In this paper we identify certain classes of non-stretch mappings that enjoy a sharp estimate of the Beurling-Ahlfors operator. We first make use of a property of subharmonic functions to prove that the Bañuelos-Wang conjecture and the Iwaniec conjecture are true for a class of mappings that satisfy a quasilinear conjugate Beltrami equation. By utilizing the principal solutions of Beltrami equations, we further explicitly construct some classes of non-stretch mappings for which the Bañuelos-Wang conjecture and the Iwaniec conjecture are true.