asked 80.9k views
0 votes
A glider has wings of elliptical planform of aspect ratio 6. The total drag is given by CD = 0.02 + 0.06G. Find the change in minimum angle of glide if the aspect ratio is increased to 10

1 Answer

7 votes

Answer:

Step-by-step explanation:

The minimum angle of glide, θ, can be calculated using the following formula:

θ = arctan(1/L)

where L is the lift-to-drag ratio.

The lift-to-drag ratio, L, is given by:

L = (CL/CD)

where CL is the lift coefficient.

For an elliptical wing, the lift coefficient is given by:

CL = (2πAR)/(2 + √(4 + (AR×e/0.9)^2))

where AR is the aspect ratio and e is the Oswald efficiency factor, which is assumed to be 0.9 for an elliptical wing.

For the given elliptical wing with an aspect ratio of 6, the lift coefficient is:

CL = (2π×6)/(2 + √(4 + (6×0.9/0.9)^2)) = 1.408

The drag coefficient is given by:

CD = 0.02 + 0.06G

where G is the lift-induced drag factor, given by:

G = (CL^2)/(π×AR×e)

For the elliptical wing with an aspect ratio of 6, G is:

G = (1.408^2)/(π×6×0.9) = 0.084

Therefore, the drag coefficient is:

CD = 0.02 + 0.06×0.084 = 0.025

The lift-to-drag ratio, L, is:

L = CL/CD = 1.408/0.025 = 56.32

The minimum angle of glide, θ, for the elliptical wing with an aspect ratio of 6 is:

θ = arctan(1/L) = arctan(1/56.32) = 1.06°

For the same elliptical wing with an aspect ratio of 10, the lift coefficient is:

CL = (2π×10)/(2 + √(4 + (10×0.9/0.9)^2)) = 1.496

The lift-induced drag factor, G, is:

G = (1.496^2)/(π×10×0.9) = 0.120

The drag coefficient is:

CD = 0.02 + 0.06×0.120 = 0.0272

The lift-to-drag ratio, L, is:

L = CL/CD = 1.496/0.0272 = 55.00

The minimum angle of glide, θ, for the elliptical wing with an aspect ratio of 10 is:

θ = arctan(1/L) = arctan(1/55.00) = 1.04°

Therefore, the change in minimum angle of glide if the aspect ratio is increased from 6 to 10 is:

Δθ = 1.06° - 1.04° = 0.02°

The change in minimum angle of glide is very small, indicating that the effect of changing the aspect ratio from 6 to 10 is not significant for the given wing geometry and drag coefficient.

answered
User Graham Povey
by
7.8k points