Introduction
The performance on Spitfire V.K.9788 (Merlin XLV engine) is given in 1st part of Report No. A.A.E.E./692,i. It was desired to check the performance obtained on K.9788 on another Spitfire V. and X.4922 was chosen for these check tests. Spitfire V. X.4922 was fitted with a standard Spitfire I. De Havilland airscrew, but with the pitch settings increased to 34° fine and 54° coarse, the same pitch settings used in the previous tests.
Tests made
The aeroplane was fitted with 8 Browning guns and, operationally equipped, weighed 6,450 lb. Because this loading represented the all-up weight of the aeroplane in Service, it was decided to carry out the trials at the above load instead of 6,070 lb. to which K.9788 was loaded. (Note: paragraph as corrected by corrigendum dated 18th June, 1941)
Climbs to ceiling and measurements of speeds over a range of heights from 10,000 feet to 26,000 feet were made. An oil cooling climb was combined with the performance climb.
Results of tests
(a) The top speed of the aeroplane is 375 m.p.h. at 20,800 feet.
(b) The maximum rate of climb is 3,140 feet per minute at 14,400 feet. The time to 20,000 feet is 7.1 minutes and the Service ceiling is 37,700 feet.
(c) The radiator is not quite suitable for English summer conditions on the climb.
(d) The oil cooler is suitable for English summer conditions on the climb.
(e) The take-off run in zero wind and standard conditions is 330 yards, and the distance to clear a 50 foot screen is 530 yards.
(f) The airscrew setting of 34 deg. to 54 deg. is suitable for the aeroplane under all conditions of flight.
Comments on results
(a) The top speed of X.4922, 375 m.p.h. at 20,800 feet, is greater than Spitfire V K.9788 (364 m.p.h. at 19,600 feet). The discrepancy is explained by the lower full throttle height of the Merlin XLV in K.9788 being 1,200 feet lower than that in X.4922.
(b) The maximum rate of climb of this aeroplane (3,140 feet/minute) is lower than that of Spitfire V. K.9788 (3,460 feet/minute). However, the total all-up weight of X.4922 was 6,450 lb. compared with 6,170 lb., the all up weight of K.9788.
(c) The Mark II radiator in X.4922 seems to be less efficient than the Mark I. radiator on K.9788. This discrepancy remains unexplained.
SUMMARY OF TRIALS
| Aeroplane Spitfire V. | No. X.4922 |
| Engine | Merlin XLV |
| At 2850 R.P.M. | and +9 lb. boost |
| At 3000 R.P.M. | and +9 lb. boost |
| Total weight = | 6,450 lb. |
| C.G. position | 6.2" aft of the datum |
| Height feet |
Top Speed M.P.H. |
Time to Climb mins. |
Rate of Climb Ft/min. |
|---|---|---|---|
| S.L. | — | 0 | — |
| 2,000 | — | 0.7 | 2765 |
| 5,000 | — | 1.9 | 2855 |
| 10,000 | 337 | 3.6 | 3010 |
| 15,000 | 355 | 5.2 | 3045 |
| 20,000 | 372.5 | 7.1 | 2280 |
| 25,000 | 364.5 | 9.6 | 1520 |
| 30,000 | — | 12.9 | 1275 |
| Service Ceiling | 37,700 ft |
| Take off run | 330 yds. |
| Distance from rest to clear 50 ft screen | 530 yds. |
CLIMBING TRIALS
| Height In Standard Atmosphere Feet |
Time From Start Min. |
Rate of Climb Ft./Min. |
True Air Speed M.P.H. |
A.S.I. M.P.H. |
P.E.C. | Comp. | R.P.M. | Boost lb./sq.in. |
|---|---|---|---|---|---|---|---|---|
| Sea Level | 0 | . | . | . | . | . | 2850 | . |
| 1,000 | 0.4 | 2735 | 171 | 170 | -1.8 | - | " | +9.0 |
| 2,000 | 0.7 | 2765 | . | . | . | . | " | +9.0 |
| 3,000 | 1.2 | 2795 | . | . | . | . | " | +9.0 |
| 5,000 | 1.9 | 2855 | . | . | . | . | " | +9.0 |
| 6,500 | 2.4 | 2900 | . | . | . | . | " | +9.0 |
| 10,000 | 3.6 | 3010 | 185 | 160 | -0.4 | -0.4 | " | +9.0 |
| 13,000 | 4.6 | 3095 | . | . | . | . | " | +9.0 |
| 15,000 | 5.2 | 3045 | . | . | . | . | " | +8.6 |
| 16,500 | 5.7 | 2815 | . | . | . | . | " | +7.6 |
| 18,000 | 6.2 | 2590 | . | . | . | . | " | +6.5 |
| 20,000 | 7.1 | 2280 | 204 | 148 | +1.5 | -0.8 | " | +5.2 |
| 23,000 | 8.7 | 1820 | . | . | . | . | " | +3.2 |
| 26,000 | 10.2 | 1810 | 211 | 136 | +3.5 | -0.9 | 3000 | +2.8 |
| 28,000 | 11.4 | 1540 | 214 | 132 | +4.3 | -1.0 | " | +1.4 |
| 30,000 | 12.9 | 1275 | 216 | 128 | +5.0 | -1.0 | " | +0.1 |
| 33,000 | 15.6 | 870 | 220 | 122 | +6.3 | -1.2 | " | -1.8 |
| 36,000 | 20.2 | 470 | 225 | 116 | +7.5 | -1.1 | " | -3.4 |
| 37,000 | 22.8 | 290 | 221.5 | 110 | +8.7 | -1.1 | " | -3.8 |
| 14,400* | 4.9 | 3140 | 193 | 155 | *0.4 | -0.6 | 2850 | +9.0 |
| Estimated absolute ceiling | 38,000 feet | Greatest height reached | 37,850 |
| R.P.M. stationary on ground | 2500 | Boost pressure lb./sq.in | +8 3/4 |
| * Full Throttle height | |||
| Service Ceiling. 37,850 ft. | |||
SPEED TRIALS
| Height In Standard Atmosphere Feet |
True Air Speed M.P.H. |
A.S.I. M.P.H. |
P.E.C. | Comp. | R.P.M. | Boost lb./sq. in. |
|---|---|---|---|---|---|---|
| 10,000 | 337 | 300 | -8.5 | -2.4 | 3000 | +9.0 |
| 13,000 | 347.5 | 296 | -8.5 | -3.2 | " | +9.0 |
| 15,000 | 355 | 294 | -8.5 | -3.8 | " | +9.0 |
| 16,500 | 360 | 291 | -8.5 | -4.2 | " | +9.0 |
| 18,000 | 363 | 287 | -8.5 | -4.5 | " | +9.0 |
| 20,000 | 372.5 | 285.5 | -8.5 | -5.2 | " | +9.0 |
| 20,800* | 375 | 276 | -8.5 | -5.8 | " | +9.0 |
| 23,000 | 370 | 270.5 | -8.5 | -5.5 | " | +6.6 |
| 26,000 | 361.5 | 252 | -8.5 | -5.5 | " | +4.2 |
| Landing and take off tests corrected to zero wind and standard atmosphere | |
| Take off run | 330 yds. |
| Distance from rest to clear 50 foot screen> | 530 yds. |
| Under conditions of test: i.e. 14.1 mph wind, +2 deg.C temp and 29.96 Hg pressure | |
| Take-off run: 250 yds | Time 12.4 seconds. |
| * Full throttle height | |
