davparlr
Senior Master Sergeant
On another thread, now closed, there was a discussion going on relative to the aerodynamic performance of the Spitfire to the Mustang. To see the actual performance differences, I thought I would do an apple-to-apple comparison between the P-51B with a Merlin -7 engine and a Spitfire Mark IX with a similar Merlin 66 engine, both operating at 67" Hg boost (18.5 lb/sqin). I will use these references. This is only a speed and climb comparison. There or other variables I did not attempt to address such as roll rate, dive rates, etc.
http://www.wwiiaircraftperformance.org/mustang/p51b-speed-wf.jpg
http://www.wwiiaircraftperformance.org/mustang/p51b-climb-wf.jpg
http://www.spitfireperformance.com/bs543climb.gif
http://www.spitfireperformance.com/lfhfspeed.gif
In order to do the apples-to-apples comparison, I had to adjust the P-51B's climb data, both rate of climb and time to climb, to reflect the discrepancy in fuel quantity. The P-51B was tested with 256 U.S. gallons of fuel, the Spitfire was tested with 110 U.S. gallons of fuel. This is almost a 900 lbs difference. This roughly worked out to be about 500 f/m improvement. Airspeed data was insignificantly affected by weight difference and was not adjusted. A note here is that I did chart interpretation on small charts with poor resolution so there is an inherent data uncertainty. But it should be accurate enough for comparison purposes.
Data will show Altitude(ft) versus airspeed(mph), rate of climb(ft per min) at every 5kft, and time to climb(min) at 10k ft, 20kft and 25kft. Also shown is the delta speed advantage for the Mustang and the delta climb advantage for the Spitfire.
SL
P-51 364 3900
Spitfire 336 4600
Delta P-51 speed + 28 mph
Delta Spit climb +700 f/m
5k ft
P-51 394 4100
Spitfire 358 4670
Delta P-51 speed +32 mph
Delta Spit climb +570 f/m
10k ft
P-51 408 3700 2.5 min
Spitfire 380 4280 2.15 min
Delta P-51 speed +28 mph
Delta Spit climb +580 f/m
15k ft
P-51 422 3680
Spitfire 383 3860
Delta P-51 speed +39 mph
Delta Spit climb +180 f/m
20k ft
P-51 425 3500 5 min
Spitfire 399 3560 4.75 min
Delta P-51 speed +26 mph
Delta Spit climb +60 f/m
25k ft
P-51 425 2810 6.5 min
Spitfire 395 2835 6.3 min
Delta P-51 speed +30 mph
Delta Spit climb +25 f/m
A favorite myth about the P-51 was that it was fast and had great range but it was not a good climber. But, as can be seen from the above comparison, the Spit had noticeable advantage at low altitudes, 700 f/m (8 mph) at SL, but above 10k ft it held only a slight edge in climb over the Mustang.
It appears that, roughly, an equally loaded P-51 taking off with a Spitfire will reach 25k ft altitude about 30 sec behind the Spitfire but with a delta speed capability of 30 mph. It seems to me that, once at altitude, the P-51 would have a much easier time chasing down an enemy and certainly more endurance to do so and that 30 sec advantage would quickly disappear.
The aerodynamic efficiency of the P-51 aids it climb, being very similar to the Spitfire even though the Mustang has a 30% higher wing loading than the Spit. It helps in acceleration by having more available hp since it uses less hp than the Spit to maintain any given airspeed. And, of course aids in endurance and/or range just because it uses less fuel per mile than other aircraft. It sent many aerodynamic engineers, both allied and German, back to the drawing board to compete with, or fight with, this new fighter. It also had a marvelous British engine that could put that great design to good use. That same marvelous British engine could not give its best in any other airframe, including the Spitfire, since it had to use more of its power just to overcome drag.
Now, the Spitfire, and also the Bf-109, were wondrous aircraft capable of great performance deserving all the accolades they got, and indeed, with upgraded engines stayed formidable for the duration of the war and more. But they were early 30s aircraft and the P-51 was a 1940 aircraft, and was basically a generation of aeronautical improvement different.
There maybe some errors in these numbers. If so, I am sure they will be pointed out and I can adjust my numbers accordingly. I think in general this is pretty accurate.
http://www.wwiiaircraftperformance.org/mustang/p51b-speed-wf.jpg
http://www.wwiiaircraftperformance.org/mustang/p51b-climb-wf.jpg
http://www.spitfireperformance.com/bs543climb.gif
http://www.spitfireperformance.com/lfhfspeed.gif
In order to do the apples-to-apples comparison, I had to adjust the P-51B's climb data, both rate of climb and time to climb, to reflect the discrepancy in fuel quantity. The P-51B was tested with 256 U.S. gallons of fuel, the Spitfire was tested with 110 U.S. gallons of fuel. This is almost a 900 lbs difference. This roughly worked out to be about 500 f/m improvement. Airspeed data was insignificantly affected by weight difference and was not adjusted. A note here is that I did chart interpretation on small charts with poor resolution so there is an inherent data uncertainty. But it should be accurate enough for comparison purposes.
Data will show Altitude(ft) versus airspeed(mph), rate of climb(ft per min) at every 5kft, and time to climb(min) at 10k ft, 20kft and 25kft. Also shown is the delta speed advantage for the Mustang and the delta climb advantage for the Spitfire.
SL
P-51 364 3900
Spitfire 336 4600
Delta P-51 speed + 28 mph
Delta Spit climb +700 f/m
5k ft
P-51 394 4100
Spitfire 358 4670
Delta P-51 speed +32 mph
Delta Spit climb +570 f/m
10k ft
P-51 408 3700 2.5 min
Spitfire 380 4280 2.15 min
Delta P-51 speed +28 mph
Delta Spit climb +580 f/m
15k ft
P-51 422 3680
Spitfire 383 3860
Delta P-51 speed +39 mph
Delta Spit climb +180 f/m
20k ft
P-51 425 3500 5 min
Spitfire 399 3560 4.75 min
Delta P-51 speed +26 mph
Delta Spit climb +60 f/m
25k ft
P-51 425 2810 6.5 min
Spitfire 395 2835 6.3 min
Delta P-51 speed +30 mph
Delta Spit climb +25 f/m
A favorite myth about the P-51 was that it was fast and had great range but it was not a good climber. But, as can be seen from the above comparison, the Spit had noticeable advantage at low altitudes, 700 f/m (8 mph) at SL, but above 10k ft it held only a slight edge in climb over the Mustang.
It appears that, roughly, an equally loaded P-51 taking off with a Spitfire will reach 25k ft altitude about 30 sec behind the Spitfire but with a delta speed capability of 30 mph. It seems to me that, once at altitude, the P-51 would have a much easier time chasing down an enemy and certainly more endurance to do so and that 30 sec advantage would quickly disappear.
The aerodynamic efficiency of the P-51 aids it climb, being very similar to the Spitfire even though the Mustang has a 30% higher wing loading than the Spit. It helps in acceleration by having more available hp since it uses less hp than the Spit to maintain any given airspeed. And, of course aids in endurance and/or range just because it uses less fuel per mile than other aircraft. It sent many aerodynamic engineers, both allied and German, back to the drawing board to compete with, or fight with, this new fighter. It also had a marvelous British engine that could put that great design to good use. That same marvelous British engine could not give its best in any other airframe, including the Spitfire, since it had to use more of its power just to overcome drag.
Now, the Spitfire, and also the Bf-109, were wondrous aircraft capable of great performance deserving all the accolades they got, and indeed, with upgraded engines stayed formidable for the duration of the war and more. But they were early 30s aircraft and the P-51 was a 1940 aircraft, and was basically a generation of aeronautical improvement different.
There maybe some errors in these numbers. If so, I am sure they will be pointed out and I can adjust my numbers accordingly. I think in general this is pretty accurate.