P.Bowers Curtiss Aircraft 1907-1947 (Putnam)
R-2 - The R-2 model that appeared late in 1915, was an extensive refinement of the original Model R, The crew was now accommodated in two separate and widely-spaced cockpits, the tail was redesigned to use a fixed vertical fin and unbalanced rudder, and the undercarriage was redesigned, The wings took on the appearance of the JN-3 and short-wing N-8 by having the upper wing span increased to 45 ft 11 1/2 in (14 m), having the ailerons in the upper wing, and dihedral. Experiments were conducted on one example fitted with a propeller spinner and dual radiators installed on the side of the fuselage, The production versions retained the nose radiator and had an enlarged vertical tail with balanced rudder that established the shape for subsequent R-models into 1918.
Twelve of the improved R-2s were sold to the US Army in 1916 for $12000 each and some saw service with the Mexican Punitive Expedition. One hundred others were sold to the RFC; the original Curtiss V-X engines were replaced by 200 hp Sunbeam Arab IIs,
US Army serial numbers: 64/75, RFC serial numbers 3445/3544,
Observation aircraft. Pilot and observer. 160 hp Curtiss V-X.
Span 45 ft 11 1/2 in (14 m) upper, 38 ft 4 7/8 in (11,7 m) lower; length 24 ft 4 3/8 in (7,42 m); wing area 504,88 sq ft (46,9 sq m).
Empty weight 1,822 lb (826 kg); gross weight 3,092 lb (1,402 kg).
Maximum speed 86 mph (138,4 km/h); climb 4,000 ft (1,219 m) in 10 min; endurance 6,7 hr at cruising speed.
R-4 - Fifty-three R-4s ordered by the Army in 1916 were improved versions of the Army R-2s using later 200 hp Curtiss V-2-3 engines. Two more were purchased in 1917. Except for a redesigned tailskid in a more forward position and strut-connected ailerons in both wings, the R-4s were hard to distinguish from the R-2s. Some R-4s also entered Mexico with Gen Pershing's Punitive Expedition. Additional Army R-4s were ordered after the US entered the war but most were cancelled to allow maximum delivery to the Navy.
US Army serial numbers: 177/192 (16), 218/316 (36), 469, 2157, 37932
R-4L - Late in 1917 several of the large single-engined aeroplanes on hand in the Army and Navy were used as test beds for the US Government's new twelve-cylinder Liberty engine. An Army R-4 was among these and, when it was found that the new engine improved the characteristics of the aeroplane, a number of other R-4s were fitted with the Liberty and redesignated R-4L (L for Liberty). Twelve production R-4Ls were then ordered. Principal recognition feature, other than the larger engine, was the enlarged nose radiator similar to that used on the famous de Havilland 4.
US Army serial numbers: 39362/39367 (6), 39954/39959 (6)
R-4LM - After the US Army started to fly the new US Air Mail on 15 May, 1918, a need for aeroplanes with greater load capacity than the JN-4Hs then being used became apparent. At Army request, Curtiss converted six R-4Ls to R-4LM by adapting the front cockpit to a mail compartment with a capacity of 400 lb (181 kg).
R-4 - Observation landplane. Pilot and observer. 200 hp Curtiss V-2-1
Span 48 ft 4 5/32 in (14,73 m); length 28 ft 11 3/4 in (8,83 m); height 13 ft 2 1/4 in (4,02 m): wing area 504,88 sq ft (46,9 sq m).
Empty weight 2,275 lb (1,032 kg): gross weight 3,242 lb (1,470 kg).
Maximum speed 90 mph (144,83 km/h); climb 4,000 ft (1,219 m) in 10 min.
R-4LM - Single-seat mailplane. 400 hp Liberty.
Span 48 ft 4 5/32 in (14,73 m); length 29 ft (8,83 m).
Maximum speed 120 mph (193,11 kmjh); range 350 miles (563 km).
R-7 - A long-wing landplane that appears to be a development of the R-3 because of similar strutting. Powerplant was the same 200 hp Curtiss V-2-3 used in the R-4. The designation appearing in contemporary publications was in quotation marks as though it were in doubt; Curtiss identified the machine only as 'New York Times' since the single example had been sold to that newspaper. Flown by Curtiss test pilot Victor Carlstrom, it attempted a nonstop flight from Chicago to New York City in November 1916. The flight ended just short of the half-way point due to a fuel leak but still set a new US nonstop record of 452 miles (727 km). This date puts the 'R-7' ahead of the military R-6 model chronologically.
O.Thetford British Naval Aircraft since 1912 (Putnam)
CURTISS R-2 and R-4
Eighty-four delivered to the RNAS in 1915 (Nos.3445 to 3529) for reconnaissance duties. The type proved unsuccessful because its 160 hp Curtiss XV engine was unreliable and in British service was replaced by a 200 hp Sunbeam but a few are believed to have served for armament training duties until as late as 1918. Nos.3455 and 3459 went to the RNAS at Luxeuil and Nos.3462, 3463 and 3464 to Mudros.