Realistic Engine thrust?

[TeeGee]

Hi everyone,

Is there a mod that changes the kerbal engines to behave more realistically? I was playing with my ssto (all stock parts) and noticed that I could build a better ssto with turbojet engines than I could with saber engines in B9 aerospace pack. That doesn't seem right to me...

In reality can a turbofan jet engine behave like it does in kerbal? I know that commercial and military airplanes that go supersonic use turbojet engines, but to carry a craft over 2,000 m/s if it had enough intake air seems extreme. Am I wrong?

Basically, is it possible to build a ssto in real life that uses turbojet engines to reach 2,000+m/s than switch over to conventional rockets to circularize its orbit? If so, whay haven't we done that yet?

And yes, I've read up on Skylon. Skylon uses the new saber engine that is a hybrid airbreathing rocket engine.

[thunderstar]

well, for what i know, its almost impossible yo build an ssto on earth due the great delta-v needed to achieve orbit, but on the other hand, earth's atmosphere doesn't have a perfect limit, it doesnt just end at certain altitude as kerbin's atmosphere, all ships in LEO need a propulsion system so every once in a while they get a little boost so they don't fall again due to a little bit of atmospheric friction, in kerbin once its in orbit, it will never fall again so intakes work differently on earth than on kerbin

[Tarrow]

Basically, is it possible to build a ssto in real life that uses turbojet engines to reach 2,000+m/s than switch over to conventional rockets to circularize its orbit? If so, whay haven't we done that yet?

At the moment - no, it's not possible. Turbofan engines (with afterburners) have only been able to reach around mach 3.3 (on the Sr-71 blackbird) which translates to somewhat less than 1000 m/s. Scramjet engines may be able to get to near the 2km/s mark. There is no existing (or proposed) air-breathing engine that'd get you to the 7.66 km/s velocity of something like the International Space Station.

[Psycix]

One reason why we haven't done this in real life is because the orbital velocity is about 8km/s of earth instead of a little over 2km/s.

On Kerbin 2 km/s is about 90+ % of the orbital speed.

On Earth, 2 km/s is only about 25% of orbital speed.

[gm537]

So this a fairly complicated issue (as are most things related to Rocket Science). So if you want a mod to go full realism check out Nathan Kell's re-scaled solar system and his Modular Fuel System in Realistic Mass mode.

Basically on earth getting into orbit requires traveling at over 7 km/s rather than 2.3 km/s. So even if we take the stock KSP turbojets and put them on Earth they only get us to about 1/3 of orbital velocity. (They will stop producing power at 2400 m/s regardless of number of intakes) From that 1/3 you would still need quite a bit of rocket to get you to orbit. Additionally the KSP turbojets are wrong. Real world turbojets pretty much stop working around Mach 2.5 or 3 aka about 900m/s. However in the real world there are things called Ramjets which have some similarities to turbojets but also some pretty big differences that allow them to work up to Mach 6 or 7 (2300 m/s) but true ramjets basically don't work below Mach 1. The SR-71 Blackbird for example used a special engine that operated like a turbo jet at low speeds but became more like a ramjet at high speeds to allow it to go above Mach 3. Also in reality there are things called SCRAM jets which are even more extreme. They can operate up to speeds of over 5000 m/s but don't really work until you get them up to 1200 m/s.

I'm guessing you've realized by now that in real life you can not build an SSTO turbojet engine. Even if you could build a ramjet that got you to 2,000 m/s you would still need over 5,000 m/s of dV which would be a LOT more than simply circularizing. Regardless lots of people have asked these kinds of questions and considered designs to do something along those lines, mostly because air-breathing engines are much more efficient than rocket engines, but to date no truly effective design has been made.

As a final point the B9 Saber's are indeed more realistic than the stock turbos. So if you want to get a decent idea of what it takes to make an SSTO stick to those not the turbojets. Obviously Squad has done many things for the sake of play-ability not realism but there are a lot of modders out there who are doing things to allow a more realistic experience if you want it.

(Disclaimer: I am not a rocket know it all so for sure some of my numbers/ data is probably a bit off but I am just trying to convey the main idea. Also I wrote this before the two guys above me posted so sorry for some repeat info...)

[gm537]

At the moment - no, it's not possible. Turbofan engines (with afterburners) have only been able to reach around mach 3.3 (on the Sr-71 blackbird) which translates to somewhat less than 1000 m/s. Scramjet engines may be able to get to near the 2km/s mark. There is no existing (or proposed) air-breathing engine that'd get you to the 7.66 km/s velocity of something like the International Space Station.

Yep pretty much what my thoughts were... But what I've read on Scramjets says they can do more like 4,000 or 5,000 m/s: Mach 12-15 (kinda a theoretical value but conservative). Which is still not 7.66 km/s so either way the idea is the same.

[TeeGee]

So this a fairly complicated issue (as are most things related to Rocket Science). So if you want a mod to go full realism check out Nathan Kell's re-scaled solar system and his Modular Fuel System in Realistic Mass mode.

Basically on earth getting into orbit requires traveling at over 7 km/s rather than 2.3 km/s. So even if we take the stock KSP turbojets and put them on Earth they only get us to about 1/3 of orbital velocity. (They will stop producing power at 2400 m/s regardless of number of intakes) From that 1/3 you would still need quite a bit of rocket to get you to orbit. Additionally the KSP turbojets are wrong. Real world turbojets pretty much stop working around Mach 2.5 or 3 aka about 900m/s. However in the real world there are things called Ramjets which have some similarities to turbojets but also some pretty big differences that allow them to work up to Mach 6 or 7 (2300 m/s) but true ramjets basically don't work below Mach 1. The SR-71 Blackbird for example used a special engine that operated like a turbo jet at low speeds but became more like a ramjet at high speeds to allow it to go above Mach 3. Also in reality there are things called SCRAM jets which are even more extreme. They can operate up to speeds of over 5000 m/s but don't really work until you get them up to 1200 m/s.

I'm guessing you've realized by now that in real life you can not build an SSTO turbojet engine. Even if you could build a ramjet that got you to 2,000 m/s you would still need over 5,000 m/s of dV which would be a LOT more than simply circularizing. Regardless lots of people have asked these kinds of questions and considered designs to do something along those lines, mostly because air-breathing engines are much more efficient than rocket engines, but to date no truly effective design has been made.

As a final point the B9 Saber's are indeed more realistic than the stock turbos. So if you want to get a decent idea of what it takes to make an SSTO stick to those not the turbojets. Obviously Squad has done many things for the sake of play-ability not realism but there are a lot of modders out there who are doing things to allow a more realistic experience if you want it.

(Disclaimer: I am not a rocket know it all so for sure some of my numbers/ data is probably a bit off but I am just trying to convey the main idea. Also I wrote this before the two guys above me posted so sorry for some repeat info...)

I installed modular fuel in realistic mass mode and still have turbofans working like before. Yeah ok now saber engines require liquid H2 and the isp for some engines is changed but my turbofans still get me to a 100km apoapsis on airbreathers alone.

[rpayne88]

Makes me wonder if we could make a "staged" engine. This engine would start out as a typical turbojet for takeoff and landing. This engine would have "hinged" compressor and turbine blades that will be spun out using centrifugal (I think that is how you spell it) force. One set of turbine blades will be magnetized and held "up" using similar polarity provided by electromagnets. The starter motor will then begin moving to crankshaft, causing the compressor blades and other turbine blades to spin out. From here it starts like any other jet engine; fuel is injected, the starter spools up the turbine and compressors until the engine can keep itself running. After takeoff, the engine will engage the afterburner located aft of the SCRAMjet portion of the engine. As the spacecraft reaches the limit of the turbojet portion, it will shut of fuel to the turbojet section of the compressor and reroute it to the SCRAMjet combustion chamber. A clutch is then applied to the crankshaft of the turbojet portion, causing the blades to spin down. This, combined with the onrush of air, would blow them flat against the crankshaft. The air then flows through what is, in essence, a tube and reaches the intake portion of the SCRAMjet. The SCRAMjet then continues to accelerate the vehicle. Obviously, you would still need a rocket engine to "kick" the spacecraft into orbit, since my whole idea of a "staged" engine is air breathing.

I'm just typing this as it comes to me head. I have done ZERO research on this idea, and more than likely, I have made some critical oversights. I'm also not an engineer.

[kurja]

I installed modular fuel in realistic mass mode and still have turbofans working like before. Yeah ok now saber engines require liquid H2 and the isp for some engines is changed but my turbofans still get me to a 100km apoapsis on airbreathers alone.

did you also install re-scaled solar system?

[Smidge204]

There is no existing (or proposed) air-breathing engine that'd get you to the 7.66 km/s velocity of something like the International Space Station.

The X-43A uses a SCRAMJet and officially reached a top speed of 10,461 m/s.

Just sayin'!

=Smidge=

[Trueborn]

Alas, the X-43A reached a top speed of 10,461 km/h, which is 2,906 m/s. Fast, but not fast enough.

[Tarrow]

The X-43A uses a SCRAMJet and officially reached a top speed of 10,461 m/s.

Just sayin'!

=Smidge=

It got to 10,461 km/h (2905 m/s) after a 10 second burn of it's own engine - after being boosted to hypersonic velocities by a solid rocket booster that weighed several times more than the test vehicle.

Impressively fast for sure. But strapping huge SRB's to an SSTO is cheating And it's still too slow

[MockKnizzle]

Actually, the article says 10,461 km/hr, not m/s. That's only 2906 m/s.

EDIT: jk, everybody beat me to it. Derp.

[Murph]

At the moment - no, it's not possible. Turbofan engines (with afterburners) have only been able to reach around mach 3.3 (on the Sr-71 blackbird) which translates to somewhat less than 1000 m/s. Scramjet engines may be able to get to near the 2km/s mark. There is no existing (or proposed) air-breathing engine that'd get you to the 7.66 km/s velocity of something like the International Space Station.

The SR-71 used a turbojet, not turbofan, unless I'm mistaken. It was a fancy ram intake, high bypass turbojet, and afterburner, with much of the thrust at Mach 3 being from the afterburner. In some ways, a hybrid turbojet / almost-ramjet. That was 1960s technology, and it's suggested that modern technology could easily take the SR-71's general design from Mach 3+ to Mach 6+. One of the major limiting factors for it was engine temperatures, which is something where modern materials and design can make a big difference.

[Grover]

If anyone ever played orbiter space flight simulator (designed as a truly realistic sim) you might remember the XR2 fictional addon spacecraft, which used rocket engines to climb to about 25km from a runway takeoff, then used scramjets to climb to around 55km and mach 23, then used its rockets again for orbital insertion and manoeuvers.

This design was developed by Moach (HarvesteR's brother I THINK*) who designed his g42 series which used conventional turbojet engines for takeoff, and a climb to around 10km, where power is taken over by RAMCASTER engnes, a proposed engine that first acted as a ramjet, then altered its internal geometery at high speeds to act as a scramjet (by moving the diffuser forward closer to the intake i think), then used either its afterburners as rocket engines, or small OMS engines like the shuttle of old for insertion and manoeuvers. Essentially an ssto

Just my ideas, im surprised orbiter sim hasnt bren mentioned yet considering HarvesteR probably got his inspiration for KSP from there (if only in part)

*DISCLAIMER : i cant remember where i knew this from, and may well be mistaken, take with a pinch if salt

[Tarrow]

The SR-71 used a turbojet, not turbofan, unless I'm mistaken. It was a fancy ram intake, high bypass turbojet, and afterburner, with much of the thrust at Mach 3 being from the afterburner. In some ways, a hybrid turbojet / almost-ramjet. That was 1960s technology, and it's suggested that modern technology could easily take the SR-71's general design from Mach 3+ to Mach 6+. One of the major limiting factors for it was engine temperatures, which is something where modern materials and design can make a big difference.

That was pretty much how it worked yes, hybrid afterburning turbojet / ramjet. The line between high-bypass turbojet and a turbofan can be a little blurry

[Murph]

That was pretty much how it worked yes, hybrid afterburning turbojet / ramjet. The line between high-bypass turbojet and a turbofan can be a little blurry

Yes, they are not too different in concept, with the core of a turbofan essentially being a turbojet, but for significantly different design reasons. The pure-turbojet bypass air doesn't go through fan blades, it's ducted direct from post-intake into the afterburner chamber. With a turbofan, the bypass air is taken after the first stage fan blades. The turbojet's bypass is all about cooling, controlling the speed and pressure of combustion air for the turbojet itself, and providing combustion air for the afterburner.

The high-bypass turbofan's bypass air provides additional cold-air thrust (i.e. the bypass air is accelerated mechanically by the fan). The bypass air also provides a noise reduction benefit, with the cylinder of cold air absorbing some of the sound from the jet combustion, something which often is of little to no concern with an afterburning turbojet.

Then there's the low-bypass turbofans with afterburners, just to blur the line down the middle.

[Smidge204]

Alas, the X-43A reached a top speed of 10,461 km/h, which is 2,906 m/s. Fast, but not fast enough.

Anyone got a towel so I can wipe this egg off my face? Quite the failure of reading comprehension on my part...

=Smidge=

[Ignamious]

While jet engines are great they are limited by the need for an oxidizer, the SABRE engines proposed for the Skylon SSTO are a great idea. Also the SABRE engines in KSP are not realistic. First the ISP is wrong. Second the precooler is only an extra part in ksp that MUST be on it to work. Now it's been a few months since I looked into the SABRE but if I remember the basics it uses a variable intake to reduce drag, uses raw air for low altitude then starts compressing it and super cooling it in the upper altitude range and then cuts of completely and uses internal oxidizer in the end.

Also to be fair... an SSTO SHouldnt be using multiple thrust sources. That's just extra mass and more things to go wrong. The SABRE is "one" engine with all ranges.

I think the best chance if an SSTO is te LASRE "Liner Aerospike rocket engine" that was to be used on the X-33. This SSTO is a VTHL and not a CTHL like the SSTO's most people build in KSP. It would use the same engine from launch to LEO. And has great promise! I've been thinking if building a replica in KSP. Another way is to use a MAL or KEL to get you up high there for using very little internal fuel but not having to rely on external staging.

In simple terms. There will be SSTO's soon, maybe very soon, but they probably will NOT act like airplanes to get into orbit.

[Andrew Hansen]

While it's probably true that the B9 Aerospace SABRE engines are more realistic, another thing you could do to limit yourself is to avoid part clipping tons of intakes onto spacecraft (in real life, there are no such things as cubic octagonal struts to allow us to fit two intakes into the space for one .) It's much more realistic to use just two intakes. Then you can see how hard it is to actually get into orbit.

That of course, is with stock KSP. If you allow mods, then, as others have said, install the Real Solar System mod, Ferram Aerospace Research, Deadly Reentry, and B9 Aerospace. Then you'll have a much more realistic experience of what it's like to make a real-world single-stage-to-orbit.

[TeeGee]

If that's true, what values should I change in B9 saber engine mods to make it more realistic?

[SpaceSphereOfDeath]

Because then a nuclear engine would be able to lift an orange tank :|

And you could build a 8 part SSTO