[ELI5] Why are planes’ engines slightly tilted down?
In: 178
They’re tilted down and usually angled inward. This is to do with efficiency in the local airflow.
The inward angle, or toe-in is usually 1-3°, (a 747 uses 2° on all 4 engines). This is because the local airflow is moving outward from the centerline of the aircraft slightly. In general, the fuselage and wing are pushing air out of the way and this accounts for a slight out washing effect. The toe-in is there to account for this and lower drag. I’ve heard that the angle is also there to mitigate asymmetrical thrust in a single-engine scenario. You see this with many twin engined fighters. But I’ve never heard anyone credible refer to this.
The downward angle is sometimes an illusion of the landing gear, with the nose gear being shorter. But most often it’s because aircraft don’t fly completely level, they fly with some angle of attack, particularly in the engine intensive parts of the flight envelope: climb and high weight cruise. So the engines are angled to optimize efficiency with regard to airflow. During descent, we don’t care much about engine efficiency as they’re running at a fraction of their max power, often idle.
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