Critical engine
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The critical engine of a multi-engine fixed-wing aircraft is the engine that, in the event of failure, would most adversely affect the performance or handling abilities of an aircraft. On propeller ai
Fig. 1. With clockwise-rotating propellers (as seen by the pilot), the operating right-hand engine will produce a more severe yawing moment towards the dead engine, thus making the failure of the left-hand engine critical.
Counter-rotating propellers
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Counter-rotating propellers are propellers which turn in opposite directions to each other. They are used on some twin- and multi-engine propeller-driven aircraft.
Critical engine
…with propellers that rotate counter-clockwise, such as the de Havilland Dove, the right engine would be the critical engine. Most aircraft that have counter-rotating propellers do not have a critical engine defined by the above mechanism because the two propellers are made to rotate inward from the top of the arc; both engines…
World War I Linke-Hofmann R.I German heavy bomber (1917) with counter-rotating propellers
He 177A Greif with counter-rotating propellers