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Aircraft speed: Difference between revisions
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In spite of this dependence on [[altitude]], IAS is a very useful quantity in flight. Many aerodynamical properties, for example drag, the stress on the airframe, stall speed or the forces on control surfaces depend on the dynamic pressure generated by the airstream, not on the actual aircraft speed. The stall speed of an aircraft at sea level is very different from the stall speed (in TAS) at 30.000 ft - but they correspond to the same IAS reading. | In spite of this dependence on [[altitude]], IAS is a very useful quantity in flight. Many aerodynamical properties, for example drag, the stress on the airframe, stall speed or the forces on control surfaces depend on the dynamic pressure generated by the airstream, not on the actual aircraft speed. The stall speed of an aircraft at sea level is very different from the stall speed (in TAS) at 30.000 ft - but they correspond to the same IAS reading. | ||
At sea level, a IAS of 400 knot roughly corresponds to 400 knot TAS. At 80.000 feet (the cruising altitude of a [[SR-71]]), the IAS of 400 knot corresponds to a TAS in excess of 1600 knot (..that corresponds with about Mach 3 at that altitude). | At sea level, a IAS of 400 knot roughly corresponds to 400 knot TAS. At 80.000 feet (the cruising altitude of a [[SR-71]]), the IAS of 400 knot corresponds to a TAS in excess of 1600 knot (..that corresponds with about Mach 3 at that altitude). | ||