Single-Turbojet SSTO Spaceplane

[Rune]

On a roll, indeed. How long did it take you to adjust to the new aero? You've been designing (awesome) spaceplanes for quite some time; I imagine some of that skill had to be re-learned. Either way, that Arrowhead is rather impressive.

Thanks! The new aero was quite the shock, suddenly everything worked completely different... yet really, the basic principles are the same, only more realistic now. And there is the small fact that I studied aeronautical engineering, speciality in aerodynamics and structures... that sure helps. That, and the long hours of KSPing, and basically once I had gotten used to the Mach wall and the thermal barrier mechanics (and installed the heating bar indicator, that one is a must), I got very quickly back to where I was on the old model: this design was entirely eyeballed, and made orbit on first try. It just got an aesthetics pass before (some) of those pics.

Rune. I will admit it is one of my most inspired ones lately. It's just so efficient in parts and flies so well!

[georgTF]

I have a question about the air intakes and air requirements of the turbojet. Does it underperform when using smaller side intakes? Or is the performance allways the same except i'm taking a drag penalty when using a nosecone or other part on the forward facing node that isn't an intake?

In the examples below, no. 1 flies like it has a backwards firing engine in the nose and cannot break the sound barrier. No. 2 is a tiny bit better but still needs a rocket push to break through. No. 3 leaves them both for dead and eases into supersonic flight without a problem.

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Is it the engine or is it drag? The difference is absurd...

(i kept all the redundant bits on the plane to keep the same drag profile)

[GoSlash27]

I have a question about the air intakes and air requirements of the turbojet. Does it underperform when using smaller side intakes? Or is the performance allways the same except i'm taking a drag penalty when using a nosecone or other part on the forward facing node that isn't an intake?

In the examples below, no. 1 flies like it has a backwards firing engine in the nose and cannot break the sound barrier. No. 2 is a tiny bit better but still needs a rocket push to break through. No. 3 leaves them both for dead and eases into supersonic flight without a problem.

http://imgur.com/a/ZOXBJ

Is it the engine or is it drag? The difference is absurd...

(i kept all the redundant bits on the plane to keep the same drag profile)

georgTF,

The difference is primarily the amount of intake area. If your intake area is insufficient, it's like an olympic sprinter trying to run while breathing through a straw.

You need "enough" intake area, but not necessarily "more". A single shock cone, or a pair of XM-G50s, or about 6 of the structural scoops is fine to feed a single turbojet. Any more than that is wasted mass and added drag.

There's also the drag coefficient of the forward-most part. A docking port is draggier than a nose cone, which is draggier than a tail cone.

Best,

-Slashy

[georgTF]

Ty very much. I had used 3 or 4 structural scoops for 1 engine. No wonder it underperformed. I wasn't sure wheter to blame the drag profile of the dock/cone or engine malnourishment.

[Postremus]

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8.15 Tons at launch, can reach an 100k by 100k orbit

[Mister Dilsby]

Hey, kind of sort of accidentally entered this challenge with my one-seat orbital rescuer, the Pogo 2. Very bare bones but gets the job done. 8700kg on the pad, one TRJ and 3x little radial rocket engines.

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craft file

ETA: action groups as follows:

1. Toggle TRJ

4. Toggle intakes

5. Toggle rockets

B. Activates A.I.R.B.R.A.K.E.S. and sets elevons to 'deploy'

Edited May 31, 2015 by Kuzzter

[Tarmenius]

... can reach an 100k by 100k orbit

Cool! I was hoping someone would bring an RCS-powered variant!

... the Pogo 2. Very bare bones but gets the job done.

Neat tailsitter! Have you considered adding landing struts, or does that induce too much drag? Either way, I like the design.

No wonder it underperformed.

In my experience so far with 1.0, the Structural Intakes are now the least effective, having more drag and less intakeAir than even the Radial Air Intake. Of course, I could be just using them improperly

[Mister Dilsby]

Neat tailsitter! Have you considered adding landing struts, or does that induce too much drag? Either way, I like the design.

thanks! I suppose I could try throwing some on the wings, or maybe just a couple of struts to keep the jet from smacking ground.

[GoSlash27]

In my experience so far with 1.0, the Structural Intakes are now the least effective, having more drag and less intakeAir than even the Radial Air Intake. Of course, I could be just using them improperly

Tarmenius,

They were always the least effective intakes (excepting the fuselage intakes). You haven't been using them incorrectly.

Best,

-Slashy

[Rune]

Actually, this thread is making me rethink the whole SSTOing thing in 1.02, too. This thing is, by any metric other than vacuum TWR, every bit as capable as the 1.0 White Dart, and comes in under 20mT.

The thing is, the RAPIERs may have the higher cutoff speed, but the turbojets give more thrust where you really need it, at the Mach barrier, so they let you go transonic with a much lower powerplant mass. That is why I think I can get higher payload out of a lower starting mass. And of course the Terriers are second to none in vacuum isp, excluding nukes, those 40s are really felt here I think.

Rune. Plus, you don't have to play chicken with the heat barrier as much.

Edited May 31, 2015 by Rune

[GoSlash27]

Rune,

I'm not so sure about that. 800m/sec at 20km takes a whole lot more DV to overcome than 1200m/sec at 23km. Plus you've got a tonne more engine mass and 2 nodes that the RAPIER doesn't need, which means it's draggier.

My experience so far has been that by the time you load down a TJ to where it's barely clearing Mach 1, it's top end is completely trashed to the point that it can't even hit Mach 2 at 18km and it's payload fraction drops precipitously.

What kind of payload fraction is this one getting?

Best,

-Slashy

Edited May 31, 2015 by GoSlash27

[Mister Dilsby]

The thing is, the RAPIERs may have the higher cutoff speed, but the turbojets give more thrust where you really need it, at the Mach barrier, so they let you go transonic with a much lower powerplant mass.

Hear, hear. I very rarely used RAPIERS in v90, just because it seemed less elegant to me than turbojet designs. I haven't unlocked them yet in 1.0.2 and I am not missing them. Also don't forget, for craft slightly larger than on this thread an all-LF SSTO is quite do-able. (I think the minimum there is 1xLVN and 2xTRJ, but someone with Slashy's skills might find a way to do it with less

[GoSlash27]

Hear, hear. I very rarely used RAPIERS in v90, just because it seemed less elegant to me than turbojet designs. I haven't unlocked them yet in 1.0.2 and I am not missing them. Also don't forget, for craft slightly larger than on this thread an all-LF SSTO is quite do-able. (I think the minimum there is 1xLVN and 2xTRJ, but someone with Slashy's skills might find a way to do it with less

haha that sounds like a challenge

RAPIERs were definitely inferior in .90 and earlier. I used to do some pretty outlandish things with turbojets and 48-7Ss back then and I didn't even need to airhog to do it.

But from what I've seen so far, those days are gone. My RAPIER designs are soundly trouncing my TJ designs.

I'll see if I can come up with an all-fuel spaceplane for this challenge.

Best,

-Slashy

[Rune]

Rune,

I'm not so sure about that. 800m/sec at 20km takes a whole lot more DV to overcome than 1200m/sec at 23km. Plus you've got a tonne more engine mass and 2 nodes that the RAPIER doesn't need, which means it's draggier.

My experience so far has been that by the time you load down a TJ to where it's barely clearing Mach 1, it's top end is completely trashed to the point that it can't even hit Mach 2 at 18km and it's payload fraction drops precipitously.

What kind of payload fraction is this one getting?

Best,

-Slashy

Yeah, on the other hand, grab this very same fuel load and payload, put a RAPIER, and it just won't break Mach unless you dive for a couple kms, then you will probably burn it up trying to speed up more than with the turbojet, and you will for sure not have enough LF to complete the climb to orbit. The payload for this thing is exactly the same as the twin-RAPIER White Dart 1.0, consider that (cockpit+2mT with >400m/s on LKO). And when I load the turbojet to the bare minimum to break mach, I still can speed up to ~1000m/s on the turbo alone, and then with some rocket help I keep it going alongside them until 1,200m/s.

So maybe this is only a marginal thing, for the extreme cases of low TWR. I do get why the RAPIERs should be better! But, this weights ~18mT and lifts ~3.3mT of useful stuff, still close to 20% payload ratio, and best of all, I can make the single-engine configuration work to lift said 18mT.

Rune. I was the most disappointed person, I like RAPIERs.

[georgTF]

At the moment i am working on perfecting 2 designs based on a single TJ that i see as usefull and possibly superoir to twin TJ builds.

One to carry 6 or 10 kerbals into 75x75 LKO without bothering with docks or refuelling. Just easy up, EVA hops to the station, and easy down. Let dedicated, non-athmospheric shuttles do the rest. I hate LKO but planes need refuelling to be usefull, i do like orbiters, and shuttling crew around the system is a fun thing to do. For a while at least. If i can get a decently high orbit out of a taxi-plane, i can move the fuel depot higher.

The other is supposed to have tanks large enough to visit Minmus, land there and return with up to 6 kerbals. Also carry some sciency doodads or whatever. Landing on the Mun may be out of the question, but orbiting could be ok. Mun is easily visited and exploited for science with small rockets so that's not a huge problem. This plane requires refuelling in LKO and seems to be working. I goofed during refuelling and failed to fill 220 units of LFO and missed the return from Minmus by Dv 60 m/s. I guess it can work but can't prove it yet. Both designs use Twitch engine clusters which are less efficient but do not require side tanks.

Satelites in Kerbin system seem to be better of using a Kickback booster + 909 to get roughly where they need to be. An Ant engine can do the rest. I don't feel like bothering with a SSTO launch + return + landing on the runway to save maybe 1-2K cash.

I don't know what else would be worth trying. I haven't tried nukes so maybe a LF interplanetary design would be a nice thing to try. I'll probably get distracted working to unlock ore refining and building a Minmus "launchpad" station for interplanetary stuff.

This thread has become very helpful regarding SSTO or other spaceplanes, so thanks everyone for contributing knowledge. Rapier or other comparisons are also helpfull, please keep those up as well.

[ABalazs]

This is my heaviest successful design so far, with full RCS system, dual cabin, docking port, and 10 carrot-rocket, in cold war fighter style:

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Seems to be pretty doable for me, the limit of a single TJ is somewhere at 15t.

Edited June 1, 2015 by ABalazs

[GoSlash27]

Yeah, on the other hand, grab this very same fuel load and payload, put a RAPIER, and it just won't break Mach unless you dive for a couple kms, then you will probably burn it up trying to speed up more than with the turbojet, and you will for sure not have enough LF to complete the climb to orbit. The payload for this thing is exactly the same as the twin-RAPIER White Dart 1.0, consider that (cockpit+2mT with >400m/s on LKO). And when I load the turbojet to the bare minimum to break mach, I still can speed up to ~1000m/s on the turbo alone, and then with some rocket help I keep it going alongside them until 1,200m/s.

So maybe this is only a marginal thing, for the extreme cases of low TWR. I do get why the RAPIERs should be better! But, this weights ~18mT and lifts ~3.3mT of useful stuff, still close to 20% payload ratio, and best of all, I can make the single-engine configuration work to lift said 18mT.

Rune. I was the most disappointed person, I like RAPIERs.

Rune,

I have no doubt that a TJ can outperform a RAPIER in an airframe designed for a TJ and likewise the opposite is equally true... but that doesn't really mean anything. An optimized RAPIER will still outperform an optimized TJ in payload fraction and operating cost and that's the important part. 18% payload fraction isn't awful (in fact it's pretty darn good), but I can get 22% with a single RAPIER.

This exercise has shown me that TJ SSTOs are still useful and I'll be making use of them in my career, so that's pretty neat. It's also very convenient that the TJ has an alternator.

Best,

-Slashy

*edit*

Oh, no dice so far on the fuel-only SSTO. The nukes keep blowing my wings off from the heat

Still trying, though...

Edited June 1, 2015 by GoSlash27

[Rune]

Rune,

I have no doubt that a TJ can outperform a RAPIER in an airframe designed for a TJ and likewise the opposite is equally true... but that doesn't really mean anything. An optimized RAPIER will still outperform an optimized TJ in payload fraction and operating cost and that's the important part. 18% payload fraction isn't awful (in fact it's pretty darn good), but I can get 22% with a single RAPIER.

This exercise has shown me that TJ SSTOs are still useful and I'll be making use of them in my career, so that's pretty neat. It's also very convenient that the TJ has an alternator.

Best,

-Slashy

*edit*

Oh, no dice so far on the fuel-only SSTO. The nukes keep blowing my wings off from the heat

Still trying, though...

I'm going to have another go at it, I still can't believe I can't make an equivalent RAPIER design... 20% payload ratio should mean that if I get it at 16.5mT on the runway, I should be able to break Mach and continue to orbit. We'll try... I am certainly learning stuff here. Can I have a peek at that 22% payload fraction single RAPIER design? I'm particularly interested in its vacuum dV readout on the runway.

Rune. This TJ design uses about 1,600m/s out of 2k to make orbit, with a pretty modest TWR.

[GoSlash27]

I'm going to have another go at it, I still can't believe I can't make an equivalent RAPIER design... 20% payload ratio should mean that if I get it at 16.5mT on the runway, I should be able to break Mach and continue to orbit. We'll try... I am certainly learning stuff here. Can I have a peek at that 22% payload fraction single RAPIER design? I'm particularly interested in its vacuum dV readout on the runway.

Rune. This TJ design uses about 1,600m/s out of 2k to make orbit, with a pretty modest TWR.

Rune,

I thought I had an example posted upstream... I'll have to take some pics after work. No DV readout though; I don't use KER.

Mine weighs 13.4 tonnes on the ramp and hauls 3 tonnes of payload.

*edit* Oh, I do have a pic of the "runabout" variant here:

http://forum.kerbalspaceprogram.com/threads/123114-Single-Turbojet-SSTO-Spaceplane?p=1981756&viewfull=1#post1981756

Best,

-Slashy

Edited June 1, 2015 by GoSlash27

[Rune]

Rune,

I thought I had an example posted upstream... I'll have to take some pics after work. No DV readout though; I don't use KER.

Mine weighs 13.4 tonnes on the ramp and hauls 3 tonnes of payload.

*edit* Oh, I do have a pic of the "runabout" variant here:

http://forum.kerbalspaceprogram.com/threads/123114-Single-Turbojet-SSTO-Spaceplane?p=1981756&viewfull=1#post1981756

Best,

-Slashy

Oh, that one. I should have checked the thread. Hum. It may very well be that over three tons and under six is just not a payload class that RAPIERs do. Or that I insist on overloading it. In any case, further experimentation is warranted, methinks... because with similar fuel/payload weights (they have a similar weight after all), the RAPIER is just anemic at 10kms and transonic speed, getting TWR 1 at most, while the turbojet easily pushes me past the Mach barrier with >1,2 TWR. That is a 20% difference... especially troubling if you think that the turbojet version is lugging two extra Terriers, or 0.8mT in extra powerplant weight. Oh, and if we are counting the shielded docking port as payload (since it carries docking fuel, could go either way, but it's not really crucial to SSTOing), then it's 4 mT over 18mT for my TJ example (cockpit, docking port, crew cabin), so right there with your RAPIER example at 22.2% payload fraction.

Rune. And I want that payload!

[GoSlash27]

Oh, that one. I should have checked the thread. Hum. It may very well be that over three tons and under six is just not a payload class that RAPIERs do. Or that I insist on overloading it. In any case, further experimentation is warranted, methinks... because with similar fuel/payload weights (they have a similar weight after all), the RAPIER is just anemic at 10kms and transonic speed, getting TWR 1 at most, while the turbojet easily pushes me past the Mach barrier with >1,2 TWR. That is a 20% difference... especially troubling if you think that the turbojet version is lugging two extra Terriers, or 0.8mT in extra powerplant weight. Oh, and if we are counting the shielded docking port as payload (since it carries docking fuel, could go either way, but it's not really crucial to SSTOing), then it's 4 mT over 18mT for my TJ example (cockpit, docking port, crew cabin), so right there with your RAPIER example at 22.2% payload fraction.

Rune. And I want that payload!

Rune,

No, that one's just the runabout. It's not loaded to full capacity and has lots of extra fuel for orbital maneuvers. I think I've only got that one loaded to 2 tonnes or so.

My cargo variant (which I don't have pics of right now) carries 3 tonnes.

Yeah, the RAPIER is anemic around Mach 1 and that sets the limit for those engines. Multiengine designs can exceed 18 tonnes per engine and still break Mach 1.

The difference is that while getting supersonic isn't a big deal for turbojets, getting hypersonic is a problem. That's the end where all the fuel gets wasted in closed cycle.

Perhaps I'm flying them incorrectly, but my TJ lifters are barely exceeding Mach 2 at 20km up. My RAPIER designs are hitting nearly mach 4 at 23 km up and that has a huge impact on the closed cycle DV budget.

Best,

-Slashy

[Rune]

Rune,

No, that one's just the runabout. It's not loaded to full capacity and has lots of extra fuel for orbital maneuvers. I think I've only got that one loaded to 2 tonnes or so.

My cargo variant (which I don't have pics of right now) carries 3 tonnes.

Yeah, the RAPIER is anemic around Mach 1 and that sets the limit for those engines. Multiengine designs can exceed 18 tonnes per engine and still break Mach 1.

The difference is that while getting supersonic isn't a big deal for turbojets, getting hypersonic is a problem. That's the end where all the fuel gets wasted in closed cycle.

Perhaps I'm flying them incorrectly, but my TJ lifters are barely exceeding Mach 2 at 20km up. My RAPIER designs are hitting nearly mach 4 at 23 km up and that has a huge impact on the closed cycle DV budget.

Best,

-Slashy

Oh, you must be totally flying the jet wrong then! Don't let them get over 15kms without at least 800m/s going to 900. They drop thrust fast with height, so they need to take their time building speed in the 10-15kms region so when they go over there, they are going so fast the lack of air doesn't matter. Watch your vertical speed! You can build it back up once the temp gauge comes up (I assume you do use that very useful mod that lets you get over the stock memory leak on temp gauges). I do overfeed them air, too, that might have something to do with it. I fact, your use of just two little radial intakes on that RAPIER runabout makes me wonder whether intake area has or hasn't a big impact on thrust and/or drag.

But in any case, I am still dumbfounded with these 15-20mT single engine experiments. Every time I think I know what is going to work and what isn't, I get it wrong.

Rune. That's half the fun!

[Warzouz]

GoSlash27, Rune,

I find this discussion very interesting : it shows that there are not any "obvious" design to do stuff in KSP (for instance plane SSTO, which I just start tweaking about very recently). For example, I worked on a passenger SSTO, (with your help BTW). I tried switching the 3 rapier with 2 TJ and 2 Aerospikes. But that didn't end well. I see now that may have to deal with the design of the ship. Some ships might get some better results with rapier, some ships with other confirguration. And I've discovered it also depends on the flight plan to orbit.

I find 1.0.x way better than 0.9 because of that game balancing SQUAD did. At first I disliked it, but now I appreciate it a LOT ! I use most of the engines where I only used a few of them in 0.9.

Sure Rapier have some downfall, but what the point if they outperform any other configuration (or the other way around) ? I find interesting we have to fly (and probably design) our planes differently depending on its engine configuration.

Thx for your valuable input

[Mister Dilsby]

Have posted this before on other threads, but here is a 3xTRJ + 2xLVN SSTO that has worked very well for me. You could replace the LVNs with LV-909 and probably carry a lot more payload. I get to orbit with a fair amount left in the tank. Available in long range config (pictured), science payload, or six passenger variant.

Taking this as a reference, I think it's reasonable to swap the two LV-Ns with a single aerospike or T-30, though then of course you have to carry oxidant. I would not add two; the limiting factor with a TRJ based SSTO is your thrust on jets, I think you only want enough rocket thrust to circularize after flameout and no more (0.55 to 0.70 TWR seems about right)

[GoSlash27]

Oh, you must be totally flying the jet wrong then! Don't let them get over 15kms without at least 800m/s going to 900. They drop thrust fast with height, so they need to take their time building speed in the 10-15kms region so when they go over there, they are going so fast the lack of air doesn't matter. Watch your vertical speed! You can build it back up once the temp gauge comes up (I assume you do use that very useful mod that lets you get over the stock memory leak on temp gauges). I do overfeed them air, too, that might have something to do with it. I fact, your use of just two little radial intakes on that RAPIER runabout makes me wonder whether intake area has or hasn't a big impact on thrust and/or drag.

But in any case, I am still dumbfounded with these 15-20mT single engine experiments. Every time I think I know what is going to work and what isn't, I get it wrong.

Rune. That's half the fun!

Rune,

Wow! I'll have to try that! Thanks for the tip

Best,

-Slashy