.......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.

1.0 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.

2.0 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:-

.......The landing run is considerably longer than expected and the reason appears to be a defective braking sytem 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.

3.0 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.

.......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.

.......There is a distint improvement in time to reach heights above 20,000 feet and in the ceiling of the aeroplane when fitted with the Merlin XII engine.

4.0 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.

Fig. 1 Rate of Climb & Time to Height

Fig. 2 Level Speeds & Boost At Heights

.......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).

.......The following remarks have been made as a result of these tests:-

(i) 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.

(ii) 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.

(iii) 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.

(iv) 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.

.......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 improvment 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-Royse,Limited. Above rated height the improvment in climb is satisfactory, as is the increase in the ceiling of the aeroplane. The cooling system is inadequate for summer conditions.

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 varient 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
Spitfire II P7420 with 19 Squadron at Fowlmere September 1940 being fueled from a bowser marked 100 Oct.
Fig. 1 Rate of Climb & Time to Height
Fig. 2 Level Speeds & Boost At Heights