1. Introduction.

...........Climb and level speed performance and position error measurements have been made on Spitfire F Mk.VIII (Conversion) JF.319, the prototype Mk.XIV. This aircraft was fitted with a Griffon RG5SM engine and a 5-bladed Rotol propeller. It is understood that the final version of the Mk.XIV will have a Griffon 65 engine which differs from the engine now installed in having a higher MS supercharger gear ratio. The external features of this aircraft were similar to the production version of the Mk.XIV, except that the shape of the fin and rudder will probably be different.

2. Condition of aircraft relevant to tests.

....2.1 General. This aircraft is basically a Mk.VIII Spitfire with a Griffon RG5SM engine (.51 reduction gear) instead of the normal Merlin. As a result the nose has been extended and the cowling modified accordingly and a larger air intake fitted. Provision was made for an air cleaner element above the air intake, which was, however, bypassed for normal use.

...........The main features of the aircraft tested were :-

...........Rotol 5-blade propeller, Type No.VP. R19/5F5/1 (See para.2.2)
...........Individual ejector exhausts.
...........The radiator installation was larger than on the standard F.Mk.VIII;
..............it consisted of a collant radiator and the oil cooler in a duct
..............beneath the port wing and a further coolant radiator, and the inter-
..............cooler radiator in a duct beneath the starboard wing.
...........Universal wings with small bulge over 20mm. guns.
...........Small span ailerons.
...........Armament :- 2 x 20mm. guns, 4 x 0.303" machine guns. Gun ports and muzzles sealed,
..............relevant ejection chutes open.
................................"Streamline" blanks over remaining 20mm. gun stubs.
...........Circular rear view mirror with hemispherical fairing above windscreen.
...........Balloon type cockpit.
...........No IFF aerials.
...........Modified rudder and fin of increased area similar to that fitted on
...........F Mk VIII (Conversion) JF.317.
...........Combined rudder balance and trimmer tab.
...........Retractable tail wheel.
...........The external surface of the aircraft had been fighly polished to give a glossy finish.
...........Details of the pressure head position are given in Fig.5.

....2.2 Propeller details. The leading particulars of the propeller were :-

....2.3 Engine numbers and limitations. The aircraft was fitted with a Griffon RG5SM engine Nos. 1282/334313. The relevant limitations applicable at the time of the tests were :-

....2.4 Loading. The take-off weight for these trials was 8,400 lb. with the centre of gravity 4.0" aft of the datum (undercarriage down).

3. Scope of tests.

...........(i) The position error was measured in level flight with flaps and undercarriage up by the aneroid method.
...........(ii) Partial climbs at combat rating were carried out at mean heights of 9,000 ft. in M.S. gear and 21,000 ft. and 36,500 ft. in FS supercharger, to determine the best climbing speeds.
...........(iii) Six climbs were made at combat rating, two using MS supercharger gear throughout, two using FS supercharger gear throughout, and two combining both.

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

...........Combat rating is normally permitted for periods of five minutes only, but a concession for test purposes allowed full climbs to be made at this rating.

...........(iv) Level speeds were measured at heights between ground level and 16,000 ft. in MS supercharger gear and between 12,000 ft. and 39,000 ft. in FS supercharger gear with the radiator flap closed.

4. Results of tests.

...........The results have been corrected to standard atmospheric conditions by the methods of Report No. AAEE/Res/170.

...........The level speed results have been corrected to 95% of the take off weight by the methods of the same Report. A 'strut' correction has been applied, the source of this correction being Report No. ARC.6420. The compressibility corrections has been determined by the method given in the Addendum to Report No. AAEE/RES/147.

...........(i) The position error correction varies from -11.2 at 380 mph ASI to +6 at 120 mph ASI being zero at 198 ASI. Full details are given in Fig.3. The altimeter corrections when the altimeter is connected to the static of the airspeed indicator are given in Fig.4. The position error correction curves have been corrected to 95% of the take-off weight, viz. 7,980 lb.

...........(ii) The best climbing speed found from the partial climbs was 175 mph ASI up to 22,000 ft. (approximate full throttle height in FS supercharger gear), decreasing by 3 mph per 1,000 ft. thereafter.

...........(iii) Full results of the climb performance at combat rating are given in Table I and Fig. 1. Briefly they are :-

...........(iv) Full results of the level speed tests are given in Table II and Fig. 2.

...........The maximum true air speeds in each supercharger are :-

5. Discussion of results.

....5.1 Correction to nominal boost value. As it was not permitted to run the engine up to +18 lb. boost on the ground difficulty was experienced in setting the boost control accurately. Consequently the controlled boost obtained was slightly higher than nominal value (18.5 lb/sq.in. in level flight and 18.3 lb/sq.in. on the climb). When corrected to +18 lb./sq.in. the results given in para.4 would be :-

...........(i) On the climb at combat rating.

...........(ii) In all-out level flight.

....5.2 Propeller tip mach number. The propeller tip mach number reached a value of 0.993 at the FS full throttle height, and 1.015 at the highest altitude tested. In correcting the results to standard atmospheric conditions, no corrections for any consequent effects of compressibility on propeller efficiency have been made.

...........The differences in air temperature on test from the ICAN standard values were within the ranges given below:-

....5.2 Compressibility effects. As already stated the compressibility corrections used in this report were calculated by the methods of the Addendum to Report No. AAEE/RES/147, which includes theoretical effects of position error on the compressibility correction and the variation of position error with Mach No.

...........It is understood that tests have been made in America at high speed and high altitude on an aircraft fitted with both a leading edge and underwing pressure head, and that different true air speeds were obtained from the two ASI systems. This may be due to known effects accounted for in calulating the compressibility correction in this report, or to other compressibility effects due to interference or other causes. Further tests will therefore be made on this aircraft with an additional pressure head located forward of the leading edge to investigate any possible effects of this nature. If these show that the speed results given in this report are not accurate an Addendum giving the revised speeds will be issued.