Blackburn Iris
Encyclopedia
The Blackburn Iris was a British
three-engined biplane
flying boat
of the 1920s. Although only five Irises were built, it was used as a long-ranged maritime reconnaissance aircraft by the Royal Air Force
, where it equipped a squadron for 4 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
.
issued Specification R.14/24 for a long-range reconnaissance flying boat
for the Royal Air Force
. To meet this requirement, Blackburn Aircraft
proposed the R.B.1 (Reconnaissance Biplane 1), designed by Major J.B. Rennie, who had previously worked with John Cyril Porte
at the Seaplane Experimental Station
, Felixstowe
.
The R.B.1 was a three-engined, three-bay
biplane
. The equal-span wings were of mixed wood-and-metal construction, with aileron
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
, with a vee-bottom with two steps to give good water handling. Three 650 hp (485 kW) Rolls-Royce Condor
III water-cooled V12 engine
s driving four-bladed propellers were mounted in individual nacelle
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 dosal gun positions mounting Lewis gun
s on Scarff ring
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.
The prototype R.B.1, with the designation
Iris I, and with the serial number
N185, made its maiden flight from Blackburn's factory at Brough
on 19 June 1926, being delivered to the Marine Aircraft Experimental Establishment
at Felixstowe the next day, being fully tested during July and August. 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
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.
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
, and the prototype wooden hulled Saunders Valkyrie
(a direct competitor to the Iris), a 3,000 mi (4,800 km) tour of Scandinavia
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.
and Air Commodore
Sir Arthur Longmore
on a tour of RAF Stations of the Mediterranean
and Middle East. It reached Karachi
on 14 October, finally returning to RAF Calshot
on 14 November, having flown a total distance of 11,360 mi (18,290 km) with a flight time of 125 hr 5 min.
The first Iris III flew on 21 November 1929, with the three Iris IIIs equipping No. 209 Squadron
which reformed at RAF Mount Batten
, Plymouth
in January 1930. 209 Squadron continued the pattern of long-range flights carried out by the Iris II, with one Iris visiting Reykjavík
in June 1930 to celebrate the 1,000th anniversary of the Icelandic Althing
(parliament), and another making the first crossing of the Bay of Biscay
by flying boat when visiting Lisbon
in August 1930.
The first Iris III was destroyed in a fatal crash on 4 February 1931, resulting in a replacement being ordered. Although still an Iris III, this had a number of changes, being fitted with provision to carry a COW 37 mm gun
in its bow. 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. The Iris II was also re-engined, being fitted with three 800 hp Armstrong Siddeley Panther
radial engine
s, with the centre engine in a pusher configuration
to become the Iris IV.
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. One of the Iris Vs was converted for use as a testbed for the Napier Culverin
, a licence built Junkers Jumo 204
diesel engine
, flying in this form in June 1937 and continuing flight trials until April 1938.
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 Royal Air Force
. 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.
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.
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
three-engined biplane
Biplane
A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing...
flying boat
Flying boat
A flying boat is a fixed-winged seaplane with a hull, allowing it to land on water. It differs from a float plane as it uses a purpose-designed fuselage which can float, granting the aircraft buoyancy. Flying boats may be stabilized by under-wing floats or by wing-like projections from the fuselage...
of the 1920s. Although only five Irises were built, it was used as a long-ranged maritime reconnaissance aircraft by the Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...
, where it equipped a squadron for 4 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
Blackburn Perth
-External links:** Popular Science, January 1934* Popular Mechanics, March 1931...
.
Development and design
In 1924, the British Air MinistryAir Ministry
The Air Ministry was a department of the British Government with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964...
issued Specification R.14/24 for a long-range reconnaissance flying boat
Flying boat
A flying boat is a fixed-winged seaplane with a hull, allowing it to land on water. It differs from a float plane as it uses a purpose-designed fuselage which can float, granting the aircraft buoyancy. Flying boats may be stabilized by under-wing floats or by wing-like projections from the fuselage...
for the Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...
. To meet this requirement, Blackburn Aircraft
Blackburn Aircraft
Blackburn Aircraft Limited was a British aircraft manufacturer that concentrated mainly on naval and maritime aircraft during the first part of the 20th century.-History:...
proposed the R.B.1 (Reconnaissance Biplane 1), designed by Major J.B. Rennie, who had previously worked with John Cyril Porte
John Cyril Porte
Lieutenant Commander John Cyril Porte CMG, DSM, Royal Navy was a flying boat pioneer associated with the World War I Seaplane Experimental Station at Felixstowe.-Biography:...
at the Seaplane Experimental Station
Seaplane Experimental Station
The Seaplane Experimental Station at Royal Naval Air Station Felixstowe was a British aircraft design unit of the early part of the 20th century.-Creation:...
, Felixstowe
Felixstowe
Felixstowe is a seaside town on the North Sea coast of Suffolk, England. The town gives its name to the nearby Port of Felixstowe, which is the largest container port in the United Kingdom and is owned by Hutchinson Ports UK...
.
The R.B.1 was a three-engined, three-bay
Interplane strut
An interplane strut is an aircraft airframe component designed to transmit lift and landing loads between wing panels on biplanes and other aircraft with multi-wing designs. They also maintain the correct angle of incidence for the connected wing panels and are often braced with wires...
biplane
Biplane
A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing...
. The equal-span wings were of mixed wood-and-metal construction, with aileron
Aileron
Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...
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
Plywood is a type of manufactured timber made from thin sheets of wood veneer. It is one of the most widely used wood products. It is flexible, inexpensive, workable, re-usable, and can usually be locally manufactured...
, with a vee-bottom with two steps to give good water handling. Three 650 hp (485 kW) Rolls-Royce Condor
Rolls-Royce Condor
|-See also:-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.-External links:*...
III water-cooled V12 engine
V12 engine
A V12 engine is a V engine with 12 cylinders mounted on the crankcase in two banks of six cylinders, usually but not always at a 60° angle to each other, with all 12 pistons driving a common crankshaft....
s driving four-bladed propellers were mounted in individual nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...
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 dosal gun positions mounting Lewis gun
Lewis Gun
The Lewis Gun is a World War I–era light machine gun of American design that was perfected and widely used by the British Empire. It was first used in combat in World War I, and continued in service with a number of armed forces through to the end of the Korean War...
s on Scarff ring
Scarff ring
The Scarff ring was a type of machine gun mounting developed during the First World War by Warrant Officer F. W. Scarff of the Admiralty Air Department for use on two-seater aircraft...
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.
The prototype R.B.1, with the designation
British military aircraft designation systems
British military aircraft designations are used to refer to aircraft types and variants operated by the armed forces of the United Kingdom.Since the end of the First World War, aircraft types in British military service have generally been known by a name British military aircraft designations are...
Iris I, and with the serial number
United Kingdom military aircraft serials
In the United Kingdom to identify individual aircraft, all military aircraft are allocated and display a unique serial number. A unified serial number system, maintained by the Air Ministry , and its successor the Ministry of Defence , is used for aircraft operated by the Royal Air Force , Fleet...
N185, made its maiden flight from Blackburn's factory at Brough
Brough Aerodrome
Brough Aerodrome is located at Brough, East Riding of Yorkshire, England.The site was first used by the Blackburn Aeroplane & Motor Company during World War I for the testing of seaplanes....
on 19 June 1926, being delivered to the Marine Aircraft Experimental Establishment
Marine Aircraft Experimental Establishment
The Marine Aircraft Experimental Establishment 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 Service seaplane base, to design, test and evaluate seaplanes,...
at Felixstowe the next day, being fully tested during July and August. Wooden hulls were prone to soaking up large quantities of water (which could amount to several hundred pounds
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
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
Duralumin is the trade name of one of the earliest types of age-hardenable aluminium alloys. The main alloying constituents are copper, manganese, and magnesium. A commonly used modern equivalent of this alloy type is AA2024, which contains 4.4% copper, 1.5% magnesium, 0.6% manganese and 93.5%...
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.
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
Supermarine Southampton
-See also:-References:NotesBibliography* Andrews, C.F. and E.B. Morgan. Supermarine Aircraft since 1914 . London: Putnam, 1987. ISBN 0-85177-800-3....
, and the prototype wooden hulled Saunders Valkyrie
Saunders Valkyrie
The Saunders A.3 Valkyrie was a large three-engined biplane flying boat with a wooden hull built to an Air Ministry specification. It was not found suitable for production and helped to confirm a preference for metal-hulled flying boats.-Development:...
(a direct competitor to the Iris), a 3,000 mi (4,800 km) tour of Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...
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.
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. 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 AirUnder-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....
and Air Commodore
Air Commodore
Air commodore is an air-officer rank which originated in and continues to be used by the Royal Air Force...
Sir Arthur Longmore
Arthur Longmore
Air Chief Marshal Sir Arthur Murray Longmore GCB, DSO was an early naval aviator, before reaching high rank in the Royal Air Force.-Biography:...
on a tour of RAF Stations of the Mediterranean
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
and Middle East. It reached Karachi
Karachi
Karachi is the largest city, main seaport and the main financial centre of Pakistan, as well as the capital of the province of Sindh. The city has an estimated population of 13 to 15 million, while the total metropolitan area has a population of over 18 million...
on 14 October, finally returning to RAF Calshot
RAF Calshot
RAF Calshot was initially a seaplane and flying boat station, and latterly an RAF marine craft maintenance and training unit. It was located at the end of Calshot Spit in Southampton Water, Hampshire, England, at...
on 14 November, having flown a total distance of 11,360 mi (18,290 km) with a flight time of 125 hr 5 min.
The first Iris III flew on 21 November 1929, with the three Iris IIIs equipping No. 209 Squadron
No. 209 Squadron RAF
No. 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 and saw active service in both World Wars, the Korean War and in Malaya...
which reformed at RAF Mount Batten
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 Cattewater in 1918 and in 1928 was re-named RAF Mount Batten...
, Plymouth
Plymouth
Plymouth is a city and unitary authority area on the coast of Devon, England, about south-west of London. It is built between the mouths of the rivers Plym to the east and Tamar to the west, where they join Plymouth Sound...
in January 1930. 209 Squadron continued the pattern of long-range flights carried out by the Iris II, with one Iris visiting Reykjavík
Reykjavík
Reykjavík is the capital and largest city in Iceland.Its latitude at 64°08' N makes it the world's northernmost capital of a sovereign state. It is located in southwestern Iceland, on the southern shore of Faxaflói Bay...
in June 1930 to celebrate the 1,000th anniversary of the Icelandic Althing
Althing
The Alþingi, anglicised variously as Althing or Althingi, is the national parliament of Iceland. The Althingi is the oldest parliamentary institution in the world still extant...
(parliament), and another making the first crossing of the Bay of Biscay
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 Brest south to the Spanish border, and the northern coast of Spain west to Cape Ortegal, and is named in English after the province of Biscay, in the Spanish...
by flying boat when visiting Lisbon
Lisbon
Lisbon is the capital city and largest city of Portugal with a population of 545,245 within its administrative limits on a land area of . The urban area of Lisbon extends beyond the administrative city limits with a population of 3 million on an area of , making it the 9th most populous urban...
in August 1930.
The first Iris III was destroyed in a fatal crash on 4 February 1931, resulting in a replacement being ordered. Although still an Iris III, this had a number of changes, being fitted with provision to carry a COW 37 mm gun
COW 37 mm gun
The COW 37 mm gun was a British automatic cannon that was developed as a heavy-calibre aircraft weapon.It was trialled in several installations and specified for the Westland C.O.W. Gun Fighter...
in its bow. 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
Rolls-Royce Buzzard
|-See also:-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6....
engines to restore performance and improve reliability, with the three re-engined aircraft re-entering service in 1932 as the Iris V. The Iris II was also re-engined, being fitted with three 800 hp Armstrong Siddeley Panther
Armstrong Siddeley Panther
|-See also:-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6....
radial engine
Radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...
s, with the centre engine in a pusher configuration
Pusher configuration
In a craft with a pusher configuration the propeller are mounted behind their respective engine. According to Bill Gunston, a "pusher propeller" is one mounted behind engine so that drive shaft is in compression...
to become the Iris IV.
The Iris Vs were replaced in squadron service in 1934 by the Blackburn Perth
Blackburn Perth
-External links:** Popular Science, January 1934* Popular Mechanics, March 1931...
, four very similar Buzzard-powered aircraft closely based on the Iris. One of the Iris Vs was converted for use as a testbed for the Napier Culverin
Napier Culverin
-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.-External links:*...
, a licence built Junkers Jumo 204
Junkers Jumo 204
-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9* Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7-External links:*...
diesel engine
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
, flying in this form in June 1937 and continuing flight trials until April 1938.
Variants
R.B.1 / Iris I: Prototype, wooden hull and mixed construction wings, powered by three 650 hp (485 kW) Rolls-Royce CondorRolls-Royce Condor
|-See also:-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.-External links:*...
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
Rolls-Royce Condor
|-See also:-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.-External links:*...
IIIA inline piston engines.
R.B.1B / Iris III: Five-seat long-range maritime reconnaissance flying boat for the Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...
. 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
Armstrong Siddeley Leopard
|-See also:-Bibliography:* Smith, Herschel. Aircraft Piston Engines. New York, New York: McGraw-Hill, 1981. ISBN 0-07-058472-9.* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6....
III radial piston engines.
R.B.1D / Iris V: This was the final variant. Three Iris Mk IIIs were fitted with 825 hp (615 kW) Rolls-Royce Buzzard
Rolls-Royce Buzzard
|-See also:-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6....
IIMS piston engines.