Which aircraft is depicted on 1941 U.S. Post Office airmail stamps? Between June 25, 1941 and October 29, 1941 a tri-tailed “Twin Motored Transport Plane” was featured on U.S. airmail stamps in 6-, 8-, 10-, 15-, 20- and 50-cent dominations.


Source

Was the aircraft featured on those stamps an actual aircraft, or was it a Postal Service graphic artist’s conceptualization of one?
It appears to be only an artist's conception and is an amalgam of several different designs, but apparently largely based on the Douglas DC-3 aircraft, the Lockheed Electra, and the Beech 18.



The livery bears a striking resemblance to American Airline's DC-3 sleeper service, which operated during that era.



http://usstampgallery.com/view.php?id=1021c6191539bc1ca404bccf78595b7fdc0f06fd