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Thread: Why planes don't fly faster

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    Default Why planes don't fly faster


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    It's a very good video.

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    Junior Member Roshni's Avatar
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    Nice video!

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    Senior Member Gabriel's Avatar
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    Why planes don't fly faster
    Answer:



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    Senior Member 3WE's Avatar
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    Quote Originally Posted by Gabriel View Post
    Answer:
    Because of the airlines strong desire to give the customer exactly what it wants.

    I did find 100 seat miles per gallon for the 787 to be impressive.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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    Member ATLcrew's Avatar
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    I particularly appreciated how the discussion of turboprops was illustrated by piston aircraft.

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    Senior Member 3WE's Avatar
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    Quote Originally Posted by ATLcrew View Post
    I particularly appreciated how the discussion of turboprops was illustrated by piston aircraft.
    That and the awfully flat-looking drag curve at sub-sonic speeds.
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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    Senior Member Gabriel's Avatar
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    Quote Originally Posted by ATLcrew View Post
    I particularly appreciated how the discussion of turboprops was illustrated by piston aircraft.
    I also noted. Several different piston aircraft and not even one single turboprop.
    Also, they explain how to fly supersonic you can't use a turbofan and need a turbojet, and illustrate the situation showing an F-15 which is supersonic and has... a turbofan.

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    Senior Member Gabriel's Avatar
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    Quote Originally Posted by 3WE View Post
    That and the awfully flat-looking drag curve at sub-sonic speeds.
    The curve is ok but the axis is wrong. It should read "Cd" or "Drag coefficient". You still need to multiply by 1/2*density*speed2. The good thing is that you can keep 1/2*density*speed2 manageable low even at high speed by reducing the density, that is, by flying high. But that will not help you with the Mach number. That's why, and I am oversimplifying, the cruise altitude of planes is where they make 0.8M (the point where the Cd curve starts to explode) equal to an INDICATED airspeed of 250 kts. In that way they plane is using fuel at a hourly rate similar to what it would at 250 kts at sea level but with a true speed of say 450 kts, thus about halving the fuel burned per mile.

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