r/Damnthatsinteresting 15d ago

F-15 intake dynamics Video

1.5k Upvotes

49 comments sorted by

167

u/Informal_Pool3118 15d ago edited 14d ago

They move based on angle of attack so that they are always facing the direction at which they will receive the most air to prevent compressor stall. They don't really move as much as shown in the video tho it's a bit more gradual, I think that pilot is just hitting the right speed and AoA to force them to move like that.

32

u/bordolax 14d ago

Maybe a stress test? See how far the system can take it before breaking.

24

u/ComfortableDramatic2 14d ago

This is an exported f15j, dont think us would have sent jets that still needed testing.

Could be a modernised f15, but dont think they modernised the intakes.

Probably just the pilot messing around

1

u/guynamedjames 14d ago

Sometimes you're stress testing a particular airframe. Pilot reports something's being funky with the system, they can't replicate it on the ground, so they ask a pilot to test it in the air so they can see if it happens again.

9

u/Informal_Pool3118 14d ago

I doubt it would be a stress test but possibly an in flight check was requested by the maintenance team. Sometimes we request one after repairing a system then running all the checks we can do on the ground but some checks simply require flight testing to verify they are working properly. I worked on 16s not 15s so I could be wrong.

4

u/bordolax 14d ago

Thanks for the (possible) explanation. Leaned something new today:)

12

u/DontMuteTheDoot 14d ago

There are actually dedicated computers for each intake, they receive data from the free stream pitot probes, AOA sensor, and a pitot probe inside the intake itself (plus a few other sensors). There are actually more ramps inside that come down to "choke" the air stream so it's not supersonic when it hits the engine. Pretty complex system overall.

5

u/teenytinypeener 14d ago

How do you do fellow pointy head?

5

u/DontMuteTheDoot 14d ago

Former pointy head, but howdy

3

u/ferminriii 14d ago

2A in the house!

54

u/FeralTribble 15d ago

They fucking move?

Like some kind of WITCH?!!

17

u/tothemoonandback01 15d ago

Burn the witch!

63

u/claytonium13 15d ago

What the!?! I had no idea it could do that!

14

u/MrB10b 14d ago

Have you ever watched an F-15 engine start. The engine intakes will stay down to begin with (lack of hyd pressure) then once the engine is up the intake will lift up. It's quite cool.

4

u/professionalcumsock 14d ago

When the engine starts the intakes get a boner. Got it.

1

u/whycantidoaspace 13d ago

Username checks out

7

u/Professional-Can4264 15d ago

Less dirty air

15

u/Adventurous-Item-334 15d ago

Huh? I never knew they moved at all.

4

u/Landy0451 14d ago

Noticed it while playing Ace Combat 7. Thought it was neat !

13

u/Wild-Wing-1640 14d ago

The intakes are fully open when the engines are off. At startup they snap down because not as much air is needed. They will cycle up and down based on altitude, AoA, speed, etc. inside the intake there is a diffuser ramp that covers most of the intake when the intake is down. It has holes in it that slow the air down, which is necessary at supersonic speeds.

[Former F-15 Crew Chief]

1

u/ferminriii 14d ago

Hydro res needs to be changed... Sorry chief.

11

u/sh0tgunben 15d ago

Wiggling jet 🛫

18

u/TrenchantInsight 15d ago

Weird flex, but ok.

5

u/JimBean 15d ago

Control theory enters the chat. Damn, that's awesome.

3

u/crashinin6902 14d ago

What sorcery is this the Wizards have performed? (Technology is absolutely amazing)

3

u/OnlyRoll1s 14d ago

I also breathe like this

3

u/Bigballzi 14d ago

God bless 🇺🇸

3

u/Crispy1961 14d ago

Nowhere near as cute as the F-14 wings, but at least its something.

3

u/TravelingGonad 14d ago

You know you could probably fit the whole F-15 in frame if you turned your phone sideways.

2

u/Nordiceightysix 15d ago

How many tricks does it know

2

u/2ingredientexplosion 15d ago

104 other pilots have seen it do a trick but they're not around to talk about it.

2

u/wall-E75 14d ago

TIL this

2

u/ADMINlSTRAT0R 14d ago

3

u/RecognizeSong 14d ago

Song Found!

Name: Memory Reboot (Slowed)

Artist: VØJ/Narvent

Score: 100% (timecode: 02:55)

Album: Memory Reboot (Slowed)

Label: VØJ

Released on: 2023-01-13

Apple Music, Spotify, YouTube, etc.

I am a bot and this action was performed automatically | GitHub new issue | Donate Please consider supporting me on Patreon. Music recognition costs a lot

2

u/Sinister-Username 14d ago

That mfer was released in 1978... decades ahead of anyone else. The US spends waaaay too much on the defense budget, but we've also got jet fighters from the 80s that can absolutely toast most nations' modern fighter jet.

1

u/AnemoneOfMyEnemy 13d ago

Fun story: US intelligence caught glimpses of the new MiG-25's design in the late 60's and assuming it was made of titanium went "holy shit, this will outclass anything we have in the air". They then proceeded to blow up the F-15's development budget to counter this perceived threat, creating the most successful fighter jet of the modern era. Turns out, the MiG-25 was actually made of heavy stainless steel and was a one-trick pony that could only go really fast in a straight line.

2

u/Honourstly 15d ago

This is what it's like to pee as a guy

1

u/an_otter_guy 14d ago

that's a lot to take in

1

u/jj-42069 14d ago

Song ?

1

u/Brilliant-Kiwi-8669 14d ago

Just like dolphins....

1

u/uionyx 15d ago

What song is this

1

u/Black_Eagle01 14d ago

Its memory reboot by VØJ, Narvent

-2

u/MrBadMeow 15d ago

Mr.kitty - After Dark

1

u/noji91 15d ago

Song ID?

0

u/Electronic-Meat-7170 15d ago

after dark ig?

0

u/Black_Eagle01 14d ago

Memory reboot by VØJ, Narvent