Quote:
Spit Ia
FTH = 16500 ft
at 6.25psi, 2750rpm (rad open) engine fails after about 3 minutes. Just enough time to get stable 245mph IAS (with 3000rpm couldn't get this alt without engine death)
245mph IAS@16500ft = 323mph TAS = 520 kmh TAS
Oh dear, this is under even B6 plot speed (560kmh TAS at 16500ft).
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What data are you looking at camber?
If it is this:
http://www.spitfireperformance.com/n3171.html
Then you are not at the same engine settings as this data.
This data is 6.5lbs @ 3000 rpm at 16,500 feet.
Unfortunately we only have the one airplane and not Supermarines mean with a percentage variation.
If you look at this test:
Quote:
Aeroplane and Armament Experimental Establishment
Boscombe Down
30 July 1940
Comparison of Performance of Rotol and DH Airscrews on Spitfire
Both the aircraft are similar externally and are fitted with bullet proof windscreen and armour plating over the tank, etc.
Aircraft R6774 is fitted with DH airscrew and N3171 with Rotol airscrew.
It will be noted that these aircraft are about 12 miles an hour down in speed against the previously tested K9793, but the relative comparison remains. This loss in speed is accounted for, by 6 miles an hour for the bullet proof windscreen and 6 miles an hour due to loss in engine power.
Level Speed miles per hour.
Aeroplane Altitude Feet
14000 16000 Max. speed 20000 22000
R6774 342 349 355 @ 17,800' 350 341
N3171 336 343 354 @ 18,900' 354 352
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The above tests were all carried out using 87 octane fuel with boost limited to +6.25 lbs./sq.in. Climb figures were achieved using the 2600 rpm 1/2 hour climb limit. By the Battle of Britain all operational squadrons had changed over to 100 octane fuel and the engine limits on the Spitfires had been increased to +12 lbs./sq.in. 3,000 rpm with 1/2 hour climb limit increased to 2850 - 3000 rpm. Royal Aircraft Establishment figures for a Spitfire I using +12 lbs/sq. in. boost are 314 mph at Sea Level and 359 mph at a full throttle height of 11,500 feet.
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We don't have the entire report but we do have the poster's comments at the bottom. Throwing those out the window we get a little closer to our 2750 rpm.
BTW, running a propeller at a higher rpm on a hot day at high altitude does not mean the airplane will go faster. Usually it will go slower than it will at a lower rpm.
On that report, the data is only between 7% to 5% off from the reported figures
at the lower rpm. We don't know the weights, so the data could be spot on or it might be off.
In order to make a definative statement we need:
1. Atmospheric conditions
2. Speed at same engine settings
3. weights of the aircraft