Sopwith Dolphin from the Front |
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The Sopwith 5F.1 Dolphin was a heavily armed and generally successful single seat fighter that was in service throughout 1918, but that was partly let down by an unreliable engine and as a result only equipped four squadrons on the Western Front.
The Dolphin differed from earlier Sopwith fighters in two main ways – the use of a 200hp Hispano-Suiza liquid cooled inline engine instead of the usual rotary engines and its backwards staggered wings.
The prototype had a large frontal radiator, with a tall, narrow shape, half above and half below the propeller. As a result the aircraft had a deep fuselage to fit the radiator.
The Dolphin had an unusual wing layout, with the upper wing further back than the lower wing, the reverse of the normal layout of a biplane. The position of the upper wing had been chosen to give the pilot as good a view as possible, and the lower wing had to be moved forward to provide balance. The two bay wings had about the same area as the Snipe and were larger than the Camel, giving it the ability to carry a heavier payload.
The upper wing was almost level with the top of the fuselage. The pilot’s cockpit was level with the upper wing, and effectively replaced any upper wing centre section. The metal tubes of the wing structure passed to the front and back of the pilot, and more tubes connected them, so the top of the cabin was surrounded by a square of pipes. The pilot sat with his head just above the upper wing, so the aircraft had a small windscreen on top of the front tube.
This layout was somewhat unpopular at first, because it was similar to the D.H.5, where it had gained a bad reputation for being dangerous in a crash, with no wing above the pilot to provide protection. In order to reduce the risk the aircraft was given easily removable panels on the side of the cockpit and crash pylons above the wing (above the inner struts) to keep the fuselage off the ground if it turned over.
The first prototype, with the nose radiator, made its maiden flight at Brooklands in May 1917 with Harry Hawker at the controls. In June 1917 it underwent official trials at Martlesham Heath, where it was found to be nose heavy. In mid June it was flown to St. Omer for service trials by H.T. Tizard (later Sir Henry Tizard of radar fame). The Dolphin performed well in these trials, proving to be more manoeuvrable than the S.E.5 and faster than the Sopwith Camel.
The main problem with the first prototype was the nose radiator, which despite its size was inefficient. On the second prototype the radiators were built into the wing roots of the upper wing, with fairings on top to carry air vents. With the radiator gone a more streamlined, pointed nose was produced. This also improved the pilot’s view, although some criticized it for making it harder for the pilot to fly level by removing the level section in front of the cockpit on most contemporary aircraft. A new fin and horn balanced rudderr was used. Gaps were cut in the lower wing to improve the view down.
The wing radiators were also a failure, so the third version of the aircraft had radiators on either side of the fuselage, near to the trailing edge of the wings. The fin was made larger. This was the point at which the aircraft’s armament was doubled. It kept the two synchronised forward firing Vickers guns in front of the cockpit, and now gained a pair of upwards firing drum fed Lewis guns, which were mounted on the front spar of the upper wing as it passed in front of the cockpit.
The fourth and final prototype, of October 1917, served as the pre-production machine. It kept the same radiators as the third prototype. The fuselage was cut down in front and behind the cockpit
The first production order, for 500 aircraft, was placed with Sopwith in late June 1917. Orders were later placed with the Darracq Motor Engineering Co Ltd and Hooper & Co Ltd, and eventually around 1,500 Dolphins were ordered, with 1,000 of those orders going to Sopwith. Production aircraft were similar to the fourth prototype, but with a slightly reduced 12in stagger between the wings and steel tube landing gear.
By the end of 1917 121 Dolphins had been delivered. The first squadron to receive the type on the Western Front was No.19, which converted to the Dolphin in 1918. It was followed by nos.79, 23 and 87, all of which operated the type to the end of the war. Major A.D. Carter of No.19 Squadron was the most successful Dolphin pilot, being credited with 31 victories in three months.
Another seven aircraft went to No.141 Squadron, which used it on home defence duties. Photographs show at least one of these aircraft armed with just a single Lewis gun, presumably to save weight and allow it to reach the height used by German raiders more quickly.
Those squadrons that received the Dolphin performed well with their new aircraft, which proved to be comfortable to fly, and performed well at altitude. In service it was common to remove one or both of the Lewis guns to save weight. However at No.87 Squadron Lt ‘Guns’ Knight produced a version in which the Lewis guns were mounted on the lower wings, firing outside the propeller arc, probably for ground attack use.
However the number of squadrons using it remained low because of problems with the geared Hispano-Suiza engine. This was a compact 200hp V-8 air cooled engine, produced in large numbers by several French companies, and under licence in Britain by Wolseley Motors Ltd. The engine was based on a 150hp direct drive engine, with reduction gear added and designed to provide 200hp at 2,000rpm. Wolseley built engines tended to have reliable reduction gear but unreliable crankshafts, while French built engines had reliable crankshafts but often had faulty reduction gear. There were also problems with the oil pump, which had been designed for the 150hp engine and didn’t always cope with the more powerful version.
By the end of the war three versions of the Dolphin had been produced in an attempt to solve the engine problems. The Mk I used the geared Hispano-Suiza engine. The Mk II used a new 300hp direct drive Hispano Suiza engine. The Mk III used a 200hp direct drive version of the Hispano Suiza engine.
The Dolphin was quickly phased out post –war with the last ones serving with the Army of Occupation at Bickendorf.
Five were bought for the American Expeditionary Force in October 1918, rather too late for any significant use.
Dolphin II
The Dolphin II was powered by a 300hp direct drive Hispano-Suiza V-8 engine. This was larger than the engine used on the Mk. I, and required more fuel. The Dolphin II was given a variable incidence tailplane to compensate for the changing centre of gravity as fuel was used up. It had a larger engine cowling to cover the larger engine. It was normally armed with the two Vickers guns only. The more powerful engine gave it a top speed of 140mph, up from the 121.5mph of the Mk.I. The Dolphin II entered production in France, and would have been used by the French and American air services, but none were completed before the end of the war.
Dolphin III
The Dolphin III used the same 200hp engine as the Dolphin I, but with the reduction gear removed. As a result the propeller rotated in the opposite direction. The Dolphin III was heavier than the Mk I, even when only carrying two guns, and was slightly slower and had a lower ceiling, but climbed slightly faster.
Dolphin Mk I
Engine: Hispano-Suiza geared liquid cooled in line engine
Power: 200hp
Crew: 1
Span: 32ft 6in
Length: 22ft 3in
Height: 8ft 6in
Empty Weight:
Maximum Weight: 1,959lb (four guns)
Gross Weight:
Maximum Speed: 121.5mph at 10,000ft; 114mph at 15,000ft
Cruising Speed:
Climb rate: 12min 5sec to 10,000ft; 23min to 15,000ft
Ceiling: 20,000ft
Endurance: 2 hours
Range:
Guns: two forward firing Vickers guns, two upward firing Lewis guns
Bomb load:
Dolphin Mk II
Engine: Hispano-Suiza direct drive in line engine
Power: 300hp
Crew:
Span: 32ft 6in
Length:
Height:
Empty Weight: 1,566lb
Maximum Weight: 2,358lb (two guns)
Maximum Speed: 140mph at 10,000ft; 133mph at 16,400ft
Cruising Speed:
Climb rate: 8min 20sec to 10,000ft; 12min 10sec to 16,400ft
Ceiling: 24,600ft
Range:
Guns: two forward firing Vickers guns
Bomb load:
Dolphin Mk III
Engine: Hispano-Suiza geared liquid cooled in line engine
Power: 200hp
Crew: 1
Span: 32ft 6in
Length:
Height:
Empty Weight: 1,466lb
Maximum Weight: 2,000lb
Maximum Speed: 117mph at 10,000ft; 110mph at 15,000ft
Cruising Speed:
Climb rate: 11min 20sec to 10,000ft; 21min 50sec to 15,000ft
Ceiling: 19,000ft
Range:
Guns: two forward firing Vickers guns
Bomb load:
Controls of Sopwith Dolphin 
Sopwith Dolphin D5263 
Sopwith Dolphin II from the front-left