The Curtiss R-6 was a twin float observation plane that was a more powerful version of the earlier R-3, and that was the first US Navy aircraft to see service overseas.
The R-3 was the first float plane version of the Model R. In order to compensate for the extra weight of the floats both wings were lengthened, with the upper wing getting a new centre section and the lower wings having a panel between the fuselage and the original wing. The innermost struts were moved from the edge of the fuselage to a position, turning the two bay wings of the R-2 into a three bay wing. The R-3 was powered by a 160hp Curtiss V-X engine.
Like the R-3, the R-6 was a three bay biplane, with unequal span wings. The two main differences were that the outer panels of both wings had three degrees of dihedral, and it was powered by a 200hp V-2-3 engine. Otherwise it used the same straight edges wing, undercarriage and fuselage, with the two crewmen in separate cockpits. The pilot sat in the rear cockpit, while the observer sat in the forward cockpit, which was between the wings. This was an awkward setup, but it meant that the aircraft’s centre of gravity remained the same if the observer wasn’t carried, as he was sitting close to the centre of gravity.
The Army placed two orders for the R-6, with serial numbers 505-521 (17 aircraft) and 2193-2264 (72 aircraft). The first order appears to have been modified from one for eighteen Curtiss R-3s, of which the first was delivered as that model. However only aircraft 505-508 from the first order were delivered to the Army. The contract for 509-521 was cancelled and the aircraft diverted to the US Navy, and the entire contract for 2193-2264 was cancelled. This gave the army four R-6s. Two more were sold to the Army by the US Navy on 1 July 1917 (A166 and A167)
The Navy received seventy-six R-6s, giving them the serial numbers A162-A197 and A302 to A341, suggesting that the original Army order was expanded and at least one extra order placed. As mentioned above, two aircraft from the first batch were sold to the US Army.
The R-6 was followed by the very similar R-9, which was structurally identical, but with the pilot moved to the front cockpit and the observer to the rear cockpit.
In 1918 forty of the R-6s were modified to use the more powerful 360hp Liberty engine, becoming the R-6L. Another fourteen R-6Ls were converted from R-9s, although it isn’t clear of the cockpits were swapped back at the same time. With the new engine the top speed rose to 100mph.
Most of the Navy’s R-6s had fairly short careers. They began to enter service in the spring of 1917, and quite a few had been struck off charge by the end of the year. More went in 1918. During this time most of them were scattered around the US coast, serving at various naval air stations. Some were also allocated to the cruiser USS Huntingdon, which was used for experiments with naval aviation.
The R-6 was the first US Navy aircraft to see service overseas. A334, A335, A336, A337 and A338 were assigned to the Marines Air Base No.13 on the Azores after the US entry into the First World War.
However some examples did have fairly lengthy careers. A168 wasn’t struck off until 1926, despite being considered as having been damaged beyond repair in November 1917! By the time it was struck off the aircraft had a total flying time of 276 hours, 35 minutes. A331 sank while being towed to shore at Pearl Harbor in 1926. A330 was struck off in 1926 with 260 hours, 15 minute son the clock. A341 was struck off in 1926 with 292 hours, 45 minutes on the clock.
The R-6L was also used for experiments with aerial torpedoes in 1920. The aircraft could carry one 1,036lb torpedo, raising its gross weight from 4,634lb to 5,662lb. The R-6L was then used as a service torpedo bomber until more powerful aircraft were available. The converted R-9s were also used as torpedo bombers.
Crew: 2 – pilot and observer
Span: 57ft 1 3/16in
Length: 33ft 5in
Height: 14ft 2 1/32in
Empty weight: 3,513lb
Gross weight: 4,634lb/ 5,662lb with torpedo
Maximum take-off weight:
Max speed: 100mph
Climb Rate: 6,000ft in 10 minutes
Service ceiling: 12,200ft
Range: 565 miles
Armament: One 1,036lb torpedo