Easy:
This is a Fokker Dr.I, on the picture (Dr. for Dreidecker=triplane) posted by Vanjast.
This flying replica on the picture, is fitted with an original overhauled Oberursel or Gnôme rotary engine, and is being piloted by Mikael Karlsson.
Here he's taking this Dr.I for a wild ride:
"Karlsson on the roof" is a swedish child's tale from Astrid Lindgren, if not connected to Mike K. of course:
http://en.wikipedia.org/wiki/Karlsson-on-the-Roof
Since a lot of those early planes ended up on roofs ..
https://www.flickr.com/photos/nlireland/5730990316/
http://flickrhivemind.net/Tags/bipla...sh/Interesting
http://www.dailymail.co.uk/news/arti...n-schools.html
Well maybe not soo easy i admit
Edit: Oh my god, i may just have killed the Funny picture thread with german humour