Ssto twr

[Comrade Jenkens]

I've decided to work on an SSTO but I have almost no experience building them. I'm getting into orbit nice and easily with Rapiers but the initial climb is so slow its painful.

What would a good TWR be for a SSTO? At them moment I'm using 4 Rapiers for a 55 ton aircraft.

Edited February 10, 2014 by Comrade Jenkens

[Vlk]

Rapiers are best combined with jet engines. I dont know an exact twr, but my sstos are able to climb almost vertically, with the speed of 90-100 at sea level.

[Kasuha]

Notice SSTO does not necessarily mean a spaceplane. SSTO is any craft that gets to orbit without staging and it can be a rocket as well as a plane.

Turbojets outperform Rapiers almost anywhere in atmosphere and in orbit you don't really need TWR, what you're going for is efficiency. To reach orbit after you have pushed yourself out of the atmosphere you only need the tiniest of engines. So it's up to what you want to do once you're in orbit, what space engine and how many of them to mount.

So I'd say, you can try replacing your Rapiers with turbojet for starters, then add one or two rocket engines to circularize and to do whatever you need to do in space.

Edited February 10, 2014 by Kasuha

[ShadowDragon8685]

Turbojets outperform Rapiers almost anywhere in atmosphere and in orbit you don't really need TWR, what you're going for is efficiency. To reach orbit after you have pushed yourself out of the atmosphere you only need the tiniest of engines. So it's up to what you want to do once you're in orbit, what space engine and how many of them to mount.

This is not, strictly speaking, true. It is possible to break atmo like a boss and have insufficient TWR to circularize. Granted, the subset of designs capable of breaching atmosphere but having insufficient TWR to circularize is very narrow, but it can happen, especially if, say, you used a crapton of air-breathing engines to get above atmo and only have a single puny rocket engine (or Kod help you, an ion,) for out-atmo thrust.

Practically speaking, though, anything that has an LFO rocket at all on it and can break atmo should be able to circularize - should be! If you think you're riding the razor's edge, though, it's best to test, test, test.

[Comrade Jenkens]

I'm using 6 Rapiers now and its working a lot better. Just to be clear I'm going for a space plane rather than rocket SSTO. Rapiers really don't seem popular though.

[Mystique]

I'm using 6 Rapiers now and its working a lot better. Just to be clear I'm going for a space plane rather than rocket SSTO. Rapiers really don't seem popular though.

Spaceplanes aren't popular, I guees. Mostly because of aerodynamics and control that makes flying them long and painful process with high risk of failure (even with FAR; though FAR maybe even makes things worse because it makes them harder and you won't be able to stabilize crazy contraption using SAS anymore). I tried using those hybrid engines, but combo of jets and one small engine for orbital maneuvers seems to be more viable. The only disadvantage is manual switching of engines and possibility of non-symmetrical flameout.

[capi3101]

I'm using 6 Rapiers now and its working a lot better. Just to be clear I'm going for a space plane rather than rocket SSTO. Rapiers really don't seem popular though.

That's because the turbojet is still a superior engine to the rapier in terms of efficiency. Rapier's one of those parts that helps pretty much just with the part count. 55 tonnes? You oughta be able to lift that with 5-6 turbojets easily.

The general rules for spaceplanes as I understand them:

One turbojet per 9-12 tonnes payload. This includes what you're wanting to lift plus whatever rockets you plan on bringing along.

One set of wings per 6 tonnes of craft. (By which I mean swept wings or delta wings)

One Mk2 Fuselage per turbojet (ideally; in practice this can be one Mk1 Fuselage)

One ram intake per tonne of aircraft (I've also heard eight intakes per engine; it works out about the same).

[Vlk]

Note that we should make a difference between air intake spammer and "realistic" designs. Especially since the last update, you can build planes that makes an orbit with apoapsis outside, periapsis barely inside the atmosphere, using only airbreathing enines. In that case you dont need twr for the rockets, thats true. But if you are using a "normal" amount of intakes (2 per engine), you will need twr (and a fair amount of oxidiser) to get out of the atmosphere.

[O-Doc]

A 55T craft should use 5 turbos, 2 basics and 3 nervas.

Edit: I get a 20T payload capacity from this setup with a 54T plane.

Edited February 10, 2014 by O-Doc

[Comrade Jenkens]

This is my current layout, the twr on the initial climb is much better though I haven't tested this version to orbit yet. (wing fell off)

It also has 8 intakes per engine.

[Claw]

Looks like you are already on your way to making a space plane.

There are a lot of design ideas out there and a lot of them work. So just keep experimenting and try things out.

RAPIERS seem less popular because there is a fairly small niche area for them. They look like they should be ideal for space planes, but with the current balance they are outperformed by a lot of other engine combinations. I suspect that will be ironed out eventually. I enjoy the way they look (even if they tend to overheat a bit).

[Dispatcher]

Without taking aerodynamics, lift and horizontal flight into account, you might find these graphs interesting: http://forum.kerbalspaceprogram.com/threads/67403-Graphs-of-Engine-Comparison-Flights?p=949688&viewfull=1#post949688 Of course one reason for the RAPIER's performance is the fact that the engine mass is limited to itself and not to a combination of jet and rocket engines. Notice that the zoomed in view (without the RAPIER) shows subtle differences in maximum ship mass, while showing reasonable differences in altitude between the remaining air breathers. Small differences in payload may affect engine choices. As others have suggested, if using multiple engines, it may be more practical to use a combination of turbojet and rocket engines rather than multiple RAPIERs.