SSTO help... again..

[Umlüx]

fellow kerbonauts..

seems i am not able to get a SSTO to orbit. i built dozens.. downloaded others.. analyzed them.. built dozens moar..

i think i am simply not able to fly them correctly...

- takeoff

- steep ascend until air intake drops

- slowly leveling off the ascend to build up speed (on average 1600m/s, 25km altitude)

- (missing the correct time to ignite rocket engines and flameout flatspin down to a horrible death)

- start rocket engines and pull the nose up

- just barely miss the orbit with empty tanks

how do you do it? are there specific keypoints you have to reach on the way up? how do you balance thrust/weight/fuel reserves?

thanks!

[cpt_nosh]

Well with that, you should get into orbit properly to be honest. 25km and 1600 m/s? That definately should be enough. What Rocket engines do you use?

[Umlüx]

mostly spikes.

[mrnicholas]

Think simple, you need a good number of RAM air intakes to jet engine radio, I use 3 but that not necessarily the optimum. only carry one, maybe two (to even out weight) liquid fuel tanks and then enough rocket fuel tanks to complete the orbit.

-With my SSTO I start with a strait up climb

-Start rounding our slowly at 10KM (bit like a normal gravity turn)

-Start lowering the throttle about 20KM

-Ignite airospike at 27KM

-Full trottle and shut down jets 30KM (im going quite fast which is why I can keep the running so long)

-Continue as normal

I hope that helps, here is a picture of my SSTO if it helps at all http://imgur.com/a/KpkiO

[bsalis]

Perhaps you could post some pictures.

Since i'm not seeing anything major wrong with how you are flying. Other than not closing air-intakes once you're done with the jets, but that should not prevent orbit in a decent craft.

[Johnno]

I managed to create my second and third ever SSTOs last night, my first one wasn't anything fancy either. So I'm still new to SSTO optimization but thought I'd toss in a few thoughts anyway.

As others have already pointed out, 1600 m/s at 25km should be more than enough. My first SSTO barely made it past 900 m/s or so before I had to hit the rocket engines, my latest gets around 1200 m/s.

A single FL-T800 tank with a LV-T45 rocket engine (or aerospike if you prefer those) should just about be enough to get you into orbit. If you have mechjeb/engineer installed look at your deltaV for the rocket engine and try to keep it around 1500 at least, if you're reaching wicked speeds like 1600 m/s without it though you can get away with less.

However the big culprit is mass. My best SSTO right now is around 16 tons, single LV-T45 engine and two turbojets. So as others have pointed out, start small. The lighter the better.

Monitor your resources (intake air), jets risk flameout at 0.10 intake air per engine, so if you have two try to ignite your rocket engine(s) and turn off your intakes just before 0.20 to be safe. I've read that it's also about air per intake, but I haven't delved into the details of that.

Action keys are your friend. I've set mine up so that my jets are on 1, rocket(s) on 2, intakes on 3. Once you get into the habit of turning on your rocket, turning off your jets and then your intakes in one motion you'll have less spin o' death. But the important part is monitoring your intake air.

Hope some of that helps. Happy flying!

[El wonso]

Steep ascend till air looks pretty thin (but not very thin).

Build up surface speed 1.5-1.6 km/s at 25-27 km.

Set mechjeb to pitch 25.

Mech jeb starts throttling down? Fire mah rockets.

Turbofan's thrust looks low (30kN for me)? Shut it down, close the intakes and full throttle.

Set pitch to 15 at 40 km.

Space.

I'm no good at SSTO Spaceplanes but I have 1 that I am proud of (lol). It uses 1 turbofan, 4 ram iar intakes and 6 Rockomax 24-77 (radial small ones with 300 ISP).

Edited June 27, 2013 by El wonso

[Umlüx]

maybe my planes really are to heavy. or i am taking too long ascending

yes, i can get up to 25km and 1600m/s, but then i tend to have fuelproblems.

and i never tried closing the intakes or throttle back the jets.

thanks for all the input!

[Alfondoo]

I reckon if you're just missing orbit that you're intakes are killing it. Try closing them with a hotkey just before flameout and if you're still missing orbit stick a few more rcs thrusters on it and finish it off with those.

[Rezolution]

I just successfully made my first SSTO plane after many, many attempts. The main issue at first was not realizing how the game handled intakes (as in, it needs a lot and it doesn't care where you put them).

I think you understand this already. However, the next issue was weight and balance. When using rockets, it is better at first to line smaller tanks up either or horizontally or vertically, directly parallel to one another and close to the CG in order to keep the weight shift to a minimum as fuel burns off, otherwise you will find yourself either too nose heavy or tail heavy during the last leap from atmosphere to space or during reentry. It sounds like you might be having the issue of the CG moving too far aft, thus making your ship impossible to control once fuel is spent.

Once I got the balancing and the intakes down, the rest was just tuning. Also, keep in mind that for me I did nothing special between jet engine shutdown and rocket burn, just one right into the other.

And, one more thing, for me I realized that I had to shut the jet engines down before leaving atmo. If I let the jets kill themselves, this usually resulted in adverse thrust for a split second, just long enough to throw the whole ship into a spin. Usually not a problem it seems if you only have one jet engine, however.

I'll post an image later today if you're interested. I hope this helps.

[Alfondoo]

And, one more thing, for me I realized that I had to shut the jet engines down before leaving atmo. If I let the jets kill themselves, this usually resulted in adverse thrust for a split second, just long enough to throw the whole ship into a spin. Usually not a problem it seems if you only have one jet engine, however.

When using more than one engine stack the jets vertically instead of horizontally you'll get a pitch error rather than a spin, usually easier to control.

[Tank Buddy]

You need MOAR intakes! you should be able to go up to 30 km. I did this with a jet (not a space plane). Your steps are correct, you just need more velocity and altitude. How many jet engines are you using? (Probably more than 1). I would hope you are using the Ramjet engines. When the air intake drops below .10, throttle back slowly. It is more difficult with multiple engines as they will vary slightly with air consumption. You should still accelerate with minimum throttle, but if you intake gets very low or you stop accelerating, cut the jets and activate your rockets.

[Aqua667]

If your not against mods you could get mechjeb and use the throttle control module, its really helpful! I like to set a action group that turns off the jets and intakes and activates the rockets. Its a lot easier than manually turning them off. Remember the first law of SSTO's:

"On rockets you want MORE BOOSTERS! On SSTOs you want EVEN MORE INTAKES"

(Search up "KSP air-hogging" on YouTube)

[Rezolution]

Thanks for the tip!

[Rezolution]

My first SSTO. It has enough delta-v to make into a low orbit and return for a safe landing. Overall fairly stable, though not much to look at it. Also, it has plenty of jet fuel to make up for any "missed approaches" one might have during the return trip.

Hope this helps!

[UmbralRaptor]

I'd recommend intake spam (>4 ram intakes per engine), and an odd number of jet engines. (Perhaps just 1 initially) Ideally, you want to have an apoapsis outside of the atmosphere, and a periapsis above the surface just from the jets. (Think of surface speeds >2100 m/s)

[Rezolution]

Thanks for the feedback. I'll give that a shot. My goal in making this craft was to do so without any online help or hints, at least for the initial design. Because of this, I know that I will defiantly be behind the curve, so to speak, and am willing to accept any help that the rest of you, more experienced SSTOers, might have to offer.

Thank you!

[arq]

People swear that intakes can kill a launch, but running Kerbal Engineer Redux I check my drag forces with them open and closed. The difference is usually 2-4% of the total drag force, so it's not that significant (especially because drag force starts dropping waaaaaay off around 20km). That step really isn't as important as most people claim, but every little bit helps.

Also, you start getting dramatically diminishing returns above 4 intakes/engine, as the air starts becoming exceedingly thin above 25km.

[Rezolution]

So any more than four intakes will not make an appreciable difference? Right now I'm hitting about 21-22Km before I loose my jets. I'll try taking away an engine and/or adding a couple more intakes and see where that gets me.

[Umlüx]

i got to nearly 26km while careful throttling down, built up speed and then fired the rockets and closed the intakes.

SPACE!

thanks again!

[arq]

Any more than 4 intakes *per turbojet* is overkill. Honestly, that is still a lot. I have an SSTO that is capable of Minmus landings and returns and it runs a 9:4 intakes-to-jets ratio. It can easily get to 23km/1500m/s on the jets (and a little more if I were patient enough to slowly back off the throttle). So a ratio anywhere from 2-4 intakes per engine is reasonable for SSTOs. I opt for the lower end for aesthetics. If I were running 15 intakes, it might get up to 27km/1700m/s (now I'm making stuff up, I'd need to do this experimentally), but placing all those intakes ('air hogging') can be a pain and it doesn't massively reduce the delta-v to get to orbit.

EDIT: After some more reading, I need to correct my above statement. With airhogging, it is possible to achieve orbital speeds, where you just need a small amount of delta-v to circularize at apoapsis. If you do not intend to airhog (some people consider it exploitative) then 2-4 intakes is fine.

Edited July 3, 2013 by arq
technical correctness

[Umlüx]

i switched over to the B9 Aerospace mod. designing a working SSTO is clearly easier now.

this baby can get up to 1800m/s and 26km on jets only. i just LOVE those sabre engines!

but i dont think there is enough fuel left for a mun visit...