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 seaplane with a hull, allowing it to land on water. It differs from a floatplane in having a fuselage that is purpose-designed for flotation, while floatplanes rely on fuselage-mounted floats for buoyancy. Though ...

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 Air force, air and space force of the United Kingdom, British Overseas Territories and Crown Dependencies. It was formed towards the end of the World War I, First World War on 1 April 1918, on the merger of t ...

, 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.

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 and civil aviation that existed from 1918 to 1964. It was under the political authority of the ...

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

for the

. To meet this requirement,

Blackburn Aircraft Blackburn Aircraft Limited was a British aircraft manufacturer from 1914 to 1963 that concentrated mainly on naval and maritime aircraft. History Blackburn Aircraft was founded by Robert Blackburn (aviation pioneer), Robert Blackburn and Jessy ...

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 aviation pioneer, pioneer associated with the First World War Seaplane Experimental Station at Felixstowe. Early life and career Porte was b ...

at the Seaplane Experimental Station,

Felixstowe Felixstowe ( ) is a port town and civil parish in the East Suffolk District, East Suffolk district, in the county of Suffolk, England. The estimated population in 2017 was 24,521. The Port of Felixstowe is the largest Containerization, containe ...

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

bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a ''gulf'', ''sea'', ''sound'', or ''bight''. A ''cove'' is a small, ci ...

. 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 aroun ...

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 composite material manufactured from thin layers, or "plies", of wood veneer that have been stacked and glued together. It is an engineered wood from the family of manufactured boards, which include plywood, medium-density fibreboa ...

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

V12 engine A V12 engine is a twelve-Cylinder (engine), cylinder Internal combustion engine#Reciprocating engines, piston engine where two banks of six cylinders are arranged in a V engine, V configuration around a common crankshaft. V12 engines are more c ...

s driving four-bladed propellers were mounted in individual

nacelle A nacelle ( ) is a streamlined container for aircraft parts such as Aircraft engine, engines, fuel or equipment. When attached entirely outside the airframe, it is sometimes called a pod, in which case it is attached with a Hardpoint#Pylon, pylo ...

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 el ...

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 (SN) is a unique identifier used to ''uniquely'' identify an item, and is usually assigned incrementally or sequentially. Despite being called serial "numbers", they do not need to be strictly numerical and may contain letters ...

''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 hardening, age-hardenable aluminium–copper alloys. The term is a combination of ''Düren'' and ''aluminium'' ...

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 I, an experimental metal-hulled

Supermarine Southampton The Supermarine Southampton was a flying boat of the interwar period designed and produced by the British aircraft manufacturer Supermarine. It was one of the most successful flying boats of the era. The Southampton was derived from the expe ...

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

Scandinavia Scandinavia is a subregion#Europe, subregion of northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. ''Scandinavia'' most commonly refers to Denmark, Norway, and Sweden. It can sometimes also ...

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 and

Air Commodore Air commodore (Air Cdre or Air Cmde) is an air officer rank used by some air forces, with origins from the Royal Air Force. The rank is also used by the air forces of many countries which have historical British influence and it is sometimes ...

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. E ...

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 east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...

and Middle East. It reached

Karachi Karachi is the capital city of the Administrative units of Pakistan, province of Sindh, Pakistan. It is the List of cities in Pakistan by population, largest city in Pakistan and 12th List of largest cities, largest in the world, with a popul ...

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, Hamps ...

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 Royal Air Force Mount Batten, or more simply RAF Mount Batten, is a former Royal Air Force station and flying boat base at Mount Batten, a peninsula in Plymouth Sound, Devon, England, UK. Originally a seaplane station opened in 1917 as a Royal ...

Plymouth Plymouth ( ) is a port city status in the United Kingdom, city and unitary authority in Devon, South West England. It is located on Devon's south coast between the rivers River Plym, Plym and River Tamar, Tamar, about southwest of Exeter and ...

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 city, capital and largest city in Iceland. It is located in southwestern Iceland on the southern shore of Faxaflói, the Faxaflói Bay. With a latitude of 64°08′ N, the city is List of northernmost items, the worl ...

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

Althing The (; ), anglicised as Althingi or Althing, is the Parliamentary sovereignty, supreme Parliament, national parliament of Iceland. It is the oldest surviving parliament in the world. The Althing was founded in 930 at ('Thing (assembly), thing ...

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

Bay of Biscay The Bay of Biscay ( ) is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Point Penmarc'h to the Spanish border, and along the northern coast of Spain, extending westward ...

by flying boat when visiting

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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. T ...

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 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

radial engine The radial engine is a reciprocating engine, reciprocating type internal combustion engine, internal combustion engine configuration in which the cylinder (engine), cylinders "radiate" outward from a central crankcase like the spokes of a wheel. ...

s, with the centre engine in a

pusher configuration In aeronautical and naval engineering, pusher configuration is the term used to describe a drivetrain of air- or watercraft with propulsion device(s) after the engine(s). This is in contrast to the more conventional tractor configuration, wh ...

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 Blackburn Perth, 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, a licence-built Junkers Jumo 204

diesel engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...

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

Specifications (Iris III)

References