Spitfire Mk IX

Aeroplane and Armament Experimental Establishment
Boscombe Down

22 October 1942

Spitfire F. Mk. IX BF.274
(Merlin 61)
Climb and level speed performance

SUMMARY

Climb and level speed performance has been measured on Spitfire F. Mk. IX B.F.274 both with and without a 30 gallon external jettisonable tank fitted.
The climb performance at combat rating and position error have also been measured without the tank fitted.
The engine was fitted with a 0.477:1 reduction gear and a Rotol R3/4F5/3 metal propeller.

Climb at normal rating:
Maximum rate of climb in M.S. supercharger	3200 ft.min at 13,500 ft.
Maximum rate of climb in F.S. supercharger	2540 ft/min. at 25,900 ft.
Service ceiling (100 ft/min)	42,100 ft.
Time to 10,000 ft.	3.1 mins.
Time to 20,000 ft.	6.5 mins.
Time to 30,000 ft.	10.7 mins
Time to 40,000 ft.	20.2 mins
Climb at Combat rating:
Maximum rate of climb in M.S. supercharger	3860 ft.min at 12,600 ft.
Maximum rate of climb in F.S. supercharger	3020 ft/min. at 25,200 ft.
Service ceiling (100 ft/min)	43,400 ft.
Time to 10,000 ft.	2.7 mins
Time to 20,000 ft.	5.6 mins.
Time to 30,000 ft.	9.2 mins
Time to 40,000 ft.	16.6 mins
Level Speeds.
Maximum true air speed in M.S. supercharger	380 1/2 m.p.h. at 15,400 ft.
Maximum true air speed in F.S. supercharger	403 m.p.h. at 27,400 ft.
Without 30 gallon tank

Performance on Climb Speed and Boost at Height

View BF.274 Report Here

Aeroplane and Armament Experimental Establishment
Boscombe Down

17 March 1943

Spitfire F. Mk. IX BS.428
(Merlin 61)

Level speed performance with and without
500 lb bomb fitted

Level speed measurements have been carried out on this aircraft to assess the effect of fitting a 500 lb bomb on an unfaired rack beneath the fuselage. The installaton was one designed and fitted by Fighter Command personnel.

Level speed performance was measured between 11,000 ft. and 21,000 ft. using all-out level power conditions in M.S. supercharger gear with the radiator flaps closed.

Condition	Max. True Air speed m.p.h.	Full throttle height feet.
With one 500 lb. bomb fitted	363	14,500
With external bomb installations removed	385	14,750

Conclusions

The reduction in maximum true air speed in M.S. supercharger gear due to fitting a 500 lb. bomb and a bomb rack without fairing is 22 m.p.h.

Level Speed Performance

View BS.428 Report Here

First flight from Eastleigh 26-8-42. Transferred to 402 Sqdn. 26-8-42, Farnborough November 42 , Boscombe Down for above trials 14-1-43, 421 Sqdn 20-5-43, 611 Sqdn 15-10-44. Sold 24-11-49

Aeroplane and Armament Experimental Establishment
Boscombe Down

4 March 1943

Spitfire F. Mk. IX BS.543 Merlin 66
Spitfire F. Mk. IX BS.551 Merlin 70

The performance of Spitfire IX aircraft fitted with high and low
altitude versions of the intercooled Merlin engine.

SUMMARY

Two low altitude versions of the intercooled Merlin engine were made which were designated the RM-9SM and RM-10 SM. In addition an improved type of high altitude engine designated the RM-11 SM was made. The RM-10 SM and the RM-11 SM were subsequently given mark numbers and are now known as the Merlin 66 and Merlin 70 respectively.

CLIMBS
Condition	Spitfire IX BS. 543 Merlin 66	Spitfire IX BS. 551 Merlin 70
Rate of climb at Sea level	4620 ft/min	4390 ft/min.
Rate of climb at full throttle height in M.S. supercharger gear	4700 ft/min at 7000 ft.	4530 ft/min. at 11,900 ft.
Rate of climb at full throttle height in F.S. supercharger gear	3860 ft/min. at 18,000 ft.	3480 ft/min. at 24,700 ft.
Rate of climb @ 30,000 ft.	2125 ft/min.	2600 ft/min.
Time to 10,000 ft	2.15 mins.	2.25 mins.
Time to 20,000 ft	4.75 mins.	4.85 mins.
Time to 30,000 ft	8.4 mins.	8.05 mins.
Height at which rate of climb is 1000 ft/min.	37,100 ft.	38,000
Time to reach above height	12.9 mins.	12.6 mins.
Service ceiling (100ft/min)	40,900 ft.	41,000 ft.
Estimated absolute ceiling	41,300 ft.	41,300 ft.
Rate of climb corrected to 18.0 lb/sq.in. boost
LEVEL SPEEDS
Maximum level speed at sea level	336 m.p.h.	329 m.p.h.
Maximum level speed at M.S. gear full throttle height	384 m.p.h. at 10,800 ft.	396 m.p.h. at 15,900 ft.
Maximum level speed at F.S. gear full throttle height	407 m.p.h. at 22,000 ft.	415.5 at 27,800 ft.
Level Speed at 30,000 f.t	395 m.p.h.	413 m.p.h.
Level Speeds corrected to 18.0 lb/sq.in. boost

RM-9SM engined Spitfire omitted

Climb Performance Level Speed Performance

View LF-HF Mk-IX Report Here

Note: BS.543 was built as a Mk V, converted to Mk IX (Merlin 61) at Rolls Royce, Hucknall. First flight 22-10-42. Transferred to AFDU, Duxford 8-11-42; AAEE, Boscombe Down 13-12-42 with Merlin 66 installed; Vickers Armstrong 22-2-43; 403 Sqdn. 9-6-43; 611 Sqdn. 10-6-43; 485 Sqdn. 6-7-43. Failed to return from operations 22-8-43.
BS.551 was built as a Mk V, converted to Mk IX (Merlin 61) at Rolls Royce, Hucknall. First flight 31-10-42. Merlin 70 installed by Rolls Royce, Hucknall 1-11-42. Flying accident, category E 4-1-43.

Aeroplane and Armament Experimental Establishment
Boscombe Down

3 Aug 1943

Spitfire HF. Mk. IX EN.524
Merlin 70

Comparitive performance trials
with three different
propeller - reduction gear combinations.

SUMMARY

Comparitive performance trials have been carried out on Spitfire HF. Mk. IX EN.524 with the following combinations of propeller and reduction gear:

(i)	0:477:1 reduction gear 10'9" diameter 4 blade propeller
(ii)	0:42:1 reduction gear 10'9" diameter 4 blade propeller
(iii)	0:42:1 reduction gear 11'1" diameter 4 blade propeller

0:477:1 reduction gear 10'9" diameter propeller results

CLIMBS
Height	Rate of climb ft/min	Time mins
10,000 ft.	4310	2.3
11,300 ft. (M.S. s/c gear F.T. ht.)	4310	2.6
20,000 ft.	3220	5.0
23,900 ft. (F.S. s/c gear F.T. ht.)	3220	6.2
30,000 ft.	2275	8.4
40,000 ft.	665	16
Service ceiling		43,200 ft.
Estimated absolute ceiling		43,800 ft.
LEVEL SPEEDS
Height	TAS mph
Sea level	326
7,000 ft.	358
15,100 ft. (M.S. gear F.T. ht.)	394
26,600 ft. (F.S. gear F.T. ht.)	413
30,000 ft.	407
39,000 ft.	369
Results of the other combinations omitted

It was stated (in the above report) that further tests were to be carried out with a modified carburettor setting as it was hoped to improve the performance of the Merlin 70 at altitude. It is understood that EN.524 incorporated this modification and a comparison of the two sets of results shows a considerable improvement has been made. The absolute ceiling is now about 2,500 feet higher than that obtained on BS.551.

Conclusion

The combination giving the best compromise between climb and level speed performance appears to be the 10'9" diameter propeller with 0.477:1 reduction gear up to about 28,000 feet. Above this height the best combination appears to be the 11'1" propeller with 0.42:1 reduction gear.

However, the differences as a whole are so small that a change from any combination already produced and in Service (0.477:1/10'9") would not appear to be worthwhile.

Climb Performance Level Speed Performance

View Mk-IX EN.524 Report Here

Aeroplane and Armament Experimental Establishment
Boscombe Down

9 April 1944

Spitfire HF. Mk. IX BS.310
Merlin 70

Comparitive performance
with 4 & 5 bladed propellers fitted

SUMMARY

Compartive climb and level speed performance trials have been made on Spitfire HF. Mk. IX BS.310 with a 0.477:1 reduction gear and a 4 blade propeller, and with a 0.42:1 reduction gear and a 5 blade propeller.

CLIMB AT COMBAT RATING
	4 blade propeller
Max. rate of climb at full throttle height in M.S. supercharger gear	4470 ft/min. (at 11,200 ft.)
Max. rate of climb at full throttle height in F.S. supercharger gear	3400 ft/min. (at 22,700 ft.)
Time to 5,000 feet	1.15 min.
Time to 11,200 feet (M.S. gear F.T. Ht.)	2.55 min.
Time to 15,000 feet	3.5 min.
Time to 22,700 feet (F.S. gear F.T. Ht.)	5.65 min.
Time to 25,000 feet	6.4 min.
Time to 35,000 feet	11.05 min.
Time to 40,000 feet	16.25 min.
Estimated service ceiling	43,100 ft.
LEVEL SPEED PERFORMANCE
Max. level speed at full throttle height in M.S. gear	388 m.p.h. (at 14,600 ft.)
Max. level speed at full throttle height in F.S. gear	405 m.p.h. (at 25,400 ft.)
5 blade propeller results omitted

Conclusion

The performance of the aircraft is similar with either propeller-reduction gear combination and no particular advantage in performance would be obtained by replacing the 4 blade propeller by a 5 blade propeller.

Climb Performance Level Speed Performance

View BS.310 Report Here

Note: BS.310's first flight took place on August 31, 1942. Performance with the original Merlin 61 installed was 381 mph at 15,700' in MS gear and 413 mph at 28,000' in FS gear. It underwent brief performance trials at Vickers Armstrong, Worthy Down in December 1942 while fitted with a Merlin 66. The level speed results were 372 mph at 8,200' in MS gear and 404 mph at 19,500' in FS gear. Rate of climb was 4,850 ft/min at 6,000' in MS gear and 4,500 ft/min at 16,500' in FS gear. Failed to return from operations 27-9-44.

Rolls-Royce, Ltd
Hucknall

8 October 1943

Spitfire J.L.165
Merlin 66 at 25 lbs. Boost Pressure

SUMMARY

The increase of boost pressure to 25 lbs/sq.inch provides a considerable improvement in the low altitude performance of the Spitfire IX aircraft, the necessary modifications to achieve this being comparitively simple.

+ 3 M.P.H.

CLIMB PERFORMANCE
Altitude feet.	Rate of climb Ft/Min.	>Improvement over climb at +18 lbs. Boost.
0	5740	780 feet/min.
5,000	5080	110 ""
10,000	5080	800 ""
15,000	4470	190 ""
20,000	3720	-
25,000	2950	-
30,000	2200	-
LEVEL SPEED PERFORMANCE
Altitude feet	+ 18 lbs. Boost.	+ 25 lbs. Boost.	Increase.
0	330 M.S.	354 M.S.	+ 24 M.P.H.
3,200	343 "	367 " (a)	+ 24 M.P.H.
8,000	364 "	367 "
10,000	367 "	377 F.S.	+10 M.P.H.
14,400	373 F.S.	397 (a)	+ 24 M.P.H.
20,000	397 (a)	397	-
25,000	394 "	394	-
(a) Full Throttle Height

Climb Performance at 25 Lbs Per Sq.In. Boost Rating Level Speed Performance at 25 Lbs Per Sq.In. Boost Rating

View J.L.165 25lbs. Rolls Royce Report Here

Note: JL.165 was manufactured at Castle Bromwich as a Spitfire V (Merlin 45) and delivered on March 27, 1943. It was subsequently converted to a LFIX (Merlin 66) at Rolls Royce, Hucknall. Performance trials at Rolls Royce, Hucknall using +25 lbs. boost in October 1943, AAEE for trials 11-11-43, Transfered to Air Service Training 3-6-44, 6 Maintenance Unit 26-10-44, 82 Maintenace Unit 10-11-44, Casablanca 15-1-45, Struck off charge 28-8-47.

Aeroplane and Armament Experimental Establishment
Boscombe Down

1 Feb 1944

Spitfire IX JL.165
Merlin 66

Trials at +25 lb/sq.inch boost
with Rotol 4 blade propeller

SUMMARY

Performance trials and a brief assessment of handling characteristics have been completed on a standard Spitfire IX with Merlin 66 engine, adjusted for maximum boost of +25 lb/sq.inch. 150 grade fuel to Specification RDE/F/253 was used through all tests.

CLIMBS
Engine conditions - 3000 rpm + 25 lb/sq.in. boost.
Max. rate of climb in M.S. gear (radiator flaps open)	5080 ft/min up to 500 feet
Max. rate of climb in F.S. gear (radiator flaps open)	4335 ft/min at 11,400 feet
Max. rate of climb in F.S. gear (radiator flaps shut)	4750 ft/min at 11,400 feet
Estimated increase in rate of climb below full throttle heights due to increase in boost from +18 to +25 lb/sq.in.	950 ft/min
LEVEL SPEEDS
Maximum true air speed in M.S. gear	364 mph at 2,800 feet
Maximum true air speed in F.S. gear	389 mph at 13,800 feet
Estimated increase in speed below full throttle heights due to increase in boost from +18 to +25 lb/sq.in.	30 mph.

Conclusions

The increase in performance with the increase in boost from +18 to +25 lb/sq.in. corresponds to :
1) 950 ft/min. in rate of climb in M.S. gear
2) 900 ft/min. in rate of climb in F.S. gear
3) 30 mph in maximum level speed in M.S. and F.S. gear

There is also an increase in fuel consumption of approximately 24%.
No maintenance difficulties of the engine were experienced.

Climb Performance Level Speed Performance

View J.L.165 Rotol 4 Blades Report Here

Aeroplane and Armament Experimental Establishment
Boscombe Down

31 March 1944

Spitfire LF Mk. IX MA.648
Merlin 66

Level speed trials with S.U. Mark II
single point fuel injection pump

SUMMARY

A Rolls Royce S.U. fuel injection pump, Mark II has been fitted to Spitfire LF Mk.IX MA.648 in place of the normal Bendix carburettor and level speed performance has been measured as part of the general schedule of tests including fuel consumption and behaviour under negative 'g'.

The principal results at combat conditions (i.e. 3000 rpm and +18 lb/sq.in. boost) are as follows:
Max. speed at F.T. height (9,400 ft.) in M.S. gear = 379 mph
Max. speed at F.T. height (21,000 ft.) in F.S. gear = 411 mph

These results compare favorably with those of other Spitfire LF Mk. IX aircraft, which fact is attributed cheifly to the higher full throttle height obtained with the S.U. pump.

Level Speed Performance

View MA.648 Speed Trials Here

Royal Aircraft Establishment
Farnborough

October 1944

Spitfire LF Mk. IX
Merlin 66

The Loss of Aircraft Performance due to the
inclusion of Air Cleaner Elements in the
Universal Intake of a Spitfire IX Aircraft

SUMMARY

When air cleaner elements are fitted to the universal air intake of the Spitfire IX aircraft, a loss of pressure in the ramming intake results, due to spoilage of the air flow by the irregular contour of these elements, and possibly in part to leakage of air through these elements into the engine bay. A louvred plate has been devised to minimize the latter effect.

The loss of performance was measured without the louvred plate in position, and was found to be considerable at high altitudes decreasing to zero below the full-throttle height of the engine. It could be reduced by between 50 and 70% at altitude by using the louvred plate.

When operating from dust free aerodromes the loss can be entirely avoided by fitting a blanking plate beneath the cleaner elements.

CONCLUSIONS

Loss of effective ram with the filter elements fitted causes a vitrually constant loss of boost pressure at heights above the full throttle heights, rather greater in F.S. gear than in M.S. gear due to the higher supercharger compression ratio. The resulting loss in performance corresponds closely to the power loss caused by the decrease in boost pressure. At the higher altitudes the proportionate loss in boost, and therefore in performance, is increased.

Since these tests show no significant performance loss below the full throttle heights, and therefore no increase in drag due to leakage through the cleaner, it appears likely that the loss of ram is caused mainly by spoilage of the smooth flow of air through the intake by the irregular contour of the cleaner elements. This effect is largely eleminated when the louvred plate is fitted beneath the cleaner elements.

The effect of the cleaner elements in climbing performance is practically negligible.

When the air cleaner can be dispensed with, all performance losses due to the air cleaner can be avoided by fitting a plain blanking plate between the air duct and the filter elements.

Flight Trials of a Spitfire IX Aircraft
Level Flight Performance

Height Ft.	T.A.S. M.P.H. Cleaner housing blanked off	T.A.S. M.P.H. Cleaner elements directly open to intake	T.A.S. M.P.H. Louvred plate fitted below cleaner elements	Supercharger
S.L.	340.8	337.6	338.9	M Gear
3,000	353.9	351.1	352.2	"
6,000	368.0	365.8	366.6	"
9,000	382.1	380.6	381.4	"
12,000	386.9	382.9	385.1	"
15,000	387.3	381.2	384.6	"
18,000	386.3	377.4	382.8	"
21,000	383.0	373.9	379.6	"
24,000	378.8	367.9	374.9	"
9,000	369.6	360.4	363.9	S Gear
12,000	381.5	373.5	376.0	"
15,000	393.8	387.2	389.0	"
18,000	406.0	401.4	401.8	"
21,000	417.8	413.7	413.8	"
24,000	418.8	412.3	415.3	"
27,000	417.3	407.7	411.8	"
30,000	412.6	401.0	406.8	"
33,000	404.9	391.0	399.8	"
36,000	391.2	374.7	387.0	"
Engine Operating Conditions: 3000 Engine R.P.M., +18 lbs./in.² Boost or Full throttle

Diagram of Universal Air Intake Louvred Plate & Cleaner Elements Level Flight Performance Climbing Performance

Air Ministry, A.I.2.(g)
Whitehall

20 March 1943

Spitfire IX v. German Fighters

Spitfire IX

No sealed cabin or pressurising equipment.

Engine Merlin 61.

Armament 2 x 20 mm. and 4 x .303" MG's.

Max. speeds

At present engine rating (+15 lb. per sq. inch boost and 3,000 r.p.m.):
380 m.p.h. at 15,000 ft.
405 m.p.h. at 28,000 ft.
394 m.p.h. at 30,000 ft.

New aircraft coming into service will be fitted with re-rated engines operating at + 18 lb. per sq. inch boost and 3,000 r.p.m.

The maximum speeds will be increased as follows:
385 m.p.h. at 15,000 ft.
409 m.p.h. at 28,000 ft.
394 m.p.h. at 30,000 ft.

Rate of climb at 20,000 ft:

The rate of climb varies according to type of reduction gear fitted.

With an 0.42 reduction gear (at + 15 lb. per sq.inch boost) the rate of climb is 2,540 per minute.

With the same reduction gear, but at + 18 lb. per sq. inch, the rate of climb is 2,750 ft. per minute.

With an 0.477 reduction gear (at + 15 per sq. inch boost) the rate of climb is 2,950 ft. per minute and increases to 3,230 ft. per minute at + 18 lb. per sq. inch boost.

Service ceiling

(Max., no load):
With 0.42 reduction gear: 41,000 ft.
With 0.477 reduction gear: 43,000 ft.

Remarks

Both the Me 109 G and the FW 190 A were originally, and in some cases still are operated at a reduced engine rating. Performances given correspond to the full engine ratings.

Remarks

Me 109 G fighters are slightly faster than the Fw 190 A at 20,000 to 22,000 ft. The difference of speed increases with altitude and is about 25 m.p.h. at 30,000 ft. in favour of the Me 109 G.

The rate of climb of the Me 109 G, without additional guns, is slightly better than that of the Fw 109 A. The same remark applies to the service ceiling.

The Spitfire IX at 28,000 to 30,000 ft. is superior in speed to the Me 109 G and the Fw 190 A.

Its rate of climb at 20,000 ft. with the 0.42 reduction gear is inferior to the Fw 190 A and the Me109 G, even when operating at +18 lb. per sq. inch boost.

When fitted with the 0.477 reduction gear and at +15 lb. per sq. inch boost the Spitfire is equal in rate of climb to the Me 109 G-2; when operating at +18 lb. per sq. inch boost it is superior to all German fighters at present in service.

The ceiling of the Spitfire IX is considerably higher than that of the Me 109 G or the Fw 190 A at present in service.

A.I.2(g)
20.3.43
Ref: 2G/GA113/P

Aircraft Data

Aircraft	Engine	Engine Power (B.H.P.)	Max. Speed	Weight Lb.	Service Ceiling Mean weight
Spitfire F IX	Merlin 63	1,710 @ 8,500' 1,520 @ 21,000'	382 mph @ 12,500' MS 408 mph @ 25,000' FS	7,450	44,000'
Spitfire LF IX	Merlin 66	1,720 @ 5,750' 1,595 @ 16,000'	384 mph @ 10,500' MS 404 mph @ 21,000' FS	7,450	42,500
Spitfire HF IX	Merlin 70	1,710 @ 11,000 1,475 @ 23,250'	396 mph @ 15,000' MS 416 mph @ 27,500' FS	7,450	45,000'

Operational Highlights

No. 64 Squadron at Hornchurch was the first squadron to go operational with Spitfire IXs (28-July-1942). Deliveries of more powerful Spitfire IXs equipped with Merlin 63, 66, or 70s commenced in early 1943. No 611 Squadron at Biggin Hill was the first to use the Merlin 66 engined Spitfire LF IX on operations (March 1943). Full service approval of +25 lbs boost was granted 10 March 1944, providing considerable improvement in low altitude performance. No. 1 and No. 165 squadrons at Predannack were the first to convert their Spitfires to +25 lbs boost, taking 2 days off from operations in early May 44 to do so.