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 propeller5 - blade propeller
Max. rate of climb at full throttle
.. height in M.S. supercharger gear
4470 ft/min.
(at 11,200 ft.)
4500 ft/min.
(at 9,900 ft.)
Max. rate of climb at full throttle
.. height in F.S. supercharger gear
3400 ft/min.
(at 22,700 ft.)
3400 ft/min.
(at 21,700 ft.)
Estimated service ceiling43,100 ft.42,400 ft.
Level speed performance
Max. level speed at full throttle
.. height in M.S. supercharger gear.
388 m.p.h.
(at 14,600 ft.)
388 m.p.h.
(at 13,700 ft.)
Max. level speed at full throttle
.. height in F.S. supercharger gear.
405 m.p.h.
(at 25,400 ft.)
408 m.p.h.
(at 24,600 ft.)

        The performance of the aircraft is in general 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.

1.     Introduction.

        Comparitive performance trials were required on Spitfire HF. Mk.IX BS.310 with the following combination of propeller and reduction gear.

        (i)      0.477:1 reduction gear, 4 - blade propeller.

        (ii)     0.42:1 reduction gear, 5 - blade propeller.

2.     Condition of aircraft relevant to tests.

        2.1.   General. The principal features of the aircraft were as follow:-

Merlin 70
Propeller as detailed in para. 2.4 below
Individual ejector exhaust stubs.
Temperate air intake.
Usual Mk.IX radiator installation
Universal wings, wing tips in place, large bulge over 20 mm guns.

2 x 20 mm. guns; 4 x 0.303" machine guns: Leading edge ports and muzzles sealed; relevant ejection chutes open;
Hemispherical blanks over remaining 20 mm. guns stubs.
Rectangular unfaired rear view mirror above windscreen.
Balloon type cockpit hood.
No W/T aerial wire.
I.F.F. aerials.
Rudder with enlarged area (Spitfire F.Mk.XII type) as now fitted to this Mk.
A Mk.VIII,c pitot-static head was fitted in the usual position beneath the port wing.

        2.2.   Loading. The aircraft was flown at the following take-off loadings:

Weight (lb)Position of Centre of gravity aft of datum
(i)73205.8" (with 4 blade propeller)
(ii)74404.5" (with 5 blade propeller)

        These centre of gravity positions are with undercarriage down.

        The difference in weight between the 4 and 5 blade propellers was 65 lb. and the above two loadings should have differed by this amount. In practice, however, some additional ballast was carried in loading (ii). The actual speed results, however, have been corrected to 95% of what the respective weights should be.

        2.3.   Engine numbers and limitations. The numbers of the Merlin 70 engines fitted were:-

A.M. No.445179
Maker's No.156737

        The following relevant limitations applied at the time of the tests:-

Engine speeds and boostR.P.M.Boost lb/
Maximum for take-off (up to 1000 ft. or for 3 mins.)3000+12
Maximum for combat (5 min. limit)3000+18
Maximum for continuous climbing (1 hr. limit)2850+12

        2.4.   Propeller details. The leading particulars of the two propellers used were as follow:-

Rotol HydraulicRotol Hydraulic
type R.12/4F5/4Mk. XH55
No of blades45
Direction of rotationR.H.R.H.
Stub serialH.3203EH.275
Blade No. 1. Serial No. JT.109318HRA.30190
Blade No. 2. Serial No. JT.109386HRA.30281
Blade No. 3. Serial No. JT.109082HRA.30339
Blade No. 4. Serial No. JT.95902HRA.30357
Blade No. 5. Serial No. -HRA.30319
Pitch range35 deg.35 deg.
Fine pitch setting-25 deg.50'
Blade materialJabloHydrulignum
Reduction gear0.477:10.42:1

3.     Tests made.

        The following tests are dealt with in this report:-

        (i)   Partial climbs were made at combat rating to determine the best climbing speeds with the 0.42:1 reduction gear and the 5 blade propeller. The climbing speed for the trials with the 0.477:1 reduction gear and the 4 blade propeller was that used on Spitfire HF. Mk.IX BS.551.

        (ii)     Ceiling climbs were made at combat rating in each case. Combat rating is normally permitted for periods of five minutes only, but a concession for test purposes allowed complete climbs at this rating to be made. The radiator flaps were fully open for climbing.

        (iii)   Maximum level speeds in both supercharger gears were measured in each case. The radiator flaps were closed during these tests.

4.     Results of tests.

        All results in this Report have been corrected to I.C.A.N. standard atmospheric conditions by the methods of Report No. A.& A.E.E./Res/170. The level speed results have been corrected to 95% of the take-off weight by the methods of the same report. In addition a "strut" correction has been applied to the level speed results, the source of this correction being report No. ARC.6420. The compressibility correction has been calculated by the methods of the Addendum to Report No. A.& A.E.E./RES/147.

        The position error correction used was that measured on Spitfire F. Mk. IX BF.274. The make, position and setting of the pitot-static head were the same on BF.274 and BS.310.

        4.1.   Climbing speeds. The climbing speed used with the 0.477:1 reduction gear and the 4-blade propeller were that deduced from tests on another aircraft as stated in para. 3 (i) above. This speed was 160 mph ASI up to 25,000 ft. (approximately full throttle height in F.S. supercharger gear) decreasing by 3 mph per 1,000 ft. thereafter.

        The partial climbs made with the 0.42:1 reduction gear and the 5 blade propeller showed the best climbing speed to be 160 mph ASI up to 22,000 ft. decreasing by 5 mph per 2,000 feet thereafter.

        4.2.   Climb performance. The results of the climbs are given in full in Tables I and II and Fig. 1 and are summarized in the table below. With the 5 blade propeller the nominal combat boost of +18 lb/ was slightly exceeded due to inaccurate functioning of the boost control, and accordingly an extra column (B) is given with the results corrected to nominal boost.

(A)   Results obtained at boost during test (Max. boost at +18.5 lb/
(B)   Corrected to nominal boost value of +18 lb/

        4.3.   Level speed performance. The results of the level speed performance obtained are given fully in Tables III and IV and Fig. 2 and are summarized in the table below. As on the climb the exact nominal boost was not obtained with the 5-blade propeller fitted and an extra column with results corrected to the nominal boost is included.

(A)   Results obtained at boost during test (Max. boost at +18.5 lb/
(B)   Corrected to nominal boost value of +18 lb/

5.     Discussion of results.

        5.1.   Full throttle heights. With the 5-blade propeller fitted the full throttle heights both on the climb and in level flight were noticeably lower. This is thought to be due to the different nature of the airflow at the entry to the air intake with the 5-blade propeller fitted. The tests with the 5-blade propeller were made after the tests with the 4-blade propeller, and to ensure that the loss of full throttle heights was not due to engine deterioration the 4-blade propeller was finally refitted (the reduction gear being 0.42:1) and a few check performance measurments made, when it was found that the full throttle height had increased almost to its original value.

        5.2.   Propeller tip Mach number. The propeller tip Mach numbers in level flight were a follow:

4-blade propeller5-blade propeller
At the full throttle height in FS supercharger gear.986.909
At the highest altitude tested, 33,000 ft.1.007.928

        In correcting the results to standard atmospheric conditions, no correction for any effects of compressibility on propeller efficiency due to these high tip Mach numbers have been made.

        The differences in air temperature on test from the I.C.A.N. standard values were within the ranges given below:-

10,000 - 20,000 ft.+5 to -9 C
20,000 - 30,000 ft.+3 to -8 C
30,000 - 33,000 ft.-2 to -8 C

6.     Conclusions

        The comparison between the two conditions is best seen from the tables given in paras, 4.2 and 4.3 or Figs. 1 & 2.

        On the climb the difference between the performance under the two conditions was within 200 ft/min. at all heights.

        In level flight the aircraft showed an increase of 3-5 mph with the 5 blade propeller in F.S. gear between 18000 ft. - 24000 ft. but at other heights the difference was small.

        In general, therefore, 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.

Performance on climb at combat rating
Reduction gear 0.477:1 4 - blade propeller
Take-off weight 7,320 lb.Radiator flaps open
Supercharger gear changed at 18,200 ft.
Rate of
Sea level0----MS
  2000  0.4543501602980+18.0  "
  40000.94375""+18.0  "
  60001.44400""+18.0  "
  8000  1.854425""+18.0  "
100002.34455""+18.0  "
  11200*  2.554470""+18.0  "
140003.24035""+15.2  "
160003.73755""+13.4  "
180004.33730""+11.9  "
200004.93400""+18.0  FS
  22700*  5.653400""+18.0  "
24000  6.053190""+16.4  "
260006.72850154"+14.2  "
28000  7.452540148"+12.1  "
32000  9.251930136"+8.4"
3400010.4  1600130"+6.5"
3600011.8  1270124"+4.7"
3800013.65  945118"+3.2"
4000016.25  610112"+1.6"
* Full throttle heights
Service ceiling (100 ft/min) 43,100 ft.
Estimated absolute ceiling 43,800 ft.

Level speed performance
Reduction gear 477:14-blade propeller
Radiator flaps closedCorrected to a weight of 6,960 lb.
Height in
std. atmos.
P.E.C.C.E.C. StrutBoost
Sea level329335-6.8+0.50+18.0  3030M.S.
18000388303-5.5-5.2+0.5+14.4  ""
21000386287-5.0-5.8+0.6+11.3  ""
18000372290-5.1-4.7+0.4+18.0  "F.S.
27000404272-4.4-7.7+1.0+16.2  ""
30000399254-3.5-7.6+1.0+12.8  ""
* Full throttle heights

Note: Tables for the 5 blade propeller omitted. It was not used in service on Spitfire Mk IXs

Fig 1. Climb Performance     Fig 2. Level Speed Performance

WWII Aircraft Performance     Spitfire Mk IX Performance