Air-Breathing Rocket

[JMBuilder]

This is a part that you could unlock very early in the tech tree. Air-breathing rockets would need intakes like jets, but would behave like a normal rocket. It would be cheap and lightweight, have high thrust, and would burn fuel somewhat slower than normal rockets. Of course, without enough air, it would cease to function.

A rocket like this would be useful for booster stages or supersonic aircraft, and could assist in accomplishing certain scientific missions related to speed.

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This may seem like a relatively useless part, but as a designer, I like having variety. I'm always wanting new parts, and I've been waiting for stock airship and seaplane parts for over a year. A new type of rocket would satisfy that unquenchable thirst for at least a little while.

[Master Tao]

What distinction are you making between this and the air-breathing rocket that's already in the game, the RAPIER?

[JMBuilder]

The RAPIER switches between jet mode and rocket mode. The air-breathing rocket is like a jet, but it burns fuel directly for thrust, unlike a jet. It's basically an afterburner.

[Tex_NL]

The parts you're suggesting is far from useless. The suggestion however is. What you're suggesting IS a jet engine, and we already have those in the game.

[JMBuilder]

The parts you're suggesting is far from useless. The suggestion however is. What you're suggesting IS a jet engine, and we already have those in the game.

Jets use fuel to heat air and blast it out of a nozzle. An air-breathing rocket burns fuel directly out of a nozzle.

[Vaporo]

The parts you're suggesting is far from useless. The suggestion however is. What you're suggesting IS a jet engine, and we already have those in the game.

I think what he's talking about is an air-augmented rocket.

It takes air and uses it as an additional source of propellant mass alongside the already-burning fuel and oxidizer.

[JMBuilder]

Not exactly. Air is the oxidizer.

Perhaps I should change the suggestion to a pulse jet, like the ones on the V1 "Buzzbombs."

Edited October 18, 2014 by JMBuilder

[Tex_NL]

Pulse jets would make very nice early tech. Pulse jets are weak, inefficient but at the same time very simple. Anybody with reasonable metal fabrication skills should be able to build one in his/her spare time.

Ramjets/scramjets are more complicated and should only come after regular jet engines.

[NathanKell]

Technically, the two jets in KSP are *exactly* this; they *really are* air-breathing rockets, not jets.

[Vaporo]

Not exactly. Air is the oxidizer.

Well in that case, all you are suggesting is a high thrust and low efficiency jet engine.

[JMBuilder]

Well in that case, all you are suggesting is a high thrust and low efficiency jet engine.

Basically, yes. It would be much cheaper and lighter than regular jet engines.

I might post another suggestion for the pulse jet. It would make more sense. Should I, or would it be a waste of time?

[The_Rocketeer]

Slightly off topic, but I think the afterburner notion deserves further consideration. The stock jet tends not to overheat and have limited thrust capability. An afterburner mode that gave an extra kick to thrust, (for short take-off, rapid ascent etc) at the cost of rapid overheating, would be a very cool part to add.

To JMBuilder, I say suggest all u like! Never know, someone might run with your idea...

[D_Zod]

I think what he's talking about is an air-augmented rocket.

Whether or not he was thinking of an air-augmented rocket design, Vaporo, I think you're onto something here... sounds like a great idea to me.

[JMBuilder]

I made a second thread for a pulse jet. It might be more useful.

[Apature rocket science]

This is basicly the rapier engine in stock with its air rocket cycling mode

[zxczxczbfg]

So far as I can tell, the OP is under a slight misconception concerning the operation of jet engines.

Jets use fuel to heat air and blast it out of a nozzle. . .

That's correct, but the heated air is not the only source of thrust; that'd be called a thermal rocket.

Jets combust their fuel with compressed air, producing a large amount of very hot, very high-pressure exhaust gas (part of which is the combustion by-products and part of which is the heated air), then blasting that out of the nozzle. In the case of turbojets, this exhaust not only generates thrust but also keeps the compressor going.

Turbojet engines are a tad complex: they use turbine compressors to suck in more air than would normally be available for combustion. Without this compression to provide large amounts of oxygen, jet engines would be very inefficient.

Ramjets are closer to what is being described, but they're hard to do correctly because they have to be carefully designed to use the forward motion of the craft to force air into the intake rather than any sort of mechanical compressor, and they can't start from a standstill and aren't very efficient until you get to very high speeds.

The OP is essentially describing a compressorless jet, but such a thing couldn't function outside of pulsejets because, in addition to providing compression, the compressor is what's stopping the exhaust gases from shooting out the intake.

Pulsejets (as mentioned above) are the closest thing to what's being described; they use valves (or sometimes the geometry of the intake itself) that open and close rapidly to provide air to sustain what is essentially a very rapid series of small explosions. The valves open to provide air for combustion, and close again when the combustion occurs to stop the exhaust gases from flowing out the intake. Pulsejets are different from other jets in terms of efficiency because they don't compress the air being combusted; their efficiency is rather poor for this reason.

TL;DR It wouldn't work because the exhaust would go out the wrong end.

EDIT: Curse the Forum's overtype function!

Edited October 20, 2014 by zxczxczbfg

[Ruedii]

Honestly, I think the stock jet engines are overpowered, but the way to address that is to simply make them overheat at over 75% throttle.

Additionally, they should have the thrust-velocity curve seriously loose power at supersonic speeds for the basic jet engine (which lacks advanced nozzle mechanics) and hypersonic speeds for the advanced jet engine.

As of what is proposed, contrary to popular belief, the combustion chamber is not in the nozzle of a rocket, but behind it. The nozzle just improves the direction of the thrust. Using the nozzle as a combustion chamber like an afterburner does is extremely inefficient, which is why it's only used in military craft that need that kind of power on demand.. While one could theoretically place the afterburner in a secondary combustion chamber, the backfeed would make the primary combustion chamber produce little to no thrust when the afterburner is off. This is a highly inefficient setup and that is why it's not used in real life.

Most jet boosters in real life are ramjets or pulse-jets depending on the size of the rocket in question. Pulsejets are very useful for small rockets that don't have to travel supersonic speeds. Ramjets on the other hand can handle fairly high speeds, but can't be activated until they reach a certain speed, due to having no mechanism other than intake force to stop backflow.

Scramjets are still experimental at best. No full-scale ships have ever used them, let alone a manned one. The most that have used them is a modified Pegasus rocket, which failed to properly ignite on the first couple tries.