Miscellaneous drag: Refers to the drag of items such as the flaps, unretracted Landing Gear, Upswept aft fuselage and fuselage base area.
Subsonic Parasite Drag Coefficient Estimation: The parasite drag consists essentially of skin friction, form, interference, miscellaneous drag and leakage or protuberance drag.
Dparasite = DSF + Dpress
Flat Plate Skin Friction Coefficient
Depends on the Reynolds number, the Mach number, and K (the Surface Roughness).
It is a strong function of the extent of Laminar Flow.
Effects of Surface RoughnessLeads to higher Cf (Skin friction coefficient).
Reynolds cutoff used for skin roughness effect.
The parameters that determine the form factor are:
Mach Number (M)
Sweep (ƛm) of maximum thickness
Thrust-to-Chord ratio (t/c) Location
(x/c) Chordwise location of maximum thickness.
Interference Factor (Q)
Is a measure of increased drag due to interference between components.
Used for Nacelle and store mounting
The value of Q factor is a function of:
Distance of store from fuselage
Vis-à-vis fuselage diameter (dfus).
Leakage is the tendency of the aircraft to inhale or exhale the air through the various holes.
Drag Estimation of Military Aircraft
Military Aircraft may fly at:
Subsonic speeds (Transport or Reconnaissance Aircraft)
Supersonic speeds (Fighter Aircraft).
Total drag coefficient Military Transport Aircraft (CD) = CD0wing + CD0body + ∆CD0 (Zero Lift drag) + CDL (Lift induced drag)
Flaps as High Lift Devices
The essence of using flaps during takeoff is to have a better climbing performance.
Types of flaps