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Thread: Aircraft speed in fsx

  1. #1

    Default Aircraft speed in fsx

    Why can n Boeing 747-400 only fly at 330 knots, when the specsheet indicates that it can cruise at 800 + knots? Is there a way around this or do i have to ignore the overspeed buzzer. If a person flies from South Africa to America it will take aprox. 24 hrs at 330 knots. Seems wrong

  2. #2
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    What you need to realize is that their are two different types of speeds that you are referring to. The 330 Knots is the aircraft's indicated airspeed. This is the speed of the air going through the aircraft’s pitot tube. This includes both the aircrafts speed and the speed of any head wind. Thus this speed is slower than the aircraft's ground speed. The 800 knots you reference in the 747 spec sheet is likely the true airspeed or ground speed. I cannot easily explain the difference to you but the aircraft’s ground speed is affected not only by the engines and wind but also by altitude. As an aircraft cruises at higher altitude the aircrafts maximum indicated airspeed gets lower. However, when an aircraft climbs its true airspeed increases. If you want proof of this get in a 747 and climb to an altitude of 35,000ft. Open your GPS and it will give you the aircrafts ground speed. This ground speed should be significantly higher than what your airspeed indicator says. Now descend to 2,000ft and you should see that the airspeed indicator and the speed on the GPS should read almost the same if not exactly. I hope this explanation helps.

    Lizardmon

    P.S. One piece of advice though. Never ignore the over speed buzzer. In the real world if you exceed the maximum safe speed and the buzzer sounds you are likely damaging the aircraft.

  3. #3
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    Quote Originally Posted by FSPeet View Post
    Why can n Boeing 747-400 only fly at 330 knots, when the specsheet indicates that it can cruise at 800 + knots? Is there a way around this or do i have to ignore the overspeed buzzer. If a person flies from South Africa to America it will take aprox. 24 hrs at 330 knots. Seems wrong
    I don't know what spec sheet you're looking at, but the 747 is not supersonic -- that 800 knots is probably somewhat under 600 knots. Mach 1 (the speed of sound) is about 660 knots at standard conditions at sea level (59º F), and almost 100 kts slower at 35,000 feet (temps well below 0º). Few civilian aircraft cruise much past mach .82 or .83, which is around 550 knots at sea level, and less at altitude.

    As for the "slow" indicated airspeed, as mentioned above there is more than one type of "speed" in aviation. That 330 kts is indicated airspeed, which merely reflects the low air density at high altitudes. Look at the Flightsim Wiki entry referenced here for quite a bit more information. Don't forget to click on the highlighted terms, as they provide additional information. Notice also the references to various Wikipedia entries (bottom of pages) which provide still more information.

    Larry N.

  4. #4
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    747 does Mach 0.85.

  5. Default

    But in FSX only .51 Mach is allowed before the over-speed alarm sounds.

  6. #6
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    At what altitude?

    Larry N.

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