Help! Help! Please help!

[quasarrgames]

I have spent the past week trying to create an SSTO lifter stage that can get a full orange tank into orbit. I want the lifter to be fully recoverable, and as realistic as possible. It must have jet engines, but it can only have one intake per engine. I also want it to be as light and have as few parts as possible.

The only problem is, i can't even get the lifters into space most of the time. I'm beginning to think that this is either impossible without using more intakes, or i am dong something REEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEAAAAAAAAAAAAAAAAAAAAAALLLLLLLLLLLLLLLLLLLLLLLLLYYYYYYYYYYYY wrong!

Please help me.

[makinyashikino]

What intakes are you using? Could you post a picture of your craft?

[Clockwork_werewolf]

If you are using stock then with only one intake it may be impossible it get a reasonable load into space. Most SSTO use between 2 and 15 intakes per engine and 2 is considered a very small number. Although it might be possible to get into space with only one intake per engine the cargo to thrust ratio may mean you need 2000 parts or more to be able to do it. Two to four intakes per engine are possible without stuffing the intakes inside of each other so I would suggest upping the intakes if you can. If you try making a craft with 15 intakes per engine mashed and clipped into each other then you will see why doing it with one is very hard.

It's also worth noting that although rapiers are less efficient than ramjets and rockets their flameout for air intake is also much lower than jets and more evenly distributed so you are less likely to spin out of control at low air pressure.

[Kasuha]

You can't have realistic SSTO, there are no SSTOs in reality.

Your insistence on one intake per engine is just personal preference - KSP intakes have set area, real life engines don't use one of pre-manufactured intake areas, their intake area corresponds to needs of the engine. The thinner the atmosphere is where the plane is supposed to fly, the bigger intake area it uses.

If you already have a small SSTO with one intake per engine which works for small payload, then just multiply it by how much you need to increase the payload.

If you don't and want to still insist on one intake per engine, then you'll need to have it more of a rocket than a plane. Big, heavy, with lots of fuel to get to orbit together with its cargo, and with enough jets to get that monster to air.

... this assumes you're using stock parts. You may find some more capable intakes in mods. But these are not any better than using more than one stock intake per engine, the only difference is that they are single part.

[quasarrgames]

Here's a picture of the newest, and possibly most successful prototype, though it can't even get into space.

I intake per jet eingine. I chose the basic jet engines because they have higher thrust, use less fuel, flameouts are generally less violent, etc. The rocket engine is a mainsail. It just gets a TWR of 1, and the jet engines have a TWR of about 1.5.

Until about 10km, it flies up on jet engines alone. At 10km, i turn on the mainsail to pick up speed. at 20km, the jet engines flame out and the mainsail takes it from there. Kerbal engineer says it has about 2.5km/s of delta V, but i can't figure out how to get more. I think Kerbal Engineer really gets messed up by jet engines.

Edited May 18, 2014 by quasarrgames

[rtxoff]

With jet engines you will want to build up as much as speed as possible while the engines still get air. So start your gravity turn very early and try to build up orbital speed before you fire the mainsail. You should reach at least 1000m/s before even thinking of starting the rocket engine. Maybe also try to mount a set of wings to help you fly through the atmosphere? You should also at least mount some docking port on your fuel tank if u want it for refueling . I generally also mount an rcs tank and rcs thrusters to be able to maneuver it in orbit. Some lights are nice also on the tank.

[Taki117]

If you want full re-usability, why not try a spaceplane? It will take some designing and fiddling to get it to haul an orange tank, but it can be done.

[allmhuran]

It looks like you're launching vertically and flying a normal rocket ascent profile. With jets you don't really want to do that. You have experienceed the fact that your jets will flameout after just a minute or two if you do this, which is wasting the advantage of jets... their high efficiency.

You want to use the jets to gain speed for as long as possible. In order to do this you're going to want to add wings and climb like an airplane. Get yourself some turbojets (not basic jet engines, turbojets work at much higher altitude) and climb to as high as you can without risking flameout. If you go with one intake per jet this will turn out to be about... uh... 25km if I recall correctly. Level out at this altitude and gain as much speed as you can. If you can gain enough speed to put your apoapsis outside the atmosphere, you're done! Coast to apoapsis and finish circularizing with the rocket.

Unfortunately I don't think this is possible at 25,000 meters. The maximum airspeed of turbojets is 2400m/s (surface speed. About 2570 m/s orbital). At this speed their thrust curve goes to zero. And 2400 m/s at 25,000m is not fast enough to get your apoapsis into space. So you're going to need to climb higher than this, reducing throttle on the jets to avoid flameout. Adding more intakes would definitely help at this point.

If you're not willing to add more intakes you'll need to switch over to the rocket by the time you reach about 30,000m. You probably don't need a mainsail from here, though. A skipper is likely to be good enough and the weight saving will help you a lot with your initial ascent.

Also, while the quad-couplers are useful, they're also heavy. You'd be better off without them. Use multiple fuel tanks with a jet and intake on each end instead of a big fuel tank with an adapter and multiple jets/intakes on each end, or use cubic octagonal struts to attach your jets and intakes.

Edited May 19, 2014 by allmhuran

[Pecan]

To reinforce the good comments above; first change engines.

Basic jets are only useful at low altitudes and speeds. Ok if that's what you want but it means you'll have to switch to the rocket earlier, using more fuel.

Using turbojets get the most from them by flying more-or-less level at 20km+. The higher the better but your intake-limit will seriously restrict you.

Lose the mainsail. It's almost the worst choice of engine in every situation. While it has high thrust it is itself heavy and has very poor fuel-efficiency.

I actually quite like using quad-adapters for the looks, but using struts instead is good advice. Try (quad, or at least multiple) T30s instead of the mainsail and see what a difference you get, for instance.

KER and others certainly aren't too useful with jets, you're right there :-(

[Claw]

Well, you're on the right track with the design. Your's just so happens to look pretty similar to one of mine. I have multiple versions in this line of TurboJet SSTOs (up to 80t or 100t, I forget). This one isn't as big as what you want, but it happens to be a handy picture I have available. This particular one also doesn't have parachutes on it, but those are easily added.

Some differences to make note of from yours:

1) Use TurboJet engines, instead of basic jets.

2) Don't asparagus your strap on tanks. Simply make them smaller and isolate them. Otherwise you either end up with an fuel/oxidizer imbalance in your main tank, or you end up carrying too much fuel around.

3) Ditch any oxidizer in your strap on tanks. (Can't tell from your pic.)

4) As has been hinted at, fly fairly horizontal at 25-ish km and let the TurboJets build up some speed. That's why you want to use them.

5) You need some more rocket fuel for your mainsail. For this family of lifters, I find that I typically need as much rocket fuel on bottom as what I'm carrying on top.

Incidentally, I also wait a bit longer before firing up my main engine. I think my 40t lifter also has a few more TurboJets on it. If you want to keep your number of Jets as it is, then you'll definitely need more rocket fuel.

You can also parachute the TurboJets and decouple them when you're done with them. That'll give you a bit more dV for your main engine's orbital insertion. If you do that, put the engines on a hotkey to shut them down before decoupling... (insert funny picture here)

EDIT:

Ahh here. I found a few more examples if you care to look. The album was for a challenge, but shows how much you can lift on just TurboJet engines. 236t at launch, it ended up with all that junk (8x 200-8 fuel tanks) + 3/4 of an orange tank when it reached orbit. I honestly can't remember the mass on orbit, but maybe around 100-110 tons. Only the first 6 or so pictures apply to this thread, but you can see that the ascent (picture #2) is done purely on TurboJets.

Plus Taki mentioned a space plane. So I put that on here too. It was another example I made a long while ago to help someone else out.

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Edited May 19, 2014 by Claw

[Hodo]

First I would like to say, I like that you are not going the space plane route. I myself always sucked at any SSTO that wasn't a space plane design.

Now that I have said that here comes the not so pretty part.

Unfortunately your craft doesn't make enough power at higher speeds with those basic jet engines on it. You should use the Turbojet engines as they make much more power at a much higher speed letting you get closer to orbital velocities before you need to switch over to your rocket stage. But I also see other issues with that craft. Mainly it looks like it would have the flight characteristics of a brick wall, this means you would be using MORE energy trying to get it to go fast in atmosphere then you would if it had a more refined aerodynamic shape. ((But I use FAR and have never used the stock aerodynamic model))

On the plus side you don't need to have 20 intakes per engine like a great many SSTO builders use. You can get away with 2-3 per engine if you are feeling really greedy, and you can find real life examples of aircraft with two intakes per engine and even up to three.

Here is one I made a few months ago for a challenge, it has I think 2 intakes per air breathing engine.

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And then there are these two tiny ugly things that have 1 intake per air breathing engine, but they are also VTOL SSTOs.

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Then my pride of my SSTO fleet that can haul 108 tons to orbit. But it has 3 intakes per air breathing engine I think.

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And my one working tail landing non-space plane SSTO.

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As you can see you can do a lot of different things, either stock or not, you may have to add more to your original design to get it to work or just change out that mainsail for something a bit more efficient.

All I do is SSTOs so I have a bit of experience with them.