SSTO Stuck at 350 m/s

[kangaroo3505]

My ssto has like 2.06 thrust to weight ratio and it gets to 350 m/s really really fast but it's stuck there and just slows down until it runs out of fuel, HELP I'VE BEEN TRYING TO TAKE IT OVER 400 m/s FOR 3 HOURS

Edited March 31, 2022 by kangaroo3505

[Echo__3]

This sounds like a issue with drag. Are you able to share some pictures of your craft?

[kangaroo3505]

55 minutes ago, Echo__3 said:

This sounds like a issue with drag. Are you able to share some pictures of your craft?

Yeah Sure here 

[darthgently]

You are apparently up against the trans-sonic barrier (mach 1) probably.    It is kind of like a planing power boat trying to climb out of "the hole" and up on top its own bow wave to get up on plane.  Maybe try climbing sooner and get up to thinner air which has less drag but still allows air breathing.  At least 10k.  As steep as you can go while still accelerating.  Also, those intakes weigh a lot, iirc.  While having so many of them will allow you to run air breathing to a higher altitude, the mass of them can make it harder to get there, so a balance must be struck

[kangaroo3505]

21 minutes ago, darthgently said:

You are apparently up against the trans-sonic barrier (mach 1) probably.    It is kind of like a planing power boat trying to climb out of "the hole" and up on top its own bow wave to get up on plane.  Maybe try climbing sooner and get up to thinner air which has less drag but still allows air breathing.  At least 10k.  As steep as you can go while still accelerating.  Also, those intakes weigh a lot, iirc.  While having so many of them will allow you to run air breathing to a higher altitude, the mass of them can make it harder to get there, so a balance must be struck

It didn't work it since I was ascending slowly I basically stalled and kept falling because I was so low on speed

[Echo__3]

I'm seeing lots of whiplash engines. What engine are you intending to use in the upper atmosphere/vacuum. 

All of those radially attached engines are adding lots of drag. And probably quite a bit from your wings and those Mk3 parts. What angle of incidence are you using on the main wings? 1 to 5 degrees is good.

[darthgently]

1 minute ago, kangaroo3505 said:

It didn't work it since I was ascending slowly I basically stalled and kept falling because I was so low on speed

You don't need 2:1+ TWR on a jet.  You are too heavy with engines and intakes maybe.  I made the same mistake initially.  You waste all your fuel trying to go too fast in air that is too thick.  I am far from an SSTO expert, but I've noticed that the successful SSTOs out there had far less engine than my initial design which looked a lot like yours.  I eventually got that design to work, but it was very inefficient compared to others out there.  My next project will have far less engine and intake, and so require far less fuel.  Look at this franken monster.  I'm shocked I got it working at all.  There are shock cone intakes on the front of nearly everything you can see (bad mistake):

[kangaroo3505]

19 minutes ago, Echo__3 said:

I'm seeing lots of whiplash engines. What engine are you intending to use in the upper atmosphere/vacuum. 

All of those radially attached engines are adding lots of drag. And probably quite a bit from your wings and those Mk3 parts. What angle of incidence are you using on the main wings? 1 to 5 degrees is good.

Yes they are radially attached and Angle of incidence... I don't even know what that is

2 minutes ago, darthgently said:

You don't need 2:1+ TWR on a jet.  You are too heavy with engines and intakes maybe.  I made the same mistake initially.  You waste all your fuel trying to go too fast in air that is too thick.  I am far from an SSTO expert, but I've noticed that the successful SSTOs out there had far less engine than my initial design which looked a lot like yours.  I eventually got that design to work, but it was very inefficient compared to others out there.  My next project will have far less engine and intake, and so require far less fuel.  Look at this franken monster.  I'm shocked I got it working at all.  There are shock cone intakes on the front of nearly everything you can see (bad mistake):

Well I'll try that in just a sec

[darthgently]

3 minutes ago, kangaroo3505 said:

Angle of incidence... I don't even know what that is

If the wings are completely flat, that is parallel with the body of the craft, that would be 0 degrees angle of incidence.  5 degrees would be tilted up at the front by 5 degrees.  It makes taking off easier and will make ascent easier

[kangaroo3505]

I give up with that ssto design

[swjr-swis]

14 hours ago, kangaroo3505 said:

 

That looks like a fairly standardf Mk3 shuttle body, with the Big-S shuttle wings. I can't see what the payload is and you don't specify, but regardless of what you're carrying... a plane of that type really shouldn't need more than two (yes, TWO) of those Whiplash ramjets to punch through the sound barrier.

A comparison: the Centurion 1 is not an SSTO, just an airliner, but it uses the same body and engine type as yours. It goes supersonic up to mach 4.2.. with a much longer and heavier body, and just two of those engines:

Spoiler

About 2-2.5 times longer and probably about as much heavier. Two Whiplash jets, that's really it.

Flying mach 4.2, or 1250 m/s at 20 km. At this point is when you would want to engage your choice of rocket engines for the second part of the ascent into orbit.

If this one can go supersonic, yours must be able to as well!

 

At this point I would give a few tips on building efficient (space)planes in KSP, like @darthgently just did about the nr of stacks and the angle of incidence... but honestly, with as many engines as your plane has (12 (2x6) Whiplash ramjets, plus maybe 3-4 RAPIERs on the tail?), you should be able to completely disregard every rule in the book and just brute force it to orbit, without any optimizations or caring about the ascent angle.

I tried, with this rebuild from your screenshots:

Spoiler

Re-created from your screenshots as best I could. Having to guess at what's on the tail though, and it's unclear what type of Mk1 size tanks you used (only LF or LFO?).

Used the Mk3 engine mount for the tail end. Testing with 12 Whiplash jets and 4 RAPIERS. It punched supersonic so fast I missed making the screenshot at 350 m/s. While climbing 10 degrees!

Here it does stop accelerating (not the most optimal ascent angle, really), but it's still thrusting and climbing at over 1500 m/s and barely slowing down.

The Whiplash ramjets flame out at this altitude and speed, but the RAPIERS keep pushing a bit longer. Normally this is where we switch RAPIERS to closed cycle (rocket mode), but I left everything at default and had no action group to do it.

Just before 30 km, the RAPIERS switch to rocket mode automatically anyway (default), and it starts accelerating again.

Final orbit after a quick and dirty test run. Not very neat, and no ox left to return, but it shows it can easily get to orbit. Much better results can be had by optimizing this. Note also there is still 2012 units of LF in the tanks - we can remove 2000+ units of LF from the tanks in the SPH. That's 10 tonnes of payload we could be carrying in the cargo bay.

 

Note that the above is NOT how I would recommend building or flying a spaceplane. Just showing that your plane, from what I can tell on those screenshots, should be able to not just go supersonic, but get to orbit too. With that many engines, it doesn't really need to be efficient... it's basically a rocket.

I notice in the meantime you've posted about giving up on this. If what I showed above renews your interest in trying, we're still willing to help. Sharing the craft file would allow us to give more accurate tips, and it would also help if you explain a bit how exactly you take off and fly the plane. (what angle of climb do you use? Are you using all engines from the start? If not, which ones and when do you stage the next ones? what does the back look like exactly? etc).

 

 

[jimmymcgoochie]

It’s hard to tell from the initial screenshots, but are you sure those Whiplash engines are actually running? They have very distinctive blue plumes when they are but I don’t see those at all; compare that to @swjr-swis’s copy.

I also believe that the underwing pods have NERVs on them rather than Whiplashes- in which case why on Earth Kerbin do they have shock cones? Swap those to NCS adapters with small nosecones on them and you’ll get more fuel and less drag.

[swjr-swis]

7 hours ago, jimmymcgoochie said:

I also believe that the underwing pods have NERVs on them rather than Whiplashes-

I think you're right, missed that detail. That would make it considerably heavier.

And you're right that neither the jets nor the Nervs seem to be firing in that screenshot. But there is a (set of?) plume(s) in the back there that I can't place either. RAPIERs in closed cycle? Not sure.

That would make things harder - if it's only whiplash+nerv, that isn't the easiest combination for a spaceplane, but it can be done with some optimizing.

 

[kangaroo3505]

10 minutes ago, swjr-swis said:

I think you're right, missed that detail. That would make it considerably heavier.

And you're right that neither the jets nor the Nervs seem to be firing in that screenshot. But there is a (set of?) plume(s) in the back there that I can't place either. RAPIERs in closed cycle? Not sure.

That would make things harder - if it's only whiplash+nerv, that isn't the easiest combination for a spaceplane, but it can be done with some optimizing.

 

Wait you also fire the Nervs even at the athmosphere?

[swjr-swis]

8 minutes ago, kangaroo3505 said:

Wait you also fire the Nervs even at the athmosphere?

Depends entirely on you. Some people feel it's inappropriate to leave radioactive plumes in the atmosphere, but kerbals are... well, kerbals. Human rules do not apply.

I just tried with 6x Whiplash, 6x Nerv, and 4x RAPIER.... and even without optimizing it still goes straight to orbit. Firing all engines, no settings changed, just nose up 10 degrees and whoosh.

[kangaroo3505]

2 minutes ago, swjr-swis said:

Depends entirely on you. Some people feel it's inappropriate to leave radioactive plumes in the atmosphere, but kerbals are... well, kerbals. Human rules do not apply.

I just tried with 6x Whiplash, 6x Nerv, and 4x RAPIER.... and even without optimizing it still goes straight to orbit. Firing all engines, no settings changed, just nose up 10 degrees and whoosh.

I mean the Nerv does produce not a lot of power at the atmosphere and uses quite a bit of fuel so...

[swjr-swis]

Just now, kangaroo3505 said:

I mean the Nerv does produce not a lot of power at the atmosphere and uses quite a bit of fuel so...

You're right: normally, one would wait until higher in the atmosphere to fire the Nervs, somewhere between 15-20 km where they already burn at almost their peak efficiency. But you hadn't yet explained how you were flying this.

And really, with this many engines it doesn't much matter... you get to the higher atmosphere before you're even close to burning all the LF:

With 6x whiplash, 6x Nerv, 4x RAPIER. Burning all engines from the start, no settings changed, no staging, RAPIERs auto-switching. Just nose up 10 degrees from the runway and go.

I mean, it's not how I'd recommend doing it, but there's more than enough raw thrust and fuel on there to do the job.

[kangaroo3505]

YES I'M AT ORBIT FINALLY (Major redesign :[ )

[swjr-swis]

11 minutes ago, kangaroo3505 said:

YES I'M AT ORBIT FINALLY (Major redesign :[ )

Welcome to space!

[kangaroo3505]

4 minutes ago, swjr-swis said:

Welcome to space!

And it has only 1400 m/s... I CAN'T GO ANYWHERE WITH THIS (is refueling allowed?)

[Curveball Anders]

2 hours ago, kangaroo3505 said:

And it has only 1400 m/s... I CAN'T GO ANYWHERE WITH THIS (is refueling allowed?)

Single Stage To Orbit ...

So of course you can.

[imcute]

sound barrier

On 4/2/2022 at 1:20 AM, kangaroo3505 said:

And it has only 1400 m/s... I CAN'T GO ANYWHERE WITH THIS (is refueling allowed?)

single stage to orbit...

dont expect a lot on this

ur wanting a ssta