Hawker Tempest Prototypes & Projects

I am trying to understand exactly what the Hawker Tempest I was and why it never went into production. After considerable reading I am left with the following understanding: The Tempest I used the Sabre IV (Napier E.107C) which was the first Napier attempt at giving the engine Hobson fuel injection, it was eventually made to work in the Sabre V used in the Tempest VI. Additionally the aircraft used Hawker's favoured wing leading edge radiators (which ultimately reappeared on the Fury Mk.I) giving it a unique look for the Typhoon/Tempest family. However, the Air Ministry didn't like the wing leading edge radiators which also suffered from manufacturing concerns and the Sabre IV suffered from development issues (apparently failing type-tests 3 times by December 1942) so the aircraft that ended up actually being built was the Tempest V with the carburettor equipped Sabre II engine and the chin mounted radiator.

What I am struggling with is the remarkable performance credited to the Tempest I; the usually given stat is 466mph at 24,500ft though BSP Fighters & Bombers states that a true air speed of 472mph was achieved (altitude not given), that makes the aircraft 30-40mph faster at that altitude than the Tempest V. According to BSP only 7-10hp of that can be accredited to the leading edge radiators.

The Sabre IV is most often quoted as giving 2,240hp which is only around what the Sabre II produced though other sources give different values, at the upper end is 2,600hp given for the E.107C though this may refer to the Sabre V rather than the IV. Is it possible that there is some misreporting of the power output of the Sabre IV or that it had a different supercharger arrangement? I assume that a relative lack of operational equipment would have helped the Tempest I but 30mph still seems like a substantial difference...?

If I understand things correctly, the Tempest I was supposed to be "the" Tempest. But the 2,240 hp Sabre IV engine was not ready. To move the "Tempest" concept along, a 2,180 hp Sabre IIA was fitted to a different airframe (HM595). HM595 first flew on 2 September 1942, and served as the prototype for the Tempest V production aircraft.

Eventually, the Sabre IV engine was mounted to airframe HM599. This aircraft, the Tempest I, first flew on 24 February 1943, nearly six months after the Tempest V.

Both HM595 and HM599 were modified Typhoon airframes with new Tempest wings.

The Tempest I continued to have issues with the Sabre IV engine and its wing radiators, but reportedly achieved a speed of 472 mph. The aircraft then recorded an official speed of 466 mph at 24,500 ft in September 1943. These speeds were made without armament.

The Air Ministry saw the Sabre IV as unreliable and believed the wing radiators were more prone to damage from enemy action. Production orders for the Tempest I started to drop in April 1944, and the last were switched to the Tempest V in May 1944.

The Tempest I was flown with a 2,400 hp Sabre V engine in 1944. It achieved 462 mph at 17,600 ft. Only the prototype Tempest I was built, and it was scrapped in late 1947.

To the pilots who flew it, the Tempest I was judged the superior aircraft. But the engine delays and the Air Ministry’s configuration preferences allowed the Tempest V to sneak ahead. Another thing to consider is that, with the wing radiators, the Tempest I had 150 rpg and 132 gallons of internal fuel. The Tempest V carried 200 rpg (33% more) and 162 gallons (23% more) of internal fuel.

Later, Tempest Vs were fitted with 2,400 hp Sabre IIB engines.

The information above was extracted form "Tempest: Hawker’s Outstanding Piston-Engined Fighter" by Tony Buttler (2011). I'm sure there is more to the story, but it is a start.

Alec Lumsden's 'British Piston Aero-Engines' has very little on the Sabre IV.
"SABRE IV, 2,240hp, (1943), as Mk VA with R.A.E.-Hobson fuel injector."

The Sabre V was a development of the II with a redesigned supercharger and induction system., it had R.A.E. BI/NS2 fuel injection. The VA had R.A.E.-Hobson NS4 fuel injection, also had a inter-connected single-lever propeller and throttle control.

As both engines were later than the IV my reading of Lumsden's brief description of the engine is that it was either; a Sabre II with the RAE-Hobson injection system added, or a Sabre II with the RAE-Hobson system and the inter-connected single-lever propeller and throttle control later used in the VA. That might explain the reluctance of the RAF given the extra complexity and maintenance required.

I am certain that the Sabre IV was essentially the Sabre II with the RAE-Hobson fuel injection system- what isn't clear in any source I have seen is what the supercharger arrangement was. I also think the Sabre V was a continuation of the work done on the Sabre IV. It's worth noting about the fuel figures that the Tempest I still had the same fuel capacity as early model Tempest V's. It wasn't until later production batches that the 30 gal wing leading edge (which the RAF insisted on calling a nose tank) tank was fitted to the Tempest V taking its fuel capacity from 132 Igal to 162 Igal. I also note that there seems to be some dispute about the actual RPG of the Tempest Hispano magazines, 200rpg is most often given in books but many of the official RAF data sheets give 150rpg.

JFC Fuller said:

... I am certain that the Sabre IV was essentially the Sabre II with the RAE-Hobson fuel injection system- what isn't clear in any source I have seen is what the supercharger arrangement was. I also think the Sabre V was a continuation of the work done on the Sabre IV.

Click to expand...

A Flight article entitled Napier Sabre VII has a little on the Sabre IV and V/VA. The article discusses all changes to the supercharger on the Sabre V. That would seem to suggest that the supercharger arrangement for the Sabre IV remained the same as for the Sabre IIs.

"The Sabre IIB was installed in the Hawker Tempest V, and this engine was closely followed by a Mk. III which was specially developed for the Blackburn Firebrand; however, only 25 Mk. III units were installed, owing to the very high priority attached to the production of the Mk. V. A preliminary flight development engine for the Mk. V was known as the Sabre IV.

Numerous modifications were incorporated into the design of the Mk.V and VA, among which were internal increases of strength to withstand higher boost pressures and r.p.m., and the use of Vandervell strip-type thin-wall bearings, this being the first occasion on which such bearings have been used in an aircraft engine with such high r.p.m. and heavy loadings. Disposition of the sparking plugs was also altered and ignition harness was re-designed to obtain more advantage from the high-altitude ignition equipment now fitted.

Supercharger Modifications

The double-entry supercharger impeller was replaced by a single-entry impeller of increased capacity, and the hydraulically operated two-speed clutch was re-designed to effect a saving of space and an increase in efficiency. Remodelling also included the addition of a boost pressure correction capsule to the boost-corrected ignition servo unit which, linked to the c.s.u. and thus responsive to engine speed, regulates the ignition timing for any engine operating condition. Perhaps the major modification of the VA over the previous marks was the replacement of the carburettor with Hobson-R.A.E. fuel injection and metering equipment, which embodies a fully automatic boost control unit and charge temperature correction of the fuel/air ratio.

The Sabre VA passed its type test at the first attempt and is now being delivered installed in the Tempest VI. Developing 2,600 b.h.p. for a weight of 2,460 lb., its specific weight is 0.94 lb./h.p. Maximum r.p.m has been increased to 3,850 and the maximum boost pressure to 15 lb.,
the unit output being equal to 71 b.h.p./litre."

Flight 22 Nov 1945 pp 551-552
https://www.flightglobal.com/FlightPDFArchive/1945/1945%20-%202284.PDF
https://www.flightglobal.com/FlightPDFArchive/1945/1945%20-%202285.PDF

Don't know if this is of any relevance, from the Tempest chapter of Roland Beamont's 'Testing Years'...

"At Langley in 1943 the new development of the Typhoon series called the Tempest was on test in three main variants; Tempest I with uprated Sabre engine, four-bladed propellor and very clean wing root leading edge radiators; the Tempest II with a Centaurus sleeve-valve radial engine and the Tempest V with the uprated Sabre, a longer nose (I assume he means relative to the Typhoon) and an extended undernose radiator...
My first experience was on...the Tempest I prototype...for a period Bill Humble and I found ourselves alternately exceeding the existing world speed record...for that stage of the war this was very high performance and it was disappointing that subsequently other operational considerations...resulted in..selection of of the Mk V configuration for production with a lower performance.
These considerations were that the wing radiators occupied valuable potential fuel tank space, and they also spread out along the underside of the wing roots where they were highly vulnerable to ground fire. Reverting to the chin-type...radiator permitted the leading edge fuel tanks to be incorporated, but before...aircraft could reach the squadrons an Air Ministry instruction arrived calling for the blanking off of the...tanks...on the grounds that rate-of-cxlimb was now more important, and that the weight of fuel was critical...
As a mere pilot this seemed to make no sense to me, the rate-of-climb loss would have been less than 1/2 minute to 20,000', and the Tempest was unlikely...to be required for high-altitude defence but would...be needed for medium level battlefield air superiority...and ground attack...This situation was obviously unsatisfactory and I joined...in lobbying for maximum fuel capacity for the operational Tempest V." (my bold)

cheers,
Robin.

Thanks lads, really facinating contributions.

When the effects of near-sonic speeds around the Typhoon airframe had been discovered the Air Ministry ordered, in September 1941, an extensive modification of the aircraft under the denomination Typhoon II.

On 18 November 1941, two Typhoon airframes were converted into Hawker P.1012 prototypes.

The HM599 was a high-altitude interceptor, with Mosquito-like leading-edge radiators, side ‘car-door’, the tailfin of Typhoon and one Napier Sabre IV engine.

The HM595 was a medium-level air-superiority and ground attack fighter, with chin radiator and Sabre II engine.

Both airplanes were fitted with a new laminar-flow wing, with a thickness reduction of five inches at the wing root and 14.5 per cent thickness/chord ratio, against the 18 per cent of the Typhoon.

The thinner wing provided less fuel capacity and a fuselage tank was added.

On 28 February 1942 the HM599 was renamed Tempest Mk.I.

It was expected the Sabre IV equipped with Hobson fuel injection system, would be ready in December 1941 and the prototype completion in January 1942, but the Sabre was not ready in time and the first flight was delayed until 24 February 1943.

Early flight trials revealed tail plane compressibility buffeting at 25,000 ft.

The HM599 proved to be the fastest of the Tempest series reaching 472 mph. in June 1943, but the Ministry saw the Sabre IV as unreliable.

In 1944 the prototype was fitted with the new Sabre V, reaching 462 mph. at 17,600 ft.

The airplane was painted in Type B camouflage pattern with Dark Green/Mixed Grey upper surfaces and Yellow under surfaces.

Tempest Mk.I technical data

Power plant: One Napier Sabre Mk IV, 24 cylinder ‘H’, liquid cooled engine, rated at 2,240 hp, driving a four-bladed constant-speed Rotol airscrew, wingspan: 41 ft (12.5 m), length: 34.2 ft (10.4 m), height: 16 ft (4.9 m), wing surface: 302 sq. ft (27.2 sq. m), maximum weight: 11,300 lbs (5,119 kg), maximum speed: 472 mph (759 kph), climb rate: 3,300 ft/min, ceiling: 39,000 ft (11,887 m), range: 770 mls (1,239 km), armament: four wing-mounted 20 mm Hispano Mk.V cannons with 150 rounds per gun.

Marvelous mate.

On 10 April, 1942 Hawker proposed two light versions of the Tempest powered by Rolls-Royce Griffon engines, as a replacement for the Hurricane.

The prototype LA610, designated Tempest Mk.III, was flown on 27 November 1944 powered by one Griffon IIB.
The prototype LA614, designated Tempest Mk.IV with Griffon 61, was never built.
Napier spent a great deal of time experimenting with annular radiators in an effort to supersede the chin radiators of the Typhoon and Tempest.

LA610 technical data

Power plant: One Rolls-Royce Griffon 85, twelve cylinder ‘V’, liquid cooled engine, rated at 2,340 hp, driving a six-bladed contra-rotating airscrew, or one Napier Sabre VII, twenty-four cylinder ‘H’, liquid-cooled engine rated at 3,055 hp, wingspan: 38.6 ft (11.77 m), length: 34.6 ft (10.54 m), height: 14.6 ft (4.5 m), wing surface: 284.5 sq. ft (25.6 sq. m), maximum weight: 12,120 lbs (4,236 kg), maximum speed: 483 m.p.h. (777 kph), climb rate: 4,706 ft/min, ceiling: 41,500 ft (12,652 m), armament: four wing-mounted 20 mm Hispano Mk.V cannons.