Blackburn Iris

In 1924, the British Air Ministry 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 John Douglas Rennie, who as

Chief Technical Officer worked with John Cyril Porte at the Seaplane Experimental Station, Felixstowe.London 2003, p. 99.{{cite book|editor1-last=Chorlton|editor1-first=Martyn|title=Aeroplane Collectors' Archive: Golden Age of Flying-boats|date=2012|publisher=Kelsey Publishing Group, Kent|isbn=978-1-907426-71-1|page=23}}

The R.B.1 was a three-engined, three-bay biplane. The equal-span wings were of mixed wood-and-metal construction, with ailerons 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 V-bottom with two steps to give good water handling. Three 650 hp (485 kW) Rolls-Royce Condor III water-cooled V12 engines driving four-bladed propellers were mounted in individual nacelles 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 rings, 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 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.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 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, 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.London 2003, pp. 100–101.

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 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.Jackson 1968, pp. 197–198.Scott Flight 9 May 1929, pp. 380–383.

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.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.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 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 engines, with the centre engine in a pusher configuration 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 Britain [http://www.rcawsey.co.uk/Acc1934.htm] 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, flying in this form in June 1937 and continuing flight trials until April 1938.Jackson 1968, pp. 203–204.

;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 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.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.

;{{UK}}

• Royal Air Force
• No. 209 Squadron RAF

{{Aircraft specs

|ref=Aircraft of the Royal Air Force 1918–57 Thetford 1957, pp. 74–75.

|prime units?=imp

|crew=5

|length ft=67

|length in=4.75

|length note=

|span ft=97

|span in=0

|span note=

|height ft=25

|height in=6

|height note=

|wing area sqft=2461

|wing area note=

|aspect ratio=

|airfoil=

|empty weight lb=19301

|empty weight note=

|gross weight lb=

|gross weight note=

|max takeoff weight lb=29489

|max takeoff weight note=Jackson 1968, p. 206.

|fuel capacity={{cvt|906|impgal|USgal l|0}} in 3 tanks above each engine{{cite book |last1=Jackson |first1=A.J. |title=Blackburn aircraft since 1909 |date=1 April 1989 |publisher=Naval Institute Press |isbn=978-0870210242 |pages=194–208}}

|more general=

|eng1 number=3

|eng1 name=Rolls-Royce Condor IIIB

|eng1 type=V-12 water-cooled piston engines

|eng1 hp=675

|eng1 note=

|prop blade number=4

|prop name=fixed-pitch propellers

|prop dia ft=

|prop dia in=

|prop dia note=

|max speed mph=118

|max speed note=

|cruise speed mph=

|cruise speed note=

|stall speed mph=

|stall speed note=

|never exceed speed mph=

|never exceed speed note=

|minimum control speed mph=

|minimum control speed note=

|range miles=

|range note=

|combat range miles=

|combat range note=

|ferry range miles=

|ferry range note=

|endurance=4 hours 54 minutes

|ceiling ft=10600

|ceiling note=

|g limits=

|roll rate=

|glide ratio=

|climb rate ftmin=630

|climb rate note=

|time to altitude=

|wing loading lb/sqft=11.8

|wing loading note=

|fuel consumption lb/mi=

|power/mass={{cvt|0.0699|hp/lb }}

|thrust/weight=

|more performance=

|guns =3 × .303 in (7.7 mm) Lewis guns, 1 mounted forward and two aft in open cockpits

|bombs= Up to 2,000 lb (910 kg) of bombs

}}

{{aircontent|

|related=

• Felixstowe Fury
• Blackburn Sydney{{cite web|title=Blackburn: Sydney|url=http://www.gracesguide.co.uk/Blackburn:_Sydney|website=Grace's Guide|publisher=Grace's Guide|access-date=15 February 2017|date=2 August 1929}}
• Blackburn Perth

|similar aircraft=

• Saunders Valkyrie
• Short Sarafand

|lists=

• List of aircraft of the Royal Air Force
• List of flying boats and floatplanes

|see also=

}}

{{commons category|Blackburn Iris}}

;Notes

{{Reflist}}

;Bibliography

• {{cite book|last=Jackson|first=A.J.|title=Blackburn Aircraft since 1909|year=1968|publisher=Putnam|location=London|isbn=0-370-00053-6}}
• {{cite book|last=London|first=Peter|title=British Flying Boats|year=2003|publisher=Sutton Publishing|location=Stroud, UK|isbn=0-7509-2695-3}}
• {{cite magazine|last=Scott|first=Sq.-Ldr C.L.|title=By Flying Boat to India: Sir Philip Sassoon's Tour in the Blackburn "Iris"|magazine=Flight|date=9 May 1929|volume=XXI|issue=19|pages=380–383 |url=http://www.flightglobal.com/pdfarchive/view/1929/1929%20-%200962.html}}
• {{Cite book|author=Thetford, Owen|title=Aircraft of the Royal Air Force 1918–57|edition= 1st |publisher=Putnam |location= London|year=1957}}

{{Blackburn aircraft}}

Iris

Category:1920s British patrol aircraft

Category:Flying boats

Category:Trimotors

Category:Biplanes

Category:Aircraft first flown in 1926

Category:Twin-tail aircraft