Experiments have shown that the transition from laminar to turbulent conditions for flow normal to the axis of a long cylinder occurs at a critical Reynolds number of Re_D,c ≈ 2 X 10⁵, where D is the cylinder diameter. Moreover, the transition from incompressible to compressible flow occurs at a critical Mach number of Ma_c ≈ 0.3. For air at a pressure of p = 1 atm and temperature T = 27°C, determine the critical cylinder diameter D_c below which, if the flow is turbulent, compressibility effects are likely to be important.