1. In accordance with instructions from Air Ministry (D.A.T.), reference C.S.16286 dated 2nd January 1943, tactical trials of the P-47C "Thunderbolt" have now been carried out at this Unit.
Aircraft Nos. 16198 (Mk.2 R.E.), 16319 and 16324 (Mk.5 R.E.) were loaned by the VIII Fighter Command of the U.S.A.A.F., together with flying and ground personnel for the duration of the trial. This report has been produced with the collaboration of their Headquarters Staff.
2. The P-47C is a single-seater, single engined, low-wing monoplane fighter.
The power unit is a Pratt & Whitney R.2800-21 (Double Wasp) radial engine developing 2000 h.p., fitted with an exhaust driven turbo-supercharger which is positioned in the fuselage aft of the cockpit.
Rated altitude is about 27,000 feet. The armament consists of either 6 or 8 x .50 calibre guns with a maximum of 425 rounds per gun.
3. The only apparent difference between the Mk.2 R.E. and Mk.5 R.E. aircraft is that the latter have had special padding fitted to the push rod housings for winter operation, in order to keep the oil from becoming too thick.
In fact these engines always ran too hot on the climb and performance checks were therefore made on the 2 R.E. aircraft, and the U.S.A.A.F. is arranging to remove this padding from the Mk.5 R.E. aircraft.
4. The aircraft were flown throughout the trials with 6 guns only and 300 rounds per gun, which is the equivalent weight of armament likely to be used during operations in Europe.
It is probable that when commencing operations 8 guns with 200 rounds each will be used. Otherwise, full war load was carried, making the all-up weight about 13,000 lbs. for take-off, and the wing loading 43.3 lbs.
5. The cockpit is enclosed by a sliding hood with jettison device, and is very roomy and comfortable.
The positioning of instruments and controls is reasonably good but the cockpit is considered complicated in a British pilot's eyes, as in addition to the normal controls, he is provided with an extra lever on the throttle quadrant to operate the supercharger, and electric switches to regulate the shutters for intercooler and oil cooler.
It must, however, be pointed out that both these shutters can be left in the neutral postion below the rated altitude except in an emergency.
The supercharger lever can be linked to the throttle so that both are operated together and in this condition, although rather heavy for a fighter pilot's controls, gives smooth operation.
An alternative method is to use the throttle only until a height has been attained at which it has reached the far end of the gate and then to bring up the supercharger lever to maintain the required boost and to use that lever only as the engine control at altitude.
The drawback to the last method is that the supercharger control by itself becomes far too sensitive as altitude is gained, very small movements on the quadrant resulting in large increases or decreases of manifold pressure. If throttle back suddenly to prevent over-shooting at target at altitudes, the supercharger appeared to take longer than an engine driven driven one before it was delivering full power again when opened up. The maximum allowable r.p.m. for the turbo-suprecharger is 18,250 and a revolution counter is included on the dashboard. This speed will not be exceeded below the rated altitude (27,000 feet) but there is a risk of it happening at greater altitudes if the supercharger control is pushed fully forward, as no governor is fitted. There are a number of occasions on record when the maximum revs. have been exceeded without failure, and it is stated that the limit set is well within the safety range.
6. The controls for the hydraulic system for undercarriage, (all wheels retract), flaps and cowling gills are accessible, but there is also a flap equalizing valve which must be operated to ensure that the flaps will come down evenly, making one more control for the fighter pilot to remember.
7. The cockpit temperatures were fairly satisfactory for English winter conditions and flying at altitude never caused the pilots any discomfort from cold.
8. Misting-up has not occurred in ay of the flights at altitude.
9. The oxygen supply is from a low-pressure system with a new American demand valve.
During the trials this was not entirely satisfactory, and the majority of flying was limited to 30,000 feet as the flow above this height was unreliable; it is understood that a modified valve system is soon to be available.
There is an aneroid control which relieves the pilot of the necessity of increasing the flow with altitude, and an indicator on the dashboard to show the oxygen delivery as each breath is taken.
In an emergency the pilot can obtain pure oxygen, in which case the total amount takes 45 minutes to consume.
10. V.H.F. radio was fitted (Set No.SCR.522A built by Bendix), but in all three aircraft suffered so badly from background noise, either due to the harness being unscreened or the faultily adjusted suppressors, that is was hardly possible to use it and it can certainly not be considered operational.
The lack of screening also led to moisture getting at the leads. The set is very inaccessibly placed above the supercharger, so that even with practice it takes 20 minutes for removal or refitting.
11. The pilot is protected by bullet-proof plate of glass set inside the 'V' shaped windscreen, and by 9 mm. armour behind his seat and head.
The fuel tanks are all self-sealing but the oil tank is not so treated. There is no protection for the supercharger turbo housing.
12. The trials consisted of comparative flying against standard operational Spitfire IX loaned by 403 Squadron, as both aircraft are designed as high altitude fighters, and against a Typhoon IB of 181 Squadron which was the nearest British equivalent in weight.
Short trials were also made against the new Mustang X (Merlin 65) and the P-38F "Lightning".
13. All pilots have commented on the ease with which the P-47 can be flown and its well-balance crisp controls.
In particular, the ailerons are so good the pilots found it very manoeuvrable and were not conscious of flying a heavy aircraft with a comparatively high wing loading.
It is straightforward for take-off, for which a fairly long run is necessary, and very easy to land at an approach speed of 110 m.p.h. I.A.S.
The stall characteristics are good there being ample warning in the form of buffeting. It is stable in all conditions of flight and can be trimmed to fly hands off easily for steady conditions.
The rudder, however, is the heaviest control and requires frequent trimming for changes in speed and engine power, as the foot loads soon become tiring, but it is thought to be better than earlier American fighters such as the Tomahawk and Mustang.
The elevator control is good and always positive and is noticeably improved when the fuel in the auxiliary tank, which is the rear tank, has been used.
Since this tank only holds 83 Imp. gallons, most of this is consumed on the climb to operating height.
The engine installation is so good that it always runs extremely smoothly, except that when throttled back at altitude it seems to work rather severely on its mountings.
14. Since the P-47C has not been through the hands of the Performance Testing Flight of the Aeroplane and Armament Experimental Establishment, some careful check flights were made at this Unit to obtain an approximate idea of its performance.
The figures set out below and on the curve shown at Appendix 'A' have been agreed with Headquarters, VIII Fighter Command, U.S.A.A.F., but can only be taken as approximate.
In an independent trial the U.S.A.A.F. obtained slightly higher figures, possibly owing to the difficulty of reading the Standard American airspeed indicator and to the different methods of reduction.
At this Unit the British Performance Reduction Methods for Modern Aircraft (A. &A.E.E./Res/170) were used.
In the appendix the A. & A.E.E. figures for the Spitfire IX and Typhoon are inserted for comparison. The maximum speeds obtained are about:-
|324 m.p.h. at 1,000 feet
|409 m.p.h. at 27,000 feet (rated altitude)
|386 m.p.h. at 32,000 feet
15. Performance data from A. & A.E.E. for the rate of climb not being available, short check flights were carried out to confirm figures obtained by the U.S.A.A.F. Fighter Command, and are set out in Appendix 'B'.
The rate of climb is comparatively low throughout, but can be improved to some extent in zoom climbs made as fighting manoeuvres which are entered from fast level flight.
The operational ceiling of 1,000 ft/min is reached at about 31,000 feet. The best climbing speed is about 165 m.p.h. throughout; if slowed down at altitude the cooling does not appear sufficient.
Even at this speed the engine runs very hot in climbs at altitude and fumes and smoke enter the cockpit.
16. The P-47C dives very fast. Its initial acceleration is good an it quickly reaches its limiting figures (520 m.p.h., I.A.S. at 10,000 feet, 450 m.p.h. at 20,000 feet).
At these speeds the recovery needs several thousand feet and can only be effected by careful use of the trimming tab.
There is no tendency to recover fiercely from the dive, but a large amount of left trim is required on the rudder to hold the aircraft straight.
17. The total fuel capacity is 202 Imp. gallons, 119 gallons in the main tank and 83 in the auxiliary, which should be the first tank to be drained.
External jettison tanks of 166 gallons are to be made available.
No specific figures for the aircraft could be obtained during the trials, but the U.S.A.A.F. is satisfied that on conservative figures a tactical radius of 240 miles is available at 25,000 feet without the jettison tank.
18. Owing to the good view forwards and downwards and to the excellent manoeuvrability of the aircraft, low flying is extremely easy.
View for Sighting and Search
19. The sight fitted is the Standard American S.T.I.A., having a 60 m.p.h. ring. The downward view for sighting is 3Ό degrees and amounts to 120 m.p.h.
There appears to be slight minification of objects viewed dead ahead or to an angle of about 15° on either side, due to the construction of the windscreen.
The 'V' shaped Perspex and internal bullet-proof screen does not provide as good and unrestricted forward view as an integral bullet-proof screen or a curved screen forward of the bullet-proof.
The centre frame causes the sight to be offset to the starboard and thus the pilot loses an important part of his view to the left of the sight.
For search the view is quite good in all directions save downwards and backwards, where the width of the fuselage causes an obstruction.
The chief criticism of pilots was against the frames on the sliding canopy, particularly the horizontal ones near eye level.
20. No night flying was attempted as the exhaust flames from the turbo supercharger preclude any possibility of the aircraft being used as a night fighter.
P-47C v. Spitfire IX
21. Trials were limited to determining the relative fighting qualities of these aircraft between 20,000 feet and 30,000 feet.
Owing to oxygen difficulties the P-47C was not taken to greater altitudes except for performance checks.
22. Performance In level speed the Spitfire always accelerated away from the P-47, but the P-47 showed itself slightly the faster at 20,000 feet and at 28,000; there was, however, very little to choose in actual performance at these heights.
Above this height the Spitfire becomes slightly the faster.
23. Climb The rate of climb if the Spitfire is much higher at these heights than that of the P-47C.
Climbing together from 25,000 to 30,000 feet, the P-47 took about ½ minute longer than the Spitfire.
The difference, however, is not nearly so marked in zoom climbs, and if the P-47 dives slightly and then pulls up in the climb, its performance is similar to that of the Spitfire over limited intervals.
24. Dive The P-47 is able to out-dive the Spitfire quite easily.
25. Manoeuvrability The good aileron control gives the P-47 an excellent rate of roll even at high speeds, and during mock combats it was considered to roll as well as, if not better than the Spitfire at about 30,000 feet.
At lower altitudes there is nothing to choose between them. The rate of turn of the Spitfire is naturally superior to the heavier P-47 and in turning circles it was found that after four turns the Spitfire could get on the P-47s tail and remain there with a chance of shooting with correct deflection.
When 'bounced'; if a climbing turn towards the attack were made, either aircraft was able to evade the other, but if the climbs were continued, the Spitfire was able to draw away above for another attack.
On the level the speeds were so much alike that if a big interval occurred between the aircraft it was difficult to re-engage decisively. When bounced, if the Spitfire used a diving turn to evade it would be caught in the dive, though the P-47 was given difficult shooting at high speed; if the P-47 dived steeply it was unable to climb back to re-engage.
P-47C v. Typhoon IB
26. Against the Typhoon, which was a standard aircraft with long exhausts borrowed from 181 Squadron, the P-47 was flown at heights up to 20,000 feet only, above which its performance is considerably better than that of the Typhoon, which is designed as a low altitude fighter.
27. Performance The Typhoon and P-47 accelerate practically together when both are opened up to full throttle, and the Typhoon was found to be the faster at all hights up to 15,000 feet.
Above this height it is very slightly faster up to 22,000 feet.
28. Climb In the zoom climbs the P-47 was always able to gain the first 1,000 feet or so more quickly than the Typhoon, but up to 10,000 feet the P-47 was out-climbed by 30 seconds.
The Typhoon climbs at a shallower angle and higher speed than the P-47. Between 10,000 and 20,000 feet the Typhoon was forced to open its radiator, which slowed its climb, and the P-47 climbed the faster by about 30 seconds.
29. Dive In full throttle dives there is nothing to choose between the Typhoon and P-47C.
30. Manoeuvrability The P-47C was considered far superior in rate of roll to the Typhoon, and at 20,000 feet in turning circles proved itself slightly better.
P-47C v. Mustang X
31. Short trials were made against the Mustang X between 20,000 and 27,000 feet, at which heights the performances of the two aircraft are most nearly related. The Mustang is designed as a low altitude fighter.
32. Performance At heights below 27,000 feet the Mustang is considerably faster than the P-47 and at that height it is faster than the P-47 by about 10 m.p.h., accelerating away better and maintaining its lead fairly easily.
Above 27,000 feet the Mustang still appears slightly faster but no trials could be carried out in the time available.
33. Climb The rate of climb of the Mustang at these heights is still better than that of the P-47, but the latter again improved in zoom climbs so that between 20,000 feet and 25,000 feet the Mustang was only 15 seconds ahead of the P-47.
Above 27,000 feet the Mustangs rate of climb is still slightly superior.
34. Dive Several full throttle dives were carried out at these heights and I each the Mustang accelerated away from the P-47 and remained in front.
35. Manoeuvrability The rate of roll of the P-47 is considerably better than that of the Mustang, which cannot follow sudden changes in direction.
In rate of turn, howeverm the two aircraft are practically identical.
P-47C v. P-38F
36. At the request of the U.S.A.A.F., the trials included comparative flights and mock flights between 20,000 and 30,000 feet against the P-38F "Lightning", which develops its full power at 25,000 feet.
37. Performance At 20,000 feet the P-38 was able to pull away from the P-47 at 10 to 15 m.p.h., though the acceleration of both was almost identical.
By 24,000 feet the performance of the two aircraft was approximately equal and above 25,000 feet the P-47 had obtained a speed superiority of about 10 m.p.h.
38. Climb In comparative climbs both between 20,000 feet and 25,000 feet, and 25,000 feet and 30,000 feet, the P-38 was easily able to out-climb the P-47 at a better rate of climb and far steeper angle.
39. Dive In comparative dives there was nothing to choose between the two aircraft, save that the P-38 is limited by buffeting in high speed accelerated flight.
40. Manoeuvrability In turning circles the P-38 was slightly better and was certainly able to turn so slowly in a climbing turn, especially to the right, that the P-47 was unable to follow.
When 'bounced' by the P-47, the P-38 was able to turn very sharply and decelerate much more quickly than the P-47.
41. Armament characteristics were reported to be satisfactory by the U.S.A.A.F., and only short check flights were carried out at this Unit.
42. The installation allows for eight .5 guns, all situated in the wings. The guns are fired by electric solenoids operated by a trigger on the front of the control column in the standard American fashion.
There is no selector switch for the pilot, to that all guns must be fired together, but there is a safety switch on the port side of the cockpit which is marked distinctively.
For operational flying the ammunition capacity is laid down to be 300 rounds per gun, but there is in fact extra room for more ammunition should it be required.
43. All guns can be harmonised very easily. The method for adjusting the guns is the best that has yet been seen at this Unit and consists merely of two controls which can be turned by hand, one for lateral and one for vertical adjustment.
The aircraft was received at this Unit with the six guns harmonised to a pattern originally drawn up for the eight guns, which was not considered to be quite adequate.
Alternative schemes were therefore suggested to which the guns can be harmonised giving a 1 degree spread either for six or eight guns. Discussions are in progress with VIII Fighter Command, U.S.A.A.F., to agree on a suitable pattern.
44. The guns were fired under positive 'G' up to about 4G, and small amounts of negative 'G' quite satisfactorily, the only stoppage that occurred being due to link trouble.
An altitude shoot at which the outside air temperature was -46°C was also satisfactory.
For this the gun heating, which consists of a duct form the engine, was used. The gun heating is turned on by a control in the cockpit.
45. The ammunition tanks are very accessible and re-arming provides no difficulties.
46. The guns are easy to maintain and can be quickly removed. In particular, the link chutes are especially effective as they are clamped into position when the breech covers are closed.
47. The P-47C is easy to fly and has light crisp controls. The ailerons are particularly good and the rate of roll even at high speed is excellent. (para. 13).
See Photograph at Appendix 'C'.
48. Approximate figures obtained at this Unit show that it is capable of about 324 m.p.h. at sea level, 409 m.p.h. at 27,000 feet (rated altitude) and 386 m.p.h. at 32,000. (para.14).
49. The rate of climb is comparatively low, but this is counter-balanced in part by good zooming climbs over limited intervals. The operation ceiling of 1,000 ft/min is reached by about 31,000 feet.
50. The best climbing speed appears to be 165 m.p.h., I.A.S., throughout. Even at this speed the engine runs very hot in climbs at altitude. (para.15)
51. The P-47 dives very fast, its initial acceleration being particularly good. (para.16)
52. The fuel capacity is 202 Imperial gallons. On conservative figures a radius of action of 240 miles at 25,000 feet is expected. Jettison tanks of 166 gallons are to be made available. (para.17)
53. The sighting view amounts to 120 m.p.h. over the nose cowlings. The forward view is hampered by the centre frame of the V shaped windscreen, and search generally by the frames of the sliding canopy. (para.19)
54. Compared with the Spitfire IX between 20,000 and 30,000 feet, both aircraft had similar performance on the level. The Spitfire could out-climb the P-47C except in short zoom climbs, but the P-47 out-dived the Spitfire. In rate of roll there is little to choose between the aircraft but the Spitfire could turn well inside the P-47. (paras. 21-25)
55. Compared with the Typhoon IB in speed, the P-47 was considerably slower up to about 15,000 feet, but slightly faster up to 22,000 feet and above. In zoom climbs the Typhoon was better below 10,000 feet, but slightly the worse above this as it was forced to climb with the radiator open. Both aircraft dive at about the same speeds. In rate of roll the P-47 was far superior to the Typhoon and in turning circles slightly better. (paras.26-30).
56. When flown against the Mustang X (Merlin 65) between 20,000 and 27,000 feet, the Mustang was the faster, and had the better rate of climb. In dives the Mustang was able to accelerate away and remain in front. The aircraft are identical in rate of turn but the P-47 superior in roll. (paras.31-35)
57. The P-47 and P38F "Lightning" were compared between 20,000 and 30,000 feet. Below 25,000 feet the P-38 is slightly faster and above this the P-47. The P-38 out-climbed the P-47 at a far steeper angle.
In turning circles the P-38 was slightly better. (paras.36-40)
58. The aircraft carried six .5 guns with 300 rounds per gun. Successful shoots were carried out in accelerated flight up to 4G and with slight negative 'G' and at altitude. (paras.42 & 44)
59. A spread harmonisation of 1 degree is suggested. (para.43)
60. The guns are easy to adjust and maintain and are quickly removed. (para.46)
3rd March 1943
Appendix 'A' Level Speeds
Appendix 'B' Rates of Climb & Times to Height
Appendix 'C' Photograph