Expert: Marc Ebelini - 4/20/2004

Question
Do port and starboard engines on a 737 for example spool-up in opposite directions and do propellors move in clock wise and counter clock wise when started? Do engine manufacturers have two assembly lines for port and starboard engines? If so, what are the differences in the two engines and where do they start?

Answer
Jet engines spool up the the same direction. All commercial propellor aircraft rotate counter clockwise when facing the front of the aircraft. Some foreign aircraft rotate clockwise. Standardizing the rotation causes less confusion and put less strain in maintaining inventory. Angle of incidence is is added to the port wing to counter torgue in propellor aircraft. Any effects of engine torgue is compensated for and can also be accomplished by vertical stabilizer offset. Only boats with two or more engines have clockwise and counterclockwise running engines. Many problems have risen from putting the engines in the wrong position. The boats performance suffers greatly when this happens and I suspect this is one reason why aircraft manufactures elected to keep making aircraft engines all running one way. There is also the problem of propellors. When turning the engine the opposite way the props would need to be match the rotation creating another possilble confusion. I hope this satisfies your question.