Space Plane basic design

[Psilocybin]

Hello!  I recently unlocked the basic space plane equipment but i have no idea how to set up a space plane. I saw lots of youtube videos but they have different parts for some reason. Can anyone help me set it up? Or show me a good tutorial? Thank you in advance!

[Edax]

Just ignore the part about nose cones increasing drag.

[Evanitis]

The image linked above is an excellent start for planes. Getting to space doesn't take much more than that. Two things in addition you need to keep in mind.

You need to get as fast and as high as possible with only using jet-engines (or the air-breathing mode of the rapier). That's with shock-cones is about 1200 m/s on like 18000 meters. Too few boosters and you won't reach that, too many and you'll burn up. One possible ascent profile that works for a balanced configuration is to pitch up enough to constantly climb but not accelerate above ~320 m/s until you reach 8-9000 meters. Than you can level the flight (adjust Angle of Attack, AoA to 5-10°) to gain speed. Once you stop accelerating, fire the rocket engine(s), and pitch up carefully.

The second thing to keep in mind (in addition what's in the above post) is that when you burn all the fuel, the CoM will shift - most likely back, as that's where one generally likes to put engines. You need to build the plane so that the CoM doesn't move when switching full and empty tanks in the VAB. Or if it moves, it shouldn't crawl behind the CoL, or you'll have trouble in re-entry.

It also helps to give the wings a tiny bit of incidence once you finished the balancing. There's an excellent guide on why that matters, though it's an intermediate SSTO course, so it takes some ingesting.

 

EDIT: If you fail, make sure to include pics of the plane (preferably in the VAB with visible wet-dry CoM-CoL), or even the .craft file with the details of how far you got. It's much easier to spot problems that way. And this forum is full of plane enthusiasts who can't wait to help.

Edited February 12, 2016 by Evanitis

[Chaos_Klaus]

With the very basic plane parts you have basically no chance to build a real "Single Stage to Orbit" space plane. The early jet engines only work at low altitudes.

[Evanitis]

15 minutes ago, Chaos_Klaus said:

With the very basic plane parts you have basically no chance to build a real "Single Stage to Orbit" space plane.

Ahh, indeed, an important observation. It's a bad habit to read 'SSTO' when someone says 'spaceplane'. The OP got me.
What I wrote above is true for Single Stage to Orbit planes. That needs Panther jet engines the very least, but Whiplash turboramjets are preferred. Though nothing stops you from getting planes to orbit before these are available, you'll just need to detach parts, or shoot the whole stuff as payload of a rocket.

 

A very basic spaceplane without any engines. It can easily deorbit and land, almost as efficient as the classic heatshield + parachute combination.

Edited February 12, 2016 by Evanitis

[Candlelight]

The parts you see other people use are still stock/vanilla parts.They are just further up the tech tree.You will have to get further then you are now to build a proper SSTO.

And as for building them, follow the guide posted above (ignore the nosecones creating drag part).

[Psilocybin]

Wow! That was quick Well the thing is i only have the small jet engine. The tiny one. I built a plane. The center of balance and mass where at the exact same spot ( i placed a rocket engine on the plane,  not a jet engine ) but when i tried to take off i had no control and it would just be destroyed and kill the pilot. Do you have any other designs i can take a look at? 

[Evanitis]

Just noticed that you are Psilocybin. I like that.

My guess is that you didn't specify how aerodynamic surfaces are controlled. You should right click those in the VAB and set if you want to yaw, pitch or roll with them. Rule of thumb: the rudder (vertical thing on the tail) should only yaw, and only the rudder should yaw. More details in the image in the first reply.

[Geschosskopf]

6 hours ago, Psilocybin said:

Hello!  I recently unlocked the basic space plane equipment but i have no idea how to set up a space plane. I saw lots of youtube videos but they have different parts for some reason. Can anyone help me set it up? Or show me a good tutorial? Thank you in advance!

Welcome aboard.

First, before starting the long, hard, and often frustrating road of spaceplanes, you need to know what you're getting into.  The main thing is, spaceplanes are a huge timesink to design, test, redesign, test, tweak, and then ultimately use.  The bigger (and thus more useful) the spaceplane, the more difficult all this is.  And for all this effort, pretty much all you get is an alternative, slower method of getting stuff to orbit.  Now, spaceplanes are cool as a general concept and look spiffy, but understand this is what you're in for.  Some folks totally groove on this and do nothing else.  Others get so frustrated that they give up before getting to orbit once.  Most folks are somewhere in between, and have a few small-medium spaceplanes they use once in a while on special occasions or for a change of pace, but primarily fly rockets.  It all depends on where your attraction to the coolness factor becomes outweighed by your frustration and the time consumed with it all.

So, ye have been warned.  Now, on with the show.

As far as general rules go, start with your desired payload as its mass pretty much determines everything else.  Keep it small to start with as smaller is easier, but have something more than just 1 joy-riding Kerbal.  After all, you want something that's actually useful after all the effort.  Besides, 1-seaters are so light that you really don't learn much about the various design compromises while building them, so you waste most of your effort.  So use a Mk2 cockpit and for payload either a small Mk2 cargo bay and a tiny probe, or (for a bit more challenge) a passenger module and an airlock.  That way, you'll end up with either a probe launcher or a station crew rotation/tourism vehicle, both of which have some practical value.  Anyway, you build the rest of the spaceplane around this.

Next, the main thing to understand is that spaceplanes are all about fuel consumption.  You design them around the necessary fuel starting with landing and then working backwards through de-orbiting, doing whatever the job is in orbit like docking with something, then getting to orbit, and finally the takeoff and initial climb.  All but the takeoff and initial climb require rockets (and RCS if you want to dock) so as an initial step, you build the payload and put enough rocket engine and fuel aboard it to give the necessary dV for all the rocket-needing parts of the flight.

So how much rocket fuel do you need?  Well, jet engines are hardwired to konk out at about 23-24km altitude.  At that altitude, a small-but-still-useful spaceplane of this size will probably be moving about 1200-1300m/s when this happens.  Because orbital velocity is about 2500m/s, this means you need about 1500m/s on the rockets just to make up the difference, plus some more because you'll lose some to drag and gravity before you clear the atmosphere.  So call that about 1800-2000m/s (you can decrease this a bit as you get better at flying the things) to get to orbit.  Then, if you're going to dock with something that's not too high above Kerbin, you'll need about 200m/s more.  If you refuel at the station, then that's all you need.  De-orbiting to a safe descent profile will cost about 200m/s as well.  So, a probe-launcher would need about 2000-2200m/s dV on the rocket, a non-refueling station bus would need 2200-2400m/s.

The actual amount of fuel (as in units in tanks) as opposed to how much energy (dV) you get out of it depends on rocket engine you use.  There are a number of options there but for a spaceplane of this size, you don't need anything huge.  Look for something with a good atmospheric Isp that will give you a TWR of about 1.0 at the minimum (you can get by with less but that's a good place to start).  Also, you'll need some mod like Kerbal Engineer or MechJeb to give you a reading on how much dV you have.

OK, so that's the rocket part.  Now you need the jet part and the wings.  If you use the RAPIER engine for the rocket part, then you already have the jet engines aboard.  Jet engines don't need nearly as much fuel as the rockets because their Isp is huge.  1 smallish tank per engine will certainly do you, and you want to burn nearly all of it on ascent so you don't add any more weight (and thus lower the dV) that the rocket has to get to orbit.  You really don't need much if any jet fuel to land, just glide down.  In any case, again try starting with a TWR of say 1.5 with full tanks (again, you can get by with less with a bit of practice).  The more thrust you have, the less wing you need and vice versa, however.  The jets also need some air intakes but not many.  At present, jet engines just run out of thrust before they run out of air.  And that's pretty much it.

You will usually find that, unless your spaceplane is severely underpowered or excessively draggy, you won't have many problems getting to 23km and 1300m/s or so.  It's getting to orbit at all after that, not to mention still having enough rocket fuel left over to do something useful and de-orbit later, that causes the most problems.  A lot of this is learning to fly the correct ascent profile---do this wrong and even a design that really can do its intended job won't make it to orbit.  But that's a subject for another lesson.  And then, assuming all this goes well, you have to survive reentry, which again is learning how to fly the proper trajectory.

A few final tips that will make your life a lot easier:

• Disable the gimbal on the jet engines.  Leaving it on causes more problems than it solves
• For rudders, use vertically oriented control surfaces attached to the wingtips.  This prevents the rudders from creating unwanted roll.
• Limit all control surfaces to 1 or 2 axes.  Rudders should only be in yaw, canards should only be in pitch.  Elevons can do both pitch and roll, or you can have separate ailerons and rear elevators.
• Create an action group that toggles the jet and rocket engines (or switches modes of the RAPIER), and also toggles the air intakes open and closed.  That way, you can do all these things on all the parts at once with a single touch of a button.
• Use RCS Build Aid from the get-go to make sure your spaceplane's CoM doesn't change much if at all as fuel burns.  This minimizes trim changes throughout the flight.  Once you've got all the other parts aboard, then use it again to balance your RCS thrusters (assuming you need to dock).

 

[Chaos_Klaus]

Actually, opening and closing air intakes no longer has an effect on drag.

[Evanitis]

@Geschosskopf Whoa, I think I never read such a comprehensive wall of text about SSTO planes and the engineering basics needed to build one. I guess I'll save the link and quote bits and pieces here and there.

[Geschosskopf]

1 hour ago, Chaos_Klaus said:

Actually, opening and closing air intakes no longer has an effect on drag.

Really?  Didn't know that.  But then why still have the functionality?  Of course, at present (which I expect to change in 1.1), you hardly need any intakes at all, so the few you have aren't making much drag anyway

59 minutes ago, Evanitis said:

@Geschosskopf Whoa, I think I never read such a comprehensive wall of text about SSTO planes and the engineering basics needed to build one. I guess I'll save the link and quote bits and pieces here and there.

Well, thanks.  But I'm no spaceplane guru.  If you want true enlightenment, there are many better sources.

That said, IMHO, the main problem most folks have with spaceplanes is not understanding their basic principles.  If you don't understand them, you don't know what to build in the first place, won't understand why it didn't work, and will have no clue what to change or how much.  This was my problem early on and led to nothing but much frustration, so I hope to help others avoid my experience.  However, articulating the basic principles is about all I'm good for.

[Evanitis]

2 minutes ago, Geschosskopf said:

Well, thanks.  But I'm no spaceplane guru.

Me neither, yet I aspire to be one one day. Though I like to offer basic advice too in such threads*. Though sometimes I don't realize that my advice isn't basic enough. I usually jump into ascent profiles and wet-dry CoM-CoL balance without noting such nuances as TWR and the need of jet and rocket engines.

*well, that ones isn't a good example, as it turned out it was about an atmospheric craft. Guess the 'SPH' acronym can be misleading first.