The principle results are as follows:-

                  Engine conditions - 3000 rpm + 25 lb/sq,in. boost.

1.     Introduction.

                  Performance, cooling and fuel consumption trials were required on a Spitfire IX aircraft fitted with a Merlin 66 engine adjusted for a maximum boost of +25 lb/sq.in. for combat climb and all-out level conditions. The performance and fuel consumption has been measured, and a brief assessement of handling characteristics made, the results of which are given in this Report. Advance information on the performance results were forwarded to M.A.P. by letter 10th January, 1944.

2.     Condition of aircraft relevant to tests.

        2.1.   General. The aircraft was a normal Spitfire F.Mk.IX. The following were the chief external features:-

        2.2.   Loading. The tests were made at T.S.L. conditions, i.e. at a take-off weight of 7400 lbs., with the C.G. at 6.4" aft of the datum point.

        2.3.   Engine details and limitations. The engine was a Merlin 66 No.156369/A444995 fitted with a Rolls-Royce version of Stromberg pressure carburettor, the "D" chamber vent of which was blanked off.

                  The engine was cleared for combat operation at +25 lb/sq.in. boost pressure for periods not exceeding 5 minutes.

                  The propeller reduction gear ratio was 0.477. 150 grade fuel to Specification RDE/F/253 was used throughout the trials.

        2.4.   Propeller.

        2.5.   Instruments. An automatic observer, comprising an altimeter, air speed indicator, boost gauge and watch was fitted in lieu of the TR.1133 radio. A type 35 control operating the 16 mm Bell-Howell cine camera photographing the instruments at 2 second intervals was installed in the pilots cockpit.

3.     Tests made.

        3.1.   F.S. gear climbs to 30,000 feet and M.S. gear climbs to 20,000 feet were made with the radiator flaps open. In addition, two climbs in F.S. gear with the radiator flaps closed were made for comparison with results as obtained by the firms.

        3.2.   All-out level speeds in M.S. gear from sea level to 12,000 feet and in F.S. gear from 6,000 to 30,000 feet were measured; fuel flowmeter readings were taken during each run in order to provide data at the increased rating.

4.     Results.

                  All performance results given in the Report have been corrected to standard ICAN atmospheric conditions and the level speeds to 95% of the take-off weight by methods of Report No. A.& A.E.E./Res/170.

        4.1.   The position error correction and altimeter correction used were those measured on Spitfire IX BF.274. The compressibility correction has been calculated by the method given in Addendum to Report No. A.& A.E.E./Res/147; a strut correction based on ARC Report No. 6420 has been used.

        4.2.   Climbs. The results which have all been obtained from automatic observer records are detailed fully in Tables I, II, and III whilst the corrected time, rate of climb and boost are plotted against height in Fig. 1

                  The time to height curve corresponds to the rate of climb in M.S. and F.S. gear, radiator flaps open - change of gear at approximately 6000 feet. An estimate of the expected performance at +18 lb/sq,in, boost is also shown in the Fig. for comparison.

        4.3.   Level speeds. The maximum level speed results are detailed fully in Table IV whist TAS and boost curves are plotted against height in Fig. 2. The estimated performance at +18 lb/sq.in. boost is also shown in the Fig. 2.

        4.4.   Comparison of performance results.

                  4.41.   An increase of about 950 ft/min in rate of climb and about 30 mph in all-out level speed is achieved by the increase of boost from +18 lb/sq.in. to +25 lb/sq.in.

                  4.42.   The comparison of this estimated performance with that obtained on Spitfire F.Mk.IX BS.543 with Merlin 66, shows rather lower figures for JL.165, particularly in all-out level speed.

                  The table below gives rough comparison of the performance of both aircraft:-

                  4.43.   For comparison purpose the climb and level speed results as obtained at the increased boost rating by:

are given below.

                  It should be noted that the climb performance was measured with radiator flaps closed by both firms.

        4.5.   Fuel flows.   The fuel flows as obtained from flowmeter readings in all-out level speed runs were corrected for instrument error and temperature deviation from standard conditions.

                  Maximum fuel flow was obtained near full throttle height in F.S. gear and was about 197 galls/hour. The corresponding value of fuel flow at +18 lb/sq.in. was estimated as 150 galls/hour.

        4.6.   Handling.   There was no appreciable change in handling of the aircraft at +25 lb/sq.in. as compared to a standard Spitfire IX at +18 lb/sq.in. There was only a slight change in directional trim when throttle was fully opened from +18 to +25 lb/sq.in.

        4.7.   Maintenance.   No difficulty was experienced in maintenance of the engine though most running was at high boost. In one case only an exhaust stub was burnt out and no plug troubles were encountered.

                  The total time flown at +25 lb/sq.in. during the tests was approximately 1 hour, 10 mins., whilst total time flown at boost higher than +18 lb/sq.in. was approximately 2 hours.

5.     Conclusions.

                  The increase in performance with the increase of boost from +18 to +25 lb/sq.in. corresponds to:

                  No maintenance difficulties of the engine were experienced.

6.     Further develpments.

                  Further trials on the same aircraft fitted with a Rotol 5-blade propeller and existing 0.477 propeller reduction gear will be carried out in due course.