Flight, October 1924

THE STOUT "AIR PULLMAN"
America's First All-Metal Commercial 'Plane

   TESTS were recently completed at Selfridge Field, U.S.A., of America's first all-metal commercial aeroplane. This machine has been built by the Stout Metal Airplane Company, of Detroit, and the main objects of its design are safe and profitable air transport. To this end no attempt has been made to follow military design in any way, nor to build from old war-stock material for the sake of economy. In short, it has been specially designed for commercial work, and embodies some of the latest refinements in aeroplane design.
   The Stout “Air Pullman," as the passenger model is called - the freight or mail model being known as the "air truck" - is a cantilever monoplane, resembling in general appearance the well-known Fokker commercial monoplanes. As a matter of fact, however, the Stout monoplane differs considerably in construction from the Fokker. In the first place, it is built entirely of metal, mainly of duralumin in corrugated form - after the style of the Junkers - and, secondly, it differs in certain aerodynamical features, while its total weight comes out some 1,000 lbs. less.
   Fitted with a 400 h.p. "Liberty" engine, this machine, when tested by Test-Pilot Walter E. Lees, carried a useful load of 2,379 lbs. (including a pay load of 1,280 lbs. and fuel for 4 hours' flight) at a speed of 116 m.p.h., and climbed to 5,000 ft. in 12 minutes.
   The overall dimensions of this machine have been chosen to suit the greatest range of commercial use and the greatest variety of aerodromes possible with present-day conditions. The major items of design were laid out for the most possible hours per day in the air, with all assemblies and units so arranged that they may be instantly inspected and quickly replaced. For instance, it is claimed that it is possible to change the complete engine unit and fit a new one ready for flight in less than half an hour.
   It is a seven-passenger-and-pilot enclosed cabin machine, and the passenger cabin is equipped with six deep upholstered seats, with plenty of leg-room. At the front of the cabin, in full view of the passengers, are mounted an air-speed indicator and an altimeter. When required, the two rear seat pairs fold together to form benches on the side facing each other, with a table arranged between. Meals can be served on this table from a small galley located at the rear of the passenger cabin. Pivoted semi-circular windows give the passengers an excellent view all round and below.
   In front of the passenger cabin are two partitions about 3 ft. apart, enclosing a toilet and washroom. From this room it is possible to reach overhead to the luggage compartment, situated out in the wings. Here also the petrol tanks can be inspected, and every part of the petrol system up to the dashboard inspected or repaired during flight. The tanks are so arranged that in filling up no fuel can possibly be spilled into the wings. Right forward, below the leading edge of the wings, is the pilot's cabin, which has two seats side by side and dual control, and is fully equipped with all necessary navigating instruments, etc. The cabin is large enough to stand up in, and the pilot's wind-shield forms a part of the leading edge of the wing in such a manner as to interfere as little as possible with the latter's aerodynamical efficiency. The sides of the pilot's cabin are left entirely open, and the pilots who prefer it may fly "out of doors." Swinging windows are arranged, however, so that if required this compartment can be entirely enclosed. The pilot has a clear view forward and downward, although the wing obstructs his view upwards and to the rear.
   Very solid doors between the passenger cabin and the pilot's compartment form two bulkheads, while the dashboard forms a third between the engine and the rest of the fuselage. Very little engine vibration or noise therefore gets to the passengers.
   The wing, which is of thick section (being almost 3 ft. deep at the centre where the chord is about 12 ft.) is mounted on the top of the fuselage. It is divided into three sections, a centre-section secured to the fuselage by six large bolts from the three main spars, and two outer sections detachable for transportation purposes or replacement.
   The engine installation is very accessible, the base of the engine mount fastening to the fuselage being extra wide, giving great rigidity and at the same time placing the structural work far enough from the engine itself so that everything is get-at-able. The engine is a standard 400 h.p. Liberty model, but fitted with a new intake manifold which is the latest development of the Air Service. New heavy timing gears have also been fitted, and the new type lump-gap "Delco” distributing system. The generator is wound for 12 volts for a large battery, which not only takes care of the ignition, but a Bijur electric self-starter with which the plane is fitted, the foot button and controls being between the pilots so that either one can operate the engine. The engine is muffled by running exhaust pipes back along the sides of the fuselage to the rear of the cabin. These pipes are constructed of duralumin and drilled for a gradual muffling effect. Openings to the cabin furnish ample heating for winter work.
   The petrol system includes two aluminium tanks of 75 gals, capacity, each placed out in the wings 12 ft. apart and well above the engine so that gravity feed is used without the complication of pump or air pressure. All petrol lines are flexibly jointed with metal connections inside the rubber hose to prevent any parts working in, and they are also wound with tape and shellaced in the engine unit to prevent vibration. The water system with radiator and shutters is a unit with the engine mount, as is the entire oil system. The oil tank is supported under the engine just forward of the pump with a line running forward to join with a copper pipe which runs through inside the bottom part of the water radiator, giving about 4 ft. of pipe inside the water. In this way the oil is warmed in winter and cooled in summer to an approximate engine temperature.
   One of the special features of the Stout "Air Pullman" is the landing gear. This is of the divided type, without axle or cross tubes which would be likely to cause trouble by catching on weeds or long grass. The wheels have 8-ft. spacing, and spring individually with 12 in. of spring action, in addition to the cushioning effect of the 8-in. by 36-in, tyres. The shock-absorber chords are arranged externally on the fuselage at the top of struts leading from the wheel hubs, and work with a sliding guide plate. This landing gear gives exceptionally soft and smooth landing. Floats can be fitted in place of the wheels if required.
   This machine is particularly suitable for carrying mails along with express matter, a spacious compartment for mails being provided. With a load of 1 ton, it will make approximately 5 miles per gallon. The main characteristics of the Stout "Air Pullman" are :-
   Span 58 ft. 4 ins.
   Chord 7 ft..9 ins. to 12 ft 10 ins.
   Height 11 ft. 10 ins.
   O.a. length 45 ft. 8 ins.
   Wing area 600 sq. ft.
   Weight, empty 3,638 lb.
   Useful load 2,379 lb.
   Total weight 6,017 lb.
   Wing loading 9-85 lb./sq. ft.
   Power loading 14-8 lb./h.p.
   Speed range 53-116 m.p.h.
   Rate of climb 500 ft./min.
   Climb to 5,000 ft 12 min.
   Ceiling 12,000 ft.
   Duration (full speed) 4 hrs.