Supermarine S.6

Supermarine

Industry	Aerospace
Founded	1913 (1913)
Headquarters	Southampton , United Kingdom
Products	Aircraft

The Supermarine S.6—subsequently known as the S.6A—was a British single-seat, single-engine racing seaplane developed in the late 1920s by Supermarine. Its design was an evolution of the earlier Supermarine S.5, refined by chief designer R.J. Mitchell to create a larger and more powerful aircraft. Two units, registered as N247 and N248, were constructed specifically for competition in the 1929 Schneider Trophy race. The powerplant was the Rolls-Royce R engine, crafted by Rolls-Royce Limited for this all-metal seaplane. Initial challenges with the engine—such as limited overhaul intervals and excessive heat output when boosted to 1,900 hp (1,400 kW)—were addressed within months before assembly was completed at Supermarine’s Woolston facility in Southampton.

On the eve of the 1929 competition, a defect was detected in one of N247’s pistons, which was replaced overnight. The following day, the British team secured victory with N247 achieving a top speed of 328.63 miles per hour (528.88 km/h). Meanwhile, N248 established new world closed-circuit records over distances of 50 and 100 kilometres. For the subsequent 1931 event, the S.6 underwent redesign into the Supermarine S.6B, incorporating an enhanced version of the R engine. Both original S.6 aircraft were upgraded to align closely with the S.6B’s specifications; however, N247 was lost due to a fatal accident prior to the race. After the 1931 contest, the S.6B models were retired from service. Today, the remaining S.6A is preserved and exhibited at the Solent Sky museum in Southampton.

Design and development

drawing of the S.6 with labels

An illustration of the S.6 from Popular Mechanics (December, 1929)

Building on the achievements of the Supermarine S.5 in the 1927 Schneider Trophy competition, Supermarine's lead designer, R.J. Mitchell, developed its successor, the Supermarine S.6, in response to Specification 8/28. Mitchell enhanced the earlier S.5 design by creating a larger aircraft constructed entirely from metal. The wings featured an aluminium framework aimed at reducing overall weight. To generate the necessary lift, the wingspan was extended by approximately 3 feet (0.91 m) compared to the lighter S.5 model.

During World War I, nearly all seasoned spruce, critical for wooden aircraft construction, had been depleted worldwide, prompting the British government to prioritise the development of metal aircraft for future military needs.

A notable advancement introduced by Mitchell was the integration of duralumin radiators along the wing surfaces. These radiators were engineered to endure forces that could induce wing twisting while also reducing aerodynamic drag. Constructed from two metal layers allowing coolant flow between them, they enhanced both cooling efficiency and structural integrity.

Rolls-Royce R engine

Main article: Rolls-Royce R

As Supermarine considered the existing 875 horsepower (650 kW) Napier Lion VIIB engine unsuitable for further refinement, the British Government authorized Rolls-Royce in February 1929 to develop the R engine specifically for Supermarine's use. This powerplant was a modified version of the Rolls-Royce Buzzard, completed by 4 May; however, initial tests revealed overheating after just 15 minutes of operation. By mid-July, many early issues had been addressed, although valve reliability remained problematic. The engine's time between overhauls was extended to five hours through fuel dilution, and its output increased to 1,900 horsepower (1,400 kW) at 3,000 rpm. Fuel consumption was significant, requiring approximately 160 imperial gallons (730 L; 190 US gal) per race at a rate of 3.6 imperial gallons per minute (0.27 L/s). By July 1928, Rolls-Royce had provided Mitchell with detailed engine schematics, enabling aerodynamic refinements on the airframe.

To address cooling challenges stemming from high heat output, surface radiators were incorporated not only into the wings but also within the floats. Additional airflow through internal wing structures further assisted engine temperature regulation. Weighing 1,530 pounds (690 kg), the heavier engine necessitated repositioning the float struts slightly forward for better support. Increased fuel demands led to steel fuel tanks being installed inside both floats.

In February 1929, Supermarine received approval to construct two aircraft intended for that year's competition. These planes, assigned serial numbers N247 and N248, were assembled concurrently at their Woolston facility in Southampton.

Operational history

File:1929 Schneider Trophy course.svg

The 1929 Schneider Trophy course

In August 1929, the pair of S.6 aircraft were delivered to Calshot for use by the RAF High Speed Flight. The first flight of N247 occurred on 10 August, followed by N248 two weeks later. Shortly after N247 arrived at Calshot, it was observed that one float sat too low in the water during takeoff, causing the aircraft to pivot on the surface. Despite this, the slight waves generated were sufficient for N247 to lift off. An overheating problem was resolved by fitting additional radiators.

When a British contender, the Gloster VI, had to withdraw due to engine malfunction, only the two S.6s remained as British entries; consequently, the S.5 (N219) was readied for competition. During a final inspection of N247, a small metal fragment was found on a spark plug, indicating a defective piston. Although replacing the entire engine after installation was prohibited, individual parts could be swapped before the race commenced. Overnight, specialist Rolls-Royce engineers—who had traveled from Derby to Southampton to watch the event—replaced the engine block, ensuring smooth operation by race day.

The 1929 Schneider Trophy race was held off England’s coast north of the Isle of Wight under perfect weather conditions, attracting crowds exceeding one million along the shoreline to observe. Piloted by Flying Officer H.R.D. Waghorn, N247 secured first place with a speed of 328.63 miles per hour (528.88 km/h). Although N248 was disqualified for cutting inside a marker pole, it nonetheless established World closed-circuit records over 50 and 100 kilometres (31 and 62 mi) during its run. Following this triumph, British Prime Minister Ramsay MacDonald publicly committed official backing for the 1931 race; however, this pledge was later rescinded by the government.

For the 1931 Schneider Trophy contest at Calshot, modifications were made to the S.6 to accommodate a more powerful 2,350 horsepower (1,750 kW) variant of the R engine. Two newly constructed aircraft, designated as the Supermarine S.6B, joined the fleet. The original S.6s were redesignated as S.6As and upgraded with new floats, enhanced cooling surfaces, and statically balanced control surfaces to match the newer models’ standards. On 2 June, during N247’’’s maiden flight in its improved configuration, dangerous levels of tail flutter—a type of resonance—were encountered; this issue was mitigated by attaching weights to the rudder.

The British strategy for the 1931 race involved flying one S.6B, S1595, solo around the course with N248 held in reserve; if both failed, then N247 would be deployed. Tragically, N247, piloted by Navy Lieutenant G.N. Brinton, was lost in a fatal crash during pre-race training takeoff. While N248 remained part of the team, it did not participate in the competition itself. Ultimately, S1595 won in a contest featuring only British aircraft.

Aircraft on display

File:Supermarine S.6A.jpg

The preserved Supermarine S.6 (N248) exhibited at the Solent Sky museum in Southampton

The aircraft known as N248 featured in the 1942 British biographical film The First of the Few, which portrayed the life of Mitchell. Up until the 1960s, it was mistakenly exhibited as the S.6B model S1596 in a venue next to the Royal Pier, Southampton. Restoration efforts for the S.6A began in 1983, during which it was repainted to reflect its authentic 1931 livery. Today, this historic plane is showcased at the Solent Sky museum located in Southampton.

Operators

Template:UK

• Royal Air Force
  • High Speed Flight

Further reading

• Graham White's Allied Aircraft Piston Engines of World War II: History and Development of Frontline Aircraft Piston Engines Produced by Great Britain and the United States During World War II (2nd edition, SAE International, Warrendale, Pennsylvania, 2019) provides an in-depth exploration of piston engine advancements during the war period.

External links

• Visual archives featuring silent newsreels from British Pathe include footage such as Transport – Aviation: Supermarine Schneider Cup Plane (1929), To Keep That Schneider Cup (1929), and 357 Miles an Hour (also known as 357.7 Miles per Hour) (1929).
• An article from Popular Mechanics delves into the S.6 aircraft and the 1929 Schneider Cup competition, drawing on content from the December 1929 issue of the magazine.