Armstrong Whitworth Ensign

The Armstrong Whitworth Ensign was a four-engine airliner designed and produced by the British manufacturing company Armstrong Whitworth. It was the largest airliner to have been build in Britain during the Interwar period.[1]

A.W.27 Ensign
AW.27 Ensign G-ADTC in typical 1940 markings
Role Airliner
Manufacturer Armstrong Whitworth Aircraft
First flight 24 January 1938
Introduction 1938
Retired 1946
Primary users Imperial Airways
British Overseas Airways Corporation (BOAC)
Number built 14

Development of the Ensign was started at the behest of the British airline Imperial Airways, who released a specification calling for a large monoplane airliner with four Armstrong Siddeley Tiger engines in 1934. Armstrong Whitworth designed it could to seat up to 40 passengers in relatively luxurious conditions for the era, having been designed for the airline's premium European and Asian routes. In addition to passengers, the aircraft also carried airmail. In Imperial Airways service, it was used to connect Britain with further seaplane flights to Australia and South Africa. While early operations were hindered by mechanical problems, modifications led to improved performance later on.

During the Second World War, the Ensign fleet was operated as transports with the newly-formed British Overseas Airways Corporation (BOAC). The type would frequently be flown between Britain and various locations with in the Middle East, usually in support of military operations. The BOAC flew Ensigns on routes between Africa and India during the war. During 1940 alone, three aircraft were destroyed by enemy action, with rumours that one was captured and subsequently operated by Nazi Germany. Shortly after the end of the conflict, the decision was taken to withdraw all Ensigns from service; following the final passenger flight of the type in June 1946 – with no buyers forthcoming – the remaining aircraft were scrapped during the following year.

Development

Background

The origins of the A.W.27 Ensign can be traced back to 1934 and the release of specification by the British airline Imperial Airways, which called for a large monoplane airliner that was to be powered by an arrangement of four Armstrong Siddeley Tiger engines.[2] The airline was keen to expand its fleet at this time, primarily due to the introduction of policy by the British Government that stipulated carriage of all first class mail between Britain and the Empire ought to be by air. While Imperial Airways had also issued a separate specification for a large flying boat, the company recognised that it would also need a new land-based airliner to serve its routes as well.[2] Armstrong Whitworth was approached directly by Imperial Airways, requesting the former produce a formal response to its specification. The company's design team examined various configurations; it was at the insistence of G. E. Woods Humphrey, Imperial Airway's managing director, that a high shoulder wing configuration was adopted as this was thought to be popular with passengers.[2]

On 22 September 1934, having been suitably impressed by Armstrong Whitworth's proposal, Imperial Airways ordered the first aircraft at a contracted price of £27,000 for its design and a further £43,300 for its manufacture; at this time, delivery of the completed airliner was anticipated to occur during 1936.[3] During May 1935, a follow-on order for eleven more aircraft, priced at £37,000 each, was received.[4] In December 1936, another order for a further two aircraft, priced at £40,000 each, brought the total number of aircraft on order to 14.[5][3] During October 1934, a final specification was drawn up by Armstrong Whitworth; amongst the details of which, it was noted that particular attention was paid to avoid wing flutter, tail buffeting, and the positioning of the tailplanes in relation to the wing.[2] Mass-balanced flight controls were adopted to avoid flutter, while wing fillets prevented eddies forming during stalls. The fuselage structure was relatively stiff, while the wing structure was comparable to those of contemporary military aircraft of the era.[6] The final specification was accompanied by various performance guarantees, including a cruise speed of 155 mph while flying at an altitude of 5,000 ft, and a take-off distance of 320 yards.[3]

During the late 1930s, production of the company's Whitley heavy bomber for the Royal Air Force (RAF) was a overriding priority for Armstrong Whitworth, leading to work on the Ensign being deprioritised and thus proceeding relatively slowly. Nor did construction ever take place at the company's main factory in Coventry, due to a lack of capacity.[7] Aviation author Oliver Tapper has questioned Armstrong Whitworth's decision to accept Imperial Airway's contract in light of its commitments to existing programmes such as the Whitley. Instead, work was performed at the production line of Air Service Training Ltd, another member of the Hawker-Siddeley group, in Hamble.[3]

Two distinct variants of the aircraft emerged, one for European services that seated a maximum of 40 passengers, and the other for the Eastern route, which had seats for 27 passengers travelling by day and 20 sleeping births for nighttime services; aside from the interior fittings, there was little different between the two variants.[1] Throughout all stages of development, a constant stream of change requests were issued by Imperial Airways, the resulting redesign work greatly slowed progress on the programme, adding up to a two year delay overall.[8] The maiden flight of the Ensign finally took place on 24 January 1938, piloted by Charles Turner-Hughes and assisted by Eric Greenwood.[9]

Flight testing and production

The Ensign's first flight revealed that there was some difficulty in the excessively heavy rudder; the issue was quickly resolved via a adjustment to the relevant servo.[8] On the second flight, the undercarriage was retracted for the first time. The prototype subject to increasingly exhaustive tests before being passing to the Aeroplane and Armament Experimental Establishment (A&AEE) for Air Ministry testing.[10] It was around this time that it was discovered that the elevator controls would intermittently jam while at altitude; this was resolved by modifying the connecting wires to account for their contraction due to the cold conditions encountered. A near disaster occurred on 8 March 1938, during which all four engines cut out due to incorrect settings of the fuel cocks, the aircraft had to be glided down to RAF Bicester, where it made a perfect "dead-stick" landing.[11]

Prototype G-ADSR in flight

Flight testing of the prototype was found to possess relatively favouring handling characteristics, although Royal Air Force pilots that reviewed it frequently criticised its slow rate of climb, which was largely attributable to the somewhat meagre output of its Tiger engines that left the aircraft relatively underpowered.[11] Upon completion of flight testing, the type was issued a certificate of airworthiness, clearing it for operational use following the completion of some modifications. These changes included a redesign of the trailing edge covering, the installation of an engine-driven compressor to charge the wheel-brake system, the addition of control locks on the throttles, and additional passenger escape hatches.[12] Once completed, the aircraft permitted the commencement of a full airline service between Croydon Airport and Paris, France on 24 October 1938.[13]

Imperial Airways had given the name "Ensign" to the prototype; shortly thereafter, the type became referred to by the same name and the "Ensign Class" moniker was applied to the whole fleet. The aircraft were fitted out for either Empire routes (eight aircraft) or European routes (four aircraft). The former carried 27 passengers in three cabins or 20 sleeping; the latter 40 passengers across three cabins and a four-person "coupe" aft of the third cabin. The only difference in crewing was a "flight clerk" replacing one of the two stewards on Empire routes.[14][1]

Design

The Ensign was a high-wing cantilever monoplane of light alloy construction and an oval fuselage with a conventional tailplane.[1] The cantilever structure of the wings was built around a single box spar, which was stabilised by internal bracing tubes and attached directly to both the front and rear rib sections. While the forward section of the wing was covered by sheet metal, aft of the box spar, the wing was covered by fabric, as was the tailplane and fin.[1] The fuselage of the Ensign was relatively long for the era, and gave the aircraft slender appearance.[15] It featured semi-monocoque construction, using a combination of stressed skin, transverse frames, and longitudinal stringers. The top of the fuselage was recessed into the wing, while its floor was strengthened by numerous tubular girders.[15]

The Ensign featured a retractable undercarrage and a castoring tail wheel; the retraction mechanism was hydraulically operated and retracted into the nacelles of the inner engines.[15] Considerable difficulties with the design of retraction mechanism were encountered, particularly due to Imperial Airways' insistence on the use of a shoulder-mounted wing. While most elements were designed and manufactured inhouse by Armstrong Whitworth, the hydraulic jacks were supplied by Automotive Products of Leamington Spa, identical jacks were used in the operation of the flaps and the undercarriage doors.[15] In practice, the retraction mechanism was often uneven and did not keep to the designed time interval. The wheels on the undercarriage were the largest to have been produced at that time.[15]

The Ensign was powered by an arrangement of four supercharged Armstrong Siddeley Tiger engines, each capable of producing 800 hp.[1] These engines were installed in the leading edge of the wing, being mounted within a tubular framework upon flexible rubber mountings and enclosed in a lengthy cowling. An auxiliary petrol-driven generator was installed to supply electricity for the lighting and to recharge the aircraft's main batteries while on the ground.[1] The cockpit was operated by two pilots, which were seated side-by-side and provided with dual controls; there was also accommodation for a radio operator.[16] It was intended for the Ensign to be typically operated by a crew of five: the two pilots, radio operator, steward, and flight clerk - on the Eastern route, the flight clerk would be replaced by a second steward instead.[8]

The Ensign's main cabin area was subdivided into separate cabins, either four cabins with accommodation for 40 passengers or three cabins with room for 27 by day or 20 at night with sleeping accommodation.[16][1] Armstrong Whitworth claimed that the interior could be changed from one configuration to the other, including the installation of partition walls and curtains, within the space of 15 minutes. The seats and backs of the day chairs would form the mattresses of the bunk beds, and further served as flotation aids in the even of a water landing.[15] The center section would typically feature a large freight compartment, pantry, lavatory on the starboard side, and a narrow corridor sometimes referred to as a 'promenade' deck between the forward and rear compartments.[15]

Operational history

Three more Ensigns – G-ADSS Egeria, G-ADST Elsinore and G-ADSU Euterpe – were completed by Christmas 1938, and were dispatched to Australia with the holiday mail.[4] All three suffered a variety mechanical problems that prevented them from reaching their destination;[9] Elsinore was forced to fly homewards, over a distance of 2,500 miles, with its undercarriage deployed throughout as it could not be retracted.[13] Consequently, Imperial Airways opted to remove all five Ensigns from active service and return them to Armstrong Whitworth, where they received modifications. The company had already been developing a series of improvements for the Ensign, and applied these to the earlier aircraft; the changes included modifications to the control runs, new constant-speed propellers, a reduction in rudder area, and the adoption of more powerful (935 hp) Armstrong Siddeley Tiger IXC engines to bolster the aircraft's performance somewhat.[17] Prior to their redelivery, the modified aircraft underwent an evaluation at Martlesham Heath, during which the type's rate of climb was demonstrated to have increased considerably. Pilot training on how to better handle the engines also led to improved levels of reliability being achieved.[17]

Starting in June 1939, the Ensigns were redelivered back to Imperial Airways, along with the sixth aircraft to be built.[17] By this time, the airline had changed its deployment plans for the type, deciding to no longer use it on the Eastern routes as had been originally intended. By September 1939, a total of eleven Ensigns had been delivered, .[18] Ambitions for four Ensigns to be serve with Indian Trans-Continental Airways, operating from Calcutta, did not come to pass, due to the modifications and the onset of war, although registrations and new names had been made and, in one case, painted on the aircraft.[19]

Shortly following the outbreak of the Second World War, it was decided to withdraw the entire fleet during October 1939.[19] The aircraft themselves were temporarily stored at Baginton Aerodrome while officials considered how they may best be used to support the war effort. Following a period of deliberation, it was decided that each Ensign would receive a camouflage scheme prior their use on a new route from Heston Aerodrome to Le Bourget Airport, Paris. The aircraft remained in service after formation of British Overseas Airways Corporation (BOAC) that November, but instead of being taken up for military service, remained under civilian control under direction of National Air Communications.[20]

Their first duties after the German invasion of the Low Countries was ferrying supplies to France. This was followed by evacuation before France capitulated in June. Despite operating away from their maintenance base for weeks at a time, Ensigns managed 100% availability and impressed folk with their short take-off run, even when fully loaded.

Three Ensigns were destroyed as a result of enemy action in 1940: G-ADSX Ettrick and G-ADSZ Elysian in France, and G-ADTC Endymion at Bristol Whitchurch in November 1940. Ettrick, which had been abandoned at Le Bourget after being damaged by bombs on 1 June 1940, was rumoured to have been used by Germany, and later given Daimler-Benz[9] engines. This is considered by most experts on the Luftwaffe to be a myth, which may have its roots in a Flight article by P.W. Moss in 1957.[21][22] However, the Database section in the March 2015 edition of Aeroplane Monthly states that the Germans may have fitted Daimler-Benz engines to G-AFZV Enterprise.[23]

As the aircraft were found to be lacking in performance for their wartime role, it was decided to give the remaining eight aircraft Wright Cyclone G.102A engines.[22] The final two aircraft that had been ordered by Imperial in 1936, were equipped with more powerful Wright Cyclone geared radial engines and completed as A.W.27A Ensign Mk IIs.[note 1] The new engines significantly improved performance and allowed the Ensign to be used in hot climates and at high altitude. At the same time, other modifications were incorporated and the prototype Mark II, G-AFZU Everest first flew in June 1941, with G-AFZV Enterprise following at the end of October.[22]

All eight surviving airframes were upgraded with these newer engines in 1941–43, as they were completed they were transferred to the Middle East and worked for BOAC on Africa to India routes.

Ensigns flew throughout the war. On a ferry flight to west Africa, following engine trouble, Enterprise made a forced landing in the desert in French West Africa (at that point under Vichy France control) about 300 miles short of their destination. Codebooks and other paperwork on board were destroyed, except for that required to show that the crew were civilian. They were picked up by an RAF Sunderland flying boat and taken on to Bathurst in Gambia. Enterprise was found by the French authorities, repaired and used as a hospital plane at Dakar before being flown to Vichy France. (During service with the French, Enterprise was initially registered as F-AFZV, later becoming F-BAHD[23]). After the German occupation of Vichy France, it was taken by the German Air Ministry and tested, before being used as transport for officers.[24] It was scrapped in Toulouse in 1943. Of those left in service, several were broken up for spare parts to support the remaining fleet.

From 1944, towards the end of their service, the Ensigns were used between Cairo and Calcutta. When taken out of use for their Certificate of Airworthiness overhauls, the camouflage dope, which, in combination with the heat, had been rotting the fabric surfaces, was removed and thereafter the Ensigns were in a "natural" finish.

After the end of the war, in part, due to their performance and the problematic maintenance of the fabric surfaces, it was decided, eventually, to remove the Ensigns from service and to return them to the UK. Euterpe, which had been out of use since February 1945, was sacrificed to make repairs to the others.[25]

The final Ensign passenger flight took place in June 1946 when G-ADSW Eddystone flew from Cairo to Hurn via Marseille, having been delayed in the Middle East by repairs. Conversion of the Ensigns was considered and they were offered for sale, but the projected costs were too much for those who showed interest. The aircraft were broken up at Hamble in March and April 1947 and removed to Cowley, Oxford where they were reduced to scrap.[26]

Accidents and incidents
  • On 15 December 1939, G-ADSU Euterpe was damaged in a forced landing at Bonnington, Warwickshire.[27] - See Talk page.
  • In December 1939, G-ADSU Euterpe overran the runway at RAF Chipping Warden and wrecked its undercarriage.[27] Unlikely - See Talk page
  • On 23 May 1940, G-ADSZ Elysean was attacked by three Messerschmitt Me 109 aircraft of the Luftwaffe whilst on the ground at Merville, Nord, France and was burnt out.[27]
  • On 23 May 1940, G-ADTA Euryalus crash-landed at RAF Lympne, Kent and was damaged. The aircraft was one of six that escaped after a Luftwaffe raid on Merville Airfield. The intended destination was Croydon. Approaching the English coast, first, she lost her port inner engine and the pilot set course for RAF Hawkinge. A short time later, her starboard inner engine also had to be shut down. The pilot changed course for Lympne. On landing, the starboard undercarriage was not fully down, causing the wing to scrape the ground and the aircraft to go through a fence as no braking was attempted. Euryalus was flown to RAF Hamble in June, but it was decided to cannibalise her to repair G-ADSU Euterpe which had been damaged in an accident at RAF Chipping Warden in December 1939. Euryalus was officially written off on 15 November 1941 and scrapped in September 1942.[28][29][30]
  • On 1 June 1940, G-ADSX Ettrick was abandoned at Le Bourget Airport, Paris, France due to the runway being strewn with time-delay bombs.[27]
  • On 9 November 1941, G-AFZU Everest was attacked by a Heinkel He 111 aircraft of the Luftwaffe over the Bay of Biscay. A safe landing was made at RAF Portreath, Cornwall. The aircraft was later repaired and returned to service.[27]
  • On 1 February 1942, G-AFZV Enterprise made a forced landing 1 nautical mile (1.9 km) from the coast of French West Africa due to problems with both port engines. The crew were rescued by a Short Sunderland of No. 204 Squadron RAF. The aircraft was later salvaged by the French and registered F-AFZV. It was later re-registered F-BAHD and entered service with Air France.Then captured by the Germans in November 1942 and re-engined with Daimler-Benz engines.[27]

Variants
A.W.27 Ensign I
Four-engine medium-range transport aircraft. Powered by four 850 hp (630 kW) Armstrong Siddeley Tiger IXC radial piston engines.
A.W.27A Ensign II
Four-engine medium-range transport aircraft. Powered by four 950 hp (710 kW) Wright GR-1820-G102A Cyclone radial piston engines.

Operators

Civil operators
 France
 United Kingdom

Military operators
Vichy France
 Germany
  • Reichsluftfahrtministerium[27]
 United Kingdom

Specifications (A.W.27A)
Armstrong Whitworth A.W.27 3-view drawing from L'Aerophile June 1937

Data from Jane's Fighting Aircraft of World War II,[16] Armstrong Whitworth Aircraft since 1913[31]

General characteristics

  • Crew: 5 (captain, first officer, radio operator, two cabin stewards)
  • Capacity:
    • European routes: 40 passengers in 4 cabins
    • Asian routes: 27 passengers in 3 cabins
  • Length: 114 ft 0 in (34.75 m)
  • Wingspan: 123 ft 0 in (37.49 m)
  • Height: 23 ft 0 in (7.01 m)
  • Empty weight: 35,075 lb (15,910 kg) [note 2]
  • Gross weight: 55,500 lb (25,174 kg)
  • Max takeoff weight: 66,000 lb (29,937 kg) [32]
  • Powerplant: 4 × Wright GR-1820-G102A geared radial engines, 1,100 hp (820 kW) each

Performance

  • Maximum speed: 210 mph (340 km/h, 180 kn) at 6,700 ft (2,000 m)[32]
  • Cruise speed: 180 mph (290 km/h, 160 kn) at 5,000 ft (1,500 m)[32]
  • Range: 1,370 mi (2,200 km, 1,190 nmi) at 173 mph (150 kn; 278 km/h)[32] and 5,000 ft (1,500 m)
  • Service ceiling: 24,000 ft (7,300 m) when fully loaded
  • Rate of climb: 900 ft/min (4.6 m/s) at sea level

See also

Related development

Aircraft of comparable role, configuration, and era

Related lists

References

Notes
  1. Moss identifies the AW.27A as a "rail-launching project to Specification 13/38".
  2. Moss gives 36,586 lb (16,595 kg)[32] while Tapper states 36,590 lb (16,600 kg)[33]

Citations
  1. Tapper 1988, p. 237.
  2. Tapper 1988, p. 235.
  3. Tapper 1988, p. 236.
  4. "Armstrong Whitworth A.W.27 Ensign." Imperial Airways, 20 April 2006. Retrieved: 31 January 2011.
  5. Flight 1957, p. 203.
  6. Tapper 1988, pp. 235-236.
  7. Tapper 1988, pp. 236-237.
  8. Tapper 1988, p. 279.
  9. Jackson, A.J. (1973). British Civil Aircraft since 1919. 1 (2nd ed.). London: Putnam & Co. ISBN 0-370-10006-9.
  10. Tapper 1988, pp. 239-241.
  11. Tapper 1988, p. 241.
  12. Tapper 1988, p. 242.
  13. Tapper 1988, p. 243.
  14. Flight 1957, p. 204.
  15. Tapper 1988, p. 278.
  16. Bridgman 1988, pp. 103–104.
  17. Tapper 1988, p. 244.
  18. Tapper 1988, p. 244, 246.
  19. Tapper 1988, p. 246.
  20. Tapper 1988, p. 247.
  21. Moss, P.W. Flight 1957, p. 206.
  22. Flight 1957, p. 247.
  23. Aeroplane March 2015, p. 94.
  24. Flight 1957, p. 249.
  25. Flight 1957, p. 249.
  26. Flight 1957, p. 250.
  27. "Database: Armstrong Whitworth Ensign". Aeroplane. Stamford: Key Publishing (March 2015): 77–94. ISSN 0143-7240.
  28. Flight 1957, p. 203.
  29. Moss, P.W. "Ensign Class." Archived 6 March 2016 at the Wayback Machine Flight, 1957. p. 204.
  30. Flight, 1957 p. 205 Archived 6 March 2016 at the Wayback Machine
  31. Tapper 1988, pp. 253-254.
  32. Moss Flight 22 February 1957, p. 250.
  33. Tapper 1988, p. 254.

Bibliography
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