Stepwise Approach to Compute Minimum Parasite Drag

In this book, the following seven steps are carried out to estimate the minimum parasite drag, CDpmn

Step 1: Dissect and isolate aircraft components such as the wing, empennage, fuselage, and nacelle. Determine the geometric parameters of the air­craft components such as the characteristic length and wetted areas.

Step 2: Compute the Re per foot at the LRC condition. Then, obtain the com­ponent Re by multiplying its characteristic length.

Step 3: Determine the basic 2D average skin-friction coefficient CFbasic, cor­responding to the Re for each component (see Figure 9.19b).

Step 4: Estimate the ACf as the increment due to 3D effects on each compo­nent.

Step 5: Estimate the interference drag of two adjacent components; avoid duplication of this effect.

Step 6: Add the results obtained in Steps 3, 4, and 5 to obtain the mini­mum parasite drag of a component in terms of flat-plate equivalent area (ft2 or m2); that is, CF = CF_2D + J2ACF for the component:

Cf)comp = (Aw’)comp CF, where (CDpmin)comp = (f)comp! Sw.

Step 7: Total all the component minimum parasite drags. Then, add other drags such as the trim and excrescence drags. Finally, add 3% drag due to surface-roughness effects. The aircraft minimum parasite drag is expressed in the coefficient form, CDpmin.

The semi-empirical formulation for each component is provided in the following subsections.

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