Airfoil Shapes Explained: Are Modern Jet Wings Really 'Curved on Top, Flat on Bottom'?

Direct Answer: Modern Jet Aircraft Are NOT "Curved on Top, Flat on Bottom"

① Commercial Jet Airliners (Boeing 787, Airbus A350, COMAC C919): Utilize supercritical airfoils with a remarkably flat upper surface (suppressing supersonic shock waves), while the lower rear section features a pronounced downward concave cusp (aft-cambered).
② Supersonic Jet Fighters (F-16, F-22, J-20): Feature razor-thin, nearly symmetrical airfoils, generating dynamic lift primarily by deflecting air downward via Angle of Attack (Newton's 3rd law).
③ The traditional "curved top, flat bottom" model is only found on low-speed general aviation props (e.g., Cessna 172) or early biplanes.

Interactive Airfoil Wind Tunnel & Flowfield Simulation

Switch airfoil types to observe streamline patterns, pressure gradients, and aft-camber downwash

Modern Supercritical Airfoil

Flattened upper crest (delays shock wave) · Lower aft concave cusp

Examples: Boeing 737MAX/787, Airbus A320neo/A350, COMAC C919

Cruise Mach Ma 0.78 ~ 0.85

Trailing Downwash Strong Downwash

Shock Wave Drag Rise Superior (Flat Crest)

Angle of Attack (AoA: +3.0°) -5° ~ +15°

Tunnel Flow Velocity Cruise Speed

Deep Dive into 3 Generations of Wing Profiles

Why do aircraft at different flight regimes possess such dramatically different wing geometries?

Low-Speed / Classic Teaching

Traditional Low-Speed Airfoil

Clark-Y or NACA 4-Digit Conventional Profile

Geometry: Classic "curved top, flat bottom", rounded leading edge, maximum thickness at ~30% chord.
Low-Speed Advantage: High maximum lift coefficient at low speeds, gentle stall characteristics, generous internal volume for fuel.
Why Modern Jets Don't Use It: Near Mach 0.8, the curved upper surface excessively accelerates airflow beyond Mach 1, generating a severe local supersonic shock wave that causes massive wave drag and buffeting.

WWII piston fighters (P-51 Mustang), Cessna 172 general aviation, RC model airplanes, low-speed trainers.

Modern Jet Airliner Standard

Supercritical Airfoil

The Core Aerodynamic Breakthrough of Transonic Civil Jets

Geometry: Upper surface is flattened to avoid excessive acceleration, while the lower rear surface has a distinct concave scoop (aft camber).
Why Flatten the Top?: Keeps local supersonic expansion gentle, pushing the onset of shock waves to higher Mach numbers and weakening shock strength.
How It Recovers Lift: The lower aft scoop forces high-pressure air downwards at the trailing edge, generating powerful aft-camber downwash lift.

Boeing 737/777/787, Airbus A320/A330/A350/A380, COMAC C919 & ARJ21.

Supersonic / Stealth Fighters

Thin Symmetric / Biconvex Airfoil

Supersonic Interceptors, Multirole Stealth Fighters

Geometry: Ultra-thin profile with razor-sharp leading edge, strictly or nearly symmetrical on top and bottom.
Supersonic Rationale: Supersonic flight produces severe oblique bow shocks. A knife-like thin cross-section minimizes wave drag so engines can sustain supersonic cruise.
How Symmetrical Wings Generate Lift: Entirely through Angle of Attack (AoA)! Pitching up by 2° to 6° physically deflects incoming air downward, producing lift via Newton's third law.

F-16 Fighting Falcon, F-15 Eagle, F-22 Raptor, Su-27/35, J-20, Concorde SST.

Debunking the Myth: "Equal Transit Time Fallacy"

Introductory physics books often claim: "Air over the curved top travels a longer distance and must meet air from the bottom at the trailing edge simultaneously, forcing it to move faster and lower pressure."

This is widely recognized by aerodynamicists as a complete fallacy!

Wind tunnel particle tracking proves that air passing over the top travels vastly faster than required by equal transit time, reaching the trailing edge far ahead of lower air. Even a perfectly flat board angled into the airflow produces substantial lift — as demonstrated by every paper airplane ever folded.

The Two Pillars of Real Aerodynamic Lift

Modern fluid dynamics explains lift through two unified physical frameworks:

① Newton's Third Law (Momentum & Downwash): An airfoil imparts a net downward momentum on the massive volume of air passing around it (Downwash). The reaction force exerted by the air onto the wing is aerodynamic lift.

② Navier-Stokes & Coandă Effect: Viscous fluids naturally adhere to curved boundaries. Wing geometry combined with angle of attack induces circulation, generating an intense suction field (negative gauge pressure) over the upper surface.

Multi-Dimensional Comparison of 3 Wing Profile Classes

Comparison Dimension	Traditional Low-Speed Airfoil	Modern Jet Airliner (Supercritical)	Supersonic Fighter Airfoil
Upper Surface Profile	Pronounced convex camber	Flattened crest (suppresses local Mach acceleration)	Thin, flat or slightly convex with sharp leading edge
Lower Surface Profile	Nearly flat or slightly convex	Pronounced aft concave scoop (aft-camber cusp)	Symmetrical or near-identical to upper surface
Relative Thickness (t/c)	Thick (12% ~ 18%)	Moderate (10% ~ 14%), ample fuel volume	Ultra-thin (3% ~ 6%)
Cruise Velocity Regimes	Mach 0 ~ 0.5 (Subsonic)	Mach 0.75 ~ 0.86 (High Transonic)	Mach 1.2 ~ 2.5+ (Supersonic)
Shock Wave Management	No shock mitigation; explosive wave drag rise	Delays shock onset and minimizes shock intensity	Pierces shocks via knife-edge sharpness & thinness
Primary Lift Mechanism	Low-speed upper curvature suction	Upper suction + lower aft downwash pressure	Angle of Attack forced downwash (Newtonian reaction)