Flight, October 1933

THE BLACKBURN "PERTH”
3 Rolls-Royce "Buzzard II" MS Engines

   FOG interfered with the official launch at Brough, on October 9, of the new Blackburn "Perth" flying boat which has just been completed by the Blackburn Aeroplane & Motor Co., Ltd., to the order of the British Air Ministry. A party of guests invited by the Blackburn and Rolls-Royce companies travelled to Hull on Sunday last in order to be at Brough in time for the launch on Monday morning at high tide, but a sea fog made the actual launch impossible, and when that cleared a gale warning was issued, so that it was not deemed advisable to send the machine for its first flight, and the visitors had to be content with witnessing the christening of the machine by Lady Atkinson, and a demonstration of the automatic quick-firing gun which has been installed in the bows of the hull.
   The Blackburn "Perth" is the last of a long family of "Iris" flying boats, the first of which was produced as long ago as 1926. Mr. Robert Blackburn is one of the pioneers of British aircraft constructors, and almost from the beginning he has been closely associated with seagoing and marine aircraft. Torpedo planes have formed the mainstay of the Blackburn business for very many years, and when it was decided to add flying boats to the aircraft types produced, the services of Mr. J. D. Rennie were secured. From the design of the first "Iris" to the present "Perth," Mr. Rennie has, under Maj. Bumpus, the chief engineer, been in charge of flying-boat design, a task which he has fulfilled with conspicuous success.
   In its general lines the latest machine follows the well-tested and proved features of the "Iris" family, the superstructure being of biplane arrangement and the hull characterised by a pronounced vee bottom which is particularly sharp towards the bows. This sharp vee serves to lessen the shocks of alighting and taxying in a seaway, and the Blackburn flying boats are noteworthy for their seaworthiness as well as for their sturdy construction.
   The "Perth" belongs to the class of flying boat designed for reconnaissance and coastal patrol, which means that it is capable of operation either in co-operation with the Fleet or independently. Its long range (1,500 miles maximum) enables it to cover a large area of coast line on patrol against hostile surface or submarine craft, or to operate over long distances when used for reconnaissance or bombing purposes. For instance, it could make a complete "circuit of the North Sea" as a normal reconnaissance flight.
   Apart from its usual armament of bombs and machine guns, the "Perth" introduces a new feature in air armament by being fitted, for the first time, with a large-calibre automatic quick-firing gun which fires l 1/2-lb. shells at a rate of 100 per minute. This gun is mounted in the cockpit in the bows, which have been specially designed to accommodate it.
   Normally, the "Perth" class of flying boat will carry a crew of five: First pilot, second pilot (who is also the navigator), bow gunner, wireless operator, and an engineer who also mans the rear guns. In addition to the new quick-firing gun the "Perth" carries three machine guns and 2,000 lb. of bombs, so that it will be realised that it is a formidable opponent and may, in fact, be regarded as the forerunner of the future cruiser of the air.
   The hull of the "Perth" is, as already mentioned, similar to those of previous boats of the "Iris" family, with two steps and a pronounced vee bottom. The construction includes full section frames attached to a full-length keelson, and the planking is of "Alclad." This material is metal sheet in the form of a "sandwich," with a central layer of duralumin and outer layers of pure aluminium. Highly-stressed fittings, etc., are of stainless steel.
   The accommodation in the hull is arranged as follows: In the extreme bows is the station equipped with the quick-firing gun and a machine gun. This cockpit also contains the bomb fusing and release gear, the anchor and winch, and the mooring and towing tackle.
   Aft of the front cockpit is the pilots' cabin, with side-by-side seating and dual controls. Then comes the navigator's station, equipped with chart table, stool, chart racks, etc. Next comes the "wardroom," which forms the officers' sleeping and living quarters, and then the men's quarters and engineer's station. The wireless cabin is on the port side and the galley on starboard, with rear gun cockpit above. Farthest aft is the lavatory, and in the extreme stern is a gunner's cockpit, whence the defence against attack from the rear is undertaken. The view and field of fire from this cockpit is unobstructed over the entire hemisphere aft of the machine. The hull is so arranged that through-communication from bow to stern is provided. The equipment includes an inflatable dinghy.
   The superstructure consists of biplane wings of equal span and chord, with the three engines carried between them. They are of all-metal construction, with spars of duralumin box section and tubular ribs. Walkways are provided on the lower centre-section for access to the engines, and on the top plane there are walkways to enable engineers to get to the ailerons.
   Like the main planes, the tail is of biplane arrangement, but the upper tailplane is of greater span than the lower. Elevators are hinged to lower as well as upper tailplane, but the lower elevator is used for trimming only. There are two vertical fins and three rudders, and servo control with clutch mechanism is incorporated in all three rudders. The construction of the tail surfaces is similar to that used in the wings, i.e., duralumin box spars and tubular duralumin ribs, with fabric covering.
   The power plant consists of three Rolls-Royce "Buzzard" engines, series II MS., placed side by side in the gap between the wings. The central engine is mounted on trestle struts from the lower centre-section, but the two outboard engines are supported on the sloping interplane struts. The radiators are mounted one on each side of the tail fairing of each engine.
   As the large series of Rolls-Royce engines is apt to be a little confusing, it is, perhaps, worth recalling that the "Buzzard" II MS. is a 12-cylinder water-cooled vee engine, with a bore of 6 in. and a stroke of 6.6 in., developing a normal power of 825 b.h.p. at sea level and a maximum of 920 b.h.p. The normal speed is 2,000 r.p.m., and the maximum 2,300 r.p.m. The compression ratio is 5.5:1 and the airscrew reduction gear ratio is 0.553:1. The letters MS. indicate that the engine is moderately supercharged.
   All the petrol is carried in three wing-section tanks in the upper wing. Each tank has a capacity of 575 gallons (2 614 litres), giving a total petrol capacity of 1,725 gallons (7 842 litres). With full tanks the range is 1,500 miles. At normal gross weight of 32,500 lb., the machine carries either a reduced military load or less than the full quantity of petrol, and the maximum gross weight of 38.000 lb. is in the nature of an overload weight.