A bit about the Merlin 46 trials at Boscombe down in early 1942, where Merlin 46 powered VC AB488 was compared with Merlin 45 powered AA873, with the following data:
Max level speed AA873 was 374 mph at 19,000 ft, with AB488 358 at 21,000 ft. Level speed at 10,000 ft: AA873 was 336 mph, AB488 was 315. Service ceiling @ 3,000 rpm: AA873 and AB488 was 38,000 ft. Max rate of climb: AA873 was 3180 ft/min at 13,400 ft and AB488 was 35,100 ft/min at 17,100 ft. Rate of climb at 10,000 ft: AA873 was 3180 and AB488 was 2670.
The Merlin 46 demonstrated significantly greater performance at altitude compared to the Merlin 45, but when fitted with a 29 gallon fuel tank behind the pilot's seat, the Merlin 46 engined Spitfire was more difficult to fly above 15,000 ft.
A further comparison between Spitfires fitted with tropical filters and without can be made between Merlin 45 engined VCs AB320 and the previously mentioned AA873. AB320 took ten minutes to reach 14,000 ft at 2,145 ft/min, with AA873 taking 7.4 minutes to reach 13,400 ft at a rate of climb of 2,900 ft/min. AB320's ceiling was 34,500 ft, AA873's was 36,400 ft, slightly lower than that recorded in the previous test above. AB320's maximum speed was 337.5 mph at 17,400 ft, while AA873's was 374 mph at 19,000 ft.
These figures clearly show the discrepancy in performance between filter equipped and non filter equipped Spitfires. Granted, the trials were carried out in Britain and not in either a tropical nor desert climate.
Max level speed AA873 was 374 mph at 19,000 ft, with AB488 358 at 21,000 ft. Level speed at 10,000 ft: AA873 was 336 mph, AB488 was 315. Service ceiling @ 3,000 rpm: AA873 and AB488 was 38,000 ft. Max rate of climb: AA873 was 3180 ft/min at 13,400 ft and AB488 was 35,100 ft/min at 17,100 ft. Rate of climb at 10,000 ft: AA873 was 3180 and AB488 was 2670.
The Merlin 46 demonstrated significantly greater performance at altitude compared to the Merlin 45, but when fitted with a 29 gallon fuel tank behind the pilot's seat, the Merlin 46 engined Spitfire was more difficult to fly above 15,000 ft.
A further comparison between Spitfires fitted with tropical filters and without can be made between Merlin 45 engined VCs AB320 and the previously mentioned AA873. AB320 took ten minutes to reach 14,000 ft at 2,145 ft/min, with AA873 taking 7.4 minutes to reach 13,400 ft at a rate of climb of 2,900 ft/min. AB320's ceiling was 34,500 ft, AA873's was 36,400 ft, slightly lower than that recorded in the previous test above. AB320's maximum speed was 337.5 mph at 17,400 ft, while AA873's was 374 mph at 19,000 ft.
These figures clearly show the discrepancy in performance between filter equipped and non filter equipped Spitfires. Granted, the trials were carried out in Britain and not in either a tropical nor desert climate.