Designing something that looks and flies like the Space Shuttle is very hard given the stock parts in KSP, many people make the mistake of not aligning engines through the center of mass, and not accommodating the change in location of the center of mass as fuel is burned. The real space shuttle used engines with a 20 degree gimbal range to account for this, and there are mods that support this. Ill take a look at the existing shuttle mods in another video.