During aviation’s multiwing era, the triplane gained little traction in the United States. Major American manufacturers built only about 50 of them.
The British had the first successful version of the type with the Sopwith Triplane, which entered combat in December 1916. “B” Flight, No. 10 Naval Squadron, Royal Naval Air Service, had great success flying the “Tripe.” Over a three-month span, the flight’s five pilots flying black-painted (cowling, wheel covers, and tail) Tripes shot down 87 German aircraft. The all-Canadian unit, famously known as the Black Flight, was commanded by Raymond Collishaw, who claimed 34 of his eventual total of 60 victories while flying the aircraft.
Although 147 Sopwith Triplanes were built, just seven months after they began entering service the type was superseded by Sopwith’s famous Camel. The Tripe’s combat service life lasted exactly one year.
The triplane’s performance impressed the enemy. In April 1917, no less than Germany’s top ace, Manfred A. F. von Richthofen, deemed the Sopwith Triplane the best Allied fighter of its time. The Central Powers built as many as 34 triplane prototypes. One, the Fokker V.4, evolved into the most famous triplane of all, the Fokker Dr.I. In March and April 1918, the “Red Baron” cemented the Fokker Dreidecker in aviation history. Over those two months Richthofen claimed 17 of his 80 victories flying four Dr.Is before being shot down and killed on 21 April. Earlier, in September 1917, he had tallied two victories flying the Fokker F.I, a preproduction Dr.I.
The Dr.I’s service life was as short as its British opposite, entering combat evaluation in September 1917 and being withdrawn from the front lines in June–July 1918. A total of 320 Dr.Is were built.
In the United States, Glenn H. Curtiss constantly was experimenting with his aircraft designs, always looking for ways to improve performance and capability. The triplane configuration was not ignored, and Curtiss built at least 28 American examples. His experiments with the configuration spanned from among his earliest aircraft in 1912 to 1921.
The most famous Curtiss triplane—if indeed any American triplane can be termed famous—would have to be the 18-T (Model 15). With just four of the type built, that airplane and the Army’s S-3 Triplane Speed Scout were the most numerous of Curtiss’s triplane designs. (The largest set of American triplanes consisted of ten Boeing GA-1s [Model 10] built for the U.S. Army in 1920.) Two 18-Ts went to the Navy, and two went to the Army; one of the latter pair would become the Bolivian Air Force’s first aircraft.
The Navy’s Bureau Numbers A-3325 and A-3326 had perhaps the most stellar careers not only of their design, but also among U.S. triplanes. They were experimental in the most basic of terms. Both flew with short- and long-span wings, as landplanes and seaplanes, and as single and dual seaters. Their record cards are rife with crossed-out designations as configurations were mixed and matched. In their prime, A-3325 was the world’s fastest and highest-flying aircraft.
Curtiss specifically built the 18-T, originally named the Kirkham Fighter but known as the Wasp, around the lightweight K-12 engine designed by Charles B. Kirkham. Weighing 695 pounds, the V-12 engine produced 465 horsepower. In comparison, the widely used and thus more famous Liberty engine weighed 872 pounds and generated a maximum of 430 horsepower.
In early 1918, when the 18-T was designed, the so-called battleplane concept was highly regarded. This was a heavily armed, two-seat defensive fighter that was also fast and nimble enough to be on an equal footing with single-seat fighters. The Bristol F.2B Brisfit is an example. The 18-T design included two forward-firing .30-caliber Marlin machine guns synchronized to fire through the propeller arc, a pair of .30-caliber Lewis guns mounted on a Scarff ring for the gunner in the rear seat, and a single Lewis firing through a belly hatch.
Although a bit rotund, the 18-T had a smooth fuselage, with a molded plywood monocoque shell nailed and glued to an internal framework. Although appearing conventional, the wings, of equal size, had no internal ribs to form an airfoil shape. Seven thick span-wise spars capped with strips provided the shape. As designed, the prototype (later A-3325) proved tail heavy, thus the wings were swept back 5 degrees after its first flight on 5 July 1918.
On 30 March 1918, the Navy had ordered two 18-Ts, the first American-designed fighters purchased by the service. The triplane checked speed and maneuverability boxes. At a time when the air speed record was 134.5 mph, Curtiss factory pilot Roland Rohlfs flew the 18-T at 163 mph on 19 August, although it was not officially recognized. But the Navy was not enamored with the three-wing layout, complaining it rendered the aircraft inadequate as a gun platform and severely hampered visibility.
Having completed its tests with A-3325, the Army agreed with the Navy’s conclusions. But it ordered a pair of 18-Ts along with two biplane versions, 18-Bs, with 37-foot, 5¾-inch wings compared with the triplane’s 31-foot, 11-inch wings. The 18-Ts were serials AS 40054 and AS 40059. The first was used as a static airframe; the second languished at Curtiss’s Long Island factory and was never delivered to the Army. Of the 18-B Hornets, the first, AS 40058, was used for static testing, and the second, AS 40064, crashed soon after delivery, effectively ending the Army’s work with the 18-B/T design.
The Navy, however, continued its work with its duo. They were fitted with a new set of double-bay wings, which extended the wing span to 40 feet, 7½ inches. This allowed them to be flown with floats from Curtiss N-9 seaplane trainers. Designations were changed once again to 18-T-1 for mounting of the short-span single-bay wings and 18-T-2 for the larger wings. Rohlfs flew a series of tests for the Navy beginning in March 1919 with A-3325 in the 18-T-2 landplane configuration. He set two Fédération Aéronautique Internationale (FAI) world records for altitude with heights of 30,318 feet on 30 July and 31,421 feet on 18 September.
The Bolivian government expressed interest in the 18-T-2 to operate from the country’s high-altitude airfields. The second Army triplane, the undelivered AS 40059, was sent south in May 1920, with Curtiss pilot Donald Hudson to demonstrate it. Based on his display, Bolivia bought the airplane and created its air force on the spot, naming Hudson its chief pilot. A year later, Bolivia’s air force ceased to be when the triplane, piloted by Hudson, crashed. He was unhurt.
Meanwhile, in April 1920, Rohlfs flew A-3325 with long wings and floats to a speed of 138 mph. That November both Navy triplanes were fitted as 18-T-1 landplanes to compete in the first Pulitzer Trophy Race at Mitchel Field, Long Island, New York. Lieutenant Commander Willis B. Haviland flew A-3325 and was fourth fastest of 34 entrants when his plane was forced down with a fuel issue. Marine Lieutenant W. D. Culberson in A-3326 flew the fastest first lap but made a forced landing on the fourth lap with a broken connecting rod.
The airplanes were moved to the Naval Aircraft Factory in Philadelphia, where they were modified to accommodate the new direct-drive 405-horsepower CD-12 engine with a four-blade Charavay propeller, instead of the K-13 and its two-blade version. In the 18-T-1 floatplane configuration with an added ventral auxiliary stabilizer, the planes were entered in the Curtiss Marine Flying Trophy Race during the National Airplane Races of the Detroit Aviation Meet on 8 October 1922. Aviation magazine (predecessor to today’s Aviation Week & Space Technology), noted that the aircraft “are believed to be the only triplanes in the country and are of considerable technical interest on this account.”
Navy Lieutenant Rutledge Irvine and Marine Lieutenant Lawson H. Sanderson flew A-3325 and A-3326, respectively. The eight competitors flew an eventful race. A-3325, which had been leading going into the sixth lap of the eight-lap contest, spectacularly crashed into a coal pile. Irvine escaped unhurt. Sanderson in A-3326 led at the start of the last lap but ran out of fuel within sight of the finish line. He flew a notable race, climbing from sixth place at the start to take the lead while also setting the fastest lap at 125.5 mph.
Of the four 18-Ts and two 18-Bs constructed, only A-3326 remained. It had just one more appearance, at the 1923 National Air Races at St. Louis, Missouri, on 4 October. The event was the 300-kilometer (186.4-mile) Liberty Engine Builders’ Trophy Race. Ensign D. C. Allen, with Chief Machinist’s Mate T. G. Hughes in the gunner’s position, flew the bright yellow triplane, but the crankshaft broke on the first of five laps, and the aircraft flipped during an emergency landing in a soggy field. Muddied but not bloodied, the crew emerged from what remained of the last Curtiss triplane.
Sincere thanks to Pam Thomas, research section volunteer at the National Naval Aviation Museum, for her invaluable assistance.
