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Why must the engine inlet air velocity be kept below Mach 1?
The job of an engine inlet is to slow incoming air to subsonic speeds before it passes through the engine. But as an airplane approaches Mach 1, it compresses the air ahead of it into shock waves—bands of air radiating from the airplane that are much hotter and denser than the ambient air.
What is inlet drag?
Inlet spillage drag is a drag that occurs when the engine cannot handle all of the flow that approaches the inlet. The airflow through the engine is set by choked conditions in the nozzle. Any excess flow that approaches the inlet is spilled around the inlet generating additional drag on the airframe.
What is subsonic inlet?
A subsonic aircraft has an inlet with a relatively thick lip. SUPERSONIC INLETS. An inlet for a supersonic aircraft, on the other hand, has a relatively sharp lip. The inlet lip is sharpened to minimize the performance losses from shock waves that occur during supersonic flight.
Why are the inlets on an aircraft important?
More exotic inlet shapes are used on some aircraft for a variety of reasons. The inlets of the Mach 3+ SR-71 aircraft are specially designed to allow cruising flight at high speed. The inlets of the SR-71 actually produce thrust during flight.
How are inlets used in a scramjet engine?
The flow exiting a scramjet inlet must remain supersonic. An inlet must operate efficiently over the entire flight envelope of the aircraft. At very low aircraft speeds, or when just sitting on the runway, free stream air is pulled into the engine by the compressor.
Where does the inlet sit in an engine?
The inlet sits upstream of the compressor and, while the inlet does no work on the flow, inlet performance has a strong influence on engine net thrust . As shown in the figures above, inlets come in a variety of shapes and sizes with the specifics usually dictated by the speed of the aircraft.
How are inlets used in supersonic jet engines?
Some supersonic inlets, like the one at the upper right, use a central cone to shock the flow down to subsonic speeds. Other inlets, like the one shown at the lower left, use flat hinged plates to generate the compression shocks, with the resulting inlet geometry having a rectangular cross section.