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Blackburn Iris

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Old March 30th 18, 10:55 AM posted to alt.binaries.pictures.aviation
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Default Blackburn Iris


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-range maritime
reconnaissance aircraft by the Royal Air Force, 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 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.

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.

Flying Boat

National origin
United Kingdom

Blackburn Aircraft

John Douglas Rennie

First flight
18 June 1926



Primary user
Royal Air Force

Number built

Blackburn Perth

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 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.

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 Reykjavk 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

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. 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. 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 engines, with the centre engine in a pusher
configuration to become the Iris IV.

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

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.

Specifications (Iris III)

General characteristics
Crew: five
Length: 67 ft 4 in (20.54 m)
Wingspan: 97 ft 0 in (29.6 m)
Height: 25 ft 6 in (7.77 m)
Wing area: 2,461 ft (228.7 m)
Empty weight: 19,301 lb (8,773 kg)
Loaded weight: 29,000 lb (13,182 kg)
Max. takeoff weight: 29,489 lb (13,404 kg)
Powerplant: 3 Rolls-Royce Condor IIIB piston engines, 675 hp (503 kW) each

Maximum speed: 102 kn (118 mph, 190 km/h)
Cruise speed: 79 kn (97 mph, 155 km/h)
Range: 691 nmi (800 mi, 1,280 km)
Service ceiling: 10,600 ft (3,230 m)
Rate of climb: 630 ft/min (3.20 m/s)
Wing loading: 11.8 lb/ft (57.6 kg/m)
Power/mass: 0.0699 hp/lb (114 W/kg)
Endurance: 4.9 hours


Guns: 3 .303 in (7.7 mm) Lewis guns, 1 mounted forward and two aft in open
Bombs: Up to 2,000 lb (910 kg) of bombs



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