Why does my Ender 6 print nicely at the bottom of the model but gets worse towards the top

I bought my 2 Ender 6 printers primarily to build airfoils. After weeks of test prints I still have the same problem, that is the prints are perfect for the first third but then as the bed drops it gets worse as the pic shows. Cheers

Might be related to Z wobble due to the vibrations caused by fast movement.
You might need to slow down or add more support to keep the part stable