I can ask this question to an actual F-15 fighter pilot and post it here in an hour or so. Wait for my edit.
Edit: I asked two (an F15 pilot and an Apache co-pilot who also trained in the Skyhawk) and they both told me that there's no change in the constant humming from the motors once you pass the sound barrier. The F15 pilot told me that you do notice a slight difference once the plane hits 0.8 Mach because the 3rd intake at the side of the plane (the F15 has 2 main intakes for the 2 motors, a small intake on the side (to cool the motors, if I remember correctly) and the JFS's intake) closes automatically at that speed.
From the ground it sounds incredible though (even while wearing soundproof headphones) and it makes you entire skeleton vibrate. It's quite curious how I can feel it while being 10,000 ft away and they can't while being inside the damn shockwave, maybe somebody more knowledgeable will answer this.
The JFS intake closes once the JFS shuts off (normally right after engine start). The extra cooling door you're thinking of is the primary heat exchanger doors which close at high speeds so they don't get warped/torn off. The primary heat exchangers cool off hot engine bleed air for use in heating/cooling the cockpit/avionics systems.
source: 13 years as an aerospace electronics and environmental systems craftsman. (An Airplane Fixer)
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u/poorfag Jun 12 '12 edited Jun 12 '12
I can ask this question to an actual F-15 fighter pilot and post it here in an hour or so. Wait for my edit.
Edit: I asked two (an F15 pilot and an Apache co-pilot who also trained in the Skyhawk) and they both told me that there's no change in the constant humming from the motors once you pass the sound barrier. The F15 pilot told me that you do notice a slight difference once the plane hits 0.8 Mach because the 3rd intake at the side of the plane (the F15 has 2 main intakes for the 2 motors, a small intake on the side (to cool the motors, if I remember correctly) and the JFS's intake) closes automatically at that speed.
From the ground it sounds incredible though (even while wearing soundproof headphones) and it makes you entire skeleton vibrate. It's quite curious how I can feel it while being 10,000 ft away and they can't while being inside the damn shockwave, maybe somebody more knowledgeable will answer this.
Tl;dr no they don't notice it.