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.

                  The principle results are as follows:-

                  Engine conditions - 3000 rpm + 25 lb/sq,in. boost.

(i)Climbs.Maximum rate of climb in M.S. gear (radiator flaps open)= 5080 ft/min up to 500 feet
Maximum rate of climb in F.S. gear (radiator flaps open)= 4335 ft/min at 11,400 feet
Maximum 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/
= 950 ft/min

(ii)Levels.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/
= 30 mph.

                  Comparison of the results with those obtained by Messrs. Vickers Armstrong (Supermarines) and Messrs. Rolls-Royce Ltd., Hucknall shows fair agreement.

(iii)Fuel flows.Maximum fuel flow obtained in all-out level at +25 lb/ and 3000 rpm was 197 galls/hour,
an increase of about 47 galls/hour above that at +18 lb/, 3000 rpm.

(iv)General.No appreciable change in handling or increase in engine maintenance was noticeable
with the use of increased boost rating.

                  Repeat performance trials on the same aircraft with a Rotol 5-blade propeller will be carried out.

1.     Introduction.

                  Performance, cooling and fuel consumption trials were required on a Spitfire IX aircraft fitted with a Merlin 66 engine adjusted for a maximum boost of +25 lb/ for combat climb and all-out level conditions. The performance and fuel consumption has been measured, and a brief assessement of handling characteristics made, the results of which are given in this Report. Advance information on the performance results were forwarded to M.A.P. by letter 10th January, 1944.

2.     Condition of aircraft relevant to tests.

        2.1.   General. The aircraft was a normal Spitfire F.Mk.IX. The following were the chief external features:-

Two 20 mm. Hispano guns with sealed muzzles.
Two 20 mm. gun stubs with hemispherical fairings.
Four .303" Browning guns, ports sealed. Ejection chutes sealed.
Internal bullet-proof windscreen.
Circular rear view mirror, with hemispherical fairing.
Multi-ejector exhaust manifolds.
Aerial mast.
New tropical pattern air intake without gauze, but blanking plate installed.
No ice guard fitted in air intake.

        2.2.   Loading. The tests were made at T.S.L. conditions, i.e. at a take-off weight of 7400 lbs., with the C.G. at 6.4" aft of the datum point.

        2.3.   Engine details and limitations. The engine was a Merlin 66 No.156369/A444995 fitted with a Rolls-Royce version of Stromberg pressure carburettor, the "D" chamber vent of which was blanked off.

                  The engine was cleared for combat operation at +25 lb/ boost pressure for periods not exceeding 5 minutes.

                  The propeller reduction gear ratio was 0.477. 150 grade fuel to Specification RDE/F/253 was used throughout the trials.

        2.4.   Propeller.

Rotol Mk.R.12/4F5/4
4 wooden blades Diameter 10'9"
Serial number of bladesNo. 1 HRA 31139
No. 2 HRA 31131
No. 3 HRA 31081
No. 4 HRA 31239
Serial number of hubH 934
Coarse pitch setting57 20'
Fine pitch setting22 20'

        2.5.   Instruments. An automatic observer, comprising an altimeter, air speed indicator, boost gauge and watch was fitted in lieu of the TR.1133 radio. A type 35 control operating the 16 mm Bell-Howell cine camera photographing the instruments at 2 second intervals was installed in the pilots cockpit.

3.     Tests made.

        3.1.   F.S. gear climbs to 30,000 feet and M.S. gear climbs to 20,000 feet were made with the radiator flaps open. In addition, two climbs in F.S. gear with the radiator flaps closed were made for comparison with results as obtained by the firms.

        3.2.   All-out level speeds in M.S. gear from sea level to 12,000 feet and in F.S. gear from 6,000 to 30,000 feet were measured; fuel flowmeter readings were taken during each run in order to provide data at the increased rating.

4.     Results.

                  All performance results given in the Report have been corrected to standard ICAN atmospheric conditions and the level speeds to 95% of the take-off weight by methods of Report No. A.& A.E.E./Res/170.

        4.1.   The position error correction and altimeter correction used were those measured on Spitfire IX BF.274. The compressibility correction has been calculated by the method given in Addendum to Report No. A.& A.E.E./Res/147; a strut correction based on ARC Report No. 6420 has been used.

        4.2.   Climbs. The results which have all been obtained from automatic observer records are detailed fully in Tables I, II, and III whilst the corrected time, rate of climb and boost are plotted against height in Fig. 1

                  The time to height curve corresponds to the rate of climb in M.S. and F.S. gear, radiator flaps open - change of gear at approximately 6000 feet. An estimate of the expected performance at +18 lb/sq,in, boost is also shown in the Fig. for comparison.

        4.3.   Level speeds. The maximum level speed results are detailed fully in Table IV whist TAS and boost curves are plotted against height in Fig. 2. The estimated performance at +18 lb/ boost is also shown in the Fig. 2.

        4.4.   Comparison of performance results.

                  4.41.   An increase of about 950 ft/min in rate of climb and about 30 mph in all-out level speed is achieved by the increase of boost from +18 lb/ to +25 lb/

                  4.42.   The comparison of this estimated performance with that obtained on Spitfire F.Mk.IX BS.543 with Merlin 66, shows rather lower figures for JL.165, particularly in all-out level speed.

                  The table below gives rough comparison of the performance of both aircraft:-

Boost +18 lb/sq.inch RPM = 3000
ConditionRadiatorsSpitfire IX
JL.165 (estimated)
Spitfire IX
  Max. rate of climb in MS gear ft/minOpen42004700
  Max. rate of climb in FS gear ft/minOpen35003850
  Max. level speed in MS gear mphShut  364  384
  Max. level speed in FS gear mphShut  388  407

                  4.43.   For comparison purpose the climb and level speed results as obtained at the increased boost rating by:

(a)Vickers Armstrongs Ltd., Supermarine Works,
Report No. 3918 of 5th October, 1943 on
Spitfire VIII JG.204

(b)Rolls-Royce, Hucknall
Report No. Dor/Chr/Rls.1/MNH 8.10.1943 on
Spitfire IX JL.165

are given below.

                  It should be noted that the climb performance was measured with radiator flaps closed by both firms.

Boost +25 lb/sq.inch RPM = 3000
Rad flaps shut
Rad flaps shut
A.& A.E.E.
Rad flaps open
A.& A.E.E.
Rad flaps shut
M.S. Climb
Rate of climb ft/min. at sea level
M.S. Climb
Rate of climb ft/min. at 20,000 feet
F.S. Climb
Full throttle height feet
F.S. Climb
Rate of climb - ft min.
at full throttle height
F.S. Climb
Rate of climb - ft min.
at 25,000 feet
M.S. gear
Maximum speed - mph
M.S. gear
Full throttle height - feet
F.S. gear
Maximum speed - mph
F.S. gear
Full throttle height - feet

                  The agreement between the Rolls-Royce and A.& A.E.E. performance figures is quite reasonable though the speeds particularly are much lower than those obtained by Messrs. Bickers Armstrong on the other aircraft.

        4.5.   Fuel flows.   The fuel flows as obtained from flowmeter readings in all-out level speed runs were corrected for instrument error and temperature deviation from standard conditions.

                  Maximum fuel flow was obtained near full throttle height in F.S. gear and was about 197 galls/hour. The corresponding value of fuel flow at +18 lb/ was estimated as 150 galls/hour.

        4.6.   Handling.   There was no appreciable change in handling of the aircraft at +25 lb/ as compared to a standard Spitfire IX at +18 lb/ There was only a slight change in directional trim when throttle was fully opened from +18 to +25 lb/

        4.7.   Maintenance.   No difficulty was experienced in maintenance of the engine though most running was at high boost. In one case only an exhaust stub was burnt out and no plug troubles were encountered.

                  The total time flown at +25 lb/ during the tests was approximately 1 hour, 10 mins., whilst total time flown at boost higher than +18 lb/ was approximately 2 hours.

5.     Conclusions.

                  The increase in performance with the increase of boost from +18 to +25 lb/ 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.

6.     Further develpments.

                  Further trials on the same aircraft fitted with a Rotol 5-blade propeller and existing 0.477 propeller reduction gear will be carried out in due course.

Full throttle climb F.S. gear
Take-off weight 7400 lb.
Radiator flaps fully open

Rate of
0425003000+25   170
  20004265  .47"+25   170
  40004280  .94"+25   170
  600042951.41"+25   170
  800043101.87"+25   170
1000043252.33"+25   170
*11400  43352.65"+25   170
2600022907.20"   +8.6148
2800020108.13"  +6.5144
3000017309.19"  +4.6140
* Full throttle height

Full throttle climb F.S. gear
Take-off weight 7400 lb.
Radiator flaps fully closed

Rate of
0472003000+25   170
  20004725  .42"+25   170
  40004730  .84"+25   170
  600047351.26"+25   170
  800047401.68"+25   170
1000047452.10"+25   170
*11400  47502.39"+25   170
2600025506.51"  +8.6148
2800022507.34"  +6.5144
3000019508.29"  +4.6140
* Full throttle height

Full throttle climb M.S. gear
Take-off weight 7400 lb.
Radiator flaps fully open

Rate of
* 5005080  .10"+25.0"
  20004855  .40"+23.2"
  40004560  .82"+20.9"
1600027954.14"  +8.7"
1800024954.90"  +7.1166
2000022005.75"  +5.6160
* Full throttle height

Maximum level speeds. Radiator flaps closed.
Take-off weight 7400 lb. Corrected to weight of 7025 lb.

  2000360358-7 3/4-10+25   3000M.S.
* 2800  364358-7 3/4-10+25   ""
  4000364352-7 1/2-1 3/40+23.2""
  8000364332-6 1/2-2 3/4+ 1/4+18.7""
10000364322-6 1/4-3+ 1/4+16.7""
12000363312-5 3/4-3 3/4+ 1/4+14.8""
  6000350328-6 1/2-20+25   "F.S.
  8000360328-6 1/2-2 3/4+ 1/4+25   ""
10000370327-6 1/2-3 1/2+ 1/4+25   ""
12000380326-6 1/2-4+ 1/2+25   ""
* 13800    389326-6 1/2-5+ 1/2+25   ""
16000389315-6-5 1/2+ 1/2+22.0""
18000388304-5 1/2-5 3/4+ 1/2+19.5""
20000388294-5-6+ 3/4+17.3""
22000387284-4 3/4-6 1/4+ 3/4+15.2""
24000386273-4 1/4-6 1/2+ 3/4+13.2""
26000385263-3 3/4-6 1/2+ 3/4+11.2""
28000383252-3 1/2-6 1/4+ 3/4  +9.3""
30000380240-2 3/4-6+ 3/4  +7.5""
* Full throttle height

Fig 1. Climb Performance     Fig 2. Level Speed Performance

See also Rolls-Royce Trials of Spitfire IX JL.165

WWII Aircraft Performance     Spitfire Mk IX Performance