In accordance with Air Ministry letter, dated 30th May, 1940, short performance and handling tests have been carried out on this aeroplane, the first Nuffield-built Spitfire II, to compare it with the standard Spitfire I.
1 Comments on Trials
This aeroplane was fitted with a bullet-proof windscreen, armour plating over the petrol tank and externally, apart from the radiator, was similar to the Rotol Spitfire I, N.3171, previously tested at this establishment. The radiator of P.7280 is of the Morris type and tests were called for to determine the suitability of this radiator under tropical conditions. Internally, one difference between this aeroplane and N.3171 has been the fitting of armour plating behind the pilot in the Spitfire II. Generally, any change in performance or handling can be attributed to the change in engine and radiator alone.
2 Take-off
The take-off and initial climb is not quite so good as with the Spitfire I, but is satisfactory, as the table shows:
| Aeroplane | Weight | Take-off run yards | Distance to 50' screen | Landing run yards |
|---|---|---|---|---|
| P.7280 | 6172 lb. | 230 | 400 | 415 |
| N.3171 | 6050 lb. | 225 | 370 | 310 |
The landing run is considerably longer than expected and the reason appears to be a defective braking system as the aeroplane runs a long way even when the speed is down to about 30 m.p.h. and the brakes are full on. The brake linings have been examined and renewed but without much success in shortening the run.
3 Climb
The climbing speed was taken as 168 m.p.h. A.S.I. up to rated height, this being slightly more than the climbing speed recommended for Rotol Spitfires Mk.I, as that speed could not be maintained comfortably owing to instability on the climb. It was found that to reach altitudes of 35,000 or 36,000 feet it was necessary to reduce the climbing speed to about 100 m.p.h. A.S.I. at 35,000 feet. The recommended climbing speed is therefore as given in the following table.
| Height Feet | 0 | 12,000 | 20,000 | 30,000 | 32,000 | 34,000 | 35,000 |
|---|---|---|---|---|---|---|---|
| A.S.I. m.p.h. | 168 | 168 | 152 | 130 | 120 | 108 | 100 |
The following table gives times to height for the Rotol Mk.I and Rotol Mk.II Spitfires, fitted with Merlin III and Merlin XII engines respectively. Also given is the time to height with a wooden fixed pitch airscrew.
| Aeroplane | Engine | Weight lb. | 10,000 | 15,000 | 20,000 | 25,000 | 30,000 | 35,000 |
|---|---|---|---|---|---|---|---|---|
| P.7280 | Merlin XII Rotol C.S. | 6172 | 3.35 | 5.0 | 7.0 | 9.6 | 13.7 | 21.3 |
| N.3171 | Merlin III Rotol C.S. | 6050 | 3.5 | 5.4 | 7.7 | 11.0 | 16.4 | - |
| K.9787 | Merlin I Wood F.P. | 5819 | 4.4 | 6.6 | 9.4 | 13.8 | 22.4 | - |
There is a distinct improvement in time to reach heights above 20,000 feet and in the ceiling of the aeroplane when fitted with the Merlin XII engine.
4 Level Speeds
The top speed of this aeroplane is the same as that of N.3171 but is reached at 17,600 feet, 1400 feet lower than the Mk.I Spitfire. Consequent upon this and the increase in power of the Merlin XII over the Merlin III below full throttle height the aeroplane is about 6 - 7 miles per hour faster at heights less than 17,000 feet and about 4 - 8 m.p.h. slower at heights above 20,000 feet. It should be noted that though the boost pressure on the Merlin XII is +9 lb. per sq.inch as against +6 1/4 lb. per sq.inch on the Merlin III there is little difference in the engine power at heights of 16,000 feet and above.
SUMMARY OF TRIALS
| Aeroplane | Spitfire Mark II | No. P.7280 |
| Engines | 1090/1135 Rated B.H.P | at Rated Altitude 13,500 ft. |
| 1140 Maximum B.H.P. | at Rated Altitude 14,750 ft. | |
| At | 2850 R.P.M. | at +9 lb/sq.inch boost |
| At | 3000 R.P.M. | at +9 lb/sq.inch boost |
| Tare weight | 4783 | |
| Weight light | 4541 | |
| Fixed military load | 241.5 | |
| Service load | 735.5 | |
| Fuel :- 84 gallons | 605 | |
| Oil 5 1/2 gallons | 49 | |
| Flying weight on trials | 6172 lb. |
| Height Feet | Top Speed M.P.H. | Time To Climb Mins. | Rate of Climb Ft./Min. |
|---|---|---|---|
| S.L. | 290 | - | - |
| 2,000 | 294 | 0.7 | 2925 |
| 5,000 | 306 | 1.7 | 2955 |
| 10,000 | 326 | 3.4 | 2995 |
| 15,000 | 345 | 5.0 | 2770 |
| 20,000 | 351 | 7.0 | 2175 |
| 25,000 | 338 | 9.6 | 1600 |
| 30,000 | 321 | 13.7 | 995 |
| Service Ceiling | 37,000Ft | Landing Speed | 67mph |
| Take off run | 230 yds Time 91/2 Secs | Distance from rest to clear 50ft screen | 400 yards |
| Stalling Speed flaps and u/c up | 73 | Glinding in A.S.I | 87mph |
| Stalling Speed flaps & u/c down | 63 | ||
| Bast Landing A.S.I | 67 |
| Position | Centre |
| Constant Speed airscrew | |
| Type | Rotol. C.S. |
| Serial No. | 5551. |
| Makers No. | - |
| Diameter | 10'-9" |
| No. of Blades | 3. |
| Direction of Blades | R.H. |
| A.M. Serial Nos. hub | 5551 |
| A.M. Serial Nos. Blade 1 | A-4367 |
| A.M. Serial Nos. Blade 2 | A-4368 |
| A.M. Serial Nos. Blade 3 | A-4369 |
| Basic Pitch Setting | - |
| Pitch Range. | Estimated 35-0' deg |
| High Pitch Setting | Estimated 63-05' deg |
| Low Pitch Setting | Estimated 28-05' deg |
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. |
|---|---|---|---|---|---|---|---|---|
| S.L. | 0 | - | - | - | - | - | Controlling at 2840 | - |
| 1,000 | 0.35 | 2915 | 168 | 168 | -1.8 | -0.1 | " | +8.8 |
| 2,000 | 0.7 | 2925 | 171 | 168 | -1.8 | -0.1 | " | +8.8 |
| 3,000 | 1 | 2935 | 173 | 168 | -1.8 | -0.1 | " | +8.8 |
| 5,000 | 1.7 | 2955 | 179 | 168 | -1.8 | -0.2 | " | +8.8 |
| 6,500 | 2.2 | 2965 | 183 | 168 | -1.8 | -0.3 | " | +8.8 |
| 10,000 | 3.4 | 2995 | 193 | 168 | -1.8 | -0.5 | " | +8.8 |
| 13,000 | 4.3 | 3010 | 201 | 167 | -1.7 | -0.7 | " | +8.7 |
| 15,000 | 5.0 | 2770 | 203 | 163 | -1.0 | -0.7 | " | +7.0 |
| 16,500 | 5.6 | 2590 | 205 | 160 | -0.5 | -0.8 | " | +5.9 |
| 18,000 | 6.1 | 2410 | 206 | 156 | +0.1 | -0.8 | " | +4.9 |
| 20,000 | 7.0 | 2175 | 208 | 152 | +0.8 | -0.9 | " | +3.5 |
| 23,000 | 8.5 | 1820 | 212 | 146 | +1.9 | -1.0 | " | +1.6 |
| 26,000 | 10.3 | 1470 | 215 | 139 | +3.2 | -1.0 | " | -0.2 |
| 28,000 | 11.8 | 1230 | 217 | 135 | +4.1 | -1.1 | " | -0.3 |
| 30,000 | 13.7 | 995 | 218 | 129 | +5.0 | -1.1 | " | -2.4 |
| 33,000 | 17.3 | 640 | 210 | 114 | +8.2 | -0.9 | " | - |
| 35,000 | 21.3 | 400 | 198 | 100 | +11.0 | -0.7 | " | - |
| 12,800* | 4.3 | 3025 | 201.5 | 168 | -1.8 | -0.7 | " | +8.8 |
| * Full throttle height | ||||||||
| Estimated absolute ceiling | 38,400 |
| Greatest height reached | 36,500 |
| R.P.M. stationary on ground | 2840 at 8.4 |
| Service ceiling | 37,600' estimated |
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 |
|---|---|---|---|---|---|---|
| 1,000 | 290 | 294 | -8.5 | -0.2 | controlling at 2990 | +8.8 |
| 2,000 | 294 | 294 | -8.5 | -0.4 | " | +8.8 |
| 3,000 | 298 | 294 | -8.5 | -0.6 | " | +8.8 |
| 5,000 | 306 | 293 | -8.5 | -1.1 | " | +8.8 |
| 6,500 | 311 | 290 | -8.5 | -1.4 | " | +8.8 |
| 10,000 | 325 | 290 | -8.5 | -2.2 | " | +8.8 |
| 13,000 | 337 | 287 | -8.5 | -3.0 | " | +8.8 |
| 15,000 | 344 | 285 | -8.5 | -3.5 | " | +8.8 |
| 16,500 | 350 | 283 | -8.5 | -4.0 | " | +8.8 |
| 18,000 | 354 | 280 | -8.5 | -4.3 | " | +8.3 |
| 20,000 | 350 | 269 | -8.5 | -4.5 | " | +6.2 |
| 23,000 | 344 | 251 | -8.4 | -4.6 | " | +3.6 |
| 26,000 | 335 | 233 | -7.8 | -4.4 | " | +1.5 |
| 28,000 | 329 | 220 | -7.2 | -4.3 | " | +0.2 |
| 30,000 | 321 | 206 | -6.3 | -4.1 | " | -0.9 |
| 17,550* | 354 | 282 | -8.5 | -4.3 | " | +8.8 |
| *Full Throttle Height |
| Take off run | 230 yds. | 9.5 secs | |
| Distance from rest to clear 50ft screen | 400 yds. | ||
| Glinding in A.S.I | 87 M.P.H. | Stalling speed flaps & u/c up | 73 M.P.H. |
| Best Glinding A.S.I. | 67 M.P.H. | Stalling speed flaps & u/c down | 63 M.P.H. | Landing run with brakes | 415 yds. |
5 SPINNING, HANDLING AND DIVING TRIALS
Spinning trials were carried out to check the behavior of the aeroplane. The conditions were as quoted:
Weight 6195 lb. Centre of Gravity 7.4" aft of datum point (Extended aft position).
| No. | No. of "Free" Turns | Height at Start | No. of Turns to recover | Height out into level flight | Tail turn |
|---|---|---|---|---|---|
| 1 | 2 | 14,800 | 1 1/2 | 11,000 | "Down" 2. |
| 2 | 2 | 14,500 | 3/4 | 11,500 | " 2. |
| 3 | 3 | 14,000 | 2-turns then spin in opposite direction | 6000 | " 2. |
| 4 | 3 | 14,000 | " " | 6000 | " 2. |
The following remarks have been made as a result of these tests:
(1°) Spins to the left are smoother than those to the right, though the recovery is slightly quicker from the latter. This is common to all Spitfires.
(2°) In Spins Nos.1 and 2 the recovery was made easily by applying full opposite rudder and easing the control column forward to just aft of central.
(3°) In Spins Nos.3 and 4, full opposite rudder was applied but the control column was held hard back. The aeroplane stopped spinning after two turns, but immediatly entered into one in the opposite direction. This could be prevented by violent use of the rudder but it was necessary to ease the control column foward to gain sufficient speed to "unstall" the aeroplane.
(4°) Generally speaking the spinning characteristics are the same as the Mark I Spitfire.
Handling Trials
There is no apparent difference in behavior in take-off, level flight, glide or aerobatics when compared with N.3171. On the climb at 160 m.p.h. A.S.I. off the ground there was slight instability at high altitudes so the climbing speed was increased to 170 m.p.h. A.S.I. up to 12,000 feet whilst retaining the same fall-off above that height.
Diving Trials
Several dives were carried out and the results are given in the following table. The diving limits for this aeroplane are:
Maximum A.S.I. = 470 (P.E. assumed as -20 m.p.h.)
Maximum Engine R.P.M. = 3000 with throttle < 1/3 open.
Maximum Engine R.P.M. = 3600 with throttle > 1/3 open.
Maximum Boost = +9.0 lb/sq.in. with throttle > 1/3 open.
The aeroplane was trimmed for full throttle level flight. Centre of Gravity 7.4" aft of datum (extended aft limit)
Weight 6195 lb.
| Dive | Throttle Position | Height IN | Height Max R.P.M. | Maximum R.P.M. | Height Start out | Height Out | Max. Accel. during recovery |
|---|---|---|---|---|---|---|---|
| 1 | Full | 14,000 | 11,000 | 3000 | 11,000 | 10,000 | 3 |
| 2 | CLOSED | 15,000 | ----- | ----- | 9,000 | 8,000 | ----- |
The following remarks have been made as a result of these tests:
The aeroplane behaves in a similar fashion to the Mark I Rotol Spitfire in a dive i.e. the controls become heavier with speed, especially near the limiting speed. Considerable forward pressure on the control column is necessary to keep the aeroplane in the dive; the elevator is sensitive throughout the speed range. The rudder and ailerons become very heavy at speeds about 400 m.p.h. A.S.I., the latter being almost immovable then. However the ailerons were, if anything, a little lighter at high speeds than has been found on other Spitfires.
Conclusions
The handling and flying characteristics are practically unaltered by the change in engine though there is a slight decrease in stability on the climb. Below full throttle height the improvement in performance of the aeroplane is less than expected when the extra power of the Merlin XII engine is taken into consideration. This matter is being investigated by Messrs.Rolls-Royce,Limited. Above rated height the improvement in climb is satisfactory, as is the increase in the ceiling of the aeroplane. The cooling system is inadequate for summer conditions.
Miscellaneous
Deliveries of Spitfire IIs began in June 1940. No. 611 fully converted to Spitfire IIs in August 1940, thus being the first squadron to become fully operational with the type. Nos. 266 and 74 followed in early September, with Nos. 19 and 66 switching during the latter half of the month. In October, it was 41 and 603 squadrons turn, bringing to 7 the number of squadrons to fully equip with this variant during the Battle of Britain.
Spitfire Mk II engine limitations from the Pilot's Notes.
Comparison of Calculated and Performance Airscrew Efficiencies
611 Squadron Operations Record Book, 13 August 1940
611 Squadron Operations Record Book, 21 August 1940
611 Squadron Form 541, 21 August 1940
Combat Report - D. H. Watkins, 21 August 1940 showing use of emergency boost, page 2
Combat Report - Sgt. N. Morrison, Spitfire II, 74 Squadron, 2 November 1940. "Pushed boost cut-out"
Combat Report - P/O H. M. Stephen, Spitfire II, 74 squadron, 30 November 1940. "tit pressed"
Combat Report - F/Lt. J. C. Mungo-Park, 74 Squadron, 30 November 1940
Fig. 1 Rate of Climb & Time to Height
Fig. 2 Level Speeds & Boost At Heights