First Spaceplane

[martincmartin]

I'm trying to make my first space plan and failing miserably, everything I make explodes on the runway.  Here's my latest:

There are elevons on the back of the wings.

So my question is: what's the simplest space plane I can make?  How can I launch it?  By "simplest," I don't mean lowest part count, I just mean easiest to build / fly / understand.

Would be great if it only used level 4 tech, the level with "Aviation" which cost 45 science.

[n.b.z.]

There are a lot of considerations that go into a good spaceplane.

I would recommend reading a tutorial (or two) on the topic, because it's near impossible to list everything in a forum post. (Skip outdated tutorials - they should at least reflect KSP version 1.0 or later.)

Try these two first:
http://wiki.kerbalspaceprogram.com/wiki/Tutorial:Basic_SSTO_Design
http://wiki.kerbalspaceprogram.com/wiki/Tutorial:_Spaceplane_basics

Don't immediately try to build everything you read somewhere - just read through one or two tutorials to get some ideas. I would then suggest using a sandbox game to be able to do a lot of experiments to learn from explosions without worrying about funds.

Looking at your plane, let me guess about a few things that could probably be improved. First, please try the 3 buttons in the bottom left corner: the left one shows the center of mass, the right one shows center of lift.

1. You probably want the center of lift to be a bit behind the center of mass, for stability. (Maybe it already is.)
2. Your elevons are probably very near the center of mass, where they have too little leverage. Try elevators at the back of the plane.
3. Your main wheels should be close to the center of mass, otherwise it's too difficult for the elevators to raise the nose for takeoff.
4. There seem to be only air-breathing engines on the plane. That's fine for an airplane, but won't work to go to space.
5. A good part of the plane's weight is the fuel. As the fuel is consumed during flight, the weight of all the parts will become larger relative to the combined weight of parts + fuel.
   Your plane has a heavy part (cockpit) in the front, and no "counter" weight in the back. As fuel gets depleted over time, the center of mass will move forward as a consequence. Which will change the way the plane flies.
   Because of this, it is desirable to have the center of mass stay in roughly the same place regardless of how full the tanks are.
6. Landing gears are a bit weird in KSP 1.1.x. Try:
   a) using bigger (=stronger) gears, like the smallest retractable ones.
   b) rotating the front gear to be exactly horizontal, just like the main gears. Use "snap" and global alignment on the rotate tool to do this.

[AeroGav]

I'd recommend learning how to build spaceplanes in sandbox mode, with all tech available to you .    

Simplest might be something with a mark 1 inline cockpit, shock cone intake, ft800 rocket fuel tank behind cockpit , and a single rapier engine at the back.  Put on a couple of Big S delta wings and fill them with your jet fuel.

But first you need to learn how to make basic, flyable aircraft in sandbox mode, and the foibles of the editor that like to misalign your landing gear by 1 degree etc.

Don't despair I actually made it to orbit first time in a spaceplane in KSP,  i mastered that before i could get rockets working.

Lowest tech spaceplane that can actually make orbit with non-superhuman skill levels would probably be something with  a single terrier motor and a pair of panthers on underwing pods that can be jettisoned when they flame out.

some tips on optimization i wrote recently , with some videos of one of my plane launches 

..this stuff applies to folks who can build spaceplanes that fly around nice but run out of juice before they get all the way up to orbit, however.

[MaxPeck]

You don't have enough control authority with that configuration. It looks like your elevons are at the wing root, which is going to make pitch control all but impossible and roll control difficult as well. 

Think of an airplane's control surfaces as levers that extend from the CG. The longer that lever arm, the more effective your control surfaces will be. Move your ailerons to the wingtip and add canards to the nose, or extend the tail and add a proper elevator. Also, make sure your main landing gear is just a hair behind your CG so your aircraft can rotate when it reaches takeoff speed. 

[Snark]

Moving to Gameplay Questions.

[AeroGav]

Basic airplane stuff -

1. turn on centre of mass and centre of lift display.  centre of lift should be a bit behind centre of mass - maybe with midpoint of the blue ball touching back of yellow one.   If you are an expert, it can be halfway between there and the centre of the yellow ball, but i'd play it safe.

2. You need a vertical stabilizer, or tailfin, at the back to control Yaw instability.  Stop it snaking/skidding.  You have one so that's probably ok.

3. Roll control - ailerons at wingtips - can't see if you got them or not.

4. Pitch control - most important.  You either need a tailplane at the back or a canard at the front.  OK, there is a third way  -  with a delta wing like the space shuttle or concorde, the trailing edge flaps (elevons) are right at the back of the plane so act like a tailplane.

 You have neither a canard nor a tailplane and your trailing edge flaps are close to your centre of gravity so won't provide any up/down control.          

Bear in mind that after adding a canard, the centre of lift will move forwards, you may need to slide wings backwards to respect point 1).    If you add a tailplane to something that didn't have one, the centre of lift moves backwards so again, you may need to reposition the wing so as to not be excessively nose heavy.

5. Landing gear kills more kerbals than anything else.   Sometimes they attach a few degrees off centre and the first you know about it is when the plane spins out and explodes on takeoff.   

to avoid this -

a) after attaching your gear,  press 3 on keyboard to go into Part Rotation Mode.  

b) Make sure angle snap mode is selected not fine rotation

c) press F on keyboard.  This toggles between "local" and "absolute" angle.   Make sure the message on screen says "Rotation : Absolute"

d) now click on the landing gear. Rotate it one notch to the left, then drag it back to the centre again.  This angle snaps the part so it is facing absolutely dead straight forward.      

 

6.  Fuel placement.  You seem to have done a reasonable job here.   If you have only one fuel tank, you want the middle of that tank to line up with your centre of mass.  That way, as the tank empties, your plane looses equal amounts of weight from the nose and the tail and will not become unstable.  In more advanced craft, you will have multiple tanks.   You might have a lot of fuel stored just behind the centre of mass, but a small tank a long way ahead of the centre of mass can counterbalance it because of the longer lever arm.

At some point however, you're probably going to put a rocket engine on a plane.   These don't drain fuel tanks evenly , like jets do.   They empty out the front tank first before going to work on the next one, until your plane becomes unstable and flips.    Have a look for the GPOSpeedFuelPump mod to fix this.

7. Engine placement.  Nothing to say here really, you've done a good job of making this symmetrical with engines either side of your centre of mass.  I've had trouble with spaceplanes that had rocket engines mounted above or below the wing (centre of mass).  I light the engine, get a huge surge of power from the underslung rocket motor,  and the nose shoots up uncontrollably.   At low altitude, this didn't happen because the air was thicker and the control surfaces were able to surpress it.

I should have either put four rocket motors on (that'd be too many unless it's a huge plane!)  with one above the left wing, one below the left wing, one above the right wing, and one below the right wing -  or mounted them at the midpoint - like this - or like you have done in your picture

 

[bewing]

This is my simplest basic airplane. A canard design is easier to make work than one with elevons. You can replace the girders with an empty fuel tank, or a SciJr or two. If you take this design, try it, and modify it repeatedly (reverting after each flight, if needed) -- you will learn a lot.