The main problem comes in frictional resistance. Why? We have seen. Let me draw it again, if I plot this as a function of Reynolds number CF- what I have seen?- I have seen the laminar flow resistance curve goes like this and the turbulent flow goes like this, this is if you remember we defined a Blasius laminar flow line and a Prandtl-Von Karman turbulence line, which was later advanced to the so called ITTC line, which is slightly higher than this straightly higher than this, slightly higher than Prandtl-Von Karman line.