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For a given IAS an increase in altitude will result in

  • an increase in induced drag.
  • no change in the induced drag.
  • an increase in profile drag.

Explanation from PART66Online

Indicated airspeed is a direct measure of dynamic pressure, so holding IAS constant holds the dynamic pressure constant at every altitude. In level flight the wing must still support the same weight, so the lift coefficient and the angle of attack are unchanged, and the induced drag coefficient and the induced drag are unchanged with them. What rises with altitude at a given IAS is the true airspeed, and therefore the power required, not the drag force. Profile drag is likewise tied to dynamic pressure and does not rise either.

W

wan.yc.justin asked · 2h ago

what i dont understand is how is the aircraft increase in altitude without an increase in AoA, hence the increase in induced drag

Community Comments (1)

T
Tomash 2h ago
It's B. Seen it from the jump seat on check flights, fly level at the same indicated speed at 5000 ft and again at 15000 ft and the pitch attitude barely changes, only the true airspeed is a lot higher. Thinner air but the wing moves through it faster, so same dynamic pressure, same AoA for the same lift and same induced drag, and the climb in between comes from extra thrust, not from holding more AoA.

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