v0.9.0 · 2026-08-25
AFAERONAUTICS

Nomenclature

Explore the components of aircraft drag. Hover over a box with a mouse, focus it with the keyboard, or tap it to reveal its definition.

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Total DragDefinitionThe total aerodynamic force opposing the aircraft's motion through the air, including friction, pressure, wave, and lift-related contributions.[1][2]
Shear ForcesDefinitionThe viscous component of drag formed by tangential friction forces acting along the aircraft's wetted surfaces.[4]
Pressure ForcesDefinitionThe drag component produced by the flight-direction result of pressure forces acting normal to the aircraft surface.[1][4]
Skin Friction DragDefinitionAerodynamic resistance produced by contact between moving air and the aircraft surface through the viscous boundary layer.[1][3]
Scrubbing DragDefinitionIn Raymer's component buildup terminology, added friction associated with locally accelerated or disturbed flow washing over another aircraft surface.[2][7]
Viscous SeparationDefinitionPressure or form drag that increases when the boundary layer separates, leaving a turbulent wake and preventing pressure recovery on the aft surface.[3][4]
Wave DragDefinitionAdditional drag caused by shock waves and compressibility effects as local flow approaches or exceeds the speed of sound.[2]
Interference DragDefinitionAdditional drag created where interacting airstreams meet, such as at a wing–fuselage junction, producing turbulence or disrupting smooth flow.[3]
Parasite DragDefinitionDrag not associated with producing lift; the FAA groups form drag, interference drag, and skin-friction drag within this category.[3]
Profile DragDefinitionThe drag associated with an airfoil section's profile, conventionally combining its friction drag and form or pressure drag.[4]
Shock-Induced SeparationDefinitionBoundary-layer separation caused when a shock wave imposes a strong adverse pressure rise; the resulting separated region increases drag and can reduce lift.[5]
Supervelocity Effect on Skin FrictionDefinitionIn Raymer's terminology, the skin-friction increment arising because local velocity over a surface can exceed the aircraft's free-stream velocity.[2][7]
Supervelocity Effect on Profile DragDefinitionIn Raymer's taxonomy, the profile-drag increment associated with locally accelerated flow and its effect on surface friction and pressure distribution.[2][7]
Trim DragDefinitionThe drag increment associated with the tail lift and control forces required to balance aircraft pitching moments in trimmed flight.[6]
Wave Drag Due to LiftDefinitionThe lift-dependent part of compressibility drag produced by the pressure field and shock waves on a lifting surface at transonic or supersonic conditions.[2][7]
Drag Due to LiftDefinitionThe portion of drag that arises from generating lift; Raymer's taxonomy includes induced drag together with lift-related trim and wave-drag increments.[1][7]
Induced DragDefinitionLift-dependent drag associated with finite-wing flow, downwash, and wingtip vortices; its magnitude depends on lift and wing geometry.[1]
We model the drag polar withCD = CDo + k1CL2 + k2CL

Drag-equation reference

Subsonic zero-lift dragCDo≈CfeSwetS
Supersonic zero-lift dragCDo≈CDo,subsonic+CD,wave
Drag-divergence MachMDD≈Mcrit≈1−0.065cos(ΛLE)0.6(100tmaxc)0.6
Mach of maximum CDoMCDo,max=(1cosΛLE)0.2
Supersonic wave dragCD,wave=4.5πS(Amax−A0l)2EWD(0.74+0.37cosΛLE)[1−0.3M−MCDo,max]
Drag PolarCD=CDo+K1CL2+K2CL
CAMBERED POLARK1=K,K2=−2KCL,minD
Supersonic polar coefficientsK1=K,K2=0
Subsonic induced-drag factork=1πe0AR
Supersonic induced-drag factork₁=AR(M2−1)4ARM2−1−2cosΛLE
Subsonic Oswald efficiencye0=4.6(1−0.033AR0.53)cos(ΛLE)0.1−3.3

CDo versus Mach

Geometry and compressibility drag rise

MDD ≈ Mcrit—
MCDo,max—
Selected CDo—
CDo ≈ Cfe(Swet/S) + CD,wave

The equations reproduce the supplied conceptual drag-rise method. The transition between MDD and MCDo,max is smoothly interpolated for plotting.

Tuning Models

Cfe = 0.0037 and EWD = 2.2 give excellent predictions of subsonic and supersonic CDo values for a wide range of relevant historical fighter aircraft.

We will tune our models after wind-tunnel experiments.

CDo≈Cfe(SwetS)
CD,wave=4.5πS(Amax−A0l)2EWD(0.74+0.37cosΛLE)[1−0.3M−MCDo,max]

EWD ≈ 2.2 for “best” fighter aircraft
EWD ≈ 2.9 for the F-15

Review

Building the aircraft drag polar

0°12°
600 ft²1,800 ft²
0.00200.0060
LessMore
Skin-Friction Drag
Pressure Drag
Drag Due to Lift
Total Drag
Skin-friction section · red · S = 300 ft²
CD,f = Cfe(Swet/S)
Pressure-drag section · blue · curvature increases with slider
CD,p,eff = CD,p + KpCL2
Drag Due to Lift · green · shifted by camber
CD,L = K1(CL - CL,c)2
Total Drag curve · black
CD = CDo + K1CL2 + K2CL

Conceptual—not-to-scale—drag buildup for instructional review.

Definition sources

  1. NASA Glenn Research Center, “Drag.”
  2. NASA Glenn Research Center, “Factors that Affect Drag.”
  3. Federal Aviation Administration, Pilot's Handbook of Aeronautical Knowledge, Chapter 5.
  4. Federal Aviation Administration, Flight Theory for Pilots, drag discussion.
  5. NASA, Research in Supersonic Flight and the Breaking of the Sound Barrier, Chapter 3.
  6. NASA Technical Paper 1805, definition of trim-drag increment.
  7. Daniel P. Raymer, Aircraft Design: A Conceptual Approach, p. 257 (classification framework and taxonomy-specific terms).