Climb and level speed performance has been measured on Spitfire F. MK. IX B.F.274 both with and without a 30 gallon external jettisonable tank fitted. The climb performance at combat rating and position error have also been measured without the tank fitted. The engine was fitted with a 0.477:1 reduction gear and a Rotol R3/4F5/3 metal propeller.

                  A summary of the results follows:-

Without 30 gallon tank

                  Performance tests were required on Spitfire F. MK.IX. B.F.274. This report deals with position error, climb, and level speed tests.

                  Preliminary results were forwarded to M.A.P. by letter, ref. A.A.E.E./4493/44/Gen-A.S. 56/50, dated 6th September 1942 and by postagram dated 17th September 1942.

2.    Condition of aircraft relevant to tests.

                  The aircraft was a standard Mk.IX fitted with a Merlin 61 engine having a 0.477:1 reduction gear. A production propeller type Rotol R3/4F5/3, having dural blades to Drg.No.RA.10061 was fitted.

                  Standard Mk.Vc (universal) wings were fitted. This wing has the large bulge in its top surface over the 20 m.m. guns. The two remaining 20 m.m. gun stubs in the leading edges were fitted with hemispherical blanks. The leading edge gun ports and the muzzles of the 20 m.m. guns were sealed. The ejection chutes beneath the wing relevant to the guns fitted were open.

                  A fuel cooler was fitted in the port wing root with an intake duct in the leading edge.

                  A rectangular rear view mirror without fairing was fitted above the windscreen. The bulletproof windscreen was fitted internally. The tail wheel was not retractable.

                  No snowgaurd was fitted over the air intake.

                  Individual ejector exhaust stubs were fitted.

                  One coolant radiator and the oil cooler were housed in a duct beneath the port wing and a second radiator and the intercooler coolant radiator in a similar duct beneath the starboard wing.

..................The aircraft was finished in normal fighter camouflage.

..................The 30 gallon external fuel tank fitted during some of the tests was of the type that can be fitted to the MK.V.

..................The take-off weights for these trials were:-

....................................7480 lb. without the 30 gallon tank.
....................................7775 lb. with the 30 gallon tank.

..................The following engine limitations were relevant to the tests made:-

                  The following tests are dealt with in this report.

         (i)      The position error in level flight was measured between 320 m.p.h. and 130 m.p.h. A.S.I. by the 'aneroid' method.

         (ii)      Partial climbs were made using both normal and combat climb ratings to establish the best climbing speed.

        (iii)      Ceiling climbs were made using both normal and combat rating. Combat rating is normally permitted only for periods of 5 minutes, but a concession was allowed on this limitation for test purposes and the full climbs were made in this rating. The rate of climb was such that the boost fell from +15 to +12 lb/sq.in. due to altitude in less than 5 minutes in each supercharger gear.

                  Climbs were also made with a jettisonable 30 gallon fuel tank fitted externally beneath the fuselage. Prior to the introduction of combat rating, 3000 r.p.m. was permitted on the climb above 30,000 ft. and this procedure was used on the climb with the 30 gallon tank.

                  On all climbs the radiator flaps were fully open. The best climbing speed found from test (ii) was used.

        (iv)     Level speeds both with and without the 30 gallon tank were measured in M.S. and F.S. supercharger gears. The radiator flaps were closed for all level speed tests, giving the minimum drag position.

                  The tests were made between 15th August and 15th September 1942.

4.    Results.

                  The performance results are summarized on the first page of this report. Reductions of the results have been made by the method of A.& A.E.E. Memorandum dated 27.8.42.

                  The position error curve is given in Fig.3, the position of the pressure head in Fig.4, and the correction to altimeter when connected to the static of the A.S.I. system in Fig.5.

                  The best climbing speed found from partial climbs was 160 m.p.h. A.S.I. up to 25,000 ft. (approximately full throttle height in F.S. supercharger gear), decreasing 3 m.p.h. per 1000 ft. thereafter. This speed applied to climbs at both normal and combat ratings.

                  Details of the climb performance are given in Tables I, II and III and are plotted in Fig 1. During the climbs the automatic supercharger gear change device was over-ridden by a specially incorporated switch in order that the gear might be changed at the height for optimum climb.

                  Details of the maximum level speed performance are given in Tables IV and V and are plotted in Fig 2.