Here’s a rare look at “magic” of the F-15 Eagle’s moving air intakes.
The video in this post is quite remarkable: shot during a recent rehearsals of the Gifu Air Base Air Festival (that will take place next weekend), it shows an F-15J of Flight Development and Experiment Wing of the JASDF (Japan Air Self-Defense Force), based at Gifu, during a series of pitch-up/pitch-down maneuvers whose purpose is to show the effect of the elevators.
The F-15’s air intakes are engineered in such a way the ramps can move up and down, so as to change their angle during flight and give the optimal air flow for the engines under the current combination of airspeed, altitude, and throttle setting. The air intakes also include a diffuser ramp and a bypass door that move not only to feed the compressor with the right amount of air, but also to slow down the airflow and make it subsonic before it reaches the engine, thus preventing shock/pressure waves on the compressor and avoid stalls.
Variable geometry air intake of F-15 pic.twitter.com/KvQBwmrAYh
— Harvey Blanquisco (@ChonkyBoi562) November 5, 2023
While you can find other videos of the air intake ramp pivoting up and down, you rarely get a chance to clearly watch it moving so fast.
By the way, you can watch one of the F-15J’s practice displays here.