Curtiss A-3

Last revised July 3, 2000

The Curtiss A-3 was an attack version of the O-1 Falcon two-seat observation aircraft of the US Army Air Service.

In 1924, the Army scheduled a competition for a successor to the aging DH-4Bs and DH-4Ms still serving with the Army Air Service. Since the Army still had a large number of surplus Liberty engines left over from the First World War, the War Department ordered that the competitors in the observation plane contest fit their first entries with this engine. The trials were to begin in November of 1924.

The Curtiss entry was the XO-1. The Curtiss XO-1 (serial number 23-1252) was powered by a 420 hp Liberty V-1650-1 water-cooled engine. The XO-1 was a fairly conventional two-seat biplane with a single bay on N-type interplane struts. The aircraft did have some unique fuselage construction techniques for its time--aluminum tubing bolted and riveted together with steel tie-rod bracing. The wings were wooden-framed with a wire trailing edge and the new Clark-Y aerofoil. The center section of the upper wing was placed well forward for good pilot access and visibility, so the upper wing panels had to be swept back nine degrees to achieve balance.

The Curtiss design took second place to the Douglas XO-2 in the 1924 observation plane contest. However, the Army was fully aware that the supply of surplus Liberty engines would not last forever, and in any case it was obvious that the Liberty was no longer suitable as a powerplant for future first-line military aircraft. Consequently, in 1925 another contest was held for observation types to be powered by the Packard 1A-1500, a more advanced V-12 liquid-cooled engine that was rated at 510 hp.

The conversion of the XO-1 to the Packard 1A-1500 was fairly straightforward. This time, the Curtiss design won the contest, and an order for ten production aircraft was issued under the designation O-1.

Unfortunately, the Packard engine did not live up to expectations, so the ten production O-1s (serial number 25-325/334) differed from the prototype in having the Packard engine replaced by the 435 hp Curtiss D-12 (V-1150) liquid-cooled engine. The D-12 was less powerful than the Packard engine, so the performance was poorer. In addition, the vertical tail surfaces were revised to increase the fin area and decrease the rudder area. The armament consisted of a single forward-firing 0.30-inch Browning machine gun in the engine cowling, and a pair of Lewis machine guns on a Scarff ring around the rear cockpit.

The O-1B was the first major production variant. Improvements included wheel brakes, a droppable 56-gallon belly tank, and provisions for dumping the fuel in the 113-gallon main fuel tank. 45 were ordered in 1927. Serial numbers were 27-243/287.

The A-3 (Model 44) was an attack version of the O-1B. The changes were fairly minor, and consisted of adding bomb racks underneath the lower wings and installing a single 0.30-inch machine gun in each lower wing outboard of the propeller arc. The A-3 was otherwise identical to the O-1B. The engine was the D-12D (V-1150-3) rated at 435 hp. A total of 66 A-3s were ordered on three contracts. Serials were 27-243/262, 27-298/317, and 28-83/108. The first A-3 was ready by October 31, 1927.

Six A-3s (27-306,310, 315, 28-116/118) were redesignated A-3A when fitted with dual controls for the training of observers.

The A-3B (Model 37H) which appeared in 1929 was an attack version of the later O-1E. The O-1E was an improved O-1B with the V-1150-5 engine. Refinements included refined engine cowling lines, balanced (Frise) ailerons, horn-balanced elevators, oleo-pneumatic shock absorbers, E-4 gun synchronizer system, and a 36-gallon belly tank. 78 attack equivalents of the O-1E were ordered under the designation A-3B (Model 37H) in two separate contracts. Serials were 30-1/28 and 30-231/280. The first A-3B was tested in April of 1930. A-3B 30-1 was converted to O-1E configuration.

Attack Falcons equipped all four of the Air Corps ground attack squadrons, the 8th, 13th, and 19th Squadrons of the 3rd Attack Group at Fort Crockett, Texas and the 26th Attack Squadron based in Hawaii. The last A-3B in service was 30-13, which was scrapped in October of 1937.

Specification of Curtiss A-3B:

Engine: One 435 hp Curtiss V-1150-5 twelve-cylinder liquid-cooled engine Performance: Maximum speed 139 mph at sea level, 136 mph at 5000 feet. Cruising speed 110 mph. Landing speed 60 mph. Initial climb rate 948 feet per minute. An altitude of 500 feet could be attained in 6.25 minutes. Service ceiling 14,100 feet. Absolute ceiling 16,100 feet. Range 628 miles. Dimensions: Wingspan 38 feet 0 inches, length 27 feet 2 inches. Height 10 feet 6 inches, wing area 353 square feet. Weights: 2875 pounds empty, 4458 pounds gross, 4476 pounds maximum. Armament: Four forward-firing 0-30-inch machine guns, two in the upper engine cowling and two the lower wings. A pair of flexible 0.30-inch machine guns were mounted in the rear cockpit. Up to 200 pounds of fragmentation bombs could be carried on underwing racks. Alternatively, a 56-gallon auxiliary fuel tank could be carried behind the tunnel radiator.


  1. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.

  2. United States Military Aircraft Since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian, 1989.

  3. Curtiss Aircraft, 1907-1947, Peter M. Bowers, Naval Institute Press, 1979.