Why do almost all aircraft have a gap between the intake and the fuselage

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Why do almost all aircraft have a gap between the intake and the fuselage it is something to do with boundary layer but how does this work wouldnt it just create the same boundary layer in the intake or are the boundary layers different in the intake to the fuselage im confused? the p51 and most modern jets are good examples.

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2 Answers

Anonymous 0 Comments

The fuselage has a layer of air flowing over it, that boundary layer. If you stick an intake right at the fuselage you will get that boundary layer air entering the intake along with the ambient air which will be going a different speed. This can cause issues, especially because it’s not constant. It will change based on angle of attack, and your engine inlet airflow will change, which is not good. It’s better to give the engine its own independent, and therefore more predictable, airflow.

Anonymous 0 Comments

It’s called a splitter plate.


You don’t want the boundary layer to go into the inlet because it is flowing at a different velocity and can starve the intake. The splitter plate divides the boundary layer from the free flowing air. The boundary layer goes past the intake (usually between the intake and the fuselage) while the free flowing air enters the intake.

Newer low observable aircraft can’t have splitter plates because the spoil the radar cross section so they use carefully shaped fuselage features to reroute the boundary layer without the sharp edge.