LinAir calculates the aerodynamic characteristics of one or more (up to eight) lifting surfaces. The wings may be tapered, twisted, and swept with any dihedral angle. See the figure below for an example configuration. The input data may be specified interactively or read from a standard, easy-to-read text file. The program then computes the lift, drag, pitching moment, and lift distribution over each element. The angle of attack, twist, incidence angles, etc. may then be changed in order to trim the aircraft, to minimize drag, or simply to examine the effects of various design changes. The program permits up to 40 spanwise panels on each linearly tapered and twisted surface. Results may be viewed on the screen, printed, or saved to a Plot file for later plotting.

The program represents the lifting surfaces with discrete horseshoe vortices with strength determined by solution of a linear system of equations. Forces and moments are computed based on the velocities in the Trefftz plane, resulting in rapid turn-around and accurate induced drag (to within about 2%-4%). The effect of Mach number (in subsonic flow) is included as the program solves the Prandtl-Glauert equation. Parasite drag of the airfoil sections may be included with a quadratic curve fit of section drag vs. local ClÑthe program integrates the profile drag along the span and includes this in the total drag.

The program is ideal for computing the basic aerodynamics of a single wing or the interference of a wing and canard system, the effect of winglets on induced drag, or the tail size required for a given stability level. By placing several wing elements right behind each other, the effect of camber or control surface deflections can be evaluated. LinAir is used at NASA for quick analysis of unconventional configurations, at many major airframe companies, and several universities.