Big B -> RE: 1000 Pounders versus Battleships (3/3/2008 4:34:25 PM)
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quote:
ORIGINAL: witpqs You mention that actual airspeed is a little higher than indicated airspeed. Why? Because Indicated Air Speed is measured from a pitot tube which is pressure sensitive. The higher in altitude - the lower the pressure in the tube: quote:
Indicated airspeed (IAS) is the airspeed read directly from the airspeed indicator on an aircraft, driven by the pitot-static system. IAS is directly related to calibrated airspeed (CAS), but includes instrument errors and position error. An aircraft's indicated airspeed in knots is typically abbreviated KIAS for "Knots-Indicated Air Speed" (vs. KCAS for calibrated airspeed and KTAS for true airspeed). IAS and V speeds Unless an aircraft is at sea level under International Standard Atmosphere conditions (15°C, 1013 hPa, 0% humidity) and no wind, the IAS bears little relation to how fast an aircraft is moving in reference to the ground; however, because the air pressure and density affect IAS/CAS and an aircraft's flight characteristics in exactly the same way, IAS and CAS are extremely useful for controlling an aircraft, and the critical V speeds are usually given as IAS. In aneroid instruments the indicated airspeed drops-off with increasing altitude as air pressure decreases, and this leads to an apparent falling-off of airspeed at higher altitudes. For this reason never exceed speeds (abbreviated VNE) are often given at several differing altitudes in the aircraft's operating manual, the VNE IAS figure falling as height is increased, as shown in the sample table below. Diving below mph IAS 30,000 ft 370 25,000 ft 410 20,000 ft 450 15,000 ft 490 10,000 ft 540
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