text: * constant strength - simple, large number of panels required
  * linear varying strength - reasonable answer, little difficulty in creating well-posed problems
  * quadratic varying strength - accurate, more difficult to create a well-posed problem
  Some techniques are commonly used to model surfaces.
  * Body Thickness by line sources
  * Body Lift by line doublets
  * Wing Thickness by constant source panels
  * Wing Lift by constant pressure panels
  * Wing-Body Interface by constant pressure panels