The zero-sideslip is necessary for a pilot to maintain control of an aircraft and have the greatest climb performance during an engine failure in a twin.
The critical engine on a multi-engine aircraft is the engine whose failure will result in the most adverse effects on aircraft performance and controllability.
Parasite drag is a combination of forces that attempt to resist an aircraft's movement. These forces include the air's displacement by the aircraft, turbulence generated in the airstream, and friction produced by air flowing over the surface of the aircraft.
