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.