Supermarine Commercial Amphibian

Supermarine Commercial Amphibian

Industry	Aviation
Founded	1920
Founder	Reginald Mitchell
Headquarters	Woolston, Southampton , United Kingdom
Products	Passenger-capable flying boat

The Supermarine Commercial Amphibian—initially called the Supermarine Amphibian and later assigned the designation N147 by the British Air Ministry—was a passenger-capable flying boat. It represented the inaugural aircraft design by Supermarine’s chief designer, Reginald Mitchell, and was constructed at the company’s Woolston, Southampton facility to enter a competition held by the Air Ministry in September 1920. Derived from the Supermarine Channel, this amphibious biplane featured a wooden hull, asymmetrical wingspans, and was powered by a single 350 horsepower (260 kW) Rolls-Royce Eagle engine. The pilot operated from an open cockpit positioned behind two passenger seats.

Though it secured second place in the contest, the Commercial Amphibian was deemed superior in both design quality and dependability compared to the other two competitors, which led to the doubling of its prize award to Template:GBPConvert. In October 1920, the aircraft suffered a crash resulting in irreparable damage, and no further units were produced. Nevertheless, its strong performance during the competition earned Supermarine a contract to develop a three-seat Fleet Spotter Amphibian prototype, later known as the Supermarine Seal II.

Background

In April 1920, the British Air Ministry announced plans to hold two separate contests for commercial aircraft: one for land-based planes and another for seaplanes. The initiative aimed to invigorate Britain's aviation industry, which had faced significant challenges following World War I. The Supermarine Commercial Amphibian—initially named the Supermarine Amphibian—was crafted by Supermarine’s lead designer Reginald Mitchell specifically to compete for the seaplane category prize; it marked his first venture into aircraft design. The Air Ministry stipulated that participating aircraft must accommodate at least two passengers who could embark either on land or water. Additionally, both crew and passengers were required to have access to lifebelts. Performance criteria mandated that entrants be capable of flying 350 nautical miles (650 km; 400 mi) at an altitude of 300 metres (980 ft) with a minimum speed of 70 knots (130 km/h; 81 mph), while carrying a payload of at least 230 kilograms (510 lb). Furthermore, aircraft had to demonstrate the ability to sustain flight for three minutes at an altitude of 914 metres (2,999 ft), and perform landings over tethered balloons set at 7.6 metres (25 ft) above ground level.

Design

File:Supermarine Commercial Amphibian layout diagrams.jpg

General arrangement drawings for the Supermarine Commercial Amphibian (Flight, September 1920)

Mitchell's concept for the Amphibian was derived from Supermarine's Channel flying boat, which itself evolved from the AD Flying Boat. The AD Flying Boat, a reconnaissance and patrol aircraft developed toward the end of World War I, did not enter combat during the conflict.

The Amphibian was a wooden-hulled, single-engine biplane flying boat featuring unequal wing spans. Its 350 horsepower (260 kW) Rolls-Royce Eagle engine was installed in a pusher arrangement between the wings, with the propeller positioned behind the engine. The tail assembly included one vertical fin and a single tailplane set midway up the fin. The aircraft’s bow was shaped to ensure it lifted clear of the water during takeoff, adopting a hull profile reminiscent of a boat’s nose. Mitchell introduced an innovative system enabling simultaneous operation of the ailerons. Additionally, the landing gear was engineered to be partially retractable.

The pilot occupied an open cockpit located just ahead of the wings, while an enclosed cabin situated further forward provided seating for two passengers. For improved maneuverability on water, a tiller was installed for the pilot’s use to facilitate navigation through confined waterways.

Operational history

File:Supermarine Commercial Amphibian.jpg

The Amphibian being wheeled out prior to testing during the Air Ministry competition (Flight, September 1920)

In September 1920, the Air Ministry organized a competition at experimental Royal Air Force sites in Martlesham Heath and Felixstowe. The Supermarine Amphibian, registered as G-EAVE and piloted by Herbert Hoare, competed alongside two other seaplanes: a Vickers Viking and a Fairey III. Two additional seaplanes intended for the event did not arrive.

Despite its heavier weight and slower speed relative to its rivals, the Amphibian was recognized as the best-built and most dependable aircraft in the contest. It was uniquely able to complete all required trials without any need for adjustments throughout the event. Ultimately, the Vickers Viking secured first place along with a prize of Template:GBPConvert, while the Amphibian finished second. The Air Ministry doubled its initial £4,000 consolation award to £8,000 in recognition of Mitchell’s outstanding design and the aircraft’s commendable performance, especially considering it had the least powerful engine among its competitors.

Approximately one month after the competition, on 13 October 1920, the Commercial Amphibian crashed near Great Bookham in Surrey following departure from Southampton. The accident caused irreparable damage to the aircraft, and no further units were manufactured.

Legacy

Following the competition, the Air Ministry assigned the designation N146 to the Vickers Viking and N147 to the Supermarine Amphibian. Based on the Amphibian's demonstrated capabilities, the Air Ministry tasked Supermarine with developing a prototype three-seat Fleet Spotter Amphibian. This prototype was created under Air Ministry specification 7/20 and was named the Supermarine Seal II. Supermarine finalized the design drawings in November 1920. Elements from the Amphibian's design were subsequently incorporated into the development of the Supermarine Walrus, of which several hundred units were produced and actively served during World War II. Additionally, Mitchell drew upon concepts from both the Amphibian and the Supermarine Channel II to design an Amphibian Flying Boat intended for Ship Work in 1920.