Orthographic projection of the Spiteful Mk.XIV. The Spiteful still has the elliptical tailplane of the Spitfire, but lacks the elliptical wing.
The very end of the Spiteful/Seafang design stream was the Supermarine Type 391 which was first proposed in June 1944. If it had ever been built the last vestiges of the Spitfire would have vanished as the Type 391 featured a revised fuselage with an enlarged tail unit of angular proportions. Although the laminar flow wing was retained, the underwing radiators were replaced by radiators mounted in the leading edge of each wing. Power was to have come from a 3,500 hp Rolls-Royce 46H engine driving contra-rotating propellers which would have given an estimated top speed of 500 mph [this engine was later known as the Eagle and powered the Westland Wyvern prototypes].
When the prototype Spitfire (K5054) was flown for the first time on 5 March 1936 it was powered by a Rolls-Royce Merlin ‘C’ of 990 hp. This engine, even at such an early stage in its development, offered half as much power again as the Rolls-Royce Kestrel and Bristol Mercury engines that had been fitted to the last of the RAF’s inter-war biplane fighters, but such was the rate of progress towards the end of the 1930s that engines of 2,000 hp were being offered to manufacturers just twelve months later. Although this appeared to be the answer to every aircraft designer’s dream, such a phenomenal increase in the level of power generated by piston engines did pose something of a dilemma.
As a high top speed had always been one of the priorities when designing a new fighter, the availability of much more powerful engines was to be welcomed, but on the downside, trials soon began to show that flight at the higher speeds now possible was producing some unwelcome aerodynamic and control problems. These difficulties were first experienced during high speed dives from high altitudes with many aircraft being prone to severe airframe buffet, immovable controls and uncommanded trim changes. Control was usually regained when the aircraft had descended to below 15,000 ft but in several cases aircraft had not been recovered before hitting the ground. It was also relatively easy for the pilot to overstress the airframe during the pullout manoeuvre resulting in structural failure. These were the first examples of aircraft being subjected to compressibility, a phenomenon that had been predicted by aerodynamicists from theoretical work carried out in the 1930s, but nevertheless it still came as something of a shock for test pilots when they experienced it for real.
The decision by R.J. Mitchell to incorporate a relatively thin wing endowed the Spitfire with an ability to fly at higher Mach numbers than any other piston-engined fighter of the period. Such a wing tended to delay the onset of compressibility effects and during diving trials carried out at Farnborough in 1943 a Spitfire XI was flown to Mach 0.89 in a full power dive from 40,000 ft. The sudden rise in drag that occurred as an aircraft approached and exceeded its critical Mach number (Mcrit) was the chief cause for concern for designers of the time and a number of theories were put forward on how it could be reduced.
Most conventional aerofoils, including that used on the Spitfire, are thickest at a point 25–30 per cent of wing chord measured from the leading edge. Aft of this point the airflow over the upper surface of the wing is likely to be turbulent (due to the adverse pressure gradient) which creates more drag than the laminar flow that exists over the first part of the wing. Shortly before Europe was plunged into another war, a low-drag, or laminar flow wing was schemed by the National Advisory Committee for Aeronautics (NACA) in the USA whereby the maximum thickness was moved further aft to a point close to mid chord. This held the prospect of achieving laminar flow over the first half of the wing which, it was hoped, would reduce the amount of drag created by a considerable amount.
Joe Smith first began to consider a laminar flow wing for the Spitfire in late 1942 and in November of that year Supermarine specification 470 was drafted. It was hoped that the new wing would raise Mcrit and thereby delay the drag rise experienced at transonic speeds, further aims being the reduction of profile drag and an improvement in the rate of roll. The wing was developed with the assistance of the National Physical Laboratory and eventually emerged as a two-spar tapered design with straight leading and trailing edges. At 210 sq.ft, the area of the new wing was 15 per cent less than that of the Spitfire F.21 and its thickest point occurred at 42 per cent chord. An official specification (F.1/43) was written for a new fighter, however, development was relatively slow and it was not until June 1944 that the laminar flow wing was ready to be fitted to a Spitfire XIV (NN660) so that flight tests could commence. As the aircraft was radically different from all previous Spitfires, it was felt that a change of name was necessary and shortly before it was completed the name Spiteful was chosen.
Jeffrey Quill flew NN660 for the first time on 30 June 1944. Apart from the wing planform, the other major difference when compared with the Spitfire was the wide track undercarriage which retracted inwards. This had become possible due to the use of a two-spar wing design and greatly altered the aircraft’s characteristics on the ground. Right from the word go it was apparent that the handling characteristics of the Spiteful were vastly different to those of the Spitfire, especially at low speeds. The Spitfire had been renowned for its high level of controllability near the stall. This was largely due to the fact that Mitchell had designed the Spitfire wing with washout whereby the angle of incidence was reduced towards the tips so that a measure of lateral control was available right down to the stall. Effectively the wing stalled from root to tip but with the Spiteful it appeared that the opposite was the case. The laminar flow wing had been designed with a constant angle of incidence along its span, as a result of which tip stalling was much more likely to occur as the wing reached the stalling angle of attack, with resultant wing drop. A certain amount of kickback could be felt through the aileron circuits and the aircraft gave the impression that it was about to take over which, in fact, it never actually did. Even so, the Spiteful was far less predictable than the Spitfire and pilots tended to be wary of it because of its capricious handling.
Another unfortunate aspect of the Spiteful’s performance was that the significant improvement in drag that had been expected with the new wing failed to materialise. This was due to the fact that the wing had to be manufactured to extremely high tolerances and had to retain its smooth surface finish at all times to obtain the desired reduction in drag. This proved to be virtually impossible during flight operations as even the smallest item of debris which adhered itself to the wing, even a squashed fly, tended to disrupt the boundary layer air and led to drag-inducing turbulence. Despite the somewhat disappointing results of the testing carried out by Supermarine the Spiteful was still faster by some margin than a standard Spitfire XIV, but not by as much as had been expected.
Flight testing continued with NN660 until 13 September 1944 when it was written off in a crash that killed Supermarine test pilot Frank Furlong. The accident occurred during a low level dogfight with a Spitfire XIV, the Spiteful suddenly rolling onto its back and diving into the ground. A thorough investigation revealed that the accident was most likely caused by jamming of the ailerons under conditions of positive ‘g’. Instead of the cable-operated ailerons of the Spitfire, those of the Spiteful were operated by push-pull rods which tended to move relative to the internal wing structure when the aircraft was subject to high ‘g’ loads. It was found that movement of the controls could cause the ailerons to jam which may have prevented Furlong from returning the ailerons to neutral, after initiated a rolling manoeuvre at low level.
The second prototype Spiteful (NN664) was flown for the first time on 8 January 1945 but as lateral control at the stall was still poor with considerable aileron snatch, a number of palliatives were tried. These took the form of reduced span ailerons, a revised wing section at the tip and root spoilers although any variation of the basic design tended to reduce performance slightly. In its original form NN664 was flown with a Spitfire XIV rear end but this was eventually swapped for an enlarged tail which brought about a considerable improvement in lateral stability. It was first flown in this form on 24 June 1945.
In the meantime the first production Spiteful F.14 (RB515) had flown on 2 April, initially with a Spitfire F.21 tail, although the larger F.24 unit was fitted later that month at the same time as the aircraft was repaired following a forced landing, the first of several. Another unscheduled return to earth was made on 28 September when Patrick Shea-Simmonds was carrying out high level longitudinal stability tests. Failure of the propeller constant speed unit (CSU) allowed the engine to overspeed to 4,000 rpm which caused the first stage supercharger to explode, resulting in major damage to the engine and cowlings and covering the windscreen in oil. The general level of vibration indicated that there was a distinct possibility that the Griffon would break free from its mountings. The only chance Shea-Simmonds had of saving his aircraft was to stall it so that the runaway propeller would cease turning. Having achieved this, the vibration stopped and he was left to fly the Spiteful as a glider to nearby Farnborough where he made a successful (wheels-up) landing, the wide-span radiator ducts under each wing acting as extremely efficient skid plates that prevented any further damage. After repairs, and with a replacement engine fitted, RB515 was returned to the test schedule.
With the end of the Second World War production orders for aircraft were slashed and a further nail in the Spiteful’s coffin was the performance of the first jet fighters, the Gloster Meteor and de Havilland Vampire which were superior to any piston-engined design. Development of the Spiteful did, however, continue for a time but of the original order of 650 (subsequently cut to 190), only nineteen were built (not including the three prototypes) although of these the last few examples were not flown. The Spiteful F.15 was fitted with a Griffon 89/90 driving a six-blade contra-rotating propeller and the one-off F.16 (RB518) had a three-speed, two-stage supercharged Griffon 101 with 25 lbs/sq.in boost. RB518 set a speed record for British piston-engined aircraft at 494 mph at 28,000 ft, but only at the expense of a number of engine failures and a total of seven forced landings. Even then the aircraft was only written off when it was dropped from a crane while being moved after its last premature return to earth.
In early 1946 the third prototype Spiteful (NN667) was delivered to Boscombe Down for an engineering and maintenance appraisal. It was fitted with a Griffon 69 driving a five-bladed Rotol propeller, this engine differing little from the Griffon 61 except that it was modified to operate at a maximum of 25 lbs/sq.in boost when using 150 octane fuel. When 100 octane fuel was used the boost had to be restricted to 18 lbs/sq.in by the fitment of appropriate throttle stops. The general condition of NN667 was found to be poor in several respects and the design of the cockpit came in for particular criticism. It was also found that servicing tasks and maintenance were not easy to perform.
For an aircraft that was supposed to extend the performance boundaries of piston-engined fighters close to the ultimate, the external condition of the Spiteful was something of a disappointment. The butt-jointing of the light alloy skinning was not very smooth in several places, particularly at the joint forward of the leading edge of the fin and that to the rear of the cockpit. This resulted in a gap which had then been filled with stopper but after a relatively short amount of time this had become loose. It was recommended that the joints could be overlapped with the top sheet then being chamfered and this was incorporated on the fin/fuselage joint of later aircraft. Another cause for complaint was the large size of the engine cowlings and the large number of fasteners that needed to be removed and then reinserted, many of which worked loose in flight due to the vibration of badly fitting cowls and panels.
Criticism was also levelled at the workmanship in the area of the cowlings, in particular the very crude packing on the formers to which the cowlings were attached. This packing consisted of thick heavy webbing with slots hacked into it at intervals to correspond approximately to the position of the fasteners. The webbing was secured, rather ineffectively, to the formers by a liquid adhesive but in as little as fifteen hours flying time it was discovered that the webbing had become detached from the stringers. This defect was general throughout the aircraft and it was considered that an alternative packing such as heavy synthetic rubber beading positively secured to the stringers be employed.
Some degree of over-elaboration was also noted on the wings, the panels that provided access to the guns being secured by no less than twenty-two fasteners and nine sets of screws. These, together with numerous other panels in the wings, made it extremely difficult for a smooth finish to be obtained. Theoretically, the fasteners were locked when their heads were flush with the skin plating, but in a number of cases they finished up below the level of the metal skinning which would have done little to help the smooth flow of air over the laminar flow wing. It was also felt that re-arming would take an excessively long time which was an obvious disadvantage for a fighter aircraft.
Other areas of the airframe which came in for adverse comment were the wing tips and the trailing edges of the rudder and elevators. ‘Anti-crack’ holes were very much in evidence in the vicinity of any awkward bends or abrupt changes of section, which on an aircraft that had only flown 14 hours 55 minutes on arrival was not a good sign. Although all control and balance surfaces were metal-covered, the elevator horns were made from laminations of wood bolted together which were tending to come apart. Poor workmanship was also evident where the navigation light was mounted on a boss on the trailing edge of the rudder. The latter had been crudely welded and was already cracking badly.
The fuel system consisted of four tanks situated forward of the pilot’s cockpit and two saddle tanks fitted one in each wing root end. The four fuselage tanks comprised one large tank with a small tank beneath it and two smaller tanks, one on each side. All were interconnected and were filled through the main filler neck on the coaming forward of the windscreen. Total capacity of these tanks was 99½ gallons with each wing tank having a capacity of 8 gallons [later aircraft had additional tankage in the rear fuselage].
From an engineering and maintenance point of view it was felt that the layout of the cockpit was one of the worst aspects of the aircraft. All items of equipment seemed to be situated either in a series of ledges or in deep cavities which would become a trap for dirt and any other contaminants, thus making it very difficult to keep the cockpit reasonably clean. The positioning of the oxygen bottles underneath the pilot’s seat was particularly criticised as they tended to foul items of equipment on the port side of the structure and the seat had to be removed each time the bottles or accumulators needed changing. It was also noted that hydraulic fluid tended to drip on the top of the oxygen bottles and adjacent piping with an attendant risk of the oxygen supply becoming contaminated. There was also a risk to the pilot in any crash-landing as he was not protected by any armour plate should the bottles explode. A particularly large cavity existed in the vicinity of the control column which would tend to collect dirt and sand etc which would lead to undue wear on the controls. Of even further concern was the fact that the controls might become jammed by the ingress of some foreign body.
Generally, the cockpit was full of projecting details that were likely to catch the clothes of both pilot and ground crew. Access to the cockpit was inadequate as no non-slip surface was provided on the wing root and there was only one foot hold on the port side of the fuselage. In their summing up, A&AEE found that normal servicing of the Spiteful was extremely difficult and even relatively simple tasks such as refuelling and rearming took an inordinate amount of time due to the inaccessibility of essential services.
- Spiteful F Mk 14 – 19 built (two prototypes and 17 production)
- Engine: Griffon 69 – 2,375 hp (1,771 kW)
- Weight: 9,950 lb (4,513 kg)
- Max Speed: 483 mph (777 km/h)
- Spiteful F Mk 15 – one built – converted to Seafang prototype
- Engine: Griffon 89 – 2,350 hp (1,752 kW)
- Weight: 10,200 lb (4,627 kg)
- Max Speed: 476 mph (766 km/h)
- Spiteful F Mk 16 – two built – simple, three-speed Griffon conversions from F Mk 14s
- Engine: Griffon 101 – 2,420 hp (1,805 kW)
- Weight: 9,950 lb (4,513 kg)
- Max Speed: 494 mph (795 km/h) at 28,500 ft, 408 mph (656 km/h) at sea level