The Blackburn Iris was a British three-engined

biplane A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While ...

flying boat A flying boat is a type of fixed-winged seaplane with a hull, allowing it to land on water. It differs from a floatplane in that a flying boat's fuselage is purpose-designed for floatation and contains a hull, while floatplanes rely on fusela ...

of the 1920s. Although only five Irises were built, it was used as a long-range maritime reconnaissance aircraft by the

Royal Air Force The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and ...

, where it equipped a squadron for four years, being used to carry out a number of notable long-distance flights. The final version of the Iris, the Iris Mark V was developed into the aircraft that replaced it in Squadron service, the

Blackburn Perth The Blackburn Perth was a British flying boat which was in service during the interwar period. It was essentially an upgraded Iris, and hence the largest flying-boat to serve with the Royal Air Force at the time (and the largest biplane flying ...

Development and design

In 1924, the British

Air Ministry The Air Ministry was a department of the Government of the United Kingdom with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964. It was under the political authority of the Secretary of State ...

issued Specification R.14/24 for a long-range reconnaissance

for the

. To meet this requirement,

Blackburn Aircraft Blackburn () is an industrial town and the administrative centre of the Blackburn with Darwen borough in Lancashire, England. The town is north of the West Pennine Moors on the southern edge of the Ribble Valley, east of Preston and north- ...

proposed the R.B.1 (Reconnaissance Biplane 1), designed by Major John Douglas Rennie, who as Chief Technical Officer worked with

John Cyril Porte Lieutenant Colonel John Cyril Porte, (26 February 1884 – 22 October 1919) was a British flying boat pioneer associated with the First World War Seaplane Experimental Station at Felixstowe. Early life and career Porte was born on 26 Feb ...

at the

Seaplane Experimental Station The Seaplane Experimental Station, formerly RNAS Felixstowe, was a British aircraft design unit during the early part of the 20th century. Creation During June 1912, surveys began for a suitable site for a base for Naval hydro-aeroplanes, with ...

Felixstowe Felixstowe ( ) is a port town in Suffolk, England. The estimated population in 2017 was 24,521. The Port of Felixstowe is the largest container port in the United Kingdom. Felixstowe is approximately 116km (72 miles) northeast of London. His ...

.London 2003, p. 99. The R.B.1 was a three-engined, three- bay

. The equal-span wings were of mixed wood-and-metal construction, with

aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around ...

s fitted to both upper and lower wings and floats fitted under the wingtips, while the aircraft had a large biplane tail (with a span of 30 ft (9.14 m)) with three fins and rudders. The aircraft's hull had a wooden structure covered in

plywood Plywood is a material manufactured from thin layers or "plies" of wood veneer that are glued together with adjacent layers having their wood grain rotated up to 90 degrees to one another. It is an engineered wood from the family of manufactured ...

, with a V-bottom with two steps to give good water handling. Three 650 hp (485 kW)

Rolls-Royce Condor The Rolls-Royce Condor aircraft piston engine was a larger version of the Rolls-Royce Eagle developing up to 675 horsepower (500 kW). The engine first ran in 1918 and a total of 327 engines were recorded as being built. Variants ''Note:'' ...

III water-cooled

V12 engine A V12 engine is a twelve-cylinder piston engine where two banks of six cylinders are arranged in a V configuration around a common crankshaft. V12 engines are more common than V10 engines. However, they are less common than V8 engines. The fi ...

s driving four-bladed propellers were mounted in individual

nacelle A nacelle ( ) is a "streamlined body, sized according to what it contains", such as an engine, fuel, or equipment on an aircraft. When attached by a pylon entirely outside the airframe, it is sometimes called a pod, in which case it is attached ...

s between the wings. It carried a crew of five, with two pilots sitting side by side in a cockpit forward of the wings, with nose and dorsal gun positions mounting Lewis guns on

Scarff ring The Scarff ring was a type of machine gun mounting developed during the First World War by Warrant Officer (Gunner) F. W. Scarff of the Admiralty Air Department for use on two-seater aircraft. The mount incorporated bungee cord suspension in eleva ...

s, with provision for a further two guns which could be operated through portholes in the rear fuselage. Bomb racks under the wings could carry up to 1,040 lb (470 kg) of bombs.Jackson 1968, pp. 194–195London 2003, pp. 99–100. The prototype R.B.1, with the designation Iris I, and with the

serial number A serial number is a unique identifier assigned incrementally or sequentially to an item, to ''uniquely'' identify it. Serial numbers need not be strictly numerical. They may contain letters and other typographical symbols, or may consist enti ...

''N185'', made its maiden flight from Blackburn's factory at Brough on 19 June 1926, being delivered to the

Marine Aircraft Experimental Establishment The Marine Aircraft Experimental Establishment (MAEE) was a British military research and test organisation. It was originally formed as the Marine Aircraft Experimental Station in October 1918 at RAF Isle of Grain, a former Royal Naval Air Serv ...

at Felixstowe the next day, being fully tested during July and August.Jackson 1968, p. 195. Wooden hulls were prone to soaking up large quantities of water (which could amount to several hundred pounds in additional weight) when kept afloat for long periods of time, so Rennie designed an all-metal hull for the Iris, constructed of

duralumin Duralumin (also called duraluminum, duraluminium, duralum, dural(l)ium, or dural) is a trade name for one of the earliest types of age-hardenable aluminium alloys. The term is a combination of '' Dürener'' and ''aluminium''. Its use as a tra ...

before the Iris first flew. ''N185'' returned to Brough in March 1927 when it was fitted with the new metal hull, together with more powerful engines and an additional gunner's position in the tail, becoming the Iris II.London 2003, p. 100. On 12 August 1927, shortly after being redelivered, the Iris II started, along with the prototype

Short Singapore The Short Singapore was a British multi-engined biplane flying boat built after the First World War. The design was developed into two four-engined versions: the prototype Singapore II and production Singapore III. The latter became the Roya ...

I, an experimental metal-hulled Supermarine Southampton, and the prototype wooden-hulled Saunders Valkyrie (a direct competitor to the Iris), a 3,000 mi (4,800 km) tour of

Scandinavia Scandinavia; Sámi languages: /. ( ) is a subregion#Europe, subregion in Northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. In English usage, ''Scandinavia'' most commonly refers to Denmark, ...

and the Baltic. The Iris performed well on the tour, particularly compared to the Valkyrie, which suffered much heavier water soakage than expected as well as engine problems, and the Air Ministry issued Specification R.31/27 for an improved version of the Iris, to act as a long-range supplement to the smaller Southampton.London 2003, pp. 100–101.

Operational history

On 4 February 1928, a contract was placed for three Iris III aircraft, similar to the Iris II but with fabric-covered metal wings.Jackson 1968, p. 199. The Iris II, meanwhile, continued in use, setting out on another long-range cruise on 27 September, carrying Sir Philip Sassoon, the

Under-Secretary of State for Air The Under-Secretary of State for Air was a junior ministerial post in the United Kingdom Government, supporting the Secretary of State for Air in his role of managing the Royal Air Force. It was established on 10 January 1919, replacing the previou ...

and Air Commodore Sir

Arthur Longmore Air Chief Marshal Sir Arthur Murray Longmore, (8 October 1885 – 10 December 1970) was an early naval aviator, before reaching high rank in the Royal Air Force. He was Commander-in-Chief of the RAF's Middle East Command from 1940 to 1941. Ea ...

on a tour of RAF Stations of the

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...

and Middle East. It reached

Karachi Karachi (; ur, ; ; ) is the most populous city in Pakistan and 12th most populous city in the world, with a population of over 20 million. It is situated at the southern tip of the country along the Arabian Sea coast. It is the former cap ...

on 14 October, finally returning to

RAF Calshot Royal Air Force Calshot or more simply RAF Calshot was initially a seaplane and flying boat station, and latterly a Royal Air Force marine craft maintenance and training unit. It was located at the end of Calshot Spit in Southampton Water, Hamp ...

on 14 November, having flown a total distance of 11,360 mi (18,290 km) with a flight time of 125 hr 5 min.Jackson 1968, pp. 197–198. The first Iris III flew on 21 November 1929, with the three Iris IIIs equipping No. 209 Squadron which reformed at

RAF Mount Batten RAF Mount Batten was a Royal Air Force station and flying boat base at Mount Batten, a peninsula in Plymouth Sound, Devon, England. Originally a seaplane station opened in 1917 as a Royal Navy Air Service Station Cattewater it became RAF Catte ...

Plymouth Plymouth () is a port city and unitary authority in South West England. It is located on the south coast of Devon, approximately south-west of Exeter and south-west of London. It is bordered by Cornwall to the west and south-west. Plymouth ...

in January 1930. 209 Squadron continued the pattern of long-range flights carried out by the Iris II, with one Iris visiting

Reykjavík Reykjavík ( ; ) is the capital and largest city of Iceland. It is located in southwestern Iceland, on the southern shore of Faxaflói bay. Its latitude is 64°08' N, making it the world's northernmost capital of a sovereign state. With a po ...

in June 1930 to celebrate the 1,000th anniversary of the Icelandic

Althing The Alþingi (''general meeting'' in Icelandic, , anglicised as ' or ') is the supreme national parliament of Iceland. It is one of the oldest surviving parliaments in the world. The Althing was founded in 930 at ("thing fields" or "assembly ...

(parliament), and another making the first crossing of the

Bay of Biscay The Bay of Biscay (), known in Spain as the Gulf of Biscay ( es, Golfo de Vizcaya, eu, Bizkaiko Golkoa), and in France and some border regions as the Gulf of Gascony (french: Golfe de Gascogne, oc, Golf de Gasconha, br, Pleg-mor Gwaskogn), ...

by flying boat when visiting

Lisbon Lisbon (; pt, Lisboa ) is the capital and largest city of Portugal, with an estimated population of 544,851 within its administrative limits in an area of 100.05 km2. Grande Lisboa, Lisbon's urban area extends beyond the city's administr ...

in August 1930.Jackson 1968, pp. 200–201. The first Iris III was destroyed in a fatal crash on 4 February 1931, killing nine of twelve aboard, when the pilot misjudged a landing approach over a glassy-smooth

Plymouth Sound Plymouth Sound, or locally just The Sound, is a deep inlet or sound in the English Channel near Plymouth in England. Description Its southwest and southeast corners are Penlee Point in Cornwall and Wembury Point in Devon, a distance of abo ...

.Associated Press, "Nine Perish in Seaplane Dive: Three Saved After British Air Force Craft Plunges Into Bay During Practice", ''The San Bernardino Daily Sun'', San Bernardino, California, Thursday 5 February 1931, Volume LXVII, Number 158, pages 1,2. A replacement was ordered. Although still an Iris III, this had a number of changes, being fitted with provision to carry a

COW 37 mm gun The COW 37 mm gun was a British automatic cannon that was developed during First World War as a large-calibre aircraft weapon. It was tested in several installations and specified for the Westland C.O.W. Gun Fighter for attacking bombers. Th ...

in its bow.Jackson 1968, p. 201–202. The weight of the Iris had grown considerably since the Iris I, and it was decided to replace the Iris III's Condors with more powerful (825 hp (615 kW)

Rolls-Royce Buzzard The Rolls-Royce Buzzard was a British piston aero engine of capacity that produced about . Designed and built by Rolls-Royce Limited it is a V12 engine of Bore and Stroke. Only 100 were made. A further development was the Rolls-Royce R e ...

engines to restore performance and improve reliability, with the three re-engined aircraft re-entering service in 1932 as the Iris V.Jackson 1968, p. 202. The Iris II was also re-engined, being fitted with three 800 hp

Armstrong Siddeley Panther The Armstrong Siddeley Panther was a 27-litre 14-cylinder twin-row air-cooled radial aero engine developed by Armstrong Siddeley. It was originally named the Jaguar Major.Lumsden 2003, p.72. Applications * Armstrong Whitworth Atlas Mk II * A ...

radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ca ...

s, with the centre engine in a

pusher configuration In an aircraft with a pusher configuration (as opposed to a tractor configuration), the propeller(s) are mounted behind their respective engine(s). Since a pusher propeller is mounted behind the engine, the drive shaft is in compression in nor ...

to become the Iris IV.London 2003, pp. 121–122. An Iris III S1263 of 209 Squadron, Mount Batten, sank following collision with dockyard launch after landing in Plymouth Sound; 12 Jan 1933; of 9 airmen, 1 drowned and 7 injured Fatal air accidents in Britai

Retrieved: 1 November 2016 The Iris Vs were replaced in squadron service in 1934 by the

, four very similar Buzzard-powered aircraft closely based on the Iris.Thetford 1957, p. 76.Jackson 1968, p. 313. One of the Iris Vs was converted for use as a testbed for the

Napier Culverin The Napier Culverin was a licensed built version of the Junkers Jumo 204 six-cylinder vertically opposed liquid-cooled diesel aircraft engine built by D. Napier & Son. The name is derived from the French word, culverin, for an early cannon o ...

, a licence-built

Junkers Jumo 204 The Jumo 204 was an opposed-piston, inline, liquid-cooled 6-cylinder aircraft Diesel engine produced by the German manufacturer Junkers. It entered service in 1932. Later engines in the series, the Jumo 205, Jumo 206, Jumo 207 and Jumo 208, dif ...

diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-call ...

, flying in this form in June 1937 and continuing flight trials until April 1938.Jackson 1968, pp. 203–204.

Variants

;R.B.1 / Iris I: Prototype, wooden hull and mixed construction wings, powered by three 650 hp (485 kW)

III engines. One built. ;R.B.1A / Iris II: The Iris I with a new, all-metal hull and three 675 hp (503 kW)

IIIA inline piston engines. ;R.B.1B / Iris III: Five-seat long-range maritime reconnaissance flying boat for the

. Metal hull and wings. Powered by three 675 hp (503 kW) Rolls-Royce Condor IIIB inline piston engines. Four built. ;R.B.1C / Iris IV: Conversion of the Iris II with three 800 hp (600 kW)

Armstrong Siddeley Leopard The Armstrong Siddeley Leopard was a British 14-cylinder twin-row air-cooled radial aero engine developed in 1927 by Armstrong Siddeley. It was the most powerful radial engine in the world when introduced. Variants ;Leopard I :700 hp, medium ...

III radial piston engines.Jackson 1968, pp. 204–205. ;R.B.1D / Iris V: This was the final variant. Three Iris Mk IIIs were fitted with 825 hp (615 kW)

IIMS piston engines.

Operators

; *

No. 209 Squadron RAF Number 209 Squadron of the British Royal Air Force was originally formed from a nucleus of "Naval Eight" on 1 February 1917 at Saint-Pol-sur-Mer, France, as No. 9 Squadron Royal Naval Air Service (RNAS)Rawlings 1978, p. 324. and saw active servic ...

Specifications (Iris III)

References

;Notes ;Bibliography * * * * {{Blackburn aircraft

Iris Iris most often refers to: *Iris (anatomy), part of the eye *Iris (mythology), a Greek goddess * ''Iris'' (plant), a genus of flowering plants * Iris (color), an ambiguous color term Iris or IRIS may also refer to: Arts and media Fictional ent ...