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    Nicknamed the “Tommy," the Thomas Morse S-4 Scout was the standard single-seat advanced-trainer used by the US Air Service during World War I. The S-4 flew at practically every pursuit flying school in the United States during 1918 and was the first plane built specifically for this purpose. Most foreign governments used obsolete or war-weary airplanes for training, but since the Unites States had no pursuit aircraft of its own, it had to build advanced-trainers from scratch.

    It was designed by Benjamin Douglas Thomas (no relation to the company owners) who also assisted with the design of the Curtiss JN-4 Jenny. The Scout was a trim little single-seat, biplane that was originally powered by a 100 hp Gnome Monosoupape 9-B rotary engine, but beginning with the fifty-second aircraft, the engine was replaced with the more reliable 80 hp (60 kW) Le Rhône C-9. The first flight was in June 1917 and it attained a speed of 95 mph (153 km/h). The first order was for six prototypes and on October 3, 1917, 100 improved S-4Bs were ordered and an additional 25 aircraft were ordered for Britain.1

    It could be easily converted into a seaplane and it was given the US Navy designation S-5. It was identical to the S-4B, but the top speed was reduced to 90 mph (145 km/h).2 It was tested at the Naval Air Station at Diner Key, off Miami, Florida and six S-5s with floats were ordered for the US Navy.

    On January 18, 1918, the US War Department placed an order for 400 improved S-4C models. Instead of using cables for the ailerons, the C model used a torque tube system, the ailerons and elevators were reduced in area and provisions were made for a .30 caliber Marlin machine gun, synchronized to fire through the propeller, although not all aircraft were delivered that way. A total of 447 S-4Cs were built.3

    The S-4C was of standard construction with a wire-braced wooden frame fuselage, fabric covered with a round top decking. It was a single-bay airplane with wooden interplane struts, braced by wire. The center section struts were slightly splayed outwards. The wings were staggered, fabric-covered, wood construction with a semicircular cut-out in the trailing-edge of the top wing to improve visibility. The top wing was flat and the lower wing had slight dihedral. Ailerons were installed on the top wing only and were operated by a torque tube system. The empennage was wood framed and fabric covered. Wooden vee struts formed the undercarriage legs and the wheels were sprung with rubber bungee cord. The engine was partly enclosed by a circular open-fronted cowling, which was faired into the flat-sided fuselage by triangular fillets.4

        The controls of the Tommy were very sensitive and in flight, it was very tail heavy. To keep the aircraft level, the pilot would have to constantly push forward on the control stick, which was very tiring for the pilot. The torque of the rotary engine made it difficult to loop and takeoffs were tricky until airspeed built up to allow rudder control. There was no carburetor and the engine ran only at full speed. In order to land, the pilot would have to 'blip' the engine (cut ignition) to reduce power.

    The last single-seat model was the S-4E and was the most attractive. It was a highly maneuverable aerobatic trainer and had short tapered wings and a mounting for a synchronized gun. It was powered with 110 hp (82 kW) Le Rhône rotary engine. It had a top speed of 104 mph (167 km/h) and could climb to 7,000 ft (2,134 m) in 10 minutes.5 The S-4E remained a prototype and never went into production.6

    After the war ended, the Air Service sold them as surplus to civilian flying schools, sportsman pilots and ex-Army fliers. Some were still being used in the mid-1930s for Hollywood WWI aviation films.

    Postwar variants included the S-6, S-7 and S-9. These had two seats, either in tandem or side-by-side. The S-9 was powered with a Wright J-3 radial engine. The total production of all S-4 models was less than 500 aircraft.

Thomas-Morse S-4C Scout
Top Wing span: 26 ft 6 in (8.07 m)
Bottom Wing Span: 25 ft 6 in (7.77 m)
Top Chord: 5 ft 6 in (1.67 m)
Bottom Chord: 4 ft 3 in (1.29 m)
Gap Between Wings: 4 ft 6 in (1.37 m)
Length: 19 ft 10 in (6.06 m)
Height: 8 ft 1 in (2.46 m)
Empty: 961 lb (435 kg)
Gross: 1,354 lb (614 kg)
Maximum Speed: 100 mph (160 km/h) @ sea Level
Service Ceiling: 15,000 ft (4,572 m)
Fuel Capacity: 27 gal (102 lt)
One 100 hp (74 kw) Gnome Mono 9-cylinder rotary engine or
one 80 hp (59 kw) Le Rhône 9-C 9-cylinder rotary engine.
One synchronized .30 caliber Marlin machine gun.

1. Frank Strnad. Aircraft in Profile: Volume 3; The Thomas Morse Scouts. Garden City, New York: Doubleday & Company, Inc., 1968. 4.
2. Fay L. Faurote, ed. Aircraft Year Book 1919. New York: Manufacturers Aircraft Association, Inc., 1919. 255.
3. Ray Wagner. American Combat Planes. Garden City, New York: Doubleday & Company, Inc., 1892. 42.
4. E. F. Cheesman. Fighter Aircraft of the 1914-1918 War Los Angeles: Aero Publishers Inc., 1964. 12.
5. Fay L. Faurote, ed. 258.
6. Kenneth Munson. The Pocket Encyclopedia of World Aircraft in Color. Fighters 1914-19. Attack and Training Aircraft. New York: The MacMillan Company, 1969. 148.

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©Larry Dwyer. The Aviation History Online Museum. All rights reserved.
Created October 3, 1997. Updated November 17, 2013.