Jet Engine First Stage Design?

[Dweeb of Kerbin]

I've been doing some experimenting with using jet engines for the first stage of my rockets and am wondering why I never really see this discussed. Is it just considered too unrealistic? Obviously you do see it discussed in terms of planes, but I am referring more to using jets as the first stage of rocket designs. For example, here is what I was just toying with. Keep in mind that the jet stage in these rockets is just the tiny part down at the bottom:

The jets are able to lift this not tiny payload to 21,000 feet meters with just this tank before you need to decouple. By contrast, the mainsail with the same fuel tank lifts the same payload to only around 400 meters before you run out on that stage. Also, although their is clearly a bit of clipping going on in this design, I actually did not need to turn clipping off to create it.

Edited June 8, 2013 by Dweeb of Kerbin

[Neotician]

First off, meters mate! big difference

well, realism may be one part of it, but then again, i've landed on a gas giant and i've seen people launch asteroids into orbit..

My best guess would be their air-breathing nature, if you stage too late, you'll send your rocket into a spin.

[Fel]

Congratulations, you've discovered why Space Planes are blatant cheats ;p

Jet Engines are so powerful that you can get an 80Mg object into space with them powering it alone. You might even manage to get an orbit... and the worst part is that you really only need a few L of fuel to get as much thrust as of typical rocket engine.

[Sliinty]

Firstly, fel, we humans like to call megagrams tons...

In real life it gets looked at, the thing is in ksp turbojets get thrust on the launchpad; IRL they have to have significant airflow before they actually work, the other problem is I imagine a launcher that used jets would be pricey and complex (remember that asparagus staging has never been done IRL for that reason). Reusable spaceplanes will use air breathing engines, as the cost of jets/SABRE engines matters less when you're not throwing them away

[cesarcurado]

I tried this once, very easy to get in orbit with their help.

The problem is exactly that, "too unrealistic" and it's just too easy.

So I don't use them anymore.

[Levelord]

I tried this once, very easy to get in orbit with their help.

The problem is exactly that, "too unrealistic" and it's just too easy.

So I don't use them anymore.

I'd argue that it's easier to just go the simple rocket-propelled first stage, since the jet engine stage gets discarded anyway like any other first stage rocket design. It's likely harder to use jet engines because you have to worry about jet flame-outs, a slow ascent speed, low TWR and higher cost of the engines (when career mode comes around).

[Sliinty]

Yeah experienced kerbal players tend to cut the meaning of easy down to "how tight are your fuel margins"

[cesarcurado]

I'd argue that it's easier to just go the simple rocket-propelled first stage, since the jet engine stage gets discarded anyway like any other first stage rocket design. It's likely harder to use jet engines because you have to worry about jet flame-outs, a slow ascent speed, low TWR and higher cost of the engines (when career mode comes around).

Whatever floats you boat

For me its just place enough rockets and when you are near stratosphere just press x and decouple.

[Scoundrel]

Levelord has it spot on. I routinely build lifters with jet engines as first stages and even with airhogging the pure vertical climb makes them only good for that first 15km. At that point I start getting twitchy with the staging button because when those suckers flame out it's bad news of epic proportions (picture saturn V doing summersaults). Even my CanUCK is pretty unforgiving, and it's just a puny little VTOL SSTO. Asparagus staging is definitely easier to use if you don't care about optimal performance.

[PIRATEONTHERUN]

Can we get the .craft? I am unable to replicate your results and I would really like to.

[Mulbin]

I use jets on my first stage on my Muna and Duna-LK1 ships... this little toothpick gets a lander, soyuz, block D tug and buggy to Duna and back. Surprisingly stable during flame out too.

http://forum.kerbalspaceprogram.com/showthread.php/26781-0-19-Duna-LK1-%28yes-Duna!%29-Soyuz-inspired-Duna-return-CM-Lander-and-micro-buggy!?highlight=DUNA-LK1

[MaddPhish]

Tried it before and fitting all the intakes and jets just kinda got annoying since I'm more interested in building the payload end. I do however use B9 SABRE's for my reusable rocket.