NAVWEPS DD-8OT-80  APPLICATION OF AERODYNAMICS  TO SPECIFIC PROBLEMS OF FLYING  ENGINE FAILURE ON THE MULTIENGINE  AIRPLANE  later portions of takeoff if the airplane is un-  able to become  airborne or if insufficient margin  above stall speed prevents successful initial  climb, In no circumstances  should a formation  of ice or frost be allowed to remain on the air-  plane wing surfaces  prior to takeoff.  In the case of the single-engine airplane,  power-plant failure leaves only the alternatives  of effecting a successful  power-off landing or  abandoning the airplane. In the case of the  multiengine airplane, the failure of a power-  plant does nor necessarily  constitute a disaster  since flight may be continued with the remain-  ing powerplants functioning.  However, the  performance of the multiengine airplane with  a powerplant inoperative may be critical for  certain conditions of flight and specific tech-  niques and procedures must be observed to  obtain adequate performance.  The effect of a powerplant failure on the  multiengine turbojet airplane is illustrated by  the first chart of figure 6.8 with the variation  of required and available thrust with velocity.  If half of the airplane powerplants are inoper-  ative, e.g., single-engine operation of a twin-  engine airplane, the maximum thrust available  at each velocity is reduced to half that avail-  able prior to the engine failure.  The variation  of thrust required with  velocity may be  affected by the failure of a powerplant in that  there may be significant increases in drag if  specific procedures are not followed.  The  inoperative powerplant may contribute addi-  tional drag and the pilot must insure that the  additional drag is held to a minimum.  In the  case of the propeller powered airplane, the  propeller must be feathered, cowl flaps closed.  etc.,  as the increased drag will detract con-  siderably from the performance.  The principal effects  of the reduced available  thrust are pointed out by the illustration of  figure 6.6. Of course, the lower available  thrust will reduce the maximum level flight  The asymmetrical power condition which  results when a powerplant fails can provide  critical control requirements. First consid-  eration is due the yawing moment produced  by the asymmetrical power condition.  Ade-  quate directional control will  be available  only when the airplane speed is greater than  the minimum directional control speed. Thus,  the pilot must insure that the flight speed  never  falls below the minimum directional control  speed because the application of maximum  power on the functioning powerplants will  produce an uncontrollable yaw if adequate  directional control is unavailable. A second  consideration which  is due the propeller  powered airplane involves the rolling moments  caused by the slipstream velocity.  Asym-  metrical power on the propeller airplane will  create a dissymmetry of the slipstream veloc-  ities on the wing and create rolling moments  which must be controlled.  These slipstream  induced rolling moments will be greatest at  high power and low velocity and the pilot  must be sure of adequate lateral control,  especially for the crosswind landing.  speed but of greater importance is the reduc-  tion in excess  thrust.  Since the acceleration  and climb performance is a function of the  excess  thrust and power, the failure of a power-  plant will be most immediately appreciated in  this area of performance. As illustrated in  figure 6.8, loss of one-half the maximum avail-  able thrust will reduce the excess  thrust to less  than half the original  value. Since some  thrust is required to sustain flight, the excess  which remains to accelerate and climb the  airplane may be greatly reduced. The most  critical conditions will  exist when various  factors combine to produce a minimum of  excess thrust or power when engine failure  occurs. Thus, critical conditions will be com-  mon to high gross  weight and high density  altitude  (and high temperatures in the case of the  turbine powered airplane) as each of these  factors will  reduce the excess thrust at any  specific flight condition.  376 