1. Introduction.
Brief performance trials were required of a Spitfire Mk VB fully operationally equipped for comparison with two other aircraft of the type not operationally equipped and previously tested at this establishment. The suffix "B" after the type denotes that the aeroplane is fitted with 2-20mm. guns and four 0.303 inch guns. A standard Spitfire I airscrew was fitted with the blade settings at 54 degrees coarse and 34 degrees fine.
The weight of the plane was 6525 lb. and the centre of gravity was at 7.8 inches aft of the datum.
It was also desired to find the effect on performance of fitting a snowguard to the air-intake.
2. Results of tests.
(a) The top speed of the aeroplane is 371 m.p.h. at 20,100 feet.
(b) With the snowguard fitted the top speed falls to 365 m.p.h. at 18,800 feet.
(c) The maximum rate of climb is 3250 feet per minute at 15,200 ft.
(d) The time to 20,000 feet is 6.4 minutes, and the service ceiling is 37,500 feet.
(e) The effect of of the snowguard on the ceiling of the aeroplane is negligible.
3. Comparison of results. For easy reference the results of the three aeroplanes considered are presented in tabular form:
| Aeroplane | weight lb. |
T.A.S. m.p.h. |
Height ft. | Climb ft/min |
Height feet |
Service Ceiling ft. |
|---|---|---|---|---|---|---|
| W.3134 | 6525 | 371 | 20,100 | 3250 | 15,200 | 37,500 |
| X.4922 | 6450 | 375 | 20,800 | 3140 | 14,400 | 37,700 |
| K.9788 | 6170 | 369 | 19,600 | 3460 | 14,000 | 38,000 |
On the whole the results agree fairly well and, with the exception of the top speed of K.9788, are within the differences to be expected between production aircraft. The low speed of K.9788 can be accounted for by the low full throttle height, but the reason for the low full throttle height is not known.
SUMMARY OF TRIALS
| Height feet |
Top Speed M.P.H. Snowguard on |
Top Speed M.P.H. Snowguard off |
Time to Climb mins. | Rate of Climb Ft/min. |
|---|---|---|---|---|
| S.L. | 0 | |||
| 2,000 | 0.6 | 3240 | ||
| 5,000 | 1.5 | 3240 | ||
| 10,000 | 331 | 331 | 3.1 | 3250 |
| 15,000 | 351 | 351 | 4.6 | 3250 |
| 20,000 | 364.5 | 371 | 6.4 | 2440 |
| 25,000 | 353 | 359 | ||
| 30,000 | 336 | 12.2 | 1170 |
CLIMBING TRIALS
With and without snowguard fitted
| 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 | 0.31 | 3240 | 171 | 170 | -1.8 | - | " | +9.1 |
| 2,000 | 0.62 | 3240 | " | +9.1 | ||||
| 3,000 | 0.93 | 3240 | " | +9.1 | ||||
| 5,000 | 1.54 | 3240 | " | +9.1 | ||||
| 6,500 | 2.01 | 3240 | " | +9.1 | ||||
| 10,000 | 3.08 | 3250 | 185 | 160 | -0.4 | -0.4 | " | +9.0 |
| 13,000 | 4.01 | 3250 | " | +9.0 | ||||
| 15,000 | 4.62 | 3250 | " | +9.0 | ||||
| 16,500 | 5.10 | 3020 | " | +7.6 | ||||
| 18,000 | 5.62 | 2770 | " | +6.3 | ||||
| 20,000 | 6.38 | 2440 | 204 | 148 | +1.5 | -0.8 | " | +4.6 |
| 23,000 | 7.76 | 1940 | " | +2.7 | ||||
| 26,000 | 9.36 | 1740 | 211 | 136 | +3.5 | -0.9 | 3000 | +2.1 |
| 28,000 | 10.62 | 1450 | 214 | 132 | +4.3 | -1.0 | " | +0.7 |
| 30,000 | 12.15 | 1170 | 216 | 126 | +5.0 | -1.0 | " | -0.5 |
| 33,000 | 15.30 | 760 | . | . | " | -2.3 | ||
| 35,000 | 18.58 | 470 | 222.5 | 118 | +7.1 | -1.1 | " | -3.4 |
| 37,000 | 200 | 228 | 114 | +8.0 | -1.0 | " | ||
| 15,200* | 3250 | 2850 | +9.0 | |||||
| Estimated absolute ceiling. 38,000 | Greatest height reached. 37,100 | |||||||
| * Full Throttle height | Service Ceiling. 37,500 ft. (estimated) | |||||||
SPEED TRIALS
with Snowguard off
| 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 | 331 | 295 | -8.5 | -2.3 | 3000 | +9.0 |
| 13,000 | 343 | 295.5 | -8.5 | -3.1 | " | +9.0 |
| 15,000 | 351 | 290 | -8.5 | -3.7 | " | +9.0 |
| 16,500 | 357 | 289 | -8.5 | -4.1 | " | +9.0 |
| 18,000 | 363 | 287.5 | -8.5 | -4.5 | " | +9.0 |
| 20,000 | 370.5 | 283.5 | -8.5 | -4.8 | " | +9.0 |
| 20,100* | 371 | 283.5 | -8.5 | -4.8 | " | +9.0 |
| 23,000 | 365.5 | 266 | -8.5 | -4.9 | " | +6.5 |
| 26,000 | 355 | 246.5 | -8.3 | -4.7 | " | +4.4 |
| * Full throttle height | ||||||
SPEED TRIALS
with Snowguard fitted
| 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 | 331 | 295 | -8.5 | -2.3 | 3000 | +9.0 |
| 13,000 | 343 | 292.5 | -8.5 | -3.1 | " | +9.0 |
| 15,000 | 351 | 290 | -8.5 | -3.7 | " | +9.0 |
| 16,500 | 357 | 289 | -8.5 | -4.1 | " | +9.0 |
| 18,000 | 363 | 287.5 | -8.5 | -4.5 | " | +9.0 |
| 18,800* | 365 | 285 | -8.5 | -4.4 | " | +9.0 |
| 20,000 | 364.5 | 279 | -8.5 | -4.6 | " | +7.9 |
| 23,000 | 358.5 | 261.5 | -8.5 | -4.6 | " | +5.4 |
| 26,000 | 349.5 | 243 | -8.2 | -4.6 | " | +3.2 |
| 30,000 | 336 | 216.5 | -7.0 | -4.3 | " | +0.4 |
| 33,000 | 323 | 197.5 | -6.5 | -4.0 | " | -1.4 |
| 35,000 | 310 | 172.5 | -3.5 | -3.5 | " | -2.5 |
| * Full throttle height | ||||||
