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The Avro 503 (Type H) was a larger but lighter development of the Avro 501 of which at least four were ordered, with three going to the Admiralty and one to the German Navy.
The Avro 501 had been built at Brownsfield Mills in November 1912 as an single float amphibian development of the Avro 500, with a similar square section to the fuselage, but with a much longer 47ft 6in upper wing. 14ft 6in longer than the lower wing. It was tested on Windermere in January 1913, where the single float proved unsatisfactory. A new twin float undercarriage was built, and the aircraft purchased by the Admiralty.
Work at Avro then moved onto the Type H (later the Avro 503). This had the same square section to the fuselage. The upper wing was made slightly longer, but the lower wing was much longer, halving the difference in length. This eliminated the need for the outer diagonal wing strut on the Avro 500. Large inversely tapered ailerons were carried on the upper wing.
The prototype was given twin two-step floats, each 14ft long and 2ft 6in wide, with a track of 6ft 6in. Each was connected to the fuselage by 14 steel struts and covered in a rubberised material.
The 501 had proved to be too heavy, so the 503 was made lighter, with an all-up weight of 2,200lb, 500lb less than the 501. It used the same 100hp Gnome engine as the Avro 500.
The Avro 503 was built around a 9ft long central section which included the centre section of the upper wing. The rest of the fuselage, the engine, the outer wing panels and the undercarriage could all be bolted to this central section to make it quick to dismantle or assemble the aircraft.
Compared to the Avro 501, the Avro 503 was slightly longer and taller, the upper wing was 2ft 6in long and the lower wing 7ft 6in longer. However its all up weight was 500lb lower. Top speed came down by 5mph.
The Avro 503 made its maiden flight from the River Adur at Shoreham on 28 May 1913 with F.P. Raynham at the controls and John Alcock (later to become famous for the first non-stop flight across the Atlantic in 1919. On 29 May the aircraft made its first landing on the open sea opposite Paston Place, Brighton. However one float was damaged when the aircraft took off again, so it had to land in Shoreham Harbour to be beached. The noses of both floats were then strengthened. On 14 June the aircraft flew with the Inspector of Naval Aircraft, Lt J.W. Seddon, on board, and reached 1,300ft in 5 minutes.
In a sign of how little the outbreak of any war was expected, the Avro 503 was then flown by Capt Schultz of the German Navy and sold to Germany. It was delivered by the end of June. On 3 September 1913 Lt W. Langfeld became the first man to fly the 40 miles across the North Sea from Wilhelmshaven to Heligoland, returning to Cuxhaven on 14 September.
At least three more Avro 503s were built for the Royal Naval Air Service. Another one that had been ordered for Peru might have been taken over at the outbreak of war.
At least one of these aircraft was delivered as a landplane. On 28 August 1913 F.P. Raynham reached 3,000ft in 19 minutes in this aircraft, during trials at Eastchurch. On this flight it started with 36 gallons of petrol, 10 gallons of oil and 182lb of ballast. In speed trials it reached 65.1mph.
The next aircraft was built as a float plane. This reached Sheerness on 8 September 1913, and was delivered to the Isle of Grain on 15 October.
The last aircraft was an improved version that was delivered to the Isle of Grain in December 1913.
One of the two machines at the Isle of Grain was damaged in a fire and had to be sent to Brooklands for repairs in July 1914.
Engine: Gnome
Power: 100hp
Crew: 2
Span: 50ft 0in (upper), 47ft 0in (lower)
Length: 33ft 6in
Height: 12ft 9in
Empty weight:
All-up weight: 2,200lb
Max speed: 50mph
Climb Rate: 225ft/ min