Derived via the design of the Model 200 Monomail and Model 215 bomber, each of which had a cantilever monoplane wing, Boeing flew the prototype of a new civil airliner which was identified by the company as the Boeing Model 247 on 8 February 1933.
A streamlined low-wing monoplane, powered by two 550 hp Pratt & Whitney radial engines, it had retractable landing gear and was the first transport aircraft to have a de-icing system for wings and tail unit. Variable pitch propellers gave maximum efficiency for take-off and cruising flight, and control surface trim tabs enabled the pilot to 'balance' the aircraft so that an automatic pilot could control the machine for long periods. It was also the first twin-engined monoplane airliner able to climb with a full load on the power of only one engine.
With accommodation for a pilot, copilot, stewardess and 10 passengers, sixty examples of the Model 247 were ordered 'off the drawing board' to re-equip the Boeing Air Transport System, shortly to become a major limb of United Air Lines, and another 15 were ordered subsequently for companies or individuals.
The Boeing 247 entered service with United Air Lines in March 1933, with a trans-continental flight time of under 20 hrs. The Boeing 247 entered service with National Air Transport (one of the companies under the United Air Lines umbrella) on June 12, 1933. United took delivery of 59 of the 61 247s built, plus 10 of the 13 improved 247-Ds; earlier 247s were modified to this standard. The sole 247-A was used by the United Aircraft Corp as an executive aircraft.
One built for Roscoe Turner and Clyde Pangborn (to compete in the England-Australia 'MacRobertson' air race of 1934) was provided with fuselage fuel tanks instead of the standard airline cabin equipment, and introduced NACA engine cowlings (to reduce drag) and controllable-pitch propellers with optimum settings for take-off and cruising performance. These improvements were incorporated retrospectively on most airline Model 247s, thus elevating them to Model 247D standard.
When the USA became involved in World War II in late 1941, these Model 247Ds remained in airline use, and 27 of them were impressed for service with the USAAF under the designation C-73. It had been anticipated that they could be used for the carriage of cargo and troops, but it was discovered that the cabin doors were too small for this purpose. Instead, they were deployed to ferry aircrew and, later in the war, were used for training. In service they were provided with 447kW Pratt & Whitney R-1340-AN-1 Wasp radials. When no longer required in late 1944, they were returned to civil airline service.
NC13347 Boeing 247D, serial n°1729 of United Air Lines
Engines: 2 x 550 hp Pratt & Whitney Wasp
Length: 51.3 ft / 16.25 m
Wing span: 74 ft / 22.6 m
Weight empty: 8,340 lb / 3,780 kg
Pax cap: 10
Max cruise: 171 mph / 275 kph
Ceiling fully loaded: 18,500 ft / 5,650 km
Engines: 2 x Pratt & Whitney R-1340 Wasp S1H1-G, 550 hp, 410kW
Props: Hamilton Standard hydromatic
Wing span: 74 ft 0 in / 22.56 m
Wing area: 77.6 sq.m / 835.28 sq ft
Length: 51 ft 4 in / 16.25 m
Height: 12 ft 1.75 in / 3.7 m)
Empty weight: 4148 kg / 9145 lb
Max TO wt: 13,650 lb / 6197 kg
Max level speed: 202 mph / 324 kph
Cruise speed: 304 km/h / 189 mph
Ceiling: 7740 m / 25400 ft
Range: 1199 km / 745 miles
Pax cap: 10