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All of the Mk Is in the above charts are using 3000 rpm at +6.25 lb boost at ~16,250 ft (no RAM) or ~17,500 ft (with RAM)
At first, I was thinking the same, but at the very top of the report it does state that it is a Tropical Spit VPS I am pretty sure that the RAAF Spitfire Mk VC performance numbers are for a standard Mk VC with Merlin 46, and not one fitted with the tropical filter - but I cannot say for sure.
How do you figure?Hurricane I tests would appear to disagree with that.
All of the Mk IIs are using 3000 rpm at +9 lbs at ~11,800/18,250 ft in low/high gear respectively (no RAM), or 12,500-13,000 ft in low gear (with RAM) and 20,000-22,000 ft in high geart (with RAM).
because the graph shows the rotol equipped Hurricane I doing 265mph at 6.25 lbs, sea level, and 12lbs boost for 285 at sea level.How do you figure?
It does seem odd as most of the intercepts were at 20 k or above. I have just received my copy of "The Darwin Spitfires" (waited patiently for years) so am currently reading it, so far very interesting.Hanging the tropical filter on it and then flying at low level was a double whammy. All (?) of the mock dogfights in the RAAF evaluation were done at heights below the FTH (full throttle height) of the Merlin 46
because the graph shows the rotol equipped Hurricane I doing 265mph at 6.25 lbs, sea level, and 12lbs boost for 285 at sea level.
To RAAF HQRS
From OHQ RAAF KWAY
6 Sept 1943
Spitfire Aircraft Engineering.
5 Spitfire Mk 5 aircraft given extensive test fights here successively with each of the following types of of air intake assembly and engine cowling. (A) original tropical (B) New Tropical with bypass valves (C) Temperate.
Average max speeds were
1 sea level) A) 312 B) 312) C) 316
2 10000ft) A) 355.5 B) 355.5 C) 360
3 at FTH ) A) 357 B) 358.5 C) 363
Considered that improvements in speed were too small to warrant departure from original type tropicalization hence new scheme will not be applied retrospectively to Mk5 aircraft. Latest tropical intake with bypass valve will be incorporated Mk 8 aircraft.
To illustrate the point, I've added the red line for what is my understanding how the speed should've been between the SL and ~18000 ft on 87 oct fuel, and the blue line for the usage of 100 octane, while to the left side is the original graph unaltered - all for the Hurri I with Merlin III and DH prop
87 oct fuel = max boost of +6.25 between SL and the rated altitude (~18000 ft with ram).The chart you added to does not show boost levels used for the results, much like the table I posted.
From the Hurricane @ manual, it gives the weight increase for the air filter on the Hurricane II, as " mod # 264 +28.92 lbs". Over all it was a fairly tidy installation that cost the Hurricane about 7 mph due to increased drag and reduced ram.
The affect on the Spit 5 is a bit more, as the nose cowling was enlarged for a larger oil tank, to help with cooling. The increased temperatures in the tropics were harder on the spit than the Hurricane as the spits wing mounted rads received very little air flow when on the ground. The Hurricanes center mounted rad got some air flow from the prop.
This from the wayback machine, https://web.archive.org/web/2016022...dex.php?page=the-vokes-air-filter-controversy