Friday, 24 August 2012

The Stranraer – Mitchell’s last flying-boat.


Supermarine Stranraer from a painting by the author


After Supermarine had received orders for the Scapa, the Air Ministry issued another specification, R.24/31, for another general purpose coastal patrol flying-boat but capable of carrying a 1,000 lb. greater load and of maintaining height on one engine with 60% of fuel on board. An enlarged and substantially altered version of the Scapa had to be projected but only the Saunders-Roe A.27 was accepted. Built as the 'London', it replaced the Southamptons and Scapas of Nos. 201 and 202 Squadron respectively. 
   At about this time, the Singapore III was ordered as a replacement for other Scapas with Nos. 204 and 240 Squadrons.This Short machine had about the same speed as the Scapa and was powered by twice as many engines.Thus, given an economic situation in which orders for larger flying-boats were likely to be kept to a minimum, it seemed a distinct possibility that a performance from Mitchell's smaller, twin-engined R.24/31 proposal might still stand a chance of winning some contracts, given the growing calls for British rearmament.
   Another reason for anticipating orders for the proposed new design was not simply based on the good performance figures that the Scapa had returned but on Mitchell’s having come to believe in the virtue of employing a thin-wing – for other than Schneider Trophy racers – contrary to the generally perceived wisdom of the day.
   The engines chosen initially to pull the new machine’s thinner aerofoil through the air, and to give it the required one-engine performance required by the Air Ministry specification, were 820 hp Bristol Pegasus IIIMs providing a combined 590 hp more than the Scapa's Kestrels. The two engines were to be mounted with the same thrust line  and in streamlined fairings but, being air-cooled radials, did not incur the extra weight and drag penalties of the Scapa's radiators; long-chord Townend drag-reducing rings surrounded the cylinder heads and their oil coolers formed part of the top centre-section leading edge.
  An extra depth of the new hull allowed the top of the enclosed cockpit to form a continuous line with the midship gunner’s cockpit which was now placed in the centre of the hull top – in the Southampton and Scapa there had been two midship gunner’s cockpits, offset from the centre-line. And now, for the first time, Supermarine were able to install the second rear gunner in a more faired-in cockpit in the tail. This had been proposed for the unsuccessful Southampton X prototype, with its wingspan of 79 feet, and so presented little difficulty for the new 85 footer.

The new prototype, K3973, was test flown by Summers on the 27th of July, 1934 and delivered in very short time to MAEE, Felixstowe for service assessment. The performance of the aircraft was such that an order for seventeen aircraft, K7287 to K7303, was placed with Supermarine by the following year. The standard service machine was fitted with the more powerful, 920 hp Pegasus X engines and could outperform all contemporary flying-boats. It had a maximum speed of 165 mph, making it the fastest biplane flying-boat to enter RAF service, yet had a stalling speed of only 51 mph. Its maximum ceiling was 20,000 feet and it could climb to the first 10,000 feet at a thousand feet per minute. As it was necessary to withhold these performance details because of the international situation, company publicity had to be content with the by-no-means despairing comment that the aircraft ‘passed all its tests brilliantly’ and went on to claim that ‘the outstanding feature of this flying-boat is that the performance obtained during a series of extended service trials, whether in respect of speed, climb, ceiling or take-off, is unequalled by any other British flying-boat. All the specification requirements were exceeded by large margins’.

The machine entered service as the 'Stranraer' and it must have been gratifying for Supermarine to see the Saunders-Roe London flying-boat replaced by their new aircraft with Nos. 201 and 240 Squadrons and to see another rival company’s aircraft, the Singapore III, superseded by the Stranraer with No. 209 Squadron. Other machines replaced the Scapas with No. 228 Squadron.

Whilst it must be acknowledged that the Stranraer, being a fabric covered biplane, was an obsolescent type, as a stop-gap it was actually operated in World War II, serving with No. 228 Squadron when it was needed to patrol the North Sea. Additionally, some of the Stranraers of this unit were transferred to No. 209 Squadron and, fitted with extra fuel tankage under one wing and bombs under the other, they conducted patrols against enemy shipping between Scotland and Norway, until replaced in April 1941 by the ubiquitous Lockheed Hudson. No. 240 Squadron was also equipped with the Stranraer and made the last operational patrol of the type on 17 March, 1941.
   In addition, the Royal Candian Air Force also adopted the Stranraer and 40 were built by Canadian Vickers and these saw a great deal more service than their British counterparts – in the battle against the U-boats in the Atlantic. They were finally replaced on active service by the Canadian Catalina, the Canso, in March 1941. The last RCAF Stranraer was retired as late as 20 January, 1946 and fourteen of the aircraft were sold to the civil sector, particularly to private airline companies in Canada. The last one of these Stranraers served in these spartan regions until 1958.




For reference sources, see my Blogpost: “Source Material and References" – an extended bibliography is included in my R.J.Mitchell at Supermarine; Schneider Trophy to Spitfire (details below) which also provides material for wider reading, grouped according to specific areas of interest. 

More information on the Stranraer, photographs, and a three-view drawing, as well as a full account of all Mitchell's completed designs and of the man behind them, will be available in a few weeks' time:
Advance Notice – 
R.J.Mitchell at Supermarine; Schneider Trophy to Spitfire.
This is a much expanded, completely up-to-date, second edition of my earlier work with 50% more photos, and 25% more text – 380 pp. instead of 250. There are general arrangement drawings of Mitchell’s 21 main aircraft types which flew, as well as 40 other drawings. There are 24 photographs, featuring or including Mitchell, as befits the first fully detailed and, I hope,  definitive account of the man and his work at Supermarine.
To obtain a copy at pre-publication prices, please enquire via the contact form in the sidebar.


Tuesday, 14 August 2012

Mitchell’s Scapa nearly went to war.



Most of Mitchell’s seaplanes were designed for war, although naval reconnaissance rather than bombing was their main requirement from the Air Ministry. They were, basically, traditional biplanes and Mitchell was also encouraged to design two other biplane flying-boats, closer to the outbreak of World War II, despite the obsolescence of the configuration.
Scapa
The first of the new designs, to become known as the Scapa, was ordered as a successor to the long-serving Southampton, to be fitted with a metal superstructure and powered bythe new Rolls-Royce Kestrel engines. Thus the Southampton IV/Scapa has been regarded as, essentially, an ‘improved Southampton’, particularly as its hull planing geometry was closely based on that of the earlier aircraft. This similarity was very much a compliment to the intuitive designers of the Southampton hull of 1925, as the later advantage of tank testing did not suggest any real need to depart from the basic shape of its predecessor – indeed, a wider beam behind the step, to discourage water striking the tail surfaces, was replaced by the older Southampton after-portion when actual take-offs revealed an unpleasant pitching when the rear step made contact with the water.
   Nevertheless, the eventual Scapa was, effectively, a new design. The need to ‘stretch’ the Southampton design resulted in a lengthened bow with a deepened forefoot which, with a flatter top-decking, altered the overall appearance of the previous Southampton hull. The Air Yacht tradition of flat plates and rectangular sections was still evident although the upswept tail section and other curvatures restored something of the elegance of the Southampton.
Two fins now replaced the triple-fin arrangement of the Air Yacht or standard Southampton and the engines were now positioned directly under the top wing.

Supermarine Scapa, from a painting by the author

This upward re-siting of the engines was probably influenced by the water ingestion problems experienced by the Seamew and allowed Mitchell to dispense with the engine supports of his previous inter-wing-engined designs and the large Warren bracing of the Southampton superstructure. His reversion with the S.5 and S.6 to wire bracing must also have been a factor here and also led to a single bay structure, even though the new machine’s wingspan was to be as large as 75 feet. Beverley Shenstone, Mitchell’s aerodynamicist, considered the resulting aircraft ‘perhaps the cleanest biplane flying-boat ever built, with minimum struttage and clean nacelles faired into the wing’. He did not mention the very ‘boxy’ radiators which projected on either side to the rear of these nacelles although this positioning least compromised the overall lines of the new design.
   No new name had been chosen when ‘Mutt’ Summers took S1648 up for its first flight on 8th July, 1932. After numerous tests, it was delivered on 29th October to MAEE, Felixstowe, for further trials which included a maximum duration flight of 10 hours over the North Sea. In the following May, the prototype was flown to the Kalafrana flying-boat base, Malta, for overseas acceptance trials with No. 202 Squadron and these involved a long-distance flight to Gibraltar and back and a cruise to Port Sudan via Sollum, Aboukir, and Lake Timsah. On its return, the Scapa took part in the 1934 fly-past of ‘the competition’ at the Hendon R.A.F. Display with, as Penrose reported, ‘the clean Supermarine twin-engined Scapa leading, followed by the four-engined Short Singapore, triple engined Blackburn Perth, the distinctive gull-winged Short Knucklduster, Saro R24/31 London and the three Saro Cloud trainers’.
The Hendon event was clearly designed to impress foreign governments of Britain’s military capabilities and, during the 1935 – 1939 period, the Scapa fulfilled its required purpose with anti-submarine patrols to protect neutral shipping during the Spanish Civil War. Some of the aircraft of No. 202 squadron were later transferred to No. 204 Squadron and were sent to Egypt during the Italian-Abyssinian confrontation. There was also a single Scapa attached to No. 228 Squadron whose contribution to the developing war preparations was involvement in early radar trials. 



For reference sources, see my Blogpost: “Source Material and References" – an extended bibliography is included in my R.J.Mitchell at Supermarine; Schneider Trophy to Spitfire (details below) which also provides material for wider reading, grouped according to specific areas of interest. 

More information on ….., photographs and three-view drawing… of the .., as well as a full account of all Mitchell's completed designs and of the man behind them, will be available in a few weeks' time:
Advance Notice – 
R.J.Mitchell at Supermarine; Schneider Trophy to Spitfire.
This is a much expanded, completely up-to-date, second edition of my earlier work with 50% more photos, and 25% more text – 380 pp. instead of 250. There are general arrangement drawings of Mitchell’s 21 main aircraft types which flew, as well as 40 other drawings. There are 24 photographs, featuring or including Mitchell, as befits the first fully detailed and, I hope,  definitive account of the man and his work at Supermarine.
To obtain a copy at pre-publication prices, please enquire via the contact form in the sidebar.