then returns to base.
science forum beginner

Joined: 03 Dec 2005
Posts: 46

Posted: Tue Jun 20, 2006 9:08 am    Post subject: Re: Turbo Scram

On Tue, 20 Jun 2006 05:42:53 GMT, in sci.engr.mech Fred J. McCall

 Quote: Ed Ruf wrote: :On Mon, 19 Jun 2006 12:47:04 GMT, in sci.engr.mech Fred J. McCall : wrote: : :>"Ed Ruf (REPLY to E-MAIL IN SIG!)" wrote: :http://hapb-www.larc.nasa.gov/Public/Facilities/hapb_facilities.html All very nice, but you still can't actually test the engine without flying it. Unless things have changed radically since the last time I looked, supersonic wind tunnels don't generally manage sustained air flows for long enough to really test the engine. At best you work your way up to something you think might fly.

This is not the case at least for flight speeds of Mach 7 and below. The
Hyper-X Mach 7 was fully ground tested before flight. The engine flowpath
was developed in the AHSTF and the verified in the 8-ft HTT. The 8-ft HTT
has recently run 2min long Mach 5 full closed loop engine fuel cooled
engine tests. See
http://www.pr.afrl.af.mil/mar/2006/feb2006.pdf
http://www.pr.afrl.af.mil/mar/2006/mar2006.pdf
The Hyper-X Mach 10 engine was testing in the Hypulse and Calspan pulsed
facilities.Above Mach 7 one is limited to very short duration pulsed
facilities. However, the comparison of ground and flight test data showed
quite good agreement.

See the bottom of
http://hapb-www.larc.nasa.gov/Public/Projects/Hyperx.html
for a list of publicly available Hyper-X references.
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)
science forum beginner

Joined: 03 Dec 2005
Posts: 46

Posted: Tue Jun 20, 2006 8:55 am    Post subject: Re: Turbo Scram

On Tue, 20 Jun 2006 06:11:14 GMT, in sci.engr.mech Fred J. McCall

 Quote: Can you get sustained hypersonic flow these days? Used to be the best you could do was measured in seconds, which isn't exactly a good engine test (although it's probably enough to see if you can get it lit).

Depends on the facility. The LaRC small scale freejet scramjet test
facilities can run 20-23 sec. The direct connect has recently run 2 min,
same for the 8-ft HTT.
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)
Ken S. Tucker
science forum Guru

Joined: 30 Apr 2005
Posts: 1230

Posted: Tue Jun 20, 2006 6:43 am    Post subject: Re: Turbo Scram

Bret Cahill wrote:
 Quote: only transferred heat to air via a heat exchanger, ie. Heat Exchanging RAM jet or HERAM jet. Cooler air enters, passes over a white hot surface and exits with a larger volume, effectively exploding the air as the air heats, What's the heat transfer coefficient? There isn't any great increase in the Nu number going from subsonic to supersonic flow.

Well Pluto proved it can be done.
Two sources of heating "air" is (1) contact or

To reduce chemical erosion, rely more on (2).
Injecting a gas opague to the infared, would
assist (2), then that gas is heated by radiation
and heats the air.

 Quote: I once did some calculations on a solar powered ram trying everything from mile long craft to flat panels of engines but could never get enough energy density (although heat transfer wasn't the problem).

Yes, I recall heating ramjets using LASERS
as well. The basic problem is getting the engine
hot enough without destroying it!
A old friend of mine flew F-86 Sabres, and I
asked him how he achieved max speed, he
said when the exhaust gets 800F that's it.
Regards
Ken
Fred J. McCall
science forum beginner

Joined: 17 Apr 2005
Posts: 8

 Posted: Tue Jun 20, 2006 6:11 am    Post subject: Re: Turbo Scram "tadchem" wrote: : :Bret Cahill wrote: :> > :>We're just looking for the cheapest recoverable test rig to experiment :> > :>with scrams. :> :> > :To test exactly what in flight which can't be tested on the ground? :> :> > Uh, how would you go about testing a scramjet on the ground, Ed? :> :> Possible but very expensive: :> :> Mount layers upon layers of bearings on a several mile diameter :> circular track so the DIN number of the bearings is never exceeded -- :> maybe 1 layer of bearings per 300 m/sec velocity. : :Alternative static testing method: : :...put it in a hypersonic wind tunnel... : :Also very expensive Can you get sustained hypersonic flow these days? Used to be the best you could do was measured in seconds, which isn't exactly a good engine test (although it's probably enough to see if you can get it lit). -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw
Fred J. McCall
science forum beginner

Joined: 17 Apr 2005
Posts: 8

 Posted: Tue Jun 20, 2006 5:42 am    Post subject: Re: Turbo Scram Ed Ruf wrote: :On Mon, 19 Jun 2006 12:47:04 GMT, in sci.engr.mech Fred J. McCall : wrote: : :>"Ed Ruf (REPLY to E-MAIL IN SIG!)" wrote: :> :>:On 18 Jun 2006 11:27:55 -0700, in sci.engr.mech "Bret Cahill" :>: wrote: :>: :>:>We're just looking for the cheapest recoverable test rig to experiment :>:>with scrams. :>: :>:To test exactly what in flight which can't be tested on the ground? :> :>Uh, how would you go about testing a scramjet on the ground, Ed? : :http://hapb-www.larc.nasa.gov/Public/Facilities/hapb_facilities.html All very nice, but you still can't actually test the engine without flying it. Unless things have changed radically since the last time I looked, supersonic wind tunnels don't generally manage sustained air flows for long enough to really test the engine. At best you work your way up to something you think might fly. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw
Fred J. McCall
science forum beginner

Joined: 17 Apr 2005
Posts: 8

 Posted: Tue Jun 20, 2006 5:38 am    Post subject: Re: Turbo Scram "Bret Cahill" wrote: : :> :>We're just looking for the cheapest recoverable test rig to experiment :> :>with scrams. : :> :To test exactly what in flight which can't be tested on the ground? : :> Uh, how would you go about testing a scramjet on the ground, Ed? : :Possible but very expensive: : :Mount layers upon layers of bearings on a several mile diameter :circular track so the DIN number of the bearings is never exceeded -- :maybe 1 layer of bearings per 300 m/sec velocity. Won't get you there, so far as I can tell. :You can do anything with enough bearings. GE once built a 4 spool :engine which is where I got the idea. : :> "The reasonable man adapts himself to the world; the unreasonable :> man persists in trying to adapt the world to himself. Therefore, :> all progress depends on the unreasonable man." :> --George Bernard Shaw : :The converse isn't necessarily true. Every unreasonable man doesn't :necessarily get results. As you demonstrate, above. -- "But if this ever changing world in which we live in Makes you give in and cry... Say live and let die." -- Paul McCartney & Wings
Bret Cahill
science forum Guru

Joined: 05 May 2005
Posts: 480

 Posted: Mon Jun 19, 2006 10:52 pm    Post subject: Re: Turbo Scram They keep saying the physics of scram is understood well enough, that it's "merely an engineering problem." Of course, that's what they keep saying about nuclear fusion so it may be a meaningless statement. Bret Cahill
science forum beginner

Joined: 03 Dec 2005
Posts: 46

Posted: Mon Jun 19, 2006 10:30 pm    Post subject: Re: Turbo Scram

On 19 Jun 2006 14:28:42 -0700, in sci.engr.mech "tadchem"

 Quote: Alternative static testing method: ...put it in a hypersonic wind tunnel... Also very expensive

What's very expensive compared to trying to flight test something? Freejet
facilities all ready exist in this country at NASA LaRC and GRC, AEDC,
ATK-GASL. Direct-connect facilities at LaRC, GRC, GASL, AFRL. even UVA.
Pulsed facilities at LaRC/GASL, Calspan, Cal-tech. et alone others around
the world. You get what you pay for. Ground test articles tend to have much
more instrumentation on them, so you can actually learn much more from the
tests. Let alone run repeated tests. No matter how you slice it duplicating
the total energy of Mach 5+ flight isn't cheap no matter how you do it.
--
Ed Ruf (Usenet2@EdwardG.Ruf.com)
Bret Cahill
science forum Guru

Joined: 05 May 2005
Posts: 480

Posted: Mon Jun 19, 2006 9:50 pm    Post subject: Re: Turbo Scram

 Quote: only transferred heat to air via a heat exchanger, ie. Heat Exchanging RAM jet or HERAM jet. Cooler air enters, passes over a white hot surface and exits with a larger volume, effectively exploding the air as the air heats,

What's the heat transfer coefficient? There isn't any great increase
in the Nu number going from subsonic to supersonic flow.

I once did some calculations on a solar powered ram trying everything
from mile long craft to flat panels of engines but could never get
enough energy density (although heat transfer wasn't the problem).

Bret Cahill

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