Spaceplane's Nose Rising

[The Wall]

I've been trying to make a reasonably small spaceplane to take a couple of Kerbals (or maybe a tiny payload instead of the added nose cockpit, if I can get this to work) to orbit, but I'm finding that after a short while in the flight the nose pitches up beyond my ability to keep it down. It varies depending on how I've configured the wings but it usually goes out of control between 300-400m/s. I've seen people manage to reach well over 1km/s before needing to hit the rockets to finish the orbit off, and I'm not sure what's causing the issue here for me. I took some screenshots showing the centres of mass/lift/thrust if they illuminate the issue to anybody better experienced with horizontal takeoffs than me.

Imgur linked to avoid filling the OP with large pictures.

Edited May 5, 2013 by sal_vager
Fixed link

[sal_vager]

It's pretty hard to tell from the pic, it might be a drag issue though, how about you post your craft file so others can try it out?

[RoboRay]

Your Center of Lift is very close to the Center of Mass. I suspect fuel burn-off is shifting the CoM to the point of instability. You want the CoL far enough behind the CoM to ensure it never approaches the CoM in flight.

[EndlessWaves]

That vessel won't be stable in space, the aerospikes aren't lined up with the center of mass.

That may be the reason it's flipping as well. I can't see the fuel tanks but assuming the inner three are two rocket tanks and a central jet tank than as the jet fuel drains the CoT will be moving upwards out of the center of thrust for the jets.

Then again, those horizontal fins at the top of the craft do look rather troublesome drag-wise.

[Kisuke]

I got the same annoying issue, the asas already loses control at 3k altitude and at 15k it is beyond my control, also drag can't be my issue since the drag is the same for top and down side. I keep transfering my fuel to the nose. I also got with some of my planes the problem that they won't pitch up even if the cg is aft and the CoL in front of the cg. Advice please

[HoY]

On another note, it would fly perfectly well with infinite fuel turned on

Yeah the problem is the CoM shifting as you burn up the fuel.

[rryy]

A tip to make sure that your CoL doesn't move in front of the CoM would be to place a small part like an RCS port or a strut on top of where the CoL is. When the plane seems to be having control issues, zoom in all the way (the camera centers on the CoM) and see if the camera is ahead or behind the CoL.