Came up with a brilliant idea for fuel efficiency

[Tortoise]

So a few days ago I was messing around with SSTOs and stuff.

Then I went back to rockets, to build a few things. And I wondered...What if I put jet engines on a rocket? And...

I got up to about 11.5km before I had to drop them and actually switch to fuel/oxidizer-guzzling rocket engines, which I used to finish gaining orbit. And it was a success!

What do you guys think about this?

[LaytheAerospace]

I don't do this because it feels very exploitative. You can quite easily make orbit on jets alone, with a small enough craft.

Grossly unrealistic, so you won't find me doing it.

[Jas1126]

Well done. I would alter it quite a bit for even more efficiency. I'd get rid of the girders for one thing. TT-38K Radial Decouplers weigh much less than girders. I'd also use the Mk2-R radial parachutes on top of the tanks. All around same stats as the chutes you used but weigh less.

It's hard to see the details; would you consider offering the file, please?

Edited April 26, 2014 by Jas1126

[Ralathon]

Meh it works, but you're not gonna get much efficiency out of it. Jet engines have terrible TWR and stop working above 30km or so without excessive intake spam. If you're only going to use them for the first few km's you might as well use a solid or liquid booster.

Jets are great for very shallow launch profiles though. Stick in the upper atmosphere as long as possible to get as much speed as possible on your efficient jets. But that's essentially a wingless space plane.

[Kerbonautical]

Personally I'd use rapiers just to make sure you're not wasting any fuel from the launch stage but good idea.

[Jas1126]

Personally I'd use rapiers just to make sure you're not wasting any fuel from the launch stage but good idea.

Maybe I'm mistaken but wouldn't the Rapier's drain the fuel much more quickly? They also weigh more.

[TheDarkStar]

This is actually used quite a bit. You can use almost no fuel to get post the first ~30km and get past the first 1-2km/s dV at the same time.

[Tortoise]

Here is the craft btw. And you guys also should know to cut out the jet engines a little bit before you go to the next stage because they take a few seconds to stop. I don't know if action groups come with the .craft file

[Jas1126]

"Contains locked or invalid parts".. Darn.. Oh well, thanks anyway.

[Random Tank]

Putting jets on a rockets isn't a bad idea, it saves a lot of weight and fuel; its also how you make wingless SSTO's easily. Though on your rocket you have added waaay to much jet fuel; 1 1.25m tank will probably do for about 3 or 4 jet engines, as you only use them for a short amount of time. You'll also want to use the Ram Intakes as much as possible, as they start on full intake air capacity (0.2, where radials don't, its about 50% - 60%) and intake air volume decreases much slower with Rams compared to Radials. Weight save as much as possible too, Jets love lighter craft!

I'd also use the Mk2-R radial parachutes on top of the tanks. All around same stats as the chutes you used but weigh less.

Weighing less is bad for a parachute, as weight increases drag (only in KSP, not in real life). So the heavier the chute, the more it can slow down heavier loads.

[Tortoise]

"Contains locked or invalid parts".. Darn.. Oh well, thanks anyway.

Oh yeah sorry, I have a part on there for my kerbal resources (water, food, and oxygen). I have a mod called TAC Life Support.

[Jas1126]

Putting jets on a rockets isn't a bad idea, it saves a lot of weight and fuel; its also how you make wingless SSTO's easily. Though on your rocket you have added waaay to much jet fuel; 1 1.25m tank will probably do for about 3 or 4 jet engines, as you only use them for a short amount of time. You'll also want to use the Ram Intakes as much as possible, as they start on full intake air capacity (0.2, where radials don't, its about 50% - 60%) and intake air volume decreases much slower with Rams compared to Radials. Weight save as much as possible too, Jets love lighter craft!

Weighing less is bad for a parachute, as weight increases drag (only in KSP, not in real life). So the heavier the chute, the more it can slow down heavier loads.

I'm looking at the stats of both and the only difference is the weight. Same drag, ect. Are there hidden stats?

[Jouni]

I'm looking at the stats of both and the only difference is the weight. Same drag, ect. Are there hidden stats?

Drag force is proportional to the mass multiplied by the drag coefficient.

[Random Tank]

I'm looking at the stats of both and the only difference is the weight. Same drag, ect. Are there hidden stats?

Drag is worked out in KSP by the weight of a part multiplied by the drag coefficient (which is 0.2 for most parts). So, both parachutes have fully deployed drag coefficient of 500, but because the Mk16 XL weighs 2x more than the radial chute, it has twice the drag; the normal Mk16 has 1/3 of the drag of the Mk16 XL.

And besides, those aren't chutes. They're nosecones

EDIT: Dammit Jouni, you sneaky ninja

[Jas1126]

And besides, those aren't chutes. They're nosecones

Oh, sorry. I'm having trouble seeing the picture clearly.

[Random Tank]

Oh, sorry. I'm having trouble seeing the picture clearly.

Don't worry, easy mistake to make, they both have very similar textures/shape. At least you now know that the Mk16 XL's are useful! (very infact)

[Tortoise]

Btw I just use FAR.

I thought I'd include that, since theres an ongoing conversation about drag and stuff.

[AustralianFries]

Didn't Scott Manley use jet engines on his main rocket design in the Reusable Space Program series he did a while ago? I can't really remember, as I don't watch his videos too much.

[Random Tank]

Btw I just use FAR.

I thought I'd include that, since theres an ongoing conversation about drag and stuff.

Ahh right; i know some stuff about FAR, but how does it treat intakes? Because yours are the wrong way round....

[Tortoise]

Ahh right; i know some stuff about FAR, but how does it treat intakes? Because yours are the wrong way round....

I purposely made my air intake face downwards due to the fact that in reality (and on KSP),

the air intakes usually suck air inside. And the higher you get, the less oxygen there is, therefore the less engine performance you have.

So, my engines would flameout sooner if they were facing upwards, because theres more air below my rocket as it ascends.

[Random Tank]

I purposely made my air intake face downwards due to the fact that in reality (and on KSP),

the air intakes usually suck air inside. And the higher you get, the less oxygen there is, therefore the less engine performance you have.

So, my engines would flameout sooner if they were facing upwards, because theres more air below my rocket as it ascends.

Hmmmmm... but in real life the slightly aerodynamic shape of the backwards intake would result in any air being forced around intake, creating a small area of vacuum behind it, and air flowing in the wrong direction; also the incoming air speed would be terrible so it would be much harder to compress. This isn't a problem with Vanilla KSP as the aero physics are mucked up, but i though FAR might simulate this...

[r4pt0r]

I have a JATO(jet assisted take-off) sub-assembly. jetfuel tank,ram intake,turbojet, mounted on a radial decoupler, with a big thick ibeam to tip it away from the rocket on release.

[xcorps]

You can put a seperatron I on the jet engine pointing away from your main rocket, staged with the decoupler. Make sure it's near the top of the engine mass, and it will fire your decoupled jet engine away from your rocket. No need to wait til the engine loses thrust.

[qromodynmc]

I used jets as a first stage,it is efficiently,but I really didnt get much fun..

[Pecan]

JATO tips in launch order:

Rocket-fuel tanks with the oxidiser tweaked down/out usually have a better ratio of fuel to mass than the 'pure' liquid-fuel tanks.

Use launch clamps to hold your vehicle down while jets spool-up to full thrust (or thereabouts, at least until TWR is around 1.4).

Stay in (high) atmosphere as long as possible to maximise the speed you get from the jets - the lift itself isn't worth it if you just go straight up. They're wingless spaceplanes as has been said.

If you shutdown jets using an action group, rather than just throttle them down, their thrust goes to 0 instantly ;-)

Vertical landing with jets can be tricky simply because the time it takes them to spool-up and -down makes it hard to control their thrust at any specific time.