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Ok, basically, aero engines require their airflow to arrive at the compressor face at subsonic speeds. At high speeds a variable intake will decelerate the air flow to a speed manageable for the engine. Fighters that go Mach 2 plus really require variable inlets. You basically design an inlet to suit the envelope your aircraft is going to operate in.
Variable mechanical intakes are heavy and expensive. A variable inlet is VERY important for high speed aircraft with conventional turbofan engines. If you want to go to Mach 2.5 + and have efficient engines, you use VARIABLE intakes. Clever computer designed fixed shock inlets are sufficient for Mach 1.5 to 2 and below. The high thrust of today`s engines makes this possible to a degree along with clever inlet geometry. It is a complex field.
The Typhoon has a fixed shock inlet, although there is a moveable "lip" at the base of the inlet to help mass flow at high Alpha. Fixed inlets tend to be inefficient above Mach 2 and tend to limit an aircrafts top speed due to lousy "stagnation pressure recovery".
The F-22 doesn`t need to go Mach 2.5 so doesn`t need variable inlets. It can cruise on mil` power at M1.7+. The F119 engines, which are beasts as far as thrust goes, may make up for any high speed inefficiencies to a degree. Another reason the F-22 won`t have variable inlets is that it difficult to make moving inlets stealthy, ie, in one position, they could be fine, in another position, they could reflect radar. Just speculation.
You will note that today`s latest fighters tend to limit their top speed to about Mach 2, hence fixed shock inlets.
On the aircraft listed,
F-22- FIXED inlet (according to Paul Metz.)
F-16- FIXED inlet.
F-14- VARIABLE.
F-35- FIXED inlet.(diverterless).
Rafale- FIXED inlet.
F-18- FIXED inlet.
Tornado- VARIABLE inlet.
MIG-25- VARIABLE inlet.
Gripen- FIXED inlet.
Viggen- FIXED inlet.
MIG-23- VARIABLE inlet.
MIG-21 FIXED inlet.
SU-27 FIXED inlet (With FOD screen).
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