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Rolls-Royce says jet engines used in air-launched missiles have a problem.
The missile’s engine works in rocket mode for the launch phase, and then
switches to a jet engine mode for cruising. But using an explosive charge to
jettison the rocket nozzle risks shooting down the aircraft that has just
launched the missile. So Rolls-Royce has designed a rocket engine with flaps
that define a nozzle-like “throat” (GB 2 333 806). After launch, latches on the
flaps break allowing the air flow to push them flat against the sides of the jet
exhaust—safely converting the motor into a steady-state jet engine.