|1......... In accordance with instructions from Headquarters, Fighter Command, one Spitfire IX aircraft, AB.505,
was delivered from Messrs. Rolls-Royce,Ltd., to this unit on 26th April 1942, for a period of one week, for tactical trials.
2......... In order to bring the weight of the aircraft up to its full war load it was necessary to fit 2 x 20 mm. cannons, full ammunition for all guns, V.H.F., and I.F.F. The aircraft has fittings for a jettisonable fuel tank but this was not available. Without this tank the all-up weight is about 7,400 lbs.
3......... During the trials minor adjustments had to be made to the undercarriage and sliding hood, and after 5 days flying engine failure occured. It was found that the butterflies in the carburettor were pitted, one spray nozzle on the enrichment side was missing, and several pieces of metal had reached the oil filters. A new engine is being sent from Messrs. Rolls-Royce, Hucknall.
4......... The Spitfire IX is a Spitfire VC modified to incorporate a Merlin 61 engine fitted with the latest negative 'G' carburettor. The main differences between the two aircraft are the slightly longer nose due to the larger engine, a 4-bladed Rotol constant speed propeller, two thermostatically controlled radiators and two-speed superchargers which are automatically controlled. The fuel capacity is increased by approximately 10 gallons and the tanks are pressurised.
5......... The cockpit is similar to that of the Spitfire VC but has additional controls for ground testing the full supercharger gear and radiators, and for pressurisng the fuel tanks. There is only one fuel cock.
6......... The supercharger gear is fully automatic, so that M.S. gear is in operation below about 22,000 feet and F.S. gear above that height. For testing there is a push button to bring the F.S. gear into operation. A light illuminates when the button is pressed and also in the event of the aneroid failing to change down to M.S. on descent so as to warn the pilot that there will be a loss of power should he have his landing baulked and have to go round again. If the aneroid is functioning correctly F.S. gear is not available below 22,000 feet, nor is M.S. available above this height.
7......... The radiator is thermostatically controlled so that the pilot does not have to operate it manually. For ground testing there is a push button which will open the radiator while the button is held down, otherwise the shutters open when the coolant temperature reaches 115 deg.C. This press button and the button for testing F.S. gear are situated on the plate aft of the throttle box and are in the way of the pilot's arm.
8......... Was skipped in report
9......... A cock is provided for pressurising the fuel tanks and must always be kept on above 20,000 feet to avoid engine failure due to vapour locks. In the event of a tank being holed by enemy action it is essential to turn off the pressure to avoid exessive loss of fuel. The cock is on the starboard side of the cockpit and is liable to be fouled by the pilot's elbow. A red fuel pressure warning light is fitted instead of a pressure gauge on the dash-board and lights when the pressure falls to 3 lbs.
10......... There is a gauge mounted on the port side of the dash-board showing the temperature of the mixture change, which should read about 40 deg.C. in M.S. gear and 60-80 deg.C. in F.S.
11......... There is an efficient system of heating the cockpit which can be regulated by the pilot.
12......... The constant speed control for the airscrew is in the usual position and controls between 1700 and 3000 r.p.m. The travel of the lever is, however, very short indeed and the selection of desired r.p.m. far too critical.
13......... The Spitfire IX is fitted with the G.M.2 pilots reflector sight and although the aircraft is longer in the nose than the Spitfire VC, the 100 m.p.h. ring of the sight is still just clear of the nose.
14......... The oxygen supply is obtained from the bottles provided with an economiser and is the same as that used in the standard Spitfire
15......... The Spitfire IX was compared with a Spitfire VC with similar armament, and a Typhoon I for performance and manoeuvrability; all aircraft were carrying full war load.
16......... The Spitfire IX is similar to the Spitfire VC for take-off and landing, although the landing speed is slightly higher. The extra weight and length of the aircraft has made the elevators a little heavier and as a result controls are better harmonised. It was noticed that during dives there was less tendency for the aircraft to yaw and this was thought to be due to the extra radiator fitted on the port wing. Tight turns were made up to 5G and there was no sign of 'tightening up', the aircraft recovering normally when the control column was released.
17......... The speed of the Spitfire IX was compared with a Spitfire VC and a Typhoon I at various heights. Its maximum true speed in M.S. gear is developed at a height of 16,300 feet and is approximately 386 m.p.h., and in F.S. gear at 28,000 feet and is approximately 409 m.p.h. Those figures are slightly less than those obtained by Messrs. Rolls-Royce, but it is understood that the aircraft they used was not fitted with cannons and did not carry full war load. The speed of the Spitfire IX at all heights was vastly superior to that of the Spitfire VC.
18......... The speed runs were made against a Typhoon I from an operational squadron. At 15,000 feet the Spitfire IX was approximately 10 m.p.h. faster, and at 18,000 feet approximately 2 m.p.h. faster.
19......... Comparitive climbs were carried out and it was found that the Spitfire IX was superior to the Spitfire VC and Typhoon I at all heights. This superiority becomes even more marked as height increases. The Spitfire IX was climbed under maximum continuous climbing conditions, to an indicated height of 39,500 feet where the rate of climb was about 700 feet per minute. It was particularly noticed that the oil and glycol temperatures were normal throughout. The operational ceiling is considered to be about 38,000 feet where the rate of climb is 1,000 feet per minute. This height can be reached by a single aircraft in 18 1/2 minutes.
20......... The Spitfire IX was compared with a Spitfire VC for turning circles and dog-fighting at heights between 15,000 and 30,000 feet. At 15,000 feet there was little to choose between the two aircraft although the superior speed and climb of the Spitfire IX enabled it to break off its attack by climbing away and then attacking in a dive. This manoeuvre was assisted by the negative 'G' carburettor, as it was possible to change rapidly from climb to dive without the engine cutting. At 30,000 feet there is still little to choose between the two aircraft in manoeurvrability, but the superiority in speed and climb of the Spitfire IX becomes outstanding. The pilot of the Spitfire VC found it difficult to maintain a steep turn without losing height, whereas the pilot of the Spitfire IX found that he had a large reserve of power which enabled him to maintain height without trouble. The all-round performance of the Spitfire IX at 30,000 feet is most impressive.
21......... Short trials were carried out against a Typhoon I and the Spitfire IX was found to be more manoeuvrable and superior in climb but inferior in dive. During a dog-fight at 18,000 feet the Spitfire out-turned the Typhoon and got on its tail after 1 1/2 turns.
22......... Several climbs were made to heights between 39,000 and 40,000 feet and the pilot felt that the aircraft was capable of going even higher. Although the operational ceiling is considered to be 38,000 feet, it is thought that Sections of two could operate up to 39,000 feet and probably higher. The aircraft is easy to fly at high altitudes, but freezing up of the trimming tabs occured. It was therefore difficult to keep the aircraft level as it was still trimmed for climb. During manoeuvres there is otherwise little tendency to lose height even at 38,000 feet. At this height the aircraft was dived for 1,500 feet and zoomed up to 39,000 feet. Steep turns were carried out at 38,000 feet where it was necessary to maintain an indicated airspeed of at least 110 m.p.h. to prevent stalling. The cockpit heating kept the pilot warm at all heights and flying clothing was unnecessary.
23......... Slight icing up of the cockpit was experienced during turns but this dispersed as soon at the aircraft was flown straight. The cold air spray to the windscreen was turned on during descents and no misting was experienced.
24......... During the high flying trials vapour trails were formed between 30,000 and 36,000 feet, but above this height trails were not visible. All flights took place under conditions of no cloud and extremely low temperatures, -64 deg.C. being reported on one occasion.
25......... The fuel capacity of the Spitfire IX is 92 gallons, 57 in the top tank and 35 in the bottom tank. This is 10 gallons more than the Spitfire VC. There are fittings under the fuselage for a jettisonable tank holding 39 gallons. Petrol consumption during the trials was high and during a comparitive flight of 75 minutes the Spitfire IX used 76 gallons and the Spitfire VC 54 gallons. In a flight of one hour, three speed runs of 4 minutes each and a maximum continuous climb to 39,000 feet were carried out and the Spitfire IX used 76 gallons. On investigation of engine trouble experienced at the latter stage of the trials it was found that the aircraft had been delivered with the mixture control locked in the "RICH" position instead of "WEAK".