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Guest bigrobmjca

Question About Crusing

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I know that most people while they are up above FL 300 usually run 470 knots +. I'm flown several aircraft, and have the autopilot setup for about mach .81 and still can't get above about 460 knots. I've tried setting up calm conditions and all. Any ideas?thanks,bigrobmjca

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I know that most people while they are up above FL 300 usually run 470 knots +. I'm flown several aircraft, and have the autopilot setup for about mach .81 and still can't get above about 460 knots. I've tried setting up calm conditions and all. Any ideas?thanks,bigrobmjca
Once you get above a certain altitude you have to switch to mach speeds as the IAS is not an accurate indicator of the aircraft's actual speed. A statement like above FL300 most people run 470kts is meaningless. Concorde cruised above FL300 (FL550-FL590) and would have had an IAS of much less than 470kts when it was travelling at Mach 2! That's how meaningless IAS is above a certain altitude. That altitude is in the range FL250-FL300.Once you're in that range forget IAS.

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Look at your TAS indicator which compensates for the thinner air at high altitudes. At higher speeds another effect called Mach effect, essentially a cone of thinner air around the aircraft that can cause TAS to be off as well due to air not fully entering the Pitot tube which is used to measure air speed. Where the Mach number is known TAS can be corrected.http://en.wikipedia.org/wiki/Mach_speed#Hi..._around_objectshttp://en.wikipedia.org/wiki/True_air_speedhttp://en.wikipedia.org/wiki/Calibrated_airspeedcan be informative. Read the descriptions and ignore the formulas if your math is not up to it. :)

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