Air Breathing for VTVL

I have contemplated an air breathing SSTO vehicle. This hypothetical
vehicle would be shaped like the DC-X and use four of my induction jet
engines. This is a cone with the four engines at the base.

The induction jet engines are like ramjets except that they work at a
standstill with an Isp of 4000. This Isp figure is only a measure of
fuel consumption and not exhaust velocity. At higher velocities to
about mach 6 they work like ramjets because they are exactly like
ramjets. I guess they could be called a version of ejector ramjet.
They have no moving parts just airflow ducting and a rocket-like
regeneratively cooled nozzle. I would expect to employ a nose cone
that can be moved forward to reduce the intake cross section and to
eventually completely close the intake. I expect to achieve 50 T/W or
better depending on the materials used and final configuration.

I expect to have the Isp drop from 4000 at launch to 500 at mach 6 and
have an average Isp of 1000 from 0 to mach 6. At this speed I close
the intakes and work like a rocket until I reach orbit, at an Isp of
350. The mass ratio is 6 for the rocket mode and 1.3 for the air
breathing mode, during which only fuel is used, no oxydizer. This
includes a small fuel reserve for vertical landing.

This vehicle is simple enough that a small team could build it with a
low budget. I built my prototype engines by welding stainless steel
sheets and turning steel parts on my lathe. I hope to build a
prototype flying car first after which I can work on flying faster and
higher.

In this thread you guys have assumed that the air breathing engines
are in addition to the rocket engine but they can be the same. You
also assume that heavy and expensive turbine blades are needed to pump
the air and they are not needed. The only weight penalty is the intake
ducting and the variable cone. The rest of it is just like the rocket
engine.

You can see:

http://www.vtol.net
http://www.vtol.net/induction.htm
http://www.vtol.net/air.htm

Zoltan

Sorry for the delay in responce.



Ok, now we get down to some numbers.







For a LOx/Kero VTVL SSTO using off the shelf engines you get a 14 ration

between in orbit weight and GLOW. I.E. if you want 50 tons of loaded ship

in orbit, your glow is about 700 tons. Using off the shelf (with water and

LOx injection ) turbo-jets up to Mach 6 drop that to a 8 to 1 ratio, and

your 50 ton in orbit in orbit craft has a glow of about 425 tons.



Now with a 10-1 t/w ration jet engine set, you add 10 tons of jet engine

but lose about 7 tons of rocket and tank dry weight. (If you assume 15-1

t/w engines their no weight gain.) As a nit the water and Lox injection

also increases thrust in the same engine, so effective T/W improves, but I

can't find out by how much. So I assume T/W stays at about 10.



Now the weight per say isn't really interesting. The important thing is

that you wind up with a smaller and more resilient craft. Its easier to a

working structure for it and likely you get more reliability.







The reason I pushed the point to a HTHL SSTO (aside from just seeing if it

would work) is that it added operational flexibility, effectively lowered

the necessary delta-v, lowered thrust needs on take off and low altitudes

over a VTVL, and (since the LOx was added in flight) lightened the landing

gear weight. The wings do double duty as fuel tanks and extra reentry

surface to allow a cooler surface temp on reentry. Note the wing in my

configuration are NOT scaled for take off with the full mass of 425 tons

needed for a boost to orbit. Since it gets LOx in mid air (from mid air

"refueling" or LOx mining from the air), its take off weight came to about

170 tons.





The fact that the cost of the jets would buy a lot of LOx is REALLY

irrelevant. Fuel is currently a virtually negligible fraction of launch

costs. Servicing the craft (or building in the case of expendables)

currently dominates launch costs, and a high dry mass fraction of structure

and hull rather then bulky tanks is likely to dramatically lower servicing

costs. Also of course the jet engines you add - replace nearly half of the

Rocket engines you'd need for the far heavier (700 tons versus 425 tons)

all rocket VTVL SSTO. Rocket engines are about as costly as, and far less

durable then, jet engines. So you save money on the total engine system

purchase and servicing costs.





As to your statement that

==="I would like to find the point where the operational flexibilities

possible

= with an airbreathing engine do not cost performance in real terms."==



Depends on what performance your concerned with, and how it works in your

design. A 15-1 T/W ration jet engine in my configuration will allow you to

boost to orbit with no added dry mass since the added weight of the jet

will be offset by the lower weight of tanks and rocket engines needed. But

is that the critical performance number? Is operational flexibility,

operational costs, development cost, etc more critical?



Also how the craft ascends effects your numbers. My HTVL configuration

needs a lot less take off thrust, hence engines, then a VTVL configuration.

So the trade off in weight and engines would be very different for VTVL

jet/rocket SSTO. Even a HTVL that does a fast acceleration up into vacuum

like Rascal would need a lot more jet engine thrust (hence weight), vrs a

HTHL that flies a more moderate ascent to max airbreathing altitude and

speed. So at what point a given engine is acceptable, depends on the

details of the craft that needs it, and what its design priorities are?







If your question is at what T/W can a jet
engines weight in a VTVL SSTO pay for itself in dry weight. That depends on
how much of the total Delta-V it can deliver.

For example. If your total delta-V to orbit (including virtical assent) is
8730 m/s (which is a standard LOx/Kero delta-v to orbit number).

If the jet can deliver 3670 m/s it would need a T/W of about 23 to break even
on the dry weight, if you ignore lower delt-v requirements due to a lower
airdrag on the smaller craft.

If the jet can deliver 1835 m/s it would need a T/W of about 40 to break
even on the dry weight.
Kelly Starks


"Humans are a race of compassionate predators."

"Kelly St" wrote in message
...


Sorry for the delay in responce.



Ok, now we get down to some numbers.







For a LOx/Kero VTVL SSTO using off the shelf engines you get a 14 ration

between in orbit weight and GLOW. I.E. if you want 50 tons of loaded ship

in orbit, your glow is about 700 tons. Using off the shelf (with water
and

LOx injection ) turbo-jets up to Mach 6 drop that to a 8 to 1 ratio, and

your 50 ton in orbit in orbit craft has a glow of about 425 tons.

I have been using 16 ratio to LEO with 9,000 m/s required. From Mach 6
there is about 6,000 m/s remaining to orbit plus fairly minor gravity and
drag
losses. At 3,500 m/s exhaust velocity of a vacuum optimised engine, you are
looking at a rocket ratio of 6. I assume you are figuring the remaining
ratio
is feeding the jets?


Now with a 10-1 t/w ration jet engine set, you add 10 tons of jet engine

but lose about 7 tons of rocket and tank dry weight. (If you assume 15-1

t/w engines their no weight gain.) As a nit the water and Lox injection

also increases thrust in the same engine, so effective T/W improves, but I

can't find out by how much. So I assume T/W stays at about 10.

High Mach jets are a bit more complex. The 10/1 jet also has an intake
system of similar mass. The variable ramps, boundary layer bleed,
subsonic diffuser, and various Mach scheduled actuators are just
as heavy as your base engine according to my references. The afterburner
with variable throat and nozzle geometries that vary with Mach,
dynamic pressure, and temperature also masses about half as much as
the dry turbojet.

The result tends toward a 1,000 lb engine producing 10,000 lbs of thrust
dry. Add 1,000 lbs for the intake system, and 500 lbs for the afterburner/
nozzle system, and you end up with a (generic) 2,500 lb system producing
15,000 lbs of thrust with afterburner. This would net a T/W ratio of 6.
Mass injection increases T/W at the expense of Isp. It quickly becomes
a trade study beyond the scope of usenet engineering.


Now the weight per say isn't really interesting. The important thing is

that you wind up with a smaller and more resilient craft. Its easier to a

working structure for it and likely you get more reliability.

We probably disagree here.






The reason I pushed the point to a HTHL SSTO (aside from just seeing if it

would work) is that it added operational flexibility, effectively lowered

the necessary delta-v, lowered thrust needs on take off and low altitudes

over a VTVL, and (since the LOx was added in flight) lightened the landing

gear weight. The wings do double duty as fuel tanks and extra reentry

surface to allow a cooler surface temp on reentry. Note the wing in my

configuration are NOT scaled for take off with the full mass of 425 tons

needed for a boost to orbit. Since it gets LOx in mid air (from mid air

"refueling" or LOx mining from the air), its take off weight came to about

170 tons.

Your article was not online when you posted the link last time. Just going
from
your posts. It would seem to me that you need at least 10% of take off mass
for
airframe and landing gear. That would be 17 tons of airframe plus 10 tons of
jet engines. ( I think jet mass is light) 3 tons of rocket engines and 7.5
tons of
various tankage for another 10.5 tons. I see a minimum 75% of your mass in
orbit being airframe, tanks, and engine systems. Not including a possible
ACES
or LOX refueling mass penalty. By the time you add TPS, cargo handling,
and control systems, you could reach negative payload.




The fact that the cost of the jets would buy a lot of LOx is REALLY

irrelevant. Fuel is currently a virtually negligible fraction of launch

costs.

Full agreement.

Servicing the craft (or building in the case of expendables)

currently dominates launch costs, and a high dry mass fraction of
structure

and hull rather then bulky tanks is likely to dramatically lower servicing

costs.

Agreement would be conditional on actually achieving the goals you
suggest.

Also of course the jet engines you add - replace nearly half of the

Rocket engines you'd need for the far heavier (700 tons versus 425 tons)

all rocket VTVL SSTO. Rocket engines are about as costly as, and far less

durable then, jet engines. So you save money on the total engine system

purchase and servicing costs.

Currently your arguement seems to make sense. If anyone produces a
reasonable
RLV rocket engine in some quantity, then no. Rockets are a relatively
immature
propulsion compared to jets. I can buy a well used 5k jet engine for ~$40k.
If I were to place a quantity order (100 units?) with XCOR, I could beat
that
price for new 5k rockets. The guts of a pump fed rocket total an easier
problem than a high Mach turbojet, if a mature RLV unit is produced. This
includes servicing access. The durability an cost problems can be made
to go away.




As to your statement that

==="I would like to find the point where the operational flexibilities

possible

= with an airbreathing engine do not cost performance in real terms."==



Depends on what performance your concerned with, and how it works in your

design. A 15-1 T/W ration jet engine in my configuration will allow you
to

boost to orbit with no added dry mass since the added weight of the jet

will be offset by the lower weight of tanks and rocket engines needed.
But

is that the critical performance number? Is operational flexibility,

operational costs, development cost, etc more critical?

Your last sentence describes the critical areas. Our disagreement is
on whether *current* jet engines are capable of doing what you suggest.


Also how the craft ascends effects your numbers. My HTVL configuration

needs a lot less take off thrust, hence engines, then a VTVL
configuration.

So the trade off in weight and engines would be very different for VTVL

jet/rocket SSTO. Even a HTVL that does a fast acceleration up into vacuum

like Rascal would need a lot more jet engine thrust (hence weight), vrs a

HTHL that flies a more moderate ascent to max airbreathing altitude and

speed. So at what point a given engine is acceptable, depends on the

details of the craft that needs it, and what its design priorities are?

Details are the thing.:-)

I feel that the mass of airframe more than offsets the engine thrust
requirement.
I don't like VTVL myself. It is however, a useful method of determining
relative penalties of equipment.


If your question is at what T/W can a
jet
engines weight in a VTVL SSTO pay for itself in dry weight. That depends
on
how much of the total Delta-V it can deliver.

For example. If your total delta-V to orbit (including virtical assent)
is
8730 m/s (which is a standard LOx/Kero delta-v to orbit number).

I use 9,000, which I got from people on this group a few years back.

If the jet can deliver 3670 m/s it would need a T/W of about 23 to break
even
on the dry weight, if you ignore lower delt-v requirements due to a lower
airdrag on the smaller craft.

If the jet can deliver 1835 m/s it would need a T/W of about 40 to break
even on the dry weight.

Another set of numbers to plug in. Thanks.

My personal opinion is that the most profitable launch system in the near
term
would be based on a HTHL launch assist platform capable of Mach 3-6 with
staging at very high altitude and low dynamic pressure. Upper stage, dunno.
Basically Len Cormiers earlier Space Van concepts. The VTVL in the subject
is to find performance levels required that are clearly not contrived to
make
my airbreathing concept look good. For what I have in mind, I need to be
able
to clearly state the performance penalty to be paid for operational
flexibility
and somewhat easier development/testing environment.

Kelly Starks


"Humans are a race of compassionate predators."

johnhare wrote

My personal opinion is that the most profitable launch system in the near
term
would be based on a HTHL launch assist platform capable of Mach 3-6 with
staging at very high altitude and low dynamic pressure. Upper stage, dunno.

Let's consider the upper stage first, and work backwards. Say we want 10
tons in LEO. A mass ratio of around 4 is good, because we can get dry mass
to around 10% without expensive scrimping, leaving 15% of the gross mass for
payload. So the gross mass is 65 tons for our 10 tons of payload.
Nice'n'easy.

If a LOX/LH2 stage is used, with an isp of 440 and a mass ratio of 4, that's
6,000 m/s delta V. To get somewhere interesting you need to start at about
1600 m/s horizontal velocity and 100 km of height (second stage start at 100
km is good, no Q to worry about so you can leave the aerodynamic structure
mass in the booster, you get vacuum isp's, plenty of coast time for
separation, and so on).

So that's the target. 65 tons to 100 km altitude and 1600 m/s horizontal.
You can mess with that a bit, but somewhere in there is what's needed.

I don't think a pure airbreather will do that, at least not easily. But I do
think a HTHL airbreather with LOX/kero rocket boost could do it. Preferably
piloted, though the second stage needn't be man-rated.

Something like:
jet fuel 70 tons
rocket fuel/oxidiser 190 tons
2nd stage gross mass 65 tons
1st stage dry weight 110 tons
flyback fuel 15 tons

for a 450 ton GLOW, suitable for standard aviation-type runways. No pads,
just an extra hanger with LOX/LH2 supplies at an airport.

You can maybe even use the jet turbines as pumps for the rocket fuel. Or
part-burn fuel to run the jet engines when there is no air. Use the rocket
engines as RATO's. And so on.

--
Peter Fairbrother

BTW - I was looking at teeny jets recently, around the 100N size. They have
a T/W around 11, and exhaust velocities around 1150 m/s. Cost a couple of
kilobucks. But, they have radial compressors .

"Peter Fairbrother" wrote in message
...
johnhare wrote

My personal opinion is that the most profitable launch system in the
near
term
would be based on a HTHL launch assist platform capable of Mach 3-6 with
staging at very high altitude and low dynamic pressure. Upper stage,
dunno.

Let's consider the upper stage first, and work backwards. Say we want 10
tons in LEO. A mass ratio of around 4 is good, because we can get dry mass
to around 10% without expensive scrimping, leaving 15% of the gross mass
for
payload. So the gross mass is 65 tons for our 10 tons of payload.
Nice'n'easy.

This is one of the reasons I suggested on SSP that a healthy suborbital
industry*
is more than halfway to a healthy orbital industry. It was fairly easy for
you to
figure the numbers on an upper stage. It will be easy for others to do the
same.

If a LOX/LH2 stage is used, with an isp of 440 and a mass ratio of 4,
that's
6,000 m/s delta V. To get somewhere interesting you need to start at about
1600 m/s horizontal velocity and 100 km of height (second stage start at
100
km is good, no Q to worry about so you can leave the aerodynamic structure
mass in the booster, you get vacuum isp's, plenty of coast time for
separation, and so on).

So that's the target. 65 tons to 100 km altitude and 1600 m/s horizontal.
You can mess with that a bit, but somewhere in there is what's needed.

I'm more in favor of flexible performance targeting early on. This involves
finding the break points of various systems and staying well under
them. If, for instance, the prefered TPS becomes a problem after Mach
5.5 on reentry, then it might be more profitable to stage at a velocity
and altitude that gives less than that.

I don't think a pure airbreather will do that, at least not easily. But I
do
think a HTHL airbreather with LOX/kero rocket boost could do it.
Preferably
piloted, though the second stage needn't be man-rated.

I'm quite sure that airbreathing will not do the whole booster job. It will
take rockets to get the Mach numbers/altitude I suggested. OTOH, if
it turns out that airbreathers can economically provide mach 2.5 at 40
km, then it might be more profitable to use the single system on boost.
Understanding that no current airbreather will do this.

Something like:
jet fuel 70 tons
rocket fuel/oxidiser 190 tons
2nd stage gross mass 65 tons
1st stage dry weight 110 tons
flyback fuel 15 tons

for a 450 ton GLOW, suitable for standard aviation-type runways. No pads,
just an extra hanger with LOX/LH2 supplies at an airport.

And smaller. There is some market for smallsats if you get the price down.

You can maybe even use the jet turbines as pumps for the rocket fuel. Or
part-burn fuel to run the jet engines when there is no air. Use the rocket
engines as RATO's. And so on.

Rocket pumps are a severe mismatch to jet turbines. Your point on looking
at all possibilities is right though, as long as you keep using numbers and
letting them do their job.
--
Peter Fairbrother

BTW - I was looking at teeny jets recently, around the 100N size. They
have
a T/W around 11, and exhaust velocities around 1150 m/s. Cost a couple of
kilobucks. But, they have radial compressors .

What is wrong with radial compressors? Any idea on the turbine inlet
temperatures?
I should mention that teeny compressors can get into trouble at altitude due
to
the drop in Renolds numbers.


*A healthy suborbital industry being 2 or more vehicle types being flown
daily
by 3 or more companies. If the operating companies have to look through
their records to figure out how many flights since the last abort, we are on
the way.

johnhare wrote
"Peter Fairbrother" wrote

BTW - I was looking at teeny jets recently, around the 100N size. They
have a T/W around 11, and exhaust velocities around 1150 m/s. Cost a couple
of kilobucks. But, they have radial compressors .

What is wrong with radial compressors?

They don't accept high inlet velocities as well as axial ones.

? Am I right? No-one since Whittle has used radials by choice, but my
understanding may be flawed.

I think teeny jets have to use radials, not axials, for Reynold-number type
reasons.

Any idea on the turbine inlet temperatures?

No, sorry. EGT max is only 700 C tho'.




Talking of models, I used to use Jetex "augmenter tubes" when I werre a lad.
They "captured and entrained" air with the the Jetex exhaust, and heated and
accelerated it (supposedly!. Long story, but they did actually work, and far
better than the static figures show when at speed and tuned up). Here's a
link:

http://jetex.org/motors/motors-accessories.html

The math possibilities are indubitable for an air-breather (tho' it need not
even "breathe" the air, just heat it and expel it, like an aircraft uses the
air all around for lift).

(Jetex motors were refuellable solid-fuel rocket motors, used mostly to
power model aircraft as opposed to rockets. They were fairly long-duration,
about 10 seconds or more. I've been told they are still made.)



--
Peter Fairbrother

Peter Fairbrother wrote in message
They don't accept high inlet velocities as well as axial ones.
Thats what a complicated and heavy intake is for. But for a given tip
velocity the inlect velovity is lower on a radial compressor

? Am I right? No-one since Whittle has used radials by choice, but my
understanding may be flawed.

The liquid air plants I have seen use large radial compressor and
expanders. For flight engines i belive thay are still used in
turboshafts IIRC. The main reason thay are avoided in aircraft is
their very large frontal area compared to axial flow types.

I think teeny jets have to use radials, not axials, for Reynold-number type
reasons.

There are blade tip clearance losses that dominate in small turbines
also. Radials don't suffer as badly from that esp. if there are of the
closed impeller type.

Greg

Greg wrote:

There are blade tip clearance losses that dominate in small turbines
also. Radials don't suffer as badly from that esp. if there are of the
closed impeller type.

Are radial compressors more subject to FOD?

Paul

(Greg) wrote:
Peter Fairbrother wrote in message
They don't accept high inlet velocities as well as axial ones.
Thats what a complicated and heavy intake is for. But for a given tip
velocity the inlect velovity is lower on a radial compressor

? Am I right? No-one since Whittle has used radials by choice, but my
understanding may be flawed.

The liquid air plants I have seen use large radial compressor and
expanders. For flight engines i belive thay are still used in
turboshafts IIRC. The main reason thay are avoided in aircraft is
their very large frontal area compared to axial flow types.

I think teeny jets have to use radials, not axials, for Reynold-number type
reasons.

There are blade tip clearance losses that dominate in small turbines
also. Radials don't suffer as badly from that esp. if there are of the
closed impeller type.


Are there some good pictures available? I've found this by googling,
does How Things Work cover both compressor types?

http://www.ist.rwth-aachen.de/en/pru...erdichter.html

Also, http://jet-engine-lab.technion.ac.il...ilities/08.jpg
at http://jet-engine-lab.technion.ac.il...cilities2.html


And http://hypertextbook.com/facts/2000/KennethKwan.shtml
quotes "Jet Propulsion and Aircraft Propellers." Marks Standard
Handbook for Mechanical Engineers, 8th Edition. New York: Zucrow &
Reese, 1978: 11-84.
"Because of the limited air induction capacity of the centrifugal
compressor, also called the radial compressor, engines for developing
thrust above 7,000*lb (31 kN) at static sea level, employ axial-flow
compressors."


And is http://www.allstar.fiu.edu/aero/tinyturbo1.html a radial, or am
I reading it wrong?

And http://www.ip.co.za/people/kalle/jtr.htm looks interesting.

Thanks.

/dps

"Paul F. Dietz" wrote in message ...
Greg wrote:

There are blade tip clearance losses that dominate in small turbines
also. Radials don't suffer as badly from that esp. if there are of the
closed impeller type.

Are radial compressors more subject to FOD?

Paul

I think so. Its more a function of tip velcity which is very high on
both radial and axil flow compressors. But i could be wrong.

Greg