A family likeness may be expected to appear in successive designs of the same company, but a more than usual close resemblance existed between the Hawker Tempest V and the Typhoon. Indeed, almost the only difference from a casual inspection was in the mainplane, straight-tapered and of rather deep section in the Typhoon, much thinner and of semi-elliptical planform in the Tempest. This difference accounted for, without justifying, the description of the Tempest as ‘… the Typhoon with a new wing,’but was by no means the only difference between the two aircraft.
As its appearance suggested, the Tempest originated in a decision to improve the aerodynamic qualities of the Typhoon with particular reference to the wing. Design work on the Typhoon began in 1937 when little was known about the phenomena and effects of compressibility which later assumed such importance with the great advance in speeds. A high-lift aerofoil with the natural accompaniment of a fairly thick section was selected for the Typhoon, partly because of the increased wing-loading - 40 lb./sq. ft. for the Typhoon as against 25 lb./sq.ft. for the Hurricane - and partly from structural and space considerations.
The wings of a fighter must necessarily be used to accommodate a large amount of equipment, and at the time it was necessary to meet a specific requirement that all fuel should be carried in the wings. As the Napier Sabre engine would develop a large increase in power over that of any existing unit, it was necessary, in order to give the Typhoon adequate range, to find space for a much larger fuel supply than had hitherto been necessary on a single-engined fighter. Provision had also to be made for mounting the armament and accommodating the undercarriage legs. In connection with the undercarriage, a minor contributory factor was the limit on tyre pressures which existed at that time. This factor in itself imposed certain minimum limits on the size of the tyre and had an influence in determining the amount of space required to accommodate the retracted wheel.
With increasing knowledge of compressibility, the need became evident for a modified wing section to improve the performance of the Typhoon in the higher speed range and take the utmost advantage of the higher power of the engine. An intensive examination of the problem began in 1940 and a special Hawker aerofoil section was evolved, much thinner than the original Typhoon wing.
Tempest port and starboard trailing sections of the wing - aft of the rear spar - were assembled in large, paired up vertical fixtures.
In order to compensate for the smaller space available for fuel in the new wing and to extend the range of the aircraft it was decided to fit a large tank in the fuselage forward of the cockpit. An extra bay to accommodate the tank became necessary in the girder portion of the fuselage with the natural result that the engine and the centre of gravity were moved forward and extra stabilising area was required in the form of a larger fin and tailplane. The sum of these modifications was, in effect, a new type of aircraft and in 1942, it was decided to give the name Tempest to what had until then been known as Typhoon II. The prototype Tempest was flown in September, 1942, and the first production aircraft in June 1943.
The Tempest II, the radial-engined version of the aircraft, derived from a prototype Tornado, the corresponding design to the Typhoon originally fitted with a Rolls-Royce 24-cylinder Vulture engine. In 1941, an experimental conversion of the Tornado prototype was made and a Bristol Centaurus radial engine was installed in place of the Rolls-Royce engine.
Inboard portions of the trailing edge assembly, showing the fixtures in position for locating the apertures of the cannon magazine and gun-bay access doors.
The Tempest II fitted with the Centaurus V radial engine.
The Tempest II was remarkable for the manner in which the very compact, but still massive, 18 cylinder 2,500 h.p.-plus Centaurus V engine had been embodied in the nose of an aircraft of truly superlative aerodynamic cleanness. A special exhaust and cooling system were designed by Hawker Aircraft, Ltd. for the installation and the engine, as might be expected, was very tightly cowled. Separate pipes from each cylinder led the exhaust back to a point behind the engine where they ejected through the sides of the cowling. Control of the cooling air past the engine was effected by sliding gills just aft of the exhaust.
The oil-cooler and carburettor air intakes were very neatly arranged in the leading edge of the wing close to the fuselage and, with the large spinner, completd a most attractive power-unit installation. The prototype Tempest II was flown in June 1943 and the first production aircraft in September 1944.
Apart from the engine mountings, the forward fuselage is exacly the same as the Sabre engined machine.
The final drill-jig in which the holes were reamed in the intermediate section of the Tempest spar for the butt-strap joint with the root section.
The first stage of leading edge assembly - The nose ribs have been located and clamped at their respective positions.
Drilling the skin panels and nose-rib flanges from cage-type jigs located over the skin.
Rivetting the skin to the ribs in the third stage of Tempest leading edge assembly. The fixture has been swung round to bring the assembly into the horizontal positition for ease of working.
Production of the Tempest’s leading-edge assembly fell into two main parts, the first - the assembly of the nosing outboard of the dihedral joint - was done in large trunnion-mounted fixtures. In this section of the leading edge, the nose ribs were designated by letters from A to O. The three at the inboard end, A, B and C, were assembled as a small unit in a separate fixture.
The main fixture consisted of two cast-iron columns with trunnion-bearings for the main assembly platform, which, in its turn, was a massive cast-iron member ribbed longitudinally to counteract bending and bolted at the ends to the trunnion brackets. These brackets carried adjustable balance-weights to reduce effort needed in handling the platform. It was possible to locate the platform in three different positions by indexing pins inserted through bushings in the end columns into bushed holes in each of the trunnion brackets.
At intervals along the platform representing the rib stations were set up a series of vertical templates which serve as locations for tlie nose ribs. Longitudinal strips along the bases of the template located the edges of the skin-plating. Each rib was located on a tooling-hole near the tip and by the spar-attachment angles at the root.
Large paired-up fixtures accommodating both port and starboard wings were used for ther assembly of the Tempest wing as a complete unit.
In the main assembly fixture the basic structure of the wing was completed. This fixture resembled that for the trailing-edge structure and accommodated both port and starboard units. It was similar to the earlier assembly fixtures used for Hurricane and Typhoon wing assembly. Three large castiron columns carried the main pick-ups and were bridged by a large-diameter tubular top-beam. These tubular members in the wing assembly fixtures were found to be essential in order to maintain rigidity as the wing structure was sufficiently strong to distort the fixture if ordinary structural-steel sections were used.
Location for port and starboard front and rear-spar root-fittings were mounted on the centre column. The two outer columns, on which the wingtip locations were mounted, were in line with each other but offset in relation to the centre column. This arrangement was adopted to simplify the build and could be dropped clear of the end of the wing and permit it to be withdrawn almost longitudinally immediately the root locations had been freed.
Leading edge and trailing sections in the main assembly fixture with the interspar ribs in position.
One of the first-stage aileron drill-jigs for the Tempest, showing the structure of the ribs, stringers and top spar flange in position. One of the tubular frames without the skin panel is shown on its four-pin location. The latticework frame shown in the vertical position holds the drill-jig bushes for drilling through the skin into the parts underneath.
The building of the aileron commenced with the riveting of the bottom surface stringers to the underside skin, and the ribs and top-surface stringers to the top-surface skin. For each surface the work is divided into two stages, the first of which was the drilling of the skin and structural members together in a single jig. Each rib was located by tooling holes, one in the web near the trailing end and one in the forward spar attachment flange, and held by quick-action toggle-clamps against location blocks at the proper stations.
Owing to the thinness of the skin plating and the consequent difficulties of obtaining a surface free from panting and buckling if the normal methods of handling were adopted, panels were prestretched on a tubular frame before being located on the jig. Both ends of the panel were turned over to form a right angled flange. Holes were pierced in each end, and the skin was clamped by pins inserted through these holes. At the tip end of the skin the pins were inserted directly into the tubular frame, and at the root end the skin was clamped between strips in a frame carried on adjusting screws. By turning the screws the skin can be stretched to remove any waves or any tendency to buckle.
The same drill jig with a skin panel tacked to the rib structure and ready for removal to the riveting stage.
A Tempest port wing on one of the mobile final assembly stands showing the undercarriage-leg wheel bay and the tank bay templates in position ready for the fitting of the underside skin.
Before assembly to the fuselage a pair of wings- complete by now with an undercarriage leg on each side - was mounted on a test stand for actuation tests on a rig that mimicked the cockpit controls and indicators.