Three airplane engines from WW1, from left to right:
1912 60 hp Curtiss Model "S" - straight six
1914 200 hp Curtiss V2C10 - V8
1918 150 hp Kirkham - straight 6

Glenn Curtiss Museum-3867 by vcheng552000, on Flickr
1912 60 hp Curtiss Model "S" - straight six

Glenn Curtiss Museum-7513 by vcheng552000, on Flickr
1914 200 hp Curtiss V2C10 - V8

Glenn Curtiss Museum-7515 by vcheng552000, on Flickr

Glenn Curtiss Museum-7514 by vcheng552000, on Flickr