Jack N. Nielsen, Edward W. Perkins
naca-tn-1780
Dec 1948
Analytical expressions have been derived for the downwash throughout the entire induced flow field of lifting triangles of infinite chord with leading edges either in front of or behind the Mach cone.
An Adobe Acrobat (PDF) file of the entire report:
http://naca.central.cranfield.ac.uk/reports/1948/naca-tn-1780.pdf