A.Jackson Avro Aircraft since 1908 (Putnam)
Designed late in 1915, the Avro 521 two seat fighter-trainer was a hybrid embodying the features of several Avro 504 variants. In side elevation the straight top longerons proclaimed it a derivative of the 504 prototype, yet the short span ailerons and the rudder/tail skid assembly were pure 504A, the cockpit positioning and centre section struts were 504E, the Vee strut undercarriage was contributed by the 504G and the streamlined headrest was copied from the Avro 519. Standard Avro 504 mainplanes were shortened to a span of approximately 27 ft. 6 in., cut away at all four wing roots to improve upward and downward vision and rigged with only a single set of interplane struts on each side. The engine was a 110 h.p. Clerget rotary in characteristic Avro cowlings.
The initial order was for one machine, test flown at Trafford Park, Manchester by F. P. Raynham with H. E. Broadsmith standing up in the rear cockpit and brandishing a dummy machine gun to enable the effect of the extra drag to be assessed. Raynham found the Avro 521 longitudinally unstable and unpleasant to fly; nevertheless it was delivered to Farnborough in February 1916 and 25 production machines were ordered for the R.F.C.
Proposals were also made for interchangeable wings to suit different roles but it is not known if any aircraft were actually modified. Designation Avro 521A was allotted to a version with mainplanes of 46 ft. span, while with standard Avro 504 mainplanes of 36 ft. span it was to have been known as the Avro 521B. It is doubtful if all were completed and there is no record of any production Avro 521 having been delivered. This strengthens the belief that the Avro 521 in which Capt. Garnett crashed and was killed at Gosport in 1917 must have been the prototype.
SPECIFICATION AND DATA
Manufacturers: A. V. Roe and Co. Ltd., Clifton Street, Miles Platting, Manchester
Power Plant: One 110 h.p. Clerget
Production: One unmarked prototype Works Order number believed 1811; and twenty-five production aircraft 7520 to 7544, believed not all built
Service Use: At the Advanced Training School, Gosport, Hants.
P.Lewis The British Fighter since 1912 (Putnam)
The unqualified success of the Avro 504 prompted the parent company to construct during early 1916 a two-seat fighter variant under the type number 521. The wing structure was cleaned up by conversion to single-bay cellules and the same streamlining process applied to the undercarriage resulted in a simple V-strut structure. The rear cockpit was set some distance behind that of the pilot, above whom was a generous cut-out in the trailing edge of the centre-section.
The 110 h.p. Clerget powered the Avro 521, which was test-flown by F. P. Raynham and found to have disagreeable flying characteristics. Nevertheless, despite the crash of the prototype in the hands of an R.F.C. pilot, twenty-five production 521s were built but did not apparently reach operational service in their intended role.
H.King Armament of British Aircraft (Putnam)
521. Designed in 1915 as a two-seat 'fighting scout#, the 521 (completed 1916) was intended to have a rear-mounted Lewis gun, though this does not appear to have materialised.
W.Green, G.Swanborough The Complete Book of Fighters
AVRO 521 UK
The Avro 521 two-seat fighter, which was flown late in 1915, was something of a hybrid in that it embodied a number of Avro 504 components. Powered by a 110 hp Clerget 9Z nine-cylinder rotary, the prototype had provision for a free-mounted 0.303-in (7,7-mm) Lewis gun fired from the rear cockpit. The prototype underwent official trials early in 1916, and 25 aircraft were ordered for the RFC, but this contract was subsequently cancelled, and there is no evidence that any Avro 521 other than the prototype (which crashed at Upavon on 21 September 1916) was built.
Max speed, 90 mph (145 km/h) at sea level.
Time to 6,000 ft (1830 m), 14 min.
Endurance, 4.5 hrs.
Empty weight, 1,150 lb (522 kg).
Loaded weight, 1,995 lb (905 kg).
Span, 30 ft 0 in (9,14m).
Length, 28 ft 2 in (8,58 m).
Wing area, 266 sq ft (24,71 m2).