quite reach Mach2. Together with the introduction of the C-D nozzle, the inlet was redesigned. The USAF subsequently set a world's speed record with the F-106 of 1526 mph (Mach2.43). Nozzle area control during dry operation Some very early jet engines that were not equipped with an afterburner, such as the BMW 003 and the Jumo 004 (which had a design ), had a variable area nozzle formed by a translating plug known as a Zwiebel [wild onion] from its shape. The Jumo 004 had a large area for starting to prevent overheating the turbine and a smaller area for take-off and flight to give higher exhaust velocity and thrust. The 004's Zwiebel possessed a range of forward/reverse travel to vary the exhaust nozzle area, driven by an electric motor-driven mechanism within the body's divergent area just behind the turbine. Afterburner-equipped engines may also open the nozzle for starting and at idle. The idle thrust is reduced which lowers taxi speeds and brake wear. This feature on the J75 engine in the F-106 was called 'Idle Thrust Control' and reduced idle thrust by 40%. On aircraft carriers, lower idle thrust reduces the hazards from jet blast. In some applications, such as the J79 installation in various aircraft, during fast throttle advances, the nozzle area may be prevented from closing beyond a certain point to allow a more rapid increase in RPM and hence faster time to maximum thrust. In the case of a 2-spool turbojet, such as the Olympus 593 in Concorde, the nozzle area may be varied to enable simultaneous achievement of maximum low-pressure compressor speed and maximum turbine entry temperature over the wide range of engine entry temperatures which occurs with flight speeds up to Mach2. On some augmented turbofans the fan operating line is controlled with nozzle area during both dry and wet operation to trade excess surge margin for more thrust. Nozzle area control during wet operation The nozzle area is increased during afterburner operation to limit the upstream effects on the engine. To run a turbofan to give maximum airflow (thrust), the nozzle area may be controlled to keep the fan operating line in its optimum position. For a turbojet to give maximum thrust, the area may be controlled to keep the turbine exhaust temperature at its limit. What happens if the nozzle doesn't open when the afterburner is selected? In early afterburner installations, the