This a report from a tactical trial conducted in 1943 using the P-38F against a Spitfire Mk IX (I believe with the Merlin 61 engine). It's a tactical trial comparing the speeds of both aircraft at various altitudes flown at full war load. The link to the report (actually a .zip file with other P-38 data) can be found at the end of the post.
Tactical Trials - P-38F ("Lightning")A.F.D.U. Report No. 56Note: This sheet is being circulated to all holders of A.F.C. 139, and should be attached to that paper.
1. Since completion of the Tactical trials carried out on the P-38F by A.F.D.U. (the report on which was issued as A.F.C., Paper No. 39), further speed trials have taken place between a standard Spitfire Mk IX aircraft and a modified P-38F. The results are shown below;
Description of Aircraft2. The Spitfire IX, BS.350 was a standard aircraft drawn from an operational squadron and was flown with full war load. The armament consisted of 2 - 20 mm cannon with 140 rounds each, and 4 - .303 guns with 350 rounds each. No jettison tank was carried. The Merlin 61 engine was fitted with the standard .42 reduction gear. Flying load for the trial - 7,400 lbs.
3. P-38F No. 17592 of the U.S.A.A.F., was supplied by the 8th Fighter Command and flown by an American pilot. This aircraft had no special finish and was fitted with blisters for external tanks which may cause a speed loss of anything up to 8mph. The aircraft was flown at full war load, the armament being 4 - .5 guns with full ammunition and 20mm cannon with drum of 60 rounds. The engines had improved inter-cooling but were otherwise in an identical condition as for the previous trials. Load for trials - 15,500 lbs.
Conduct of Trial4. The heights at which the speed runs were attempted were as follows:
(a) 1,000ft
(b) 10,000ft
(c) 20,000ft
(d) 27,000ft
(e) 35,000ft
The test at 20,000 feet had to be abandoned owing to cloud conditions. All runs were for 3 minutes duration at full throttle, the aircraft in formation, and i the P-38F the allowable turbo supercharger speed of 22,600rpm was never exceeded.
Results of Trials (For the sake of this post, only the speeds are included. Boost, RPM and ASI can be found in the reported linked in this post.)
5. [All speeds are TAS]
1,000ft
P-38F - 352mph
Spitfire - 322mph
10,000ft
P-38F - 373mph
Spitfire - 356
27,000ft
P-38F 393
Spitfire - 405
35,000ft
P-38F - 364
Spitfire - 385
6. The pilots did not consider that the difference in speeds at any height were as great as those represented above, but they admit that any attempt to guess at the amount of relative overtaking speeds is extremely difficult. They reported that the superiority of the P-38F at 1,000 feet was most marked but that at other heights the aircraft seemed to gain little ground on each other after the Spitfire's initial acceleration, which was always noticeably more rapid than that of the P-38F. In a long run of say 8 to 10 minutes at full throttle, the P-38F might show even better results.
This post is in no means to show one plane being better than the other, I thought this might be of interest to the P-38 and Spitfire drivers.
P-38 manuals and reports.
ack-ack
