Spitfire Mk IIA Performance Testing

.......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:-

Corrected to zero wind and standard atmosphere

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 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.

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.

Time to height mins.

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 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.

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	37,000 ft.	Landing speed	67 m.p.h.
Take off run	230 yds Time 9 1/2 secs.	Distance from rest to clear 50 ft. screen	400 yards
Stalling speed flaps and u/c up	73	Gliding in A.S.I.	87 m.p.h.
Stalling speed flaps & u/c down	63
Best landing A.S.I.	67

Landing and take off tests corrected to zero wind and standard atmosphere.

Airscrews

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 65-05' deg
Low Pitch Setting	Estimated 28-05' deg

CLIMBING TRIALS

Spitfire P.7280

Weight = 6172 lb.

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	.	.	.	.	.	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	1.0	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

Estimated absolute ceiling	38,400	Greatest height reached	36,500
R.P.M. stationary on ground	2840 at 8.4
* Full throttle height	Service ceiling	37,600' estimated

Fig. 1 Rate of Climb & Time to Height

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	292	-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

Landing and take off tests corrected to zero wind and standard atmosphere.

Take off run	230	9.5 secs.
Distance from rest to clear 50 foot screen	400 yds.
Gliding in A.S.I.	87 M.P.H.	Stalling speed flaps & u/c up M.P.H.	73
Best landing A.S.I.	67 M.P.H.	Stalling speed flaps & u/c down M.P.H.	63
Landing run with brakes	415 yds.
*Full throttle height

Fig. 2 Level Speeds & Boost At Heights

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:-

(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.

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 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.

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 varient during the Battle of Britain.

Spitfire Mk II engine limitations from the Pilot's Notes.
Comparison of Calculated and Performance Airscrew Efficiencies

Main