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Came up with a brilliant idea for fuel efficiency


Tortoise

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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).

I haven't found this to be necessary in my experimentation with jet boosters. As long as the rocket is reasonably symmetrical it lifts off gracefully as TWR passes 1.

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As long as the rocket is reasonably symmetrical it lifts off gracefully as TWR passes 1.

Yes, to be honest I don't bother most of the time. On the other hand acceleration can be very slow and if you're following a rocket ascent-path instead of spaceplane you can get halfway through the atmosphere without actually building-up much speed. It's all a matter of balance, of course, but just as pilots 'hold the plane on the brakes' so they don't use-up the runway at low speed clamps serve the same purpose vertically. Not much in it but it could make the difference to launch or falling-over to some ships.

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Yes, to be honest I don't bother most of the time. On the other hand acceleration can be very slow and if you're following a rocket ascent-path instead of spaceplane you can get halfway through the atmosphere without actually building-up much speed. It's all a matter of balance, of course, but just as pilots 'hold the plane on the brakes' so they don't use-up the runway at low speed clamps serve the same purpose vertically. Not much in it but it could make the difference to launch or falling-over to some ships.

It's a tradeoff, I suppose. Holding the ship (and I assume we're talking about a VTOL rocket, not a spaceplane) in clamps wastes fuel that could otherwise be spent increasing altitude or speed, even if slowly. For a ship that's going to skitter across the pad as TWR crosses 1 or that needs a large amount of vectored thrust to remain upright they may be a necessity. Not really analogous to brakes on the runway, where you've got a finite space to build enough speed for takeoff; a VTOL can begin ascent as soon as it has the thrust to get off the pad.

Mostly I just like the slow, ponderous liftoff as the thrust builds. That and the sound. :)

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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.

Actually NASA has been looking into similar concepts for years. Largely theoretical but possible for a massive cost saving measure. Modern engines aren't efficient though and take up too much mass for the lift they supply. The most plausible has been attaching a rocket onto a jet, get it up to near stall altitude then jettison the rocket and let it rip. Not terribly safe though.

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I've launched some pretty silly stuff with turbojets before.

I actually like the idea, but I haven't gotten around to it as much now that career is a thing (I haven't unlocked the higher thrust engines yet)

I launched a jool-tour probe with a turbojet ascent stage.

I can't seem to find a picture of the ascent stage...

Here's a kethane mining rig destined for Minmus, though

http://i1273.photobucket.com/albums/y402/UU92/KSP/screenshot277_zps980496c6.png

(photobucket is over bandwidth, can't embed pics)

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This works great for getting high efficiency and (unless outlawed) appears in challenge entries frequently where people are optimizing for weight. With intake spam you can get very, very high before using rockets.

I sometimes use launch clamps and it mostly depends on whether the bottom side of the craft is suitable for resting on the pad. If it can sit on the pad and not break the engines off, then I go without launch clamps. There is no need to hold it down to spool up the engines. Especially with SAS, the craft will just slowly lift off the pad when TWR exceeds 1, probably gentler than using clamps in fact.

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I like using JATO; often I use it in conjunction with SRBs and LRBs; largely for fun but they can really help make the difference. The pic in my sig line is simply for showing off parts, since that behemoth doesn't need any boosters at all.

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

Huh? I thought it was the same or worse ratio... you could be right. Otherwise its a really good idea, because if you're keeping the jet boosters on a SSTO, you can then refill those fuel tanks with oxidizer while in orbit and use them as rocket fuel tanks; I do this with all my space-planes because it allows you to carry extra fuel.

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.

I find this is optional; you can use the jets to build up some orbital velocity like spaceplanes do, or you can just use them like SRB's that take you up to 30km.... Ofc it's more efficient to use them to gain orbital velocity, but this is more difficult with heavy craft and requires some fine tuning when making.

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

Good point; usually I just sue them until they start pitching the craft, then ditch them, as they'll flame out very soon afterwards, and the extra drag from intakes on the outer side of the jet booster pulls them away from my craft. That's if i'm ditching them at all; half my JATOs/SSTOs are going to Laythe, so I keep the jets on them.

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