Spaceplane SSTO Troubleshooting

[Mitch2511]

When I get to an altitude of about 14km up and I try to level my planes angle it just dives forwards out of control, has fuel changed the COM or is it a lift thing?

Edited August 10, 2014 by Claw

[Wanderfound]

When I get to an altitude of about 14km up and I try to level my planes angle it just dives forwards out of control, has fuel changed the COM or is it a lift thing?

Could be a bunch of things; if you can give us side and top screenshots in the SPH with the CoL/CoM/CoT indicators on, we'd have more chance of figuring it out. But for a few possibilities:

* Yes, it could be a fuel use CoM shift. Try to cluster your fuel tanks as close as you can around CoM, and use fuel lines to control the order in which the tanks drain. Avoid putting tanks near the nose. In the SPH, always check to see how the CoM moves when the tanks empty; you can empty tanks by right clicking on them and adjusting the tweakables. You may also want to shift your CoL a bit further behind CoM to make the plane less sensitive to mass shift.

* You may have problems the other way, with CoL too far behind CoM. Too far forward is unstable, but too far back makes it hard to keep the nose up.

* You may have been climbing too steeply, leading you into a stall when levelling due to insufficient speed. This can be related to insufficient wing area; the less wing, the higher the stall speed.

* You may have insufficient pitch authority. To control pitch, you want substantial control surfaces that are placed as far away from CoM as possible. Surfaces on mid-mounted wings are for roll; they're useless for pitch.

...and an assortment of other things that aren't coming to mind right now. Post the screenshots if you can.

[Claw]

Hey Mitch,

That other thread was a bit old. Plus I think your questions would get lost in with the rest what was in there. So I've made a new thread for you.

One thing that would really help us from just guessing is pictures (like Wanderfound said).

Cheers,

~Claw

[Master Tao]

It would also help to know whether you're using stock aerodynamics, Stock Drag Fix, NEAR, or FAR.

[O-Doc]

The short answer is not enough control surfaces. The slightly longer answer is that your control surfaces are not arranged correctly around your CoM/CoL. Without pics it's impossible to give you anything but a vague response.