How can I prevent this spaceplane from getting violently ripped apart at high speeds?

[TheWildDefender]

I am attempting to build a SSTO spaceplane. However, at high speeds (about 1.3 km/s), if I turn (even slightly to change pitch a few degrees), it is easy to turn too violently and have my plane break apart from the extreme g-forces. I have already strutted my wings and engines together. Also, I have tried reducing the authority on the control surfaces, but reducing it too far has made it hard to take off. The center of lift is always behind the center of mass during flight.

Here are screenshots of my spaceplane:

Thanks for any help!

Edited May 15, 2018 by TheWildDefender

[Vanamonde]

Those large control surfaces may be imposing excessive forces while steering. I'd suggest using smaller wings and flaps up front. 

[bewing]

Are all your nacelles physically attached directly to the wings? Or are they attached to the fuselage and then offset into their current positions?

 

[Geonovast]

Also, if you're brute forcing your way out of the atmosphere, you don't want to touch the controls, at all, untill you're basically out of the atmosphere.  My only SSTO is built similar to yours, to get as much speed as quickly as possible.  I take off, set the pitch at 10 degrees, and don't touch any controls until I'm 30 km up, when I switch to prograde.  The curvature of the planet will effectively cause you to pitch up as you fly.