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What is best Rate of descent and how is it different from minimum rate of descent ?

Asked by: 7916 views Aerodynamics

how are minimum Rate of Descent and best rate of descent different ?

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2 Answers

  1. Brian on Mar 06, 2011

    Might you be referring to best glide versus minimum sink airspeeds?
    Best glide airspeed – The speed that provides the greatest gliding distance (assuming no winds). This speed is published, but only for gross weight. To correct for weight we can take the square root of (actual weight / gross weight) and multiply it by the published best glide speed.
    Best glide speed corresponds to the angle of attack that yields minimum drag. It is because best glide is based on an angle of attack that best glide speed varies with weight. A similar relationship can be seen with stall speed. In fact, the above formula will work where published best glide speed is replaced with publish stall speed.
    Minimum sink – The speed that yields the greatest time aloft, or minimum rate of descent. Typically, this speed is not published. However, in small aircraft, it will occur about 5 knots below the published best glide speed corrected for current aircraft weight.
    Minimum sink corresponds to the speed of minimum power required.

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  2. Heather McNevin on Mar 10, 2011

    I’m not sure but I’m thinking maybe you’ve heard a controller say “give me your best rate of descent”.  Pilots and controllers may have different views on descending, that might be where your question lies.  As a pilot, I descend at a rate that is confortable for me and my passengers, one that is acceptable for the aircraft limitations, and one that I plan that puts me at my desired altitude when I want to be there.  Many times, this is a nice gentle descent.  Of course, if I have an engine failure, I’m aiming for best glide and a minimum descent angle – I want to stay airborne as long as possible.  Controllers are often looking at traffic, and may want you to get out of the way quickly.  If a controller says, best rate; its not you’re best glide, its your maiximum descent rate.  Descend and get out of the way is what theyre saying!

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