Space Plane Help?

[Jstone39]

I've been trying to make a plane that can reach orbit and I've always managed with planes pretty well but with this plane I have to hit 120 m/s to takeoff and even then it just flips around uncontrollably (with SAS on or off) until it crashes. Any ideas how I can fix this?

Edit: and suddenly 4 intakes isn't enough for two engines. greeaaaat.

P.S. Thanks to everyone for the help. In the end I started over and ended up with a 3 seater atomic rocket powered space plane that can reach orbit with about 5,000 delta-v left over.

Edited September 14, 2013 by Jstone39

[Mr.Rocket]

Im not an expert at space planes, but i think you should make it longer, lengthwise, or at least longer wings. This will (hopefully) make it harder to spin around or flip i think.

[antbin]

Your fuselage should be longer, and you have too many pitch control surfaces (canards+small+large). Also your rudders should be at the back of the plane not the middle.

Click the green buttons at the bottom-left of the SPH controls to show the Center of Mass, Center of Lift indicators. Move the wings around and try to line them up (yellow CoM should be just forward of blue CoL).

Good luck!

[Sirine]

To make takeoff easier...move your back wheel front a little bit, somewhere near the center of mass. (near the center).

To reach higher altitude 'air ceiling' put more intake. (Only use Ram-Air-Intake, other are useless at higher altitude).

1 ram 1 engine = 17km

2 ram 1 engine = 20km

4 ram 1 engine = 23km

8 ram 1 engine = 32km. (Yes, up to 32km with Turbo Jet only).

Fly to 27km, and maintain it for your speed gain until you are happy, then you go orbit with the super speed.

[Stochasty]

I have to hit 120 m/s to takeoff and even then it just flips around uncontrollably

This is indicative of two problems. The first is a landing gear issue; in order to take off, your plane must rotate around the rear landing gear. Think of that gear as a fulcrum, with the weight of your plane on one side and the downforce provided by your control surfaces on the other. If the gear are to close to the control surfaces and too far from the center of mass, you won't get enough torque to lift your nose off the ground.

The second is an aerodynamic stability issue. Your plane looks negatively stable, which means that once you manage to get your nose in the air, it wants to keep turning (basically, the plane wants to fly backwards). The solution to this is to move your center of lift so that it is behind your center of mass.

[Hodo]

The Center of Lift is to far forward. On a plane that small I would keep it JUST behind the Center of Mass.

Aerospikes a cool, but I would run a LV-909 on a craft that small. It only weighs .5 tons, has great fuel burn use, and has thrust vectoring.

[Kerbolnaut]

To takeoff at a lower speed, tilt your wings upward slightly. Wings in KSP act like flat boards, you have to angle them against the wind to get any lift.

To deal with stability, you'll want your center of lift behind your center of mass. Also, try turning on precision control and have SAS on at all times (or almost all times). I can sometimes get away with the center of lift being a little bit ahead of the center of mass when I use precision controls and SAS.

To deal with going fast enough to reach orbit, you'll probably want 8 or more ram air intakes, and not too much heavy rocket fuel (your rocket fuel payload looks excessive). Right now, drag is more or less proportional to mass, so that heavy rocket fuel adds a lot of drag that you don't need. You'll only need about 1/2 to 1/4 of that to achieve a stable orbit when you're going fast enough and high enough on jet engines.

Basically, the approach that I use is to get up to about 32K and build up speed. I carefully maintain my altitude at 32K until my speed is above 1,700 m/s, and preferably 2,200 m/s if I'm still gaining speed at a reasonable pace. When I'm going about as fast as I can go at 32K, I'll gently increase my altitude and I'll throttle down the engines when the oxygen reserve is low to avoid a flameout. Gradually, I'll get to higher altitudes and velocities and I'll end up on a trajectory that will take me briefly out of the atmosphere. I'll continue running my engines as long as I can to maintain my speed, and then I'll close my intakes and coast into orbit. I'll switch to the rocket engine and gently use it to maintain enough speed to reach an apoapsis of 100K or so. At the apoapsis, I'll gently burn into a stable orbit.