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Avro 531 Spider

Single-Seat Biplane Fighter Prototype

The Avro 531 Spider failed to overtake the venerable Sopwith Camel in terms of performance - leaving just two prototypes completed.
Authored By: Staff Writer | Edited: 8/21/2018
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Year: 1918
Status: Cancelled
Manufacturer(s): A.V.Roe (Avro) - United Kingdom
Production: 2
Capabilities: Fighter; X-Plane;
Crew: 1
Length: 20.51 ft (6.25 m)
Width: 28.54 ft (8.7 m)
Height: 7.87 ft (2.4 m)
Weight (Empty): 970 lb (440 kg)
Weight (MTOW): 1,543 lb (700 kg)
Power: 1 x Clerget (Gwynnes) 9B air-cooled rotary piston engine developing 130 horsepower and driving a two-bladed wooden propeller at the nose.
Speed: 121 mph (195 kph; 105 kts)
Ceiling: 19,685 feet (6,000 m; 3.73 miles)
Range: 249 miles (400 km; 216 nm)
Rate-of-Climb: 1,250 ft/min (381 m/min)
Operators: United Kingdom (cancelled)
The Avro 531 "Spider" began life as a private venture attempt by the company to provide an all-modern biplane fighter for British service during the latter stages of World War 1 (1914-1918). Its design was attributed to Roy Chadwick and was influenced heavily by work related to the company's earlier Type 504 biplane (detailed elsewhere on this site). With a first-flight held during April of 1918, the Avro 531 was not adopted for service as British authorities committed to the competing Sopwith Snipe (detailed elsewhere on this site) going forward. This left just two Spider prototypes completed.

In the Model 531 design, the traditional biplane arrangement of the period was featured. However, the upper wing section was held close to the dorsal surface of the fuselage thus affording the pilot with better vision over and around his aircraft. Additionally, the lower wing section was of much smaller surface area than the larger (sesquiplane). V-type (Warren truss-style) interplane struts were used for bracing the wing members to one another and this gave the appearance of a spider's web when viewing the aircraft from the front profile - hence the aircraft's name of "Spider". The engine was held in a forward compartment and the tail unit was wholly traditional. The undercarriage was fixed and of a tail-dragger arrangement. Seating was for one in an open-air cockpit and proposed armament being 1 x 7.7mm Vickers machine gun sat over the nose and synchronized to fire through the spinning propeller blades.

Power was from a French-originated, British-produced (by Gwynnes Ltd) Clerget 9B air-cooled rotary piston engine of 130 horsepower output driving a two-bladed propeller at the nose. Maximum speed became 120 miles per hour with an operational range out to 250 miles and a service ceiling of 19,000 feet. Rate-of-climb was listed at 1,250 feet per minute.

All told, the Spider exhibited excellent control and was highly agile in addition to providing better situational awareness for the pilot when compared to contemporaries. However, in the opinion of the War Office, it did not best the overall performance of the competing in-service Sopwith Camel fighter and the Air Service moved on the Sopwith Snipe instead.

The Model 531A (with revised strutworks) was also in development at the time and was to appear as a refined version of the original. It appears that this variant was not finished and went on to influence the related high-speed Model 538 racer. This design, too, failed to see completion and the whole airframe was scrapped by 1920.


1 x 7.7mm Vickers machine gun over the nose synchronized to fire through the spinning propeller blades.

Graphical image of an aircraft medium machine gun

Variants / Models

• Model 531 "Spider" - Base Series Name; two prototypes completed.
• Model 531A - Proposed refined variant; left incomplete.
• Model 538 - Proposed racer form built upon the Model 531 framework.
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