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Old 03-26-2010, 03:21 AM   #16
Moach
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yeah, iīm going for more realistic than the DG, thatīs the whole point... the DG is far too overpowered and extraordinarily fuel-efficient

the star-liner is designed to fly the high stratosphere relying mostly on itīs lift, rather than muscle it out with thrust, thus the air-breathers make some more sense...

this helps to minimize the amount of liquidO2 needed... a DG-like craft would burn O2 from itīs internal tanks from wheels up all the way to orbit, quite a waste, since thereīs plenty of that around the ship for as long as thereīs air


so, when in atomespheric flight, the star-liner chugs air from the upper inlets, cools it and feeds it pressurized from the turbines into the aerospikes for final combustion which generates tons of thrust (but not impossibly high, like the DG)

the pre-coolers and shock gates on the inlets ensure maximum efficiency of the turbines all the way up to mach 5...

then the scramjets go into action, and propel us to half of orbital speed... then the aerospikes fire again, this time on internal liquid O2


after reentry, whateverīs left of fuel, if any, can be used for a powered descent


and i imagine the turbo-rocket engines would sound like the utmost tower of all that is awesome in this earth and near systems
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Old 03-26-2010, 08:41 AM   #17
jedidia
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Quote:
a viable (yet made-up) alternative, would be a hybrid rocket engine, the ram inlets would provide O2 for them while in atmospheric flight, allowing the ship to carry more liquid fuel, and switch to the internal O2 supply only when air is no longer available...
sounds a lot like the skylon, which is actually being developed currently, so I'd say that's a great otpion.
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Old 03-26-2010, 08:55 AM   #18
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Moach, I presume you have seen these?

http://www.reactionengines.co.uk/
animation here:
http://www.reactionengines.co.uk/skylon_ops_anim.html

and a Orbiter version:
HOTOL v1.02


N.
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Old 03-26-2010, 10:20 AM   #19
Chub777
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Nice project there. I think it would be better if you have an EVA port on the top (like the XR5). Also the cockpit looks small for something that big...

And yes, SCRAMs are dead weight for most of the flight. It would be hard to use SCRAMs or ramjets during take-off. Maybe some JATO thrusters would be put to good use. They're light enough and can put that big hunk of DG on steroids to 500 metres a second in less than the length of a runway.
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Old 03-26-2010, 02:38 PM   #20
Izack
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That is looking GOOD, Moach!
A giant Deltaglider with nicer curves!
And this talk of aerospikes and SABREs is getting me excited, too. A nice wide linear aerospike would complete the ship's futuristic appearance.
A combination SABRE/aerospike wouldn't be too hard to pull off. The exhaust method shouldn't have too much effect on the type of engine, so long as it's still a rocket.
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Old 03-26-2010, 04:38 PM   #21
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Having air inlets on top of the wings seems quite unusual. Could this cause problems with air intake during high AOA maneuvers (in particular given the massive chord length of this plane), even before a stall?
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Old 03-26-2010, 05:46 PM   #22
Moach
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well, the Northrop b2 seems to pull off the same upper-wing inlets without much trouble (that iīve heard of, at least)

but it makes sense that a drop in air pressure caused by high AoA could cause a performance drop.... but well, this thing is not made to go through stalls during powered ops, so i guess if you keep your nose low, there should be no problems...

also, this ship has considerably more lift than the DG, so itīs less likely to need such high AoA for maneuvering

in the up-front shot, you can see how the wings are curved along the leading edge, this, like in the concorde, creates a large vortex above the wing at high AoA, which allows it a slower stall speed


anyways, with the suction from the SABRE engines, the performance drop from a stall could be less than noticeable, at least for the pilot, who will definitely have more urgent matters to worry about


as for the engines, right now we have two radial aerospikes instead of linear, looks more delta-glider-ish, but if you guys want i can just as well switch those for a linear model
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Old 03-26-2010, 05:57 PM   #23
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Quote:
Originally Posted by Moach View Post
 well, the Northrop b2 seems to pull off the same upper-wing inlets without much trouble (that iīve heard of, at least)
But the B2 has the inlets much closer to the front, meaning a higher AOA would be needed for the airflow to the inlets to be disrupted. Making the inlets farther back might mean that airflow would be disrupted even at minor AOA. Though all hypothetical, you would have to test in a wind tunnel to get real data to make it as realistic as possible.

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Old 03-26-2010, 06:30 PM   #24
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Quote:
Originally Posted by Moach View Post
 well, the Northrop b2 seems to pull off the same upper-wing inlets without much trouble (that iīve heard of, at least)
Different flight conditions, the B-2A doesn't reach high AOAs at all and flies always subsonic. As long as the wing doesn't stall in front of the air inlet, the inlet works - at subsonic speeds.

You're flying at supersonic speeds, so the position of the air inlets does matter much more. At very high supersonic speeds, the position is even critical, the whole fuselage of the plane is the inlet. Which is why all SCRamjet prototypes either use annual inlets (cone at the front) or have an rectangular inlet at the bottom of the plane, with a specially curved lower side of the plane.

The inlet is not just "the point where the air goes in", it has more jobs, the term "inlet pressure ratio" is a good hint... the inlets also compress the air initially for having the right conditions for the compressor to work.

Quote:
Originally Posted by Moach View Post
 but it makes sense that a drop in air pressure caused by high AoA could cause a performance drop.... but well, this thing is not made to go through stalls during powered ops, so i guess if you keep your nose low, there should be no problems...
At supersonic speeds, it is even more extreme. Tiny variations in AOA or sideslip angle can mean a complete inlet stall, which means the airflow inside the inlet reverses direction, air is pulled through the inlet out of the engine. That is why the inlet cones of SR-71 or ReactionEngines Skylon move forward and backward, and why the cones are so exposed compared to the rest of the plane. They need it for positioning the Mach shock waves of the tip of the inlet cone right at the lip of the inlet, so the reflected shock waves compress the air without stalling.

Quote:
Originally Posted by Moach View Post
 in the up-front shot, you can see how the wings are curved along the leading edge, this, like in the concorde, creates a large vortex above the wing at high AoA, which allows it a slower stall speed
And have the engine awash in the vortex in this case. Bad bad bad idea. also your curve is not strong enough, you wouldn't get a vortex with such a small angle.

Quote:
Originally Posted by Moach View Post
 anyways, with the suction from the SABRE engines, the performance drop from a stall could be less than noticeable, at least for the pilot, who will definitely have more urgent matters to worry about

as for the engines, right now we have two radial aerospikes instead of linear, looks more delta-glider-ish, but if you guys want i can just as well switch those for a linear model
Where are the inlet spikes of the SABRE? Also, suction from an engine works at low mach numbers to supply air, but at supersonic speeds, the air simply doesn't notice that your engine exists.
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Old 03-26-2010, 06:47 PM   #25
Linguofreak
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Originally Posted by Andy44 View Post
 If you're using DeltaGlider-tech rocket engines than all the airbreathing technology is a waste, since the specific impulse of the rockets is greater than that of the scramjets on the DG-S.

If you're going for a more realistic rocket engine, though, some of this exotic air-breathing tech may be worth the extra mass.
Nah. With a realistic rocket engine, a multi-stage-to orbit tower design is much more reasonable than any sort of horizontal-takeoff SSTO.

What you really need is to distribute some of the magic on the DG-S from the rockets to the airbreathers.

Since your engine is presumably nuclear, use the same reactor (or whatever), instead of jet fuel to heat the airstream. You can then tone some of the magic in the rocket phase down (by reducing thrust and/or ISP), and try an integrate your engines, so that instead of having turbos, scrams, and rockets for the three different speed regimes (or, in the case of the DG-S, just scrams and rockets, and having to use rockets at low speeds), you have one engine that works across your entire flight regime in three modes. It also helps if your scram mode has a high cutoff speed, a la the XR1, rather than the DG-S.
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Old 03-26-2010, 07:01 PM   #26
Moach
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hmm no... nothing here is "nuclear", iīm not going so sci-fi with this thing... so i guess i should move those inlets to the bottom side... can be done, no problems there

or could them somehow share the inlets for the scramjets, some sort of internal splitter valve? nah... scram inlets are highly specialized, better not mess with them...

let me think of something else...
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Old 03-26-2010, 07:11 PM   #27
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If you have pure SCRAMs, you don't want hybrid rocket engines. That is actually a penalty. Better use rocket engines for launch, so you exceed the critical Mach number quickly, then switch to SCRAMs and power down the rocket engines, and then go back to use rocket engines when the SCRAMs overheat. The SCRAMs can use the air far better as any hybrid rocket engine can, the SABRE is even just a RAMJET/rocket combination, that works at lower Mach numbers.

Last edited by Urwumpe; 03-26-2010 at 07:15 PM.
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Old 03-26-2010, 07:26 PM   #28
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Quote:
Originally Posted by Moach View Post
 hmm no... nothing here is "nuclear", iīm not going so sci-fi with this thing...
Well, if it contains nuclei, it's nuclear. Sort of.
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Old 03-26-2010, 07:46 PM   #29
Moach
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hereīs a variant with ram spikes... not sure what i think of it...



another possibility is to add the inlets on the bottom, next to the scram doors


any thoughts?
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Old 03-27-2010, 01:16 AM   #30
Andy44
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The problem with having inlet cones like that is that the tips will melt on re-entry. Maybe put the scram inlets somewhere on the belly with retractable heat-shielded doors.

Personally, I liked the look of the dorsal inlets better, maybe there's a way to choose a different engine configuration so that you can keep it...but for realism, engineering beats aesthetics.
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