Airfoil theory for unsteady motion has been developed extensively assu
ming the undisturbed medium to be of uniform density, a restriction ac
curate for motion in the atmosphere, Glauert (1929), Burgers (1935), T
heodorsen (1935), Kussner (1936), Karman and Sears (1938), Kinney and
Sears (1975). In some instances, notably for airfoils comprising fan,
compressor and turbine blade rows, the undisturbed medium may carry de
nsity variations or ''spots,'' resulting from non-uniformaties in temp
erature or composition, of a size comparable to the blade chord. This
condition exists for turbine blades, Marble (1975), Giles and Krouthen
(1988), immediately downstream of the main burner of a gas turbine en
gine where the density fluctuations of the order of 50 percent may occ
ur. Disturbances of a somewhat smaller magnitude arise from the ingest
ion of hot boundary layers into fans, Wortman (1975), and exhaust into
hovercraft. Because these regions of non-uniform density convect with
the moving medium, the airfoil experiences a time varying load and mo
ment which we propose to calculate.