We can't possibly let this page go by without bringing to light the reason for this promising design's miserable performance. According to Wm. Green's book "Famous Bombers of the Second World War", Volume 2, (Hanover House,1960)the government's design specification required that the wingspan be less than the 100-foot wide door opening of standard R.A.F. hangers. The resulting low-aspect ratio wing of 99-ft 1 inch span with its high induced drag had the expected adverse effect on performance. The maximum loaded service ceiling was thus only 16,500 ft, forcing pilots who were attacking targets in Italy to fly through the Alps rather than over them! Not only that, but the size of the fuselage cross-section was dictated by the size of standard packing cases! The design of its bomb bay, divided into three longitudinal cells by two strengthening girders, prevented the carrying of the really large "blockbuster" size weapons which came into use later in the war. Another drawback was the mid-mounted wing. Though offering certain advantages in flight, the mid-wing location required an exceptionally tall undercarriage that resulted in a tendency of the loaded aircraft to swing dangerously on takeoff, especially on muddy grass fields. Only 2,375 Stirlings were ever built owing to the impossibility of modifying the design to meet the later wartime requirements.
The figures given above are for the half-scale flyable model built to perform certain aerodynamic tests and are, naturally, scaled down. The actual dimensions of the Stirling were:
Span: 99 ft. 1 inch
Length: 87 ft. 3 inches
Height: 22 ft. 9 inches
Wing area: 1,460 sq. ft.
Engines: Four Bristol Hercules XI 14-cylinder sleeve- valve, double-row, radial air-cooled engines rated at 1,590 hp for takeoff.
Weight: 59,400 lb. normal loaded; 70,000 lb. max. permissable.
Max. speed: 245 mph at sea level; 260 mph at 10,500 ft; Economical cruising speed: 200 mph at 15,000 ft
Range: 1,930 miles with 5,000 lb bombload; 740 miles with 14,000 lb bombload.