SSTO ascent path/fuel ratio optimisation

[Rodyle]

Hello there,

I've been ....ing around with SSTOs again, and I've got a design I'm sort of happy with and gets to a 100 km orbit with roughly 2.8km/s left on my last try. However, I am pretty sure that I managed to get the same aircraft into space on at least one occasion with a bit over 3 km/s in the tanks. I was wondering what kind of methods you guys use to optimise the ascent path and fuel ratios of your SSTOs.

[numerobis]

Slashy has written this useful guide. I agree with the broad strokes of it (I have nits but nothing major).

[Rodyle]

Slashy has written this useful guide. I agree with the broad strokes of it (I have nits but nothing major).

That's a nice guide. However, the guide assumes that you have sufficient airhogging and sufficient thrust/drag. I'm currently not airhogging to the max, which means I have to disengage some of my engines at the 30-ish kilometer mark, leaving me with a 200+ part, 16 tonnes airplane with a single jet engine. In these circumstances, the standard ascent path is not correct.

[numerobis]

16t is well within the bounds of what I normally fly for a single-engine plane. How much intake area do you have?

[capi3101]

I generally use DocMoriarty's guide both to determine fuel and ascent profile. Couldn't say whether it's optimal or not; I will say that it works.

Here's my general spaceplane advice - the guide is linked in there.

Here's DocMoriarty's ascent profile in a nutshell:

45+ degrees above the horizon to 15k

30 degrees from 15-20k

20 degrees from 20-25k

15 degrees from 25-27.5k

10 degrees from 27.5k onward

That kinda works; sometimes I find that I have to start descending to pick up more speed while still in air-breathing mode. That's generally a sign of a bad profile; I'm aware of this fact...

Edited January 7, 2015 by capi3101

[Rodyle]

16t is well within the bounds of what I normally fly for a single-engine plane. How much intake area do you have?

Correction: 17 tonnes at launch. Total intake area: 0.064. And yeah. I tried a single-engined version, but I found it too anemic in the early stages of the flight. I felt that I was losing too much fuel by staying in the atmosphere for that long and it required too much focus to fly.. I'll test the single-engine version and see what kind of delta-v that gives.

I generally use DocMoriarty's guide both to determine fuel and ascent profile. Couldn't say whether it's optimal or not; I will say that it works.

Here's my general spaceplane advice - the guide is linked in there.

Here's DocMoriarty's ascent profile in a nutshell:

45+ degrees above the horizon to 15k

30 degrees from 15-20k

20 degrees from 20-25k

15 degrees from 25-27.5k

10 degrees from 27.5k onward

That kinda works; sometimes I find that I have to start descending to pick up more speed while still in air-breathing mode. That's generally a sign of a bad profile; I'm aware of this fact...

Even if I remove 2 lt200's (reducing the weight to 12.5ish tonnes), doing a 45+ degrees ascent path to 15K is impossible with a single engine.

Edited January 7, 2015 by Rodyle

[numerobis]

My low flight (1km to 15km) is typically on stability assist, at 2x acceleration, running in the background.

With that amount of area and mass you should be able to get about 1600 m/s with two jets, about 1650 m/s with one (with the one jet you need to be higher up), and about 1700 m/s if you have one engine and a lot of Mk2 parts.

So my guess is that your goal should be to speed up to about 1500 m/s at ~30km altitude or so, then pitch up steeply to push apoapsis as high as you can. When you're about to flame out, fly surface prograde or a bit steeper pitch than that, and gradually throttle back until you get close to apoapsis (a few seconds). Finally, switch to rockets to finish off your burn.

[Rodyle]

My low flight (1km to 15km) is typically on stability assist, at 2x acceleration, running in the background.

Doable, depending on angle to the horizon, although I do have some issues with sudden dropping of the nose for some reason.

With that amount of area and mass you should be able to get about 1600 m/s with two jets, about 1650 m/s with one (with the one jet you need to be higher up), and about 1700 m/s if you have one engine and a lot of Mk2 parts.

So my guess is that your goal should be to speed up to about 1500 m/s at ~30km altitude or so, then pitch up steeply to push apoapsis as high as you can. When you're about to flame out, fly surface prograde or a bit steeper pitch than that, and gradually throttle back until you get close to apoapsis (a few seconds). Finally, switch to rockets to finish off your burn.

Thanks. I'm now trying to improve the 1 engine version (bit less weight, bit more wings).

That profile is actually quite similar to the one I was using, albeit slightly more aggressive. I'll try it asap (tomorrow at the earliest, probably) and post results.

EDIT:

Huh. Whaddyaknow. Those changes (replaced two of the three engines with backwards air intakes, increased total wing surface, moved centre of lift slightly forward, decreased mass by removing 2 lt200 tanks) made a difference. I used to get the single engine version into orbit with roughly 2.8km/s with difficulty. I now got it into orbit with relative ease and roughly 3.1Km/s, with some room for improving the fuel ratios.

I felt like they slightly changed the rules of the game between 0.24 and 0.9. I never would've even tried to do such a heavy thing on a single engine back then.

Edited January 7, 2015 by Rodyle

[capi3101]

Correction: 17 tonnes at launch. Total intake area: 0.064. And yeah. I tried a single-engined version, but I found it too anemic in the early stages of the flight. I felt that I was losing too much fuel by staying in the atmosphere for that long and it required too much focus to fly.. I'll test the single-engine version and see what kind of delta-v that gives.

Even if I remove 2 lt200's (reducing the weight to 12.5ish tonnes), doing a 45+ degrees ascent path to 15K is impossible with a single engine.

I beg to differ...if you're having issues holding the profile, the design either has insufficient lift, insufficient SAS, insufficient pitch authority or the CoL is a bit too far behind the CoM (i.e. you've got inherent lawn dart behavior). Without looking at the design, my guess is insufficient pitch authority, but to know for sure I'd have to see a picture.

[GoSlash27]

That's a nice guide. However, the guide assumes that you have sufficient airhogging and sufficient thrust/drag. I'm currently not airhogging to the max, which means I have to disengage some of my engines at the 30-ish kilometer mark, leaving me with a 200+ part, 16 tonnes airplane with a single jet engine. In these circumstances, the standard ascent path is not correct.

That design isn't airhogging at all. It's got .024 m^2 intake area, which is a little over 1/3 of what you're using. In fact, you could use 3 of those radials and they'd be fine with a single engine.

It is assuming that you have an adequate intake area and adequate wing loading.

1 turbojet is marginal for 17 tonnes of aircraft; you should really be using 2. 3 would be overkill. You said you're disengaging "some of" your engines?

If that's the case, you have way too many engines for a 17 tonne aircraft.

The basic idea of getting to orbit efficiently is that you get all the speed you can from the turbojets instead of rockets. It's not a matter of getting to altitude quickly, but rather getting to *speed* without flaming out. The fact that you're running out of air at 30km tells me that you're climbing too rapidly and don't have enough speed. Increasing intake area will keep your engines fed, but so will increasing speed at a given altitude.

Don't worry about low acceleration at the bottom end. Ditch the extra engines; they're dead weight and drag.

You want at least .018m^2 intake area per engine, 1.0 Cl worth of wings per tonne of aircraft, and 1 engine for each 15 tonnes of aircraft.

Once you meet those requirements, you have to fly the plane differently in different phases of the launch to maximize your efficiency.

Phase 1, 0-15km: Climb as steeply as you can while maintaining a minimum of 100 m/sec airspeed.

Phase 2: 15-25km: Reduce your climb rate to maintain NMT 100 m/sec climb rate.

Phase 3: 25-32km: Maintain a pitch of NMT 22* and let the plane build speed.

Phase 4: 32-38km: Throttle back as necessary to keep the engines lit while maintaining NMT 100 m/sec climb rate.

Once airspeed is no longer increasing, transition to rockets and pitch up 45* to establish apoapsis.

Best,

-Slashy

Edited January 7, 2015 by GoSlash27

[Rodyle]

I beg to differ...if you're having issues holding the profile, the design either has insufficient lift, insufficient SAS, insufficient pitch authority or the CoL is a bit too far behind the CoM (i.e. you've got inherent lawn dart behavior). Without looking at the design, my guess is insufficient pitch authority, but to know for sure I'd have to see a picture.

It's a lift issue. I can get to the 45 degrees mark easily, but you have deceleration at that point. I would love to add more wing area than what I have now, but I wouldn't be able to without destroying the aesthetics of the it.

Doesn't mean I don't have the CoL/CoM problem and the insufficient SAS issue though. Before I added more wing surface on the front end it had issues keeping 50+m/s upwards velocity above 13 kilometres. It's a bit more decent now.

That design isn't airhogging at all. It's got .024 m^2 intake area, which is a little over 1/3 of what you're using. In fact, you could use 3 of those radials and they'd be fine with a single engine.

I think you mean 2/3s. And yes, that is less, but it still means his airtake/engine ratio is twice as high as mine.

It is assuming that you have an adequate intake area and adequate wing loading.

1 turbojet is marginal for 17 tonnes of aircraft; you should really be using 2. 3 would be overkill. You said you're disengaging "some of" your engines?

If that's the case, you have way too many engines for a 17 tonne aircraft.

I had three on them. I had two on the original design, but I increased it due to fake laziness: on two engines, I had to look up the flame-out thresholds for 2 engines at a given thrust, while with three, I could slowly decrease the thrust to 2/3s, then shut down the middle engine and turn the thrust up and, turn it down slowly again and at 1/2 thrust turn on the middle and turn off the outer engines.

Apart from that, I a big fan of the Clarkson method of design. Even my Duna (possibly Laythe) capable SSTO could probably have done with 2, maybe even 4 less engines, but this way it took 5 to 10 minutes less to get to orbit, which, given the size of the vehicle, was a lot more real time.

The basic idea of getting to orbit efficiently is that you get all the speed you can from the turbojets instead of rockets. It's not a matter of getting to altitude quickly, but rather getting to *speed* without flaming out. The fact that you're running out of air at 30km tells me that you're climbing too rapidly and don't have enough speed. Increasing intake area will keep your engines fed, but so will increasing speed at a given altitude.

Eh. I got to the 30Km mark with 18Km/s. I wasn't climbing too rapidly I think.

Don't worry about low acceleration at the bottom end. Ditch the extra engines; they're dead weight and drag.

You want at least .018m^2 intake area per engine, 1.0 Cl worth of wings per tonne of aircraft, and 1 engine for each 15 tonnes of aircraft.

Once you meet those requirements, you have to fly the plane differently in different phases of the launch to maximize your efficiency.

Phase 1, 0-15km: Climb as steeply as you can while maintaining a minimum of 100 m/sec airspeed.

Phase 2: 15-25km: Reduce your climb rate to maintain NMT 100 m/sec climb rate.

Phase 3: 25-32km: Maintain a pitch of NMT 22* and let the plane build speed.

Phase 4: 32-38km: Throttle back as necessary to keep the engines lit while maintaining NMT 100 m/sec climb rate.

Once airspeed is no longer increasing, transition to rockets and pitch up 45* to establish apoapsis.

Best,

-Slashy

I normally don't really worry about intake area numbers and lift, to be honest, but yes, the launch profile is quite similar to the one I usually use. However, since that was what I did when I got a lower delta-v in orbit then before, I started wondering about a way to optimise launch profiles for generic SSTOs, in stead of the optimal launch profiles for an well-designed vehicle.

Edited January 7, 2015 by Rodyle

[GoSlash27]

It's a lift issue. I can get to the 45 degrees mark easily, but you have deceleration at that point. I would love to add more wing area than what I have now, but I wouldn't be able to without destroying the aesthetics of the it.

Doesn't mean I don't have the CoL/CoM problem and the insufficient SAS issue though. Before I added more wing surface on the front end it had issues keeping 50+m/s upwards velocity above 13 kilometres. It's a bit more decent now.

You don't have to necessarily hit 45 degrees pitch. In fact, the exact pitch angle early on is not critical. Maintaining airspeed is.

If you have insufficient lift, it's not going to hamper you in the early climbout, it's going to kill you in the 25-32km "wall" phase. You're never getting past it without enough wings, which is why it's referred to as "the wall".

More engines or more intakes aren't the answer there. In fact, they'll just make the problem worse.

What you need is proper wing loading, which means either ditching excess weight or increasing wing area.

Best,

-Slashy

- - - Updated - - -

I think you mean 2/3s. And yes, that is less, but it still means his airtake/engine ratio is twice as high as mine.

That'd be "my" intake/ engine ratio, and no, it's 1/3. .024 m^2 per engine in my tutorial design vs. .0213 per engine in yours. And as I said, it will actually work fine down to .018.

Rule #1: Engine/ intake ratio is meaningless. The extra engines aren't using the air from "their" intakes when you shut them down. What you have here isn't insufficient intakes per engine, but rather excessive engines per ton of aircraft. You need 2 engines and .36m^2 of intakes. That extra engine is nothing more than a boat anchor when you've got it turned off.

And honestly, you could probably save a few tons by ditching 2 engines/ structure/ intakes/ fuel, allowing you to fit in the range where 1 engine is adequate for the job.

I had three on them. I had two on the original design, but I increased it due to fake laziness: on two engines, I had to look up the flame-out thresholds for 2 engines at a given thrust, while with three, I could slowly decrease the thrust to 2/3s, then shut down the middle engine and turn the thrust up and, turn it down slowly again and at 1/2 thrust turn on the middle and turn off the outer engines.

You need 2 and you need to keep them lit. Also check my tutorial on multiengine spaceplanes and how to fix asymmetric flameout issues.

Apart from that, I a big fan of the Clarkson method of design. Even my Duna (possibly Laythe) capable SSTO could probably have done with 2, maybe even 4 less engines, but this way it took 5 to 10 minutes less to get to orbit, which, given the size of the vehicle, was a lot more real time.

I'm not familiar. I just know how to efficiently get spaceplanes into orbit. 2 turbojets and 1 LV-N are adequate to get you to Laythe and back with passengers if done correctly.

Eh. I got to the 30Km mark with 18Km/s. I wasn't climbing too rapidly I think.

I guarantee you were if you're starving for air at 30km. You want to transition to rockets about 500 m/sec faster than that.

I normally don't really worry about intake area numbers and lift, to be honest, but yes, the launch profile is quite similar to the one I usually use. However, since that was what I did when I got a lower delta-v in orbit then before, I started wondering about a way to optimise launch profiles for generic SSTOs, in stead of the optimal launch profiles for an well-designed vehicle.

You solved your problem in the first sentence.

The best remedy for an efficient launch with a poorly designed aircraft is replacing it with a properly designed aircraft.

After that, it is as I said; fly it to efficiently build speed and use the rockets as little as possible.

Best,

-Slashy

Edited January 7, 2015 by GoSlash27

[Rodyle]

You don't have to necessarily hit 45 degrees pitch. In fact, the exact pitch angle early on is not critical. Maintaining airspeed is.

To some extent: yes. However, we can both agree that a plane not being able to climb at a sufficient rate is going to lose a lot of efficiency due to drag and gravity.

If you have insufficient lift, it's not going to hamper you in the early climbout, it's going to kill you in the 25-32km "wall" phase. You're never getting past it without enough wings, which is why it's referred to as "the wall".

More engines or more intakes aren't the answer there. In fact, they'll just make the problem worse.

I don't know. Given enough air intakes to support those engines, you can overcome a too low lift. But yes, this will decrease the efficiency drastically.

What you need is proper wing loading, which means either ditching excess weight or increasing wing area.

Which has been done. The weight has gone down from 17 to 13 tonnes and extra wing surface has been added. For reference: it looks like this after those changes.

That'd be "my" intake/ engine ratio, and no, it's 1/3.

Rule #1: Engine/ intake ratio is meaningless. The extra engines aren't using the air from "their" intakes when you shut them down.

Will you at least grant me that someone with a low engine/intake will have to shut down engines earlier than someone with a higher E/i ratio, given that the aircraft are functionally the same otherwise?

What you have here isn't insufficient intakes per engine, but rather excessive engines per ton of aircraft. You need 2 engines and .36m^2 of intakes. That extra engine is nothing more than a boat anchor when you've got it turned off.

And honestly, you could probably save a few tons by ditching 2 engines/ structure/ intakes/ fuel, allowing you to fit in the range where 1 engine is adequate for the job.

Yup. I got stuck on a wrong path by trying to fix the issue by adding that third engine. I will stand my ground though on that the decision isn't as bad as you say it is. Yes, it decreased the delta-v once in space. However, it did so by a smaller fraction than I imagined. I think I lost something like 100 m/s by doing so.

You need 2 and you need to keep them lit. Also check my tutorial on multiengine spaceplanes and how to fix asymmetric flameout issues.

I know, I should probably fix that in the design stage. However, I'm inherently a lazy person, and bad at it. If I can save a few minutes work in the early phases, I'll do so even if it costs me over half an hour to fix it later on.

I'm not familiar. I just know how to efficiently get spaceplanes into orbit.

It's colloquially known as "MORE POWER!!!!!!!!!!!!!!"

2 turbojets and 1 LV-N are adequate to get you to Laythe and back with passengers if done correctly.

I don't doubt it, but we're getting kind of off-topic.

I guarantee you were if you're starving for air at 30km. You want to transition to rockets about 500 m/sec faster than that.

My velocity was increasing slowly enough at that point that I felt that I'd be better off increasing altitude and switching off those engines, rather than hanging around, getting a bit more speed but losing a lot of fuel due to drag and whatnot.

You solved your problem in the first sentence.

The best remedy for an efficient launch with a poorly designed aircraft is replacing it with a properly designed aircraft.

I completely agree. However, I don't always build for efficiency. This craft was designed around an aesthetic first, and then optimised to make it as efficient as possible without losing that aesthetic. If that means I have to much around for hours to get it working to the degree I want it to, so be it.

EDIT: I was looking at your thread on the different air intakes, and I saw how badly the shock cone and the structural intake perform. Since I use 4 of the first and 16 of the latter, it may have had something to do with my problems. Can't explain all of it with that, but it could explain why I wasn't getting up to the speeds necessary.

Edited January 8, 2015 by Rodyle

[GoSlash27]

Rodyle,

A lot of individual points in your response, and I probably can't address them all...

To some extent: yes. However, we can both agree that a plane not being able to climb at a sufficient rate is going to lose a lot of efficiency due to drag and gravity.

No, Sir. Executing that phase on jets means that the losses are trivial due to the high Isp. "Sufficient" merely means "climbing" in that situation.

I don't know. Given enough air intakes to support those engines, you can overcome a too low lift. But yes, this will decrease the efficiency drastically.

Again, no Sir. You will not ever overcome insufficient lift with more intakes, particularly in the "wall" and "runway" phases.

Will you at least grant me that someone with a low engine/intake will have to shut down engines earlier than someone with a higher E/i ratio, given that the aircraft are functionally the same otherwise?

Sorry, but no. Ultimately, you make the same thrust from a given intake area/ altitude/ airspeed regardless of the number of engines. You could shut down engines and throttle up the others, or just throttle down all the engines. It works out the same way regardless; you have too many engines.

Having more engines merely means that you have more mass and drag. Where you need the thrust is in the "wall" phase, where your engines are fully- fed and you're exceeding your induced drag to allow you to continue climbing.

It's colloquially known as "MORE POWER!!!!!!!!!!!!!!"

A bad philosophy for spaceplane design. More power or more wings or even more intakes isn't how you need to be thinking. It's "less pork".

Spaceplanes are all about balance. You need "enough" of each attribute, not "more" of one at the expense of others.

My velocity was increasing slowly enough at that point that I felt that I'd be better off increasing altitude and switching off those engines, rather than hanging around, getting a bit more speed but losing a lot of fuel due to drag and whatnot.

No doubt it was, but shutting down engines and dragging them along as drag and cargo is hampering your efforts. That costs you way more time and fuel than simply getting rid of them and feeding one engine.

I completely agree. However, I don't always build for efficiency. This craft was designed around an aesthetic first, and then optimised to make it as efficient as possible without losing that aesthetic. If that means I have to much around for hours to get it working to the degree I want it to, so be it.

To each his own, but in that case you're asking a question that's impossible to answer. You're building a spaceplane that's not efficient by design and then asking how to fly it to make it efficient. The short answer is that you can't. You can fly it in a less inefficient manner, but it will never be "efficient" because you didn't design it to be capable of efficient operation.

Personally, I always design my spaceplanes to be efficient and then let form follow function. Elegant designs tend to have their own aesthetic simply from having been designed to be efficient.

Best,

-Slashy

Edited January 8, 2015 by GoSlash27

[numerobis]

There's two fun bits to spaceplanes:

1. Designing them.

2. Flying them efficiently.

I have no trouble giving advice about both. You can have fun flying a suboptimal plane, and trying to optimize the flight plan.

For example, I'm somewhat interested (but not enough to put in a lot of work for it) into trying to optimize the flight plan for a basic jet SSTO. I've noticed that things change: with a turbojet it's all about picking up a lot of horizontal speed. For the basic jet it appears to be all about picking up a lot of altitude, because you can't pick up that much speed. Clearly the answer to the optimal jet-based flight path will change according to the top speed you can achieve.

[Rodyle]

Rodyle,

A lot of individual points in your response, and I probably can't address them all...

No problem. I was defending points which were either technicalities or things I admitted to be wrong.

To each his own, but in that case you're asking a question that's impossible to answer. You're building a spaceplane that's not efficient by design and then asking how to fly it to make it efficient. The short answer is that you can't. You can fly it in a less inefficient manner, but it will never be "efficient" because you didn't design it to be capable of efficient operation.

You misunderstand me. I was not asking help on optimising the flight path so a less than optimal design performs as well as the most efficiently designed ship possible. I was asking for help optimising the flight path so it uses the optimal flight path for that particular design. IE: how do I get it to space with as much fuel remaining, and how much of both types of fuel should I take along to follow that path. It was mostly an academic question.

Personally, I always design my spaceplanes to be efficient and then let form follow function. Elegant designs tend to have their own aesthetic simply from having been designed to be efficient.

I agree there can be, but you still have to make the choice at some point to start designing it elegantly, in stead of sticking on the required bits at whatever place possible.

There's two fun bits to spaceplanes:

1. Designing them.

2. Flying them efficiently.

I have no trouble giving advice about both. You can have fun flying a suboptimal plane, and trying to optimize the flight plan.

For example, I'm somewhat interested (but not enough to put in a lot of work for it) into trying to optimize the flight plan for a basic jet SSTO. I've noticed that things change: with a turbojet it's all about picking up a lot of horizontal speed. For the basic jet it appears to be all about picking up a lot of altitude, because you can't pick up that much speed. Clearly the answer to the optimal jet-based flight path will change according to the top speed you can achieve.

Indeed. And this is at the crux of what I was wondering about. I was looking around, but I have never seen someone do the math on this.

[GoSlash27]

Indeed. And this is at the crux of what I was wondering about. I was looking around, but I have never seen someone do the math on this.

Honestly, I doubt anybody *could* do the math on this. Simply too many interdependent variables.

The phases of the launch aren't determined by the t/w, wing loading, or intake area, but rather the rate of change of atmospheric density. They would be handled using the same philosophy, even if your turbojet SSTO doesn't have any wings at all.

0-15km is the "soup" phase. High drag, terminal velocity doesn't change much, Isp isn't very good, thrust isn't very good. The best thing to do here is climb out of it as rapidly as you can without inducing a lot of drag by high angle of attack.

15-25km is the "cork" phase. Everything is improving at an increasing rate, and it's easy to end up too high and too slow. The climb rate must be limited to keep this from happening.

25-32km is the "wall" phase. Air is thin enough that generating lift is a problem. AoA must be managed to ensure that the wings are operating at their most efficient point, which is 22* AoA. If you have no wings, you need adequate thrust to keep you climbing (barely) and near terminal velocity. Pitch angle will peak out around 30* without wings.

>32km is the "runway" phase. Angular momentum becomes the major contributing factor of lift. The wings are no longer useful, and although thrust is miniscule, so is drag. Climb rate must be managed to ensure maximum velocity occurs before flameout.

Best,

-Slashy

[numerobis]

I can do an awful lot of the math using the KSP-scripts' plane designer.

That 1650 m/s is calculated from how fast you can go with 17t of 0.2-drag payload and one turbojet and 0.64 intake area, taking into account drag but ignoring gravity.

From there to an *optimal* path is a long way, but at least it gives you bounds on what you can expect will work or not.

It would be nice if someone (not me) ran that code on a server somewhere, with a nice little UI for it.

[Pappus]

You don't have to necessarily hit 45 degrees pitch. In fact, the exact pitch angle early on is not critical. Maintaining airspeed is.

If you have insufficient lift, it's not going to hamper you in the early climbout, it's going to kill you in the 25-32km "wall" phase. You're never getting past it without enough wings, which is why it's referred to as "the wall".

More engines or more intakes aren't the answer there. In fact, they'll just make the problem worse.

What you need is proper wing loading, which means either ditching excess weight or increasing wing area.

Best,

-Slashy

- - - Updated - - -

That'd be "my" intake/ engine ratio, and no, it's 1/3. .024 m^2 per engine in my tutorial design vs. .0213 per engine in yours. And as I said, it will actually work fine down to .018.

Rule #1: Engine/ intake ratio is meaningless. The extra engines aren't using the air from "their" intakes when you shut them down. What you have here isn't insufficient intakes per engine, but rather excessive engines per ton of aircraft. You need 2 engines and .36m^2 of intakes. That extra engine is nothing more than a boat anchor when you've got it turned off.

And honestly, you could probably save a few tons by ditching 2 engines/ structure/ intakes/ fuel, allowing you to fit in the range where 1 engine is adequate for the job.

You need 2 and you need to keep them lit. Also check my tutorial on multiengine spaceplanes and how to fix asymmetric flameout issues.

I'm not familiar. I just know how to efficiently get spaceplanes into orbit. 2 turbojets and 1 LV-N are adequate to get you to Laythe and back with passengers if done correctly.

I guarantee you were if you're starving for air at 30km. You want to transition to rockets about 500 m/sec faster than that.

You solved your problem in the first sentence.

The best remedy for an efficient launch with a poorly designed aircraft is replacing it with a properly designed aircraft.

After that, it is as I said; fly it to efficiently build speed and use the rockets as little as possible.

Best,

-Slashy

Hello could you elaborate a bit more concerning the wall? I am working on my first SSTO and well it isn't a heavy thing its weight is ~ 21t and it has 2 turbo engines. I tried it with more rocket fuel, tried it with more intakes, slapped a couple of extra wings on it but I can't do the ascension profiles because I don't reach them. I didn't try too long for today, but my engines would go out at 21km and it largely didn't matter how I went there although the best tries where when I accelerated more in the lower spheres while burning. Lost a couple of wheels to those.

I also have a problem to get my center of mass forward enough so I can reasonly have my delta wings behind that (including center of lift). I don't have all possible parts yet so my "rocket" part is a swivel. So how are you guys transferring the gravity forward without the whole thing looking dumb? I mean literally the only things I have at the end are the engines. The heaviest stuff (crew transport) and my fuel is on the sides/front as much as I can, but it simply doesn't weigh enough.

How is lift helping me in the higher regions roughly? I thought lift is enough when you have no troubles maneuvering, which I don't I can ascend like 90° at the start if I want to, but that doesn't change the fact that I can't climb to 32 with 2 turbo engines alone

[DeMatt]

Hello could you elaborate a bit more concerning the wall? I am working on my first SSTO and well it isn't a heavy thing its weight is ~ 21t and it has 2 turbo engines. I tried it with more rocket fuel, tried it with more intakes, slapped a couple of extra wings on it but I can't do the ascension profiles because I don't reach them. I didn't try too long for today, but my engines would go out at 21km and it largely didn't matter how I went there although the best tries where when I accelerated more in the lower spheres while burning. Lost a couple of wheels to those.

I also have a problem to get my center of mass forward enough so I can reasonly have my delta wings behind that (including center of lift). I don't have all possible parts yet so my "rocket" part is a swivel. So how are you guys transferring the gravity forward without the whole thing looking dumb? I mean literally the only things I have at the end are the engines. The heaviest stuff (crew transport) and my fuel is on the sides/front as much as I can, but it simply doesn't weigh enough.

How is lift helping me in the higher regions roughly? I thought lift is enough when you have no troubles maneuvering, which I don't I can ascend like 90° at the start if I want to, but that doesn't change the fact that I can't climb to 32 with 2 turbo engines alone

Those posts were written before version 1.0 came out and changed both aerodynamics (and thus wing designs) and the air-breathing engines (and thus which engines you use where). Try looking for a more recent thread - say, one started in May of this year.

[Claw]

Yes, actually I'm really sorry but I'm going to lock this thread. I appreciate that you have a question and are looking for help, but this thread contains very outdated information, and nearly every post to follow will likely completely miss out on your question (many people only look at the OP before they reply).

My recommendation is to repost most of your questions (without reference to the outdated posts) and include a picture of your craft from several angles in the SPH. That will allow us to give more specific advice.

Cheers,

~Claw