Northrop proposed 4-engine bomber version, XB-35; 2 prototypes and 13 service evaluation aircraft ordered. Also part of order were 4 60 ft flying scale models (about 1/3rd scale) which Northrop designated N9M. Each weighed about 7100 lbs and had 300 hp Franklin engines. Serious problems encountered in designing propellers which had to be able to rotate in either direction. First flight of XB-35 prototype 25 Jun 46. By this time, jet age had arrived and Air Force decided to convert 35s to 8-engine jets designated YB-49. YB-49 made first flight 21 Oct 47; officials working on project called it one of the most trouble-free and ready-to-fly bombers ever received. After more testing, 30 ordered but order was later cancelled in favor of buy of B-36s. Instability typical of flying wings influenced Air Force's decision.