Disk Pr Pressure Velocity PE Stream Tube P V (1+b) V (1+ a) V Upstream Downstream Figure adapted from Archer & Saarlas, An Introduction to Aerospace Propulsion, Prentice Hall, 1996. For a helicopter, the thrust developed by the actuator disk is: T = m(Vout - Vin), where Vout = Vw and Vin = V = 0. The mass flow rate of air through the disk is m = PAV, where V, is the induced velocity at the disk. Apply Bernouilli's equation to this system to find an expression a) for the pressure upstream of the actuator disk, and b) for the pressure downstream of the actuator disk.