British naval aircraft prototypes – Part 6: Gloster Gnatsnapper

Parts 4 and 5 of this series dealt with the Admiralty’s attempts to procure a single-seat fleet fighter, with Specification 21/26. Few aircraft typify the drawn-out nature of this contest than the Gloster Gnatsnapper.

Gloster was naturally interested in 21/26, as the company had been pursuing all-metal structures for several years and the new requirement demanded construction to be of this nature (for the first time in a naval fighter). The new specification would give Gloster the chance to develop their structural concepts in practical ways in response to a challenging set of requirements.

Work on the new fighter was begun in June 1927. Construction was based around four steel-tube longerons and square steel-tube frames, with light alloy formers fairing the fuselage to a more aerodynamic form. The wing cellule was a single-bay biplane unit with ailerons on all wings, the lower wing smaller than the upper in chord and span. The overall form of the Gnatsnapper recalled Henry Folland’s slightly earlier Goldfinch fighter, which itself resembled a stretched and cleaned-up Gamecock. The fin and rudder in particular was Gamecock-like, with a low aspect-ratio fin and a square-tipped balanced rudder that extended well above the fin. Unlike those two aircraft, the Gnatsnapper’s upper and lower wings were of similar planform, with rounded tips. The engine mount was hinged so it could be swung to either side for maintenance – this is sometimes described as an innovative feature unique to the Gnatsnapper, while in fact Specification 21/26 called for it.

The Gnatsnapper, in common with most entrants, was designed to be powered by the Bristol Mercury nine-cylinder supercharged radial air-cooled engine, but as with most those other designs (such as the Fairey Flycatcher II and Hawker Hoopoe), the engine was not ready when the airframe was. When the Gnatsnapper first flew, therefore, (in February 1928) it was driven by a Bristol Jupiter VII. According to Putnam’s ‘Gloster Aircraft Since 1917’, the prototype Gnatsnapper was not delivered to the Aeroplane and Armament Experimental Establishment (A&AEE), Martlesham Heath, for testing until May 1929, “too late for the Ship Fighter Competition.” This latter statement seems unlikely, as the Admiralty’s efforts to find a suitable aircraft dragged on well into the early 1930s (and in fact a second Gnatsnapper was ordered and by January 1929 was under construction). This was only a few months after other entrants had delivered their aircraft, and while the testing was ongoing. (The Hawker Hoopoe arrived in January, and the Vickers 141, for example, undertook deck-landing trials in June that year).  The Putman book describes the prototype, now given the serial N227, as having a “very satisfactory” performance and manoeuvrability in its Martlesham trials.

The first Gloster Gnatsnapper, N227, as it was originally completed (author’s photo)

Gloster appeared to regard the 21/26 competition as having two distinct phases. A caption attached to a Gloster press photograph of the Gnatsnapper states: “As a result of the failure of the Mercury IIA engines…the Air Ministry decided to hold a new competition”. The Putman book quoted above refers to “the organization of a second competition.” In reality, Air Ministry documents suggest that the process was simply one, ongoing effort, but that several manufacturers were asked to further develop their aircraft as the Fleet Air Arm’s requirements evolved.

Another commonly repeated inaccuracy about the 21/26 contest is that the Mercury engine was the only one specified, and its early failure was the reason the initial submissions were all rejected. In fact, the Rolls Royce ‘F’ (later the Kestrel) was also permitted (as seen with the Vickers 141 post) – most manufacturers had plumped for the Mercury because it appeared to be ahead in development and offered certain advantages in weight and hot climate performance.

In any event, Gloster went back to the drawing board and various modifications were tested either on the full size aircraft or on models in an RAE wind-tunnel, including variable camber wings and anti-stall slats. The variable-camber wings were more complex than those of the Flycatcher (which were essentially full-span ‘flaperons’) and involved the portion of the wing aft of the rear spar hinging downward, with separate ailerons. In this period N227 also had its square-tipped rudder replaced with a rounded one. When the second Gnatsnapper, N254, emerged in around March 1930, it was largely similar to N227 in this phase of its life, though it seems to have been fitted with long-stroke oleo undercarriage unlike the simple bungee-sprung undercarriage on N227.

N227 as first modified – the wings’ variable camber can be seen clearly with the dark line just aft of the interplane struts marking the hinge point (author’s photo)

Due to the ongoing problems with the Mercury, N227 was rebuilt with an Armstrong Siddeley Jaguar VIII, being delivered to Martlesham at the end of 1930. It was also fitted with a revised fin and rudder, larger than the earlier one, of triangular form. The armament, of two .303in machine guns, was moved from the sides of the fuselage to the upper deck in front of the cockpit. In this state the aircraft was dubbed Gnatsnapper Mk II. Towards the end of trials in this condition, N227 turned over during landing and had to be returned to the factory. ‘Gloster Aircraft Since 1917’ and the Gloster press photograph state that this accident ended Gloster’s hopes of winning the competition, “owing to lack of time to carry out repairs,” although in fact the Admiralty was still pursuing a radial engined fighter as an alternative to the inline-engined Nimrod well into 1932. The simple truth seems to be that the Gnatsnapper was not good enough compared with the competition. Two aircraft with air-cooled engines were still under serious consideration by the Admiralty at this stage, one of them being the Armstrong-Whitworth AW.XVI and the other probably being the Hawker Hoopoe, while investigations were made into converting the Nimrod to Mercury power. The Gnatsnapper went no further as a serious candidate for the Fleet Air Arm.

N227 in its penultimate form, with the variable camber removed, a cowled Jaguar engine and a tall, rounded fin and rudder (author’s photo)

Work on N227 continued, however – the Jaguar engine was cowled with a Townend ring, and yet another fin and rudder was fitted – this time a tall, rounded unit that resembled that of the prototype Gauntlet. After taking part in armament trials, yet more modifications were made, including two-bay wings and a Rolls-Royce Kestrel IIS liquid-cooled engine, the same type as fitted to the Nimrod Mk I. After this layout was trialled, the Kestrel was replaced by a steam-cooled Goshawk III, with condensers along the leading edges of the wings. Rolls-Royce at Hucknall used N227 from 1931 in this, its final form, as a testbed for the Goshawk and then as a company ‘hack’ until 1934, when it was retired and scrapped. The fate of N254 is unclear, but available photographs suggest it was not much modified from its original form and was probably disposed of as surplus to requirements when the Gnatsnapper was ruled out of the competition for 21/26.

Matthew Willis – navalairhistory.com