Why is it harder to maintain laminar flow on larger aircraft?
Sort of interesting that very slow, lower Reynolds number airfoils, such as models, actually have to trip the airflow to form a boundary layer.

Surface friction causes the air near the wing surface to move at the wings speed.  In a wind tunnel this is slower than the free stream, in the air, the moving wing speeds up the air around it.  In relative terms, the effect is the same.

Boundary layers are draggier than laminar flow, but much less draggier than turbulent flow.  The boundary layer is like "grease", helping reduce drag and create lift.

At higher subsonic Mach numbers, early efforts at a "laminar flow wing"  for long range escort fighters  resulted in something resembling an airfoil flown backwards, with a sharp leading edge, a very gently increasing thickness (to keep laminar flow), maximum thickness further back towards the trailing edge, and a much shorter taper to the trailing edge. 
This is reminiscent of the blunt "boat tail" approach being tried these days, also found in bullets.

Though successful, low speed handling and stall characteristics led to some needed modifications.

But chord length, and airspeed, as well as airfoil type and surface smoothness, are very important parameters in predicting airflow around a wing.  Airfoil Tools, on the web, is a great place to begin to explore airfoil types for various applications.  Particularly of interest are Coefficient of Lift vs AOA, and Lift/Drag ratio.