Spaceplane Help

[Dekkars]

Hey all,

So I'm building my first spaceplane. I've ironed out almost all the issues except for the fact that around the 17km point in the atmosphere the plane uncontrollably pitches up and goes into a death spiral. Here is what I'm working with.

Advice? My goal is to have a plane that can carry three kerbals to my orbiting space station for refuelling, then land back at KSP.

Edited November 13, 2013 by Dekkars

[celem]

At about 17km you run out of air. If you hover the mouse over 'resources' where fuel is displayed you will see intakeair dropping as you climb. A spaceplane design needs to switch to a liquid-fuelled rocket by around the 17km point (can stretch it with more intakes).

The beauty of spaceplanes is that by the time you have to kill the jets and close the intakes in favour of the rocket, you can already have a good 80% of your orbital velocity, you just light a rocket and pull the nose up to pop the apoapsis clear of the atmosphere

Im guessing the pitching is an asymmetrical flameout of the jets or something. You want to manually kill them before they choke (use action groups for that and open/close intakes)

[Nasakev]

When a plane is at high altitude and intake air runs out, the jet engines don't all cut off at once. One will cut, then another, then a third, etc, causing uneven thrust. Could this be your issue?

[Vanamonde]

The first thing I notice is that the net thrust of your engines is below the centerline, which produces a bit of nose-up torque. That's a good thing, and helps the plane get off the runway. But your control surfaces are counter-acting it until you reach an altitude where the air grows too thin to apply much force to the control surfaces, and then the torque gets out of control. Try shutting off the lower 2 engines with an action group when you get close to that. This will have the additional benefit of channeling their intake air to keep the other engines running at higher altitudes.

[Dekkars]

Vanamonde - Nailed it. Thanks. Works beautifully now!

[celem]

You found your issue, but i'm curious.

Thats an aerospike on the centre fuselage, yes? What is that central body/tank? Not sure I recognise the part. Im guessing it's a rocketry part rather than an aircraft body since your aerospike needs oxidizer to light and wont ignite at all if stuck on an airframe body.

(Im guessing its a proper rocket body, im sure you would have mentioned if the aerospike wouldnt ignite, just curious which part it actually is.)

[Cruzan]

Looks like it's attached to the Mk3 Fuselage which is an aircraft body, but you can see the fuel lines are going in and out from that fuselage, meaning that the aerospike can drain oxidizer from the side pods as needed