Hi, well if this doesn’t prove how interesting stamp collecting is nothing will 🙂   This stamp I found in a kiloware packet I am sorting. Nothing really special in terms of value but how interesting to do some research. I found this picture (below) and in it you will see, third aircraft from the furthest end, the aircraft shown on the stamp.  
This picture taken around 1926 of some visitors to the DAR (State Aircraft Factory) at the airport Bozhurishte at the launch of the first mass-produced aircraft in Bulgaria. 

The stamp was issued in 1981 in a set of 6. It shows a Flugzeugwerke DFW CV biplane actually catalogued as SG 2951, under Bulgaria. 

If I have it correctly, this plane was from a family of German reconnaissance aircraft first used in 1916 in WW1. They were conventionally configured biplanes, as the picture clearly shows, but with unequal-span unstaggered wings and seating for the pilot and observer in tandem,

Have a great weekend, hope the weather is good if you are flying and if not, well I hope you enjoy your stamps.