convergence problems with transonic missile
 

I have a fine mesh of a smooth symmetrical missile. It's in 3D since I later want to add some fins and angle of attack.

M=1.2 and I have coupled explicit solver with RSM-turbulence model. I started with first order discretizations and got convergence and then changed to second order for flow and power law for the rest.

I have tried to lower the Courant number (from 1 to 0.3) and the under-relaxation factors (from default values to 0.3 on all of them) but the solution diverges or at least do not converge.

What am I doing wrong??

Please help!