Why isn't this plane "stable"

[waterlubber]

I tried making a liquid-only SSTO. It looks perfectly fine. I'm using 1.0 aero, because 1.0.2 is, IMHO, worthless. Anyway, here are some images:

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The plane doesn't fly straight. It pitches wildly up and down with little control input, and is extremely hard to keep straight. On another note, what's a good 1.0 SSTO ascent profile?

Edited May 31, 2015 by waterlubber

[Guest Darth Gerbil]

It needs a tailplane.

http://upload.wikimedia.org/wikipedia/commons/5/53/ILA-A380-tailplane.jpg

[Xannari Ferrows]

Most likely due to your CoM and CoL being in the same spot. Move your CoL slightly behind, and it should fly.

[SAI Peregrinus]

It has pretty much no pitch control authority, since your elevators are so close to the COM. And the COL is rather close to the COM. It also has no yaw control, so you should expect it to enter a flat spin at the slightest provocation. Add a tail.

[Chaos_Klaus]

Everything everybody else said ... + you have this very heavy nuclear engine mounted so far back. This will pull your center of mass towards the rear of your plane, making it hard to get the center of lift even further behind ... especially when some fuel is drained.