An aircraft has an untwisted, elliptic wing of aspect ratio 9 with a symmetrical aerofoil section....

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An aircraft has an untwisted, elliptic wing of aspect ratio 9 with a symmetrical aerofoil section. Its zero-lift drag coefficient (due to viscous effects) is 0.01. (a) Ignoring fuselage and tail contributions, and assuming that the lift-dependent drag is entirely due to inviscid effects, calculate: i. the maximum lift-to-drag ratio of the aircraft; and ii. the incidence at which it is achieved. (b) Two-dimensional measurements on the aerofoil section show that the additional viscous drag due to lift increases the (2D) drag coefficient by 0.004C1^2, where C1 is the (2D) lift coefficient. i. Assuming that the 2D results apply to local lift and drag coefficients on the wing, recalculate the maximum lift-to-drag ratio of the aircraft. ii. Comment on the accuracy of your previous calculation, and discuss how this would be affected by changes in wing aspect ratio and flight Reynolds number. An aircraft has an untwisted, elliptic wing of aspect ratio 9 with a symmetrical aerofoil section. Its zero-lift drag coefficient (due to viscous effects) is 0.01. (a) Ignoring fuselage and tail contributions, and assuming that the lift-dependent drag is entirely due to inviscid effects, calculate: i. the maximum lift-to-drag ratio of the aircraft; and ii. the incidence at which it is achieved. (b) Two-dimensional measurements on the aerofoil section show that the additional viscous drag due to lift increases the (2D) drag coefficient by 0.004C1^2, where C1 is the (2D) lift coefficient. i. Assuming that the 2D results apply to local lift and drag coefficients on the wing, recalculate the maximum lift-to-drag ratio of the aircraft. ii. Comment on the accuracy of your previous calculation, and discuss how this would be affected by changes in wing aspect ratio and flight Reynolds number.

Answer rating: 100% (QA)

Solution To calculate the maximum lifttodrag ratio of the aircraft we need to consider two cases a ignoring viscous effects and b considering the additional viscous drag due to lift a Ignoring Viscous ... View the full answer