Blackburn R.B.1 Iris and R.B.3A Perth

Three-bay biplane long-range reconnaissance flying boat to meet the requirements of Specification R.14/24. The three engines were mounted in individual nacelles within a three-bay centre section, to which two-bay outer wings were attached on each side. A 302-gallon fuel tank was mounted on the underside of the upper wing above each engine. These tanks gravity-fed a collector unit in the lower wing centre section from which supply to the individual engines was controlled. The equal-span wings used a wooden structure, with duralumin drag struts and steel tie rods, with ailerons fitted to both upper and lower wings and floats fitted under the wingtips. A biplane tail unit was fitted, with the upper tailplane carrying the elevators whilst the reduced span lower surface acted solely as a trimming surface. Three aerodynamically balanced rudders were fitted in between. The aircraft's hull had a wooden structure covered in plywood, with a V-bottom with two steps to give good water handling.
Two pilots sat side-by-side in an open cockpit with a second cockpit provided behind the pilots for use by the navigator and other crew members. There was access from this cockpit to a central cabin which was equipped with four bunks, a chart table, wireless telephone equipment and a galley. The normal crew complement was five which included two pilots, a navigator and two additional crew variously acting as engineers, gunners or as observers. 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 of bombs. Three 650 h.p. Rolls-Royce Condor III powerplants driving 4-bladed fixed-pitch propellers.

Iris I rebuilt with a new, all metal hull of generally similar external design to that of the prototype, other than the inclusion of small circular portholes to provide light to the cabin area. It featured an upswept tail section to accommodate a defensive gun position, aft of the tail unit. The central rudder was deleted and metal wing-tip floats were fitted. Three 675 h.p. Rolls-Royce Condor IIIA powerplants, fitted in a more refined installation.

Similar to the Iris II but with fabric covered all-metal wings, to meet the requirements of Specification R.31/27. The cabin could now be accessed from the pilots cockpit and additional portholes were also added. Gun positions were provided in the nose, midships and at the tail with bomb racks provided under the wing roots, typically carrying a load of two 520 lb bombs. Three 675 h.p. Rolls-Royce Condor IIIB powerplants.

Conversion of the Iris II with three 800 h.p. Armstrong Siddeley Leopard III powerplants, the outer two engines being installed driving tractor propellers, whereas the central engine was faced backwards to drive a pusher propeller.

Conversion of the Iris III with three 825 h.p. Rolls-Royce Buzzard IIMS powerplants. A more streamlined engine nacelle was adopted and a reduction drive allowed larger diameter propellers, which were a better match to the power available.

R.B.1D featuring a bow mounted 37mm C.O.W. quick firing cannon.

Developed from the R.B.3 Iris V to meet the requirements of Specification 20/32 and having an enclosed cockpit for the pilots. A 37 mm Coventry Ordnance Works (COW) automatic cannon was fitted in the Bow-gunner’s position, which was supplemented by three machine guns in bow, dorsal and tail positions. The 37 mm cannon was intended for anti-ship use, firing 1.5 lb shells at 100 rounds per minute whilst a maximum bomb payload of 2,000 lb could be carried.. Three 825 h.p. Rolls-Royce Buzzard IIMS powerplants driving 2-bladed fixed-pitch propellers, with the outer units mounted on the inner inter-plane struts and a central pylon supporting the middle engine. Each engine was fed by its own 575 gallon fuel tank, these having been streamlined into the wing leading edge above each engine.

R.B.3A Perth Specification
Span	Length	Height	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
97 ft	70 ft	26 ft 5.5 in	2461 sq ft	20927 lb	32500 lb	109 mph/ 95 kn	132 mph/ 115 kn	1300 mi	11500 ft
29.57 m	21.34 m	8.06 m	228.63 m2	9492 kg	14742 kg	175 km/h	212 km/h	2092 km	3505 m