The Curtiss R-4 was an improved version of the Curtiss R-2 observation aircraft, and was ordered in larger numbers by the US Army in 1916.
The Curtiss R-2 was an enlarged development of the Curtiss J and Curtiss N tractor biplanes. It was produced in 1915, and had uneven span wings, with a larger upper wing carrying the ailerons. The crew of two were carried in widely separated cockpits, with the pilot in the rear cockpit and the observer in the forward cockpit carried between the wings. This was an awkward arrangement for both men, with the observer’s view blocked by the wings, and the pilot’s view blocked by the observer, but it did mean that the aircraft’s centre of gravity remained the same when flown without the observer. Twelve R-2s entered service with the US Army in 1916.
These aircraft must have been satisfactory, for in 1916 the Army ordered another fifty-three aircraft, this time as the improved R-4. These were delivered with the serial numbers 177-192, 281-316 and 469.
The R-4 was very similar to the R-2, but was powered by a 200hp Curtiss V-2-3 engine, and had strut connected ailerons in the upper and lower wings. They also had a redesigned tailskid, which was moved forward. Some of these aircraft took part in General Pershing’s Punitive Expedition to Mexico, where aircraft generally failed to impress (often because they were operating in very harsh conditions with very limited facilities). More R-4s were ordered after the US entry into the war (serial numbers 2157 to 2192), but only 2157 was delivered before the contract was cancelled. One more aircraft, with the much later serial number 37932 was also delivered.
Late in 1917 one of the R-4s was used to test the new twelve-cylinder Liberty engine. The combination was a success, and a number of other R-4s were also given the new engine, becoming the R-4L. A further twelve R-4Ls were then built from new, with the serial numbers 39362-39367 and 39954-39959. Of these three later went to McCook Field for various experiments, where they were given the McCook designations P15, P20 and P27. Another batch of six was ordered (40012-40017) but the contract was cancelled before they were delivered.
In May 1918 the US Army began to operate an air mail service. It soon became clear that this required larger aircraft than the Curtiss JN-4Hs that were initially used, and as response Curtiss converted six R-4Ls to the R-4LM by converting the front cockpit into a small cargo compartment capable of carrying 400lb of post.
Engine: Curtiss V-2-3
Crew: 2 – pilot and observer
Span: 48ft 4 5/32in
Length: 28ft 11 3/4in
Height: 13ft 2 1/4in
Empty weight: 2,275lb
Gross weight: 3,242lb
Maximum take-off weight:
Max speed: 90mph
Climb Rate: 4,000ft in 10 minutes