write:Any additional yawing moment that opposes the operating engine’s yaw will decrease it. For twin engine airplanes whose engines rotate in the same direction the en-gine whose pro

the aero-dynamic force produced by the rudder will decrease while the force produced by engine thrust will remain relatively constant.A combination of rudder and bank into the operating engine will be necessary to maintain control of the airplane as speed is decreased toward VMC.By reviewing Figures 31-12 and 31-13
it should be apparent that any additional yawing moment that enforces the yawing produced by the operating engine will increase VMC. Any additional yawing moment that opposes the operating engine’s yaw will decrease it.For twin engine airplanes whose engines rotate in the same direction
the en-gine whose propeller blade is moving downward while it is closest to the airplane’s CG will be the critical engine since its failure will produce the highest VMC. The reason for this phenomena is related to the “P” factor associated with operation at high angle of attack in single engine airplanes. At the higher angles of attack normally associated with engine out operation
the downgoing propeller blade will produce slightly more thrust
the upgoing blade will produce slightly less thrust and the engine’s center of thrust will shift toward the downgoing blade. Thus
failure of the “critical” engine (the one whose inboard blade is moving down) will result in more thrust from the engine whose downgoing blade is furthest from the airplane’s longitudinal axis
thereby creating the maximum yawing moment. On the other hand
the yawing moment created by the vertical tail will not change as a function of the engine which has failed. It should be obvious that loss of a “critical” engine will present the pilot with a more challenging (and dangerous) situation. The con-cept of a “critical” engine is shown in Figure 31-14.For twin engine airplanes whose propellers rotate in opposite directions
both engines are equally critical with respect to the magnitude of asymmetric thrust they produce. It should be noted that
all other things being equal
air-planes whose counter-rotating propellers move downward when they are furthest from the longitudinal axis will have higher VMCs than airplanes whose propellers are moving downward when they are closest to the longitudinal axis. Since this second propeller configuration results in a higher and therefore more dangerous VMC
there should be strong aerodynamic reasons for the selection of this propel-ler rotation configuration.Figure 31-13. Use of Bank to Oppose the Moment Caused by Engine-Out Operation.