The LOD already set to 100 before.
I have change some graphics settings and switch back to dx11 but seem still useless.
Even I got more than 60 fps on ground, the fps will significantly drop to single number after take off.
Really not sure what happen.
Thanks for the suggestion.
I have try that before which not much help also.
Also, there are some post that mentioned disable HPET may also have more harm than good.