What the downside of early Mig layout and air intake?

[Nodeo-Franvier]

Why aren't early Mig (Mig15-21) air intake layout use anymore? Even in a light fighter like JF-17 and Chinese development of Mig-21.

 

[FLYBOYJ]

Why aren't early Mig (Mig15-21) air intake layout use anymore? Even in a light fighter like JF-17 and Chinese development of Mig-21.

Because they are giant FOD traps and engineers have figured out how to get enough air into turbine engines efficiently without having a gaping hole in the front of the aircraft.

 

[tomo pauk]

Why aren't early Mig (Mig15-21) air intake layout use anymore? Even in a light fighter like JF-17 and Chinese development of Mig-21.

Circular intakes that have no slant are, for example, bad at high angle of attack.
Angle of attack is angle between aircraft's actual speed vector and it's datum line. During the 'normal' straight line flight, the AoA is close to zero. When aircraft pitches (pilot has pulled the stick toward himself), the datum line gets lined at the angle preferred by pilot, but speed vector is not, it kinda lags after the direction of datum line, thus the difference between two starts growing. Aircraft can achieve very high AoA, the super-maneuverable aircraft can do 90 deg - basicaly the aircraft is pointed vertically, while it is moving horizontally. Soviets were supposed to do 180 deg AoA with Su-27 - aircraft is moving backward in that moment; we can just speculate the unenviable task the compressor needs to do in that case in order for engine not to starve for air in the critical few seconds.
High AoA will also happen during 'normal' horizontal high G maneuvering.
We've also saw Western aircraft moving from the circular air intakes (or the ones that are D-shaped), especially since they don't make much sense in 2-engined fighter aircraft that Soviets were also moving on by 1960s.
This is where the slanted, usually 'boxy' air intakes start making sense - the intake scoops the air much better at higher AoA.
Another very important thing is that circular air intakes, even the bigger ones like on MiG-21, Lightning etc. limit the size of radar aerial, that in turn limits the radar range. Having air intakes going through 100% fuselage eats a lot of internal volume, thus limiting the fuel tankage and/or electronics.

However, do not despair the newest touted Russian fighter is supposed to have a single nose air intake, although not of circular shape: video

 

[pbehn]

The nose is the best place to put a radar set isnt it?

 

[FLYBOYJ]

The nose is the best place to put a radar set isnt it?

I would think so

 

[SaparotRob]

Circular intakes that have no slant are, for example, bad at high angle of attack.
Angle of attack is angle between aircraft's actual speed vector and it's datum line. During the 'normal' straight line flight, the AoA is close to zero. When aircraft pitches (pilot has pulled the stick toward himself), the datum line gets lined at the angle preferred by pilot, but speed vector is not, it kinda lags after the direction of datum line, thus the difference between two starts growing. Aircraft can achieve very high AoA, the super-maneuverable aircraft can do 90 deg - basicaly the aircraft is pointed vertically, while it is moving horizontally. Soviets were supposed to do 180 deg AoA with Su-27 - aircraft is moving backward in that moment; we can just speculate the unenviable task the compressor needs to do in that case in order for engine not to starve for air in the critical few seconds.
High AoA will also happen during 'normal' horizontal high G maneuvering.
We've also saw Western aircraft moving from the circular air intakes (or the ones that are D-shaped), especially since they don't make much sense in 2-engined fighter aircraft that Soviets were also moving on by 1960s.
This is where the slated, usually 'boxy' air intakes start making sense - the intake scoops the air much better at higher AoA.
Another very important thing is that circular air intakes, even the bigger ones like on MiG-21, Lightning etc. limit the size of radar aerial, that in turn limits the radar range. Having air intakes going through 100% fuselage eats a lot of internal volume, thus limiting the fuel tankage and/or electronics.

However, do not despair the newest touted Russian fighter is supposed to have a single nose air intake, although not of circular shape: video

That was a very informative post and one even I could understand. I always suspected it was something more than just making jets look cooler.

 

[tomo pauk]

People are probably aware of MiG-29 and Su-27 doing the 'Cobra' maneuver in many of airshows, be it in clean or armed configuration (although the 'missiles' are just models in the airshows). Here is the SAAB Draken doing quick 90 deg cobras: video

 

[Admiral Beez]

Circular intakes that have no slant are, for example, bad at high angle of attack.

That makes sense for the straight and level EE Lightning.