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The Hawker Tornado and Typhoon Prototypes

The first Hawker Typhoon P5212 as it first appeared, with small fin and rudder, and solid fairing behind the cockpit. Note the large, low-pressure tyres (World War photos)

Sydney Camm

Sydney Camm

By Matthew Willis

In March 1937, some seven months before the first production Hawker Hurricane was delivered to the RAF, Sydney Camm began work on a new single-seat interceptor fighter. The initial schemes pre-dated the official release of Specification F.18/37 – the Air Ministry’s requirement for a Hurricane and Spitfire replacement – by a year. Even at this early stage, the preferred engine was a somewhat radical new design from D Napier and Sons, which the Air Ministry had just placed a development order for – a 36L liquid-cooled horizontal H-24 using sleeve-valves. An alternative was the Rolls-Royce Vulture, another 24-cylinder engine but in an X-configuration, and using conventional valves, and 42L capacity. Both engines were expected to produce around 2,000hp. They were early in their development and, along with engines like Bristol’s air-cooled radial Centaurus of similar power, were a significant step up in complexity from the current generation of engines. Unlike the Spitfire and Hurricane, adapted early in their development to the Rolls-Royce Merlin and thereafter with no other powerplants seriously considered, the next-generation fighter would need to hedge its bets over which of the next-generation engines would be most likely to succeed.

The Air Ministry was aware that Hawker was working on a new fighter, and offered some opinions on his early sketches in advance of F.18/37. Most notably that they felt given the maximum speed expected, a “fully stressed-skin wing” was necessary to ensure the requisite torsional rigidity. This suggests that even in late 1937, Camm was still considering a partially fabric-covered wing, despite the fact that a stressed-skin wing for the Hurricane had been initiated in 1935. Camm was advised to delay submitting the design until F.18/37 had been issued, so he could ensure the aircraft fully suited the Air Ministry’s requirements.

In the event, the fighter submitted by Hawker to F.18/37 had a completely metal skinned airframe, the only fabric covering being on some control surfaces. The design included a stressed-skin rear fuselage in addition to the wings suggested by the Air Ministry. The design bore a considerable family resemblance to the Hurricane, and its form could be described as a larger, slightly cleaned-up version of the earlier aircraft. In addition to the more innovative features, the aircraft followed tried-and-tested Hawker practices going back to the mid-1920s. For example, the built-up tubular metal spaceframe structure first introduced in the Horsley Mk III day/torpedo bomber was retained for the forward fuselage, from the rear of the cockpit to the engine mounting – the section of the airframe that took the greatest loads.

There were other, less visible refinements – the wing aerofoil was a more modern NACA section (indeed, from the same NACA 22 family used by the Spitfire) rather than the Clarke YH of the Hurricane, for example. However, that wing section was as thick as that of the Hurricane, at 19% at the root, and even slightly thicker at the tip (13% vs 12.2%). The benefits of a thicker wing were well established. It made for a stiffer structure without an excessively heavy or complex construction – compare the significantly greater complexity of the Spitfire’s ‘nested’ spar booms and boxed-in leading edge, which required specialist manufacturing processes and high levels of precision to allow a wing 13% at the root and 9% at the tip. The thicker wing preferred by Hawker also allowed greater space for armament and fuel, useful considering F.18/37’s requirement for 12 0.303in machine guns, not to mention fuel for engines that were significantly thirstier than the Rolls Royce Merlin. Unfortunately, Camm was still labouring under the misapprehension that reducing wing thickness-chord below 20% would not result in an appreciable reduction in drag. This information from the National Physical Laboratory, based on their Compressed Air Tunnel (CAT) was compromised by excessive turbulence from the walls of the tunnel interfering with the airflow, but this was not realised until after the design for the new Hawker fighter was finalised.

Hawker proposed two versions of the fighter, consistent with the schemes it had produced in early 1937. One, known as the ‘R’ type was to be powered by a Rolls-Royce X-24 (now known as the Vulture), and the other, the ‘N’, by the Napier H-24 (known as the Sabre). Hawker’s submissions won the competition against submissions from Bristol, Gloster and Supermarine, which had proposed a range of configurations and engines. (These included Supermarine schemes with twin pusher or tractor Bristol Taurus or Rolls-Royce Merlin engines, a twin-boom single Sabre aircraft from Gloster, and a compact twin-tail monoplane from Bristol designed to fit the Sabre, Vulture or Bristol’s own Centaurus radial). The Ministry ordered two prototypes of each ‘R’ and ‘N’.

There were various differences between the two schemes (Hawker had not introduced type numbers at this point so they are simply referred to as the F.18/37 ‘N’ and F.18/37 ‘R’) to the extent that they were effectively different aeroplanes, albeit with a great deal of commonality. That adaptable Hawker fuselage structure enabled this to a very large extent. The chief difference was in the forward fuselage on which hung the rear fuselage, wings and engine.

In their initial forms, the two aircraft nevertheless looked significantly different. The ‘R’ (named the Tornado in 1938) had its radiator mounted in a fairing beneath the fuselage, while the ‘N’ (named the Typhoon in December 1939) had its radiator beneath the nose from the start. This adjustment was made to the first Typhoon prototype as it was under construction. The engine was moved 7in aft, enabling simplification of some of the forward fuselage structure, and a useful reduction in weight, with the radiator and oil cooler, apparently brought forward to redress the movement in the centre of gravity. As a result, of the two aircraft, the Tornado more strongly resembled the Hurricane. The four prototypes took shape at Canbury Park Road, Kingston, throughout 1938 and 1939, with the serials P5212 and P5216 allocated to the Typhoon and P5219 and P5224 to the Tornado.

The Tornado Prototypes

Tornado P5219

The first prototype Hawker Tornado in its original configurationThe first prototype Hawker Tornado P5219 in its original configuration

Initially, Vulture development outstripped that of the Sabre and was due to be ready for testing and production much sooner. Neither engine was entirely problem free, but the Sabre was experiencing greater difficulties at this stage, partly as a result of its newer technology. Nevertheless, it was expected that the Napier had more potential, despite its lower displacement, on account of the greater thermal efficiency afforded by its sleeve valves. It was also a more compact engine – the deeper Vulture necessitated the Tornado having its wing set lower and further aft than the Typhoon’s to enable the engine to clear the main spar. However, the different development states of the two engines meant that a Vulture was delivered to Hawker in December 1938, a full year before a Sabre arrived. The Air Ministry already ordered 500 of both types in July even though neither had yet flown in prototype form.

Test pilot Philip Lucas took the first Tornado prototype, P5219, into the air for the first time on 6 October 1939. As soon as P5219 began test flights, it was evident that some revision was needed. It is often said that the deep fairing under the centre section, housing the Vulture’s large radiator, created severe local airflow reversal at speeds approaching 400mph, leading to high drag. Certainly, cooling was marginal on early flights, and high oil consumption and metal particles found in the oil filter led to concerns about engine wear, and the first Tornado was grounded to enable the Vulture to be examined after just a few flights. While the aircraft was waiting, the opportunity was taken to modify the cooling arrangement. It may be that a better overall solution was already apparent in the arrangement planned for the Typhoon – and sure enough, the Tornado emerged with a very similar ‘beard’ fairing to its half-sister. A larger rudder was fitted at this stage, having a similar overall chord to the original item but being wider along more of its height, as directional stability on take-off had been marginal with the original radiator fairing, and was now bordering on inadequate. The new radiator installation and rudder meant the Tornado now looked much less like a Hurricane than it had originally.

The Rolls-Royce powered machine was now most easily identifiable by the twin row of exhaust stubs along each cowling, unlike the single row on the Sabre powered Typhoon; P5219 flew in the new form on 6 December 1939. The fact that this took place a mere two months after the first flight in the initial layout demonstrates how little the aircraft flew before being grounded for alterations (and how straightforward it was to modify the aircraft, especially with the prototype Typhoon to hand to assess the ‘chin’ radiator). As originally stipulated in F.18/37, P5219 had provision for a 12-machine gun armament. Unlike the 8-gun Hurricane arrangement, all six guns in each wing were grouped together. The first prototype was later fitted with guns and related paraphernalia, and a larger vertical tail and its radiator fairing were altered further, being lengthened aft to improve cooling and reduce drag.

Tornado P5224

The second prototype Tornado P5224 showing the Typhoon-like radiator fairing. Although this aircraft was equipped to fit cannon in the wings, they had not been installed yet. The carburettor scoop on the top of the cowling was introduced when the radiator was moved beneath the engineThe second prototype Tornado P5224 showing the Typhoon-like radiator fairing. Although this aircraft was equipped to fit cannon in the wings, they had not been installed yet. The carburettor scoop on the top of the cowling was introduced when the radiator was moved beneath the engine

The second Tornado flew one year less a day after the first returned to the air, 5 December 1940. The chief reason for the delay was the absolute priority placed on Hurricanes and the suspension of programmes but those absolutely essential when it became apparent that France would soon fall.

Hawker’s ongoing priorities meant that production of the Tornado would be subcontracted to another member of the Hawker-Siddeley Group, AV Roe Ltd (Avro). When P5224 finally appeared, it was fitted with a 1,760 Vulture II and Rotol constant-speed propeller. This engine was almost as problematic as the one fitted to P5219, although the oil cooling problems seemed to have been remedied by then. P5224 was slightly damaged in a forced landing in March but was flying again in June – by which time Hawker had been informed that the Tornado might be cancelled.

The major difference between P5219 and P5224 was its armament. Due to the developments in armament over the previous two years, it was now expected that 20mm cannon would be the typical fighter armament in future after the Air Ministry had moved on from its idea that the cannon-armed fighter was something of a specialist type needing twin engines. The Tornado/Typhoon were in reality eminently suitable for cannon installation – Camm suggested this as early as August 1938 – and P5224 was built to accept four Hispano Mk I (a licence-built HS.404).

As development continued, P5224 (along with P5219) was fitted with a Vulture V of 1,980hp, the engine it was to have in production and which was considerably more reliable than the engines originally fitted to both prototypes. However, due to the delays in the Tornado programme, problems with the engine were more apparent from its use in the Avro Manchester bomber, which had been in service since November 1940.

The second prototype was tested at the A&AEE at Boscombe Down in late 1941 for handling and performance, where worrying vibrations in certain engine regimes were identified. Due to ongoing problems with the Vulture, and the labour- and resource-intensiveness of the engine next to the continuing need for Merlins, Rolls-Royce secured an agreement to stop producing the Vulture. The Tornado programme was cancelled in October 1941. The fates of the first two Tornado prototypes are unclear, but both were probably scrapped after they ceased to be used, especially when Typhoons began to arrive from Gloster for that aircraft’s test programme.

Tornado R7936

The sole Avro-built Tornado R7936 seen here at Rotol in 1945 for trials with contra-rotating propellersThe sole Avro-built Tornado R7936 seen here at Rotol in 1945 for trials with contra-rotating propellers

The third Tornado to be built is sometimes described as the first (and only) production aircraft, and sometimes as an additional prototype. In reality, the first ‘production standard’ aircraft to major contracts were often a small number of hand-built machines completed before the full production tooling was set up, and R7936 probably fits into that category. In any event, early aircraft to the production contract were fully intended to join the test flying programme, which included R7936 and the next two Avro-built Tornados, which were to be transported to Hawker in unassembled form.

R7936 was first flown on 31 August 1941, and test flying proceeded at Avro by company test-pilots according to the programme developed there, even though by this time it was all but certain that the Tornado would be cancelled. After initial flights, Avro test pilots were joined in the trials by RAF pilots. This aircraft appears to have been the fastest Tornado, and the only one to have exceeded 400mph, with a recorded 402mph at 21,800ft.

There was no longer any use for a Vulture Tornado programme, and with plenty of Typhoons available for that aircraft’s development by the end of 1941, R7936 was available for other work. It went to the A&AEE, Royal Aircraft Establishment and Rolls Royce, before ending up as a test-bed for de Havilland contra-rotating propellers at Hatfield, and Rotol for similar work, where it was still present in May 1945. With the increasing power and torque of aircraft engines, contra-rotating propellers were increasingly seen as the solution for single-engined aircraft, with further benefits in the reduction of overall airscrew diameter potentially lowering undercarriage length and allowing multi-engine aircraft to have their engines set closer to the fuselage. The much lower diameter of the Rotol six-bladed propeller is apparent from photographs of R7936.

Tornado HG641

Centaurus Tornado HG641 in its initial form, showing the compact but problematic engine installation. Note the earlier style inner undercarriage doors

Centaurus Tornado HG641 in its initial form, showing the compact but problematic engine installation. Note the earlier style inner undercarriage doors

The last Tornado to fly was completed just after the decision to cancel the Tornado production contracts, although it had been apparent for some time that the programme was unlikely to continue. As early as 1940, problems with the Napier Sabre led Hawker to consider that an alternative might need to be found, with the air-cooled Bristol Centaurus 18-cylinder sleeve-valve radial an obvious option as it offered similar power. The Centaurus only had slightly higher frontal area than the Sabre with its radiator, so a closely-cowled installation was begun using staff from the Tornado design programme when that aircraft was put on hold in 1940.

An airframe became available to test the Centaurus installation when the Tornado programme was halted, as the second and third aircraft Avro had built were to be passed to Hawker to assist the development programme. These had not been completed, but such work as had been carried out was delivered to Hawker and the company set about modifying one of the forward fuselage spaceframes, taking a rear fuselage and wings from the Typhoon production line. The aircraft was allocated the serial HG641 and first flew on 23 October 1941.

The Centaurus was incorporated into the Tornado airframe in a way that was as compact as possible within the conventional state of the art, including an exhaust collector ring forming the leading edge of the cowling in typical Bristol fashion, and a single exhaust tube on the lower left side discharging beside the oil cooler fairing on the centre-section underside. Early tests revealed poor oil and engine cooling, which in turn led to high CO levels in the cockpit, and though the aircraft reached a speed of 378mph, the engine installation was clearly unsatisfactory. Wind-tunnel tests suggested that airflow was unstable around the lower cowling, considerably reducing air pressure in the oil cooler scoop. Revisions were made purely to improve cooling, and a rather bulky fairing was added beneath the cowling, extending from the leading edge to well under the centre section. The new arrangement, which debuted in December 1942, helped engine performance significantly, though the increased drag meant that overall performance was not markedly better.

In the meantime, interest in the Centaurus had increased, and Camm was now working on the ‘Typhoon II’, later known as the Tempest, having benefited from a study of a Focke-Wulf Fw190 captured in July 1942, not least in the way its two-row radial engine was integrated into the airframe.

Given the ongoing difficulties with the Sabre, the Air Ministry showed interest in switching the Typhoon to the Centaurus, especially as performance at higher altitudes looked to be improved. However, by now, Camm was well advanced on the Typhoon II, which incorporated completely new wing among other improvements. The work on this alongside the Centaurus design would become the Tempest MkII. At this point, HG641 essentially became an engine testbed for the Typhoon II/Tempest programme.

HG641 after modifications including a fairing around the oil cooler intake, and a four-blade propeller with a larger spinnerHG641 after modifications including a fairing around the oil cooler intake, and a four-blade propeller with a larger spinner

The Typhoon Prototypes

Typhoon P5212

The first Hawker Typhoon P5212 as it first appeared, with small fin and rudder, and solid fairing behind the cockpit. Note the large, low-pressure tyres (World War photos)

The first Hawker Typhoon P5212 as it first appeared, with small fin and rudder, and solid fairing behind the cockpit. Note the large, low-pressure tyres (World War photos)

This came to a dramatic halt on 9 May when during a test flight at the hands of Philip Lucas, the rear fuselage of P5212 almost separated from the forward part. Lucas managed to land the damaged prototype, which was found to be the result of vibration causing a longeron joint to fail. The aircraft was repaired and sent to the Aeroplane and Armament Experimental Establishment (A&AEE) at Boscombe Down in late summer. However, a continuing problem was the reliability of the Sabre, which meant the unusual step was taken of conducting the remainder of the service trials at Hawker’s Langley base, so engine changes would hold up the programme less.

Handling was found to be good, with responsive and well-harmonised controls, though there was vibration experienced in certain conditions and the stalling speed was rather higher than that of the Tornado. In many respects, early reports from the Typhoon were very good, but problems highlighted included poor rear visibility (thanks to the solid Hurricane-style ‘doghouse’ fairing behind the cockpit) and performance falling off at higher altitudes. Like the first Tornado, P5212 was armed with twelve machine guns. When the second prototype and early production aircraft began to appear, P5212 was used for testing various improvements, such as ‘quarter lights’ in the rear fairing to improve the rearward view. Initially, P5212 was fitted with large-diameter low-pressure tyres but these were found to be unnecessary.

P5212 after some revisions had been made – note the hinged outer undercarriage doors and the small quarter light window behind the cockpit. A larger fin and rudder has been fitted but this is less apparent from this angle. The doped fabric over the six machine gun ports in each wing can just be made outP5212 after some revisions had been made – note the hinged outer undercarriage doors and the small quarter light window behind the cockpit. A larger fin and rudder has been fitted but this is less apparent from this angle. The doped fabric over the six machine gun ports in each wing can just be made out

Typhoon P5216

The second prototype Typhoon P5216, showing the later style inner undercarriage doors and partially fared cannon barrels (BAE Systems)The second prototype Typhoon P5216, showing the later style inner undercarriage doors and partially fared cannon barrels (BAE Systems)

The second Typhoon prototype, P5216, first flew on 3 May 1941 – just over three weeks before the first production aircraft built by Gloster took to the air. Part of the reason for the delay was the modification of the second prototype to represent the definitive armament of four 20mm Hispano cannon, like the second Tornado prototype, and unlike the early production aircraft which were delivered with machine guns (as the Mk IA – the cannon-armed machines were designated Mk IB). In the form it originally appeared, the forward gun barrels including the recoil spring were exposed, in a similar fashion to the Hurricane MkIIc, with only part of the barrel covered by a fairing.

P5216 was initially used as part of the general development programme, its first major modification being an alteration to the oil cooling system to help deal with persistently high lubricant temperatures.

Typhoon R8694

One of the earlier Typhoons R8694 with ‘car door’ cockpit modified for trials with the Sabre IV and annular radiator plus four-blade propeller and cooling fan, at NapierOne of the earlier Typhoons R8694 with ‘car door’ cockpit modified for trials with the Sabre IV and annular radiator plus four-blade propeller and cooling fan, at Napier

The second batch of 250 Typhoons ordered from Gloster was delivered between April and November 1942. At least two of these, R8694 and R8762, were delivered to Napier for engine-related testing. The former was extensively modified to test a new version of the Sabre and an experimental cooling arrangement. The Sabre IV was a developed version of the Sabre II used in production Typhoons, and was slightly more powerful than the earlier versions of that sub-type – 2,240hp as opposed to 2,200hp in the Sabre II and 2,235hp in the IIA. However, the most significant change was the adoption of an annular radiator, which encircled the engine’s reduction gear. Cooling air was introduced through a small central intake in a cowling similar to that of an air-cooled radial engine and turned outward to pass through the radiator, exiting to the rearward through a ring-shaped gap at the aft end of the cowling. Increased mass flow was achieved with a propeller driven fan inside the intake, allowing a significant reduction in the size of both the intake and outlet, thus reducing drag. R8694 thereby became the fastest Typhoon of all, clocking a speed of 452mph. The programme was transferred to the Tempest, with that aircraft beginning to supplant the Typhoon.

About the Author

Matthew Willis is a writer, editor and expert on naval aviation history. Matt is the biographer of test pilot Duncan Menzies and his last book is on the Fairey Barracuda which is out now through MMP Books (Orange Series no.8117).

You can follow Matthew Willis on Twitter at @NavalAirHistory

Matt’s website can be found at https://navalairhistory.com/

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