SSTO - flying procedure and build

[phemark]

Hi,

I can make pretty good rockets now, so decided to start learning SSTO. Could you tell me:

1) The procedure of flight? (i.e. reach X km high with X speed, then activate engines etc).

2) What should I look for building SSTO?

3) Below is my first attempt (I know its a bit big) - it flies perfectly fine, and I can reach 15km with 400m/s horizontal speed, but then I start dropping down. Do I need bigger wings? More jet power? (I reach 0.1 for air intakes, but engines never flameout - I just start losing vertical speed).

http://imgur.com/VFntonS (bigger image)

Thanks

Edited November 6, 2014 by phemark

[Oafman]

Your wings seem big enough. But you definitely need more power.

User turbojets. And find a way to add more air intakes (radial intakes are available).

Also, you'll need LFO rockets too (or hybrid engines like rapiers). These will be used to convert your airspeed into an actual orbit, pushing you through the upper atmosphere where there is insufficient oxygen for your jets.

In terms of your flight plan, there are lots of good guides in the tutorials folder. But basically, you need to get most of your orbital speed from your jets (at least 1500m/s, ideally a lot more), between 20km and 30km altitude, then switch to your rockets, pitch up, and complete your orbit

Edit: just noticed you do have some LFO engines

Edited November 6, 2014 by Oafman

[DrMonte]

Much more and no simple Jets for SSTO.

You can start from 4 Turbo Jets.

Shock Cone air intakes might be useful as much more air will be required.

[phemark]

Thanks for some tips, will try adding more turbo jets and intakes later.

Will update a bit later:)

[Axelord FTW]

Wings are important but power is king.

That's a pretty big plane for only two basic jet engines.

Also, you might prefer aerospikes over those.

[InterCity]

You have done a pretty good job for the first time. The COM and COL alignment is very good and it's not that ugly either .

The problem with the loss of thrust and eventual stalling is probably (But I'm not sure about that, since i usually fire my rockets at 30 km and use sh*tloads of intakes) that the jets tend to lose power as the air levels drop.

My advice? a) Add stronger engines and moar intakes

If you refuse to add engines and intakes, fire your rockets as soon as you start losing power, but that might be bad because you would waste A LOT of LFO.

c) Keep practicing. Practice makes perfect.

d) Make sure that your plane can soar at 100 m/s. That makes it way more pilotable.

Also, generally the bigger the aircraft is, the more stable it is (Unless your design of the big one is really bad ). So it's not so bad that you build big at first, because the small planes can be real jerks due to their lack of mass/lift.

About the ascent path: I fire my engines to full throttle and then I tend to pitch up to 45/50° as soon as I leave the runway with more than stall speed (I use FAR), and then fly as such until I hit the point where I start losing air or speed, then I pitch down and tend to hold my attitude at about +5 - +10 degrees, during the early ascent more and decreasing as the air gets thinner, I use RAPIERs, that change mode automatically, but if they don't, I fire my rockets at 30 km altitude. Then it's just like rocket.

Hope I am helping

[Laie]

I can reach 15km with 400m/s horizontal speed,

That is pretty much the most you can get out of basic jets. Adding more basic jets may get you to 500m/s@18km, but that's not worth the additional weight. See this thread for details.

Generally, an SSTO with basic jets is hardly worthwhile; getting to 15km before you ignite the rockets may seem like a lot, but actually it isn't. It's still a long way to space, and the (now useless) weight from all the plane parts will eat most of the gains you had so far. If you replaced the wings&engines with a pair of the tall SRBs, you'd get very similar performance.

Other than that, this is a good-looking plane. And if it really flies as well as you say it does, you may have great sucess if you just replace the basic jets with turbojets. Take-off and early climb will be slower, but it should last to something like 1000m/s@20km -- much better, but not yet good (most people here think that if a plane can't make 2000ms@30km, it is a failure).

You can tickle even speed/altitude out of it if you use more intakes. From the look of it, you don't really need more jets, only more air to run them. If you then unload most of the rocket fuel (which you won't need anymore), breaking the 2000m/s barrier should be possible without changes to the basic design.

I expect that you will soon find out about asymmetric flameout. Once that happens, have a look at this thread.

Edited November 6, 2014 by Laie

[Alshain]

Ascending an Spaceplane is all about maximizing horizontal speed before switching to rockets. The idea is to raise your Periapsis as far out of the middle of the planet as you can (resulting in a wider suborbital arc) while using the significantly more fuel efficient jet engines.

1. Ascend up to around 25km where every you can just before intake air gets too low.

2. Level off and go horizontal until you reach your highest speed based on the engines your using and whether or not your using FAR/NEAR. You can even descend a little during this speed up if necessary.

3. When you can't go any faster or speed isn't climbing very quickly, activate the rockets and pitch up a bit.

4. If you have more than 1 jet you will need to shut them down before they run out of intake air or bad things will happen*

*There are way to design around this but most just use action groups.

For your plane, I'd almost say the wings are too big. Spaceplanes's don't need a whole lot of wing and adding more wing just adds more mass. Inability to ascend is the result of a lack of power in most cases. The higher you go, the more airspeed you need. For more temperamental planes you can "Stair step" them up. That is ascend as high as you can, level off, allow speed to build, then try to ascend some more. However it is best to try and design those faults out so you can get a steady ascent.

Your rocket engines are heavy and in-efficient. The LVT-45 is not a great spaceplane engine unless your trying to build in a low tech tree. For a plane this size, the toroidal aerospike is wonderful and in space it's the most efficient outside of the LV-N (which is incredibly heavy and very low power and is not great for a plane). The downside... it has no thrust vectoring so it must be perfectly placed to avoid rotation. That shouldn't be a problem for you plane as it has it's center of mass right across the center. The RAPIERS are also good choices. For smaller planes the 24-77 and 48-7S are good choices. For a low tech tree, the LV-909 is also a good choice. You don't need a lot of rocket power, jet power is more important. By the time you use the rockets your up high in the atmosphere.

You also have a lot of fuel in that plane. For your first plane you shouldn't try to go to the moon or anything, just get to a 150km orbit, or even just a 75km orbit. You shouldn't need that much fuel to do that, even in stock. That will just weigh your plane down. Don't worry about putting jet fuel on a Spaceplane. The little fuel your jet engines use does not outweigh the cost of adding the mass of a jet fuel tank. Just run fuel lines from your LFO tank and use that for both jets and rockets.

FYI, I do use FAR. I tried to keep the tips generic, but if I let a FAR-only practice creep in I apologize and I'm sure someone will point it out.

Edited November 6, 2014 by Alshain

[phemark]

Thanks for all the tips guys!

I replaced 2 basic jets with 4 turbo jets, added moar intakes, and managed to reach orbit and land! THANKS!

Now, to finish up and go build more SSTO with payloads, a couple of questions:

1) In the picture bellow, you see I am at 23.5km doing 1300m/s and I am flaming - is this normal, or should I be higher before I start doing this kind of speeds?

2) (Not a question) After hitting ~25km and 1500m/s I engaged rockets and reached orbit!

3) Cargo bay - how do I add "things" to it? Do I need to attach something somehow?

4) Landing was easy, but landing at exact spot was quite difficult - aerobraking to a precise location was hard, and didnt have enough fuel to correct that much (this landing was after a couple of autosaves ). Any tips on how to judge aerobraking, or will that come with practise?

5) I dont really like the look of many intakes on a plane, but I guess it will always be like that for plane SSTO? Or is there a way to minimize them?

Once again, thank you for your advice, and I'm off to building more SSTO with payloads now (once I know how to put them in cargo:) ).

[ratchet freak]

You need to put the things in the cargobay in the SPH, hold down alt to turn off surface attachment to make it easier. Start with a docking port for maximum reusability

If you didn't flame out during ascent then you have more than enough intakes and can go remove a few

[Pecan]

SSTO = Single Stage To Orbit, wings and jets not required.

Spaceplane = thing relying on aerodynamic lift, which may or may not also be a SSTO.

[capi3101]

I generally point spaceplane newbs to two places - Keptin's Basic Aircraft Design Explained - Simply with Pictures post (a great place to begin) and to DocMoriarty's KSP Space Plane Construction and Operation Guide (a great place for specifics and ideas on what exactly you can do with planes). DocMoriarty's guide focuses on use of the RAPIER engine. It's slightly out of date (by slightly I mean it was designed for 0.24.2 and he hasn't yet updated it for the changes in 0.25), but so far the only thing I've seen that's major is that the new Wing Connectors are functionally equivalent to Delta Wings.

In answer to your specific questions...

1) You want to get up above 10,000 as quickly as possible. Assuming you've got what it takes to do that (in my experience, most spaceplanes fail either because they veer off course and crash during take-off - which keptin explains - or they haven't got sufficient lift/thrust and wind up going in the drink), start off by getting your prograde marker to at least 45 degrees above the horizon as quickly as you can after takeoff. Depending on your AoA, this may mean getting the nose up to 55-60 degrees or more; so be it. You can start leveling off after 10,000; at that point you don't want to be ascending greater than 100 m/s. Shoot for this velocity profile: 350 m/s at 11k, 450 at 14k, 650 at 16k, 850 at 19k and 1300 at 23 km. If your speed is increasing rapidly, you are going up too fast; if it's barely budging, you're going up too slowly. You want to try to get most of your orbital velocity before your engines start running out of air (or, if you use RAPIERS like DocMoriarty, before they kick over) - but, you want to keep the turbojets running for as long as you can. If they start flaming out, throttle back. Eventually, you'll stop accelerating on turbojets alone - that's when you kick on the rockets. If you're above 30k when that happens, you're probably okay to shut off your jets, close your intakes and angle up to 45 degrees - at that point your plane is a rocket and you want to get it out of the atmosphere as quickly as you can.

2) There are so many things to look for when you're building a spaceplane it's not funny. Refer to the guides I linked for specifics. As a rule - you want your CoL slightly behind and slightly above the CoM for maximum control, and preferably you want to design your plane so the CoM doesn't shift around too much - you definitely don't want it to where it shifts behind the CoL (if it does, you're more likely to lithobrake than land). You want your CoT aligned with the CoM, again for control. You want sufficient lift and sufficient thrust - sufficient thrust being 1 Basic Jet engine per ten tonnes of craft, 1 RAPIER engine per thirteen tonnes of craft, or 1 Turbojet engine per 15 tonnes of craft; sufficient lift is generally 1 lift unit per tonne (or roughly 2.3 tonnes per Delta Wing, like DocMoriarty says). You want good steering authority on all three axes, and if necessary you want sufficient SAS to hold your craft's attitude. And you want to be able to takeoff and land safely.

3) As others have suggested, I'd use Turbojets or RAPIERs for a proper spaceplane - Basic Jets excel for low-level aircraft (like you would want for parts testing) and for VTOL capabilities. You're short on thrust and short on intakes - thrust can be remedied by swapping out the engines for your design. You want no less than three Ram Air Intakes or the equivalent per turbojet - that's your craft's big weakness at the moment if you want to make space (you have the equivalent of three at the moment; you want at least twice that amount). You're awesome on the lift department. That CoM might shift a bit too far aft...I'd have to run your craft through the RCS Build Aid mod to know for sure, though.

EDIT: These would be the OP's original questions, not the second set. Going to address those next...

Edited November 6, 2014 by capi3101

[capi3101]

1) In the picture bellow, you see I am at 23.5km doing 1300m/s and I am flaming - is this normal, or should I be higher before I start doing this kind of speeds?

That's fairly normal, actually. 1300 is about where you want to be at that altitude.

3) Cargo bay - how do I add "things" to it? Do I need to attach something somehow?

Well, you can start by attaching things to either wall. A docking port is a good start. You do have to add your payload at launch or pick it up in orbit.

Myself, I use cargo bays to hide un-aerodynamic bits (totally unnecessary, as I don't use NEAR or FAR). Stuff like batteries, control stabilizers, RCS tanks, etc. all nicely fit inside one. I will say that you should probably strut down anything you stick in the bay.

4) Landing was easy, but landing at exact spot was quite difficult - aerobraking to a precise location was hard, and didnt have enough fuel to correct that much (this landing was after a couple of autosaves ). Any tips on how to judge aerobraking, or will that come with practise?

DocMoriarty's got pointers on that. Basically, you can set yourself out a primitive ILS with flags, probes or anything else you can align with the runway. NavUtilities is a mod that will give you a runway ILS if you prefer to go that route. I use both methods my own self.

5) I dont really like the look of many intakes on a plane, but I guess it will always be like that for plane SSTO? Or is there a way to minimize them?

Probably the best way to avoid the spammy look of too many Ram Intakes is to use Structural Intakes - but yeah, if you want your plane to make orbit, you've got to have a lotta air. Keeps the jets running at higher altitudes, see.

[Alshain]

Let me start by saying... Welcome to the Spaceplane club!

1) In the picture bellow, you see I am at 23.5km doing 1300m/s and I am flaming - is this normal, or should I be higher before I start doing this kind of speeds?

Absolutely perfect. 1200-1500m/s is what your going to want. ~25km is about as high as most planes can get before losing too much air, unless they are air hogging, which I despise personally.

3) Cargo bay - how do I add "things" to it? Do I need to attach something somehow?

All your typical methods. Decouplers, Separators, and Docking Ports. Remember, docking ports only require a mate to dock, you can decouple a single docking port from anything it was attached to in the VAB, regardless of what it is. Hold the MOD key to disable surface attachment, that makes it easier.

One thing you have to be careful of is your Center of Mass, it changes when you unload your cargo so test it with and without a load or you may get it to space and find out you can't get it back to the ground. DCoM (Dry Center of Mass... i.e. no fuel) needs to be tested to because you typically land without (or with little) fuel. The RCS Build Aid mod will show you a DCoM marker, you can test it the hard way by emptying each tank and looking at the normal CoM marker. Remember... test with a load and full fuel for takeoff and without a load and little fuel for landing.

4) Landing was easy, but landing at exact spot was quite difficult - aerobraking to a precise location was hard, and didnt have enough fuel to correct that much (this landing was after a couple of autosaves ). Any tips on how to judge aerobraking, or will that come with practise?

For the most part, yes practice. There are several approaches, but remember you have these miraculous things called wings, you can glide. Descend shallow, lower the Pe while on the other side of the planet so it takes nearly a half orbit of landing. This will allow you to pitch up and down to expand and contract your arc, aim so the end of your arc is near the mountains outside of the KSC, then you can do a powered landing. If your still too fast, don't be afraid to pass it by and come around and land at 270. Don't be afraid to fire up the jets, unpowered deorbital landing is going to be one of the last things you learn about planes, when you master that it will prepare you for shuttles, which once deorbited don't fire an engine ever again (because they don't have jets).

5) I dont really like the look of many intakes on a plane, but I guess it will always be like that for plane SSTO? Or is there a way to minimize them?

You don't have to have a lot of intakes. However it depends on the intake choice, some are better than others. The new ones (the shock cone and the structural) are very good, the XM-G50 is also good. You really only need 1 per engine with the good ones, 2 per engine with the mid ranged ones.

Edited November 6, 2014 by Alshain

[phemark]

Thanks guys, I really learned a lot!

I just researched Aerospike/Rapier, so will try to use them next.

I will also start adding something in the cargo bays... em.. for testing .

Thanks, but I'm also sure I will create more threads in the future about other things

[phemark]

Rapier is a beast! 2-in-1 and powerful!

Question - how to know how much extra LF or less Oxidiser to take? Take a rough guess?

[capi3101]

DocMoriarty answers that - if you're using RAPIERs, assume 39 units of Liquid Fuel per tonne of take off weight and 23-24 units of Oxidizer per tonne of take-off weight. This give you enough to take off, make orbit, fool around in orbit a bit, deorbit and give you some flying time before you land. For any additional fuel you bring (say, if you're planning to use the plane to go fly around on Laythe a bit), you can just use the Rocket Equation to figure out your delta-V like any other rocket.

[Alshain]

Rapier is a beast! 2-in-1 and powerful!

Question - how to know how much extra LF or less Oxidiser to take? Take a rough guess?

Kind of, yeah. It's something you learn with time as you figure out the best engines and what they require to reach distances with certain weights. Just when you arrive in orbit, look how much fuel you have left. When you land look again. Adjust future designs to minimize waste. Unlike rockets, delta V isn't as telling when ascending from Kerbin because of Jet engine performance and piloting skill.

Planes take a lot more testing than rockets in my experience. You can slap together a rocket rather quickly, but a plane takes patience and finesse and a lot of test flights. That's why I find planes more reusable, where rockets I just tend to build one for each payload. You spend hours designing a plane and you want to use it a lot.

Edited November 6, 2014 by Alshain

[phemark]

Ok, I get it now.

So, I made another SSTO plane, using RAPIER - this one is so much easier to fly - lift of, straight to 10km, then quickly go to 30' to reach ~25km 1600m/s, then switch to rockets. I liiike Rapier.

(But, to be fair, I made sure that CoM doesnt change much with fuel and payload detaching, this makes a big difference, as you mentioned).

However, I barely, but made to orbit - last 15delta m/s was using RCS . I guess RCS will be used to deorbit as well (I still have LF to land).

(And my Mun satallite is launching for the first time from a plane - cooool!)

P.S. Good suggestion putting stuff inside cargo (like RCS tanks)

P.P.S. I just dont like all those air intakes........

Thanks!

[Alshain]

Some tips for fuel. Your plane doesn't have to be all in line, you can mount tank radially. Most of my planes are in the second link in my signature. Take a look at the Shrike and the Vireo. Now, as mentioned, I use FAR so these plane may or may not work well in stock aerodynamics, but they can still give you some design ideas.

[capi3101]

Ok, I get it now.

So, I made another SSTO plane, using RAPIER - this one is so much easier to fly - lift of, straight to 10km, then quickly go to 30' to reach ~25km 1600m/s, then switch to rockets. I liiike Rapier.

Hmm...1,600 is a low switchover speed; that's probably why you ran out of oxidizer. Much above 20k you want your elevation to be relatively shallow - generally eight to ten degrees is sufficient, so long as you don't start heading back down again.

Like 'em or not, without enough air you won't get going fast enough or high enough to head to space. 's true regardless of which engine you use.

[Alshain]

P.P.S. I just dont like all those air intakes........

They are meant to go under the wing. I mean it's not a hard fast rule, but it's designed based on the Concorde.