Lift myth debunked

Lift does not come from air parcels “meeting up” behind a wing. NASA says the equal-transit explanation is wrong; lift comes from pressure differences and the wing turning airflow downward. (nasa.gov 1) (nasa.gov 2) NASA’s Glenn Research Center says even a symmetric airfoil, with the same path length on top and bottom, can generate lift. Its explainer says both wing surfaces contribute to flow turning, and “no fluid, no lift” because lift is a mechanical force from contact with air. (nasa.gov) The Smithsonian’s National Air and Space Museum makes the same point in plainer terms: the visible downwash behind a wing is an effect of pressure differences around it, not a separate rival theory. In other words, Bernoulli and Newton describe the same flow from different angles when the explanation is done correctly. (si.edu) That matters because the bad classroom version is still common: air on top is said to move faster only because it has a longer path and must reunite at the trailing edge. NASA says experiments and simulations show the top-side flow often reaches the trailing edge first, which breaks the “equal transit time” claim. (nasa.gov) The same pressure-field picture also explains spoilers. NASA says a spoiler is a hinged plate on the top of the wing that flips into the airstream, disturbs the flow, increases drag, and decreases lift; airlines raise them after touchdown to dump lift and improve braking. (nasa.gov) The thread that revived the debate also veered into computational fluid dynamics, the software used to predict airflow around wings before wind-tunnel or flight tests. One camp pointed to lattice Boltzmann methods, which track how particle distributions stream and collide on a grid and are often used for unsteady, separated flows. (nasa.gov) (mdpi.com) NASA researchers compared lattice Boltzmann and hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation methods on separated-flow test cases in 2018. Their paper said both approaches were being evaluated inside NASA’s Launch Ascent and Vehicle Aerodynamics framework for the agency’s separated-flow benchmarks. (nasa.gov) RANS, the older workhorse method in aircraft design, still has a defined lane. A 2024 German Aerospace Center presentation said RANS remains necessary for clean-wing cruise design and steady adjoint optimization, while flows with “massive flow unsteadiness” may require hybrid RANS/large-eddy simulation methods instead. (dlr.de) Lattice Boltzmann advocates argue the method can handle detached turbulent flows and dynamic stall with less meshing pain on complex shapes. An Airbus-linked 2020 study using Dassault’s XFlow said the solver performed well on five detached-flow benchmarks, including a NACA0012 airfoil under dynamic stall conditions. (mdpi.com) So the online argument landed on two old aerodynamic lessons at once. Wings fly by building a pressure field that bends air downward, and the “best” simulation method still depends on whether the flow is mostly steady cruise or a messy, time-varying separation problem. (nasa.gov) (dlr.de)