[Secret Agent Man]

That, and the cone inlets to the engine can move quite a bit depending on speed and altitude to adjust for proper fuel burning.

[Bryanw92]

>>That, and the cone inlets to the engine can move quite a bit depending on speed and altitude to adjust for proper fuel burning.

But that’s a controlled change for engine operation and not just a shape change due to heating that makes it impossible to calculate the speed of the aircraft as post #4 claimed.

[doorgunner69]

Not for fuel burn, but to control the inlet shock waves.

The shock waves can disrupt the airflow and "un-start" the engines, which was a rather violent event from reading Brian Schul's book.