Mahoney X-1 Special / Sportster
The 1928X-1 Special aka Sportster experimental lightplane was designed by Don Hall and first flown in September 1928 (piloted by Red Harrigan, registered NX7621). Power was an 80hp Siemens-Halske.
Repowered with 90hp Warner Scarab as a 1929 Safety Plane entry with a variable-airfoil wing ("no two ribs are alike") controlled by a lever in the cockpit. No fin or stabilizer, which were replaced by a large, moveable "stabilator" and a longitudinally adjustable 50 lb weight on a track to shift the c/g. All that resulted in enough stability problems to cancel the project.
Only the one was built, reportedly flown several times by Charles Lindbergh.
Wing span: 27'0"
Max speed: 135 mph