X.4922

1. Introduction: The performance on Spitfire V.K.9788 (Merlin XLV engine) is given in 1st part of Report No. A.A.E.E./692,i. It was desired to check the performance obtained on K.9788 on another Spitfire V. and X.4922 was chosen for these check tests. Spitfire V. X.4922 was fitted with a standard Spitfire I. De Havilland airscrew, but with the pitch settings increased to 34 deg. fine and 54 deg. coarse, the same pitch settings used in the previous tests.

2. Tests made: The aeroplane was fitted with 8 Browning guns and, operationally equipped, weighed 6,450 lb. Because this loading represented the all-up weight of the aeroplane in Service, it was decided to carry out the trials at the above load instead of 6,070 lb. to which K.9788 was loaded. (Note: paragraph as corrected by corrigendum dated 18th June, 1941)

.......Climbs to ceiling and measurements of speeds over a range of heights from 10,000 feet to 26,000 feet were made. An oil cooling climb was combined with the performance climb.

3. Results of tests:

.......(a) The top speed of the aeroplane is 375 m.p.h. at 20,800 feet.

.......(b) The maximum rate of climb is 3,140 feet per minute at 14,400 feet. The time to 20,000 feet is 7.1 minutes and the Service ceiling is 37,700 feet.

.......(c) The radiator is not quite suitable for English summer conditions on the climb.

.......(d) The oil cooler is suitable for English summer conditions on the climb.

.......(e) The take-off run in zero wind and standard conditions is 330 yards, and the distance to clear a 50 foot screen is 530 yards.

.......(f) The airscrew setting of 34 deg. to 54 deg. is suitable for the aeroplane under all conditions of flight.

4. Comments on results:

.......(a) The top speed of X.4922, 375 m.p.h. at 20,800 feet, is greater than Spitfire V K.9788 (364 m.p.h. at 19,600 feet). The discrepancy is explained by the lower full throttle height of the Merlin XLV in K.9788 being 1,200 feet lower than that in X.4922.

.......(b) The maximum rate of climb of this aeroplane (3,140 feet/minute) is lower than that of Spitfire V. K.9788 (3,460 feet/minute). However, the total all-up weight of X.4922 was 6,450 lb. compared with 6,170 lb., the all up weight of K.9788.

.......(c) The Mark II radiator in X.4922 seems to be less efficient than the Mark I. radiator on K.9788. This discrepancy remains unexplained.

SUMMARY OF TRIALS

Aeroplane Spitfire V.No. X.4922
EngineMerlin XLV
At 2850 R.P.M.and +9 lb. boost
At 3000 R.P.M.and +9 lb. boost
Total weight = 6,450 lb.
C.G. position6.2" aft of the datum

Height
feet		Top
Speed
M.P.H.		Time to Climb mins.Rate of
Climb
Ft/min.
S.L. 0 
  2,000 0.72765
  5,000 1.92855
10,000337   3.63010
15,000355   5.23045
20,000372.57.12280
25,000364.59.61520
30,000 12.9  1275
Service Ceiling37,700 ft
Take off run330 yds.
Distance from rest to clear 50 ft screen530 yds.
Take off tests corrected to zero wind and standard atmosphere

CLIMBING TRIALS

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 Level0.....2850.
  1,0000.42735171170-1.8- " +9.0
  2,0000.72765.... " +9.0
  3,0001.22795.... " +9.0
  5,0001.92855.... " +9.0
  6,5002.42900.... " +9.0
10,0003.63010185160-0.4-0.4 " +9.0
13,0004.63095.... " +9.0
15,0005.23045.... " +8.6
16,5005.72815.... " +7.6
18,0006.22590.... " +6.5
20,0007.12280204148+1.5-0.8 " +5.2
23,0008.71820.... " +3.2
26,00010.2  1810211136+3.5-0.9 3000 +2.8
28,00011.4  1540214132+4.3-1.0 " +1.4
30,00012.9  1275216128+5.0-1.0 " +0.1
33,00015.6    870220122+6.3-1.2 " -1.8
36,00020.2    470225116+7.5-1.1 " -3.4
37,00022.8    290221.5110+8.7-1.1 " -3.8
  14,400*4.93140193155*0.4-0.6 2850 +9.0
Estimated absolute ceiling38,000 feetGreatest height reached37,850
R.P.M. stationary on ground2500Boost pressure lb./sq.in+8 3/4
* Full Throttle height
Service Ceiling. 37,850 ft.

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.
10,000337   300   -8.5-2.43000+9.0
13,000347.5296   -8.5-3.2 " +9.0
15,000355   294   -8.5-3.8 " +9.0
16,500360   291   -8.5-4.2 " +9.0
18,000363   287   -8.5-4.5 " +9.0
20,000372.5285.5-8.5-5.2 " +9.0
  20,800*375   276   -8.5-5.8 " +9.0
23,000370   270.5-8.5-5.5 " +6.6
26,000361.5252   -8.5-5.5 " +4.2
Landing and take off tests corrected to zero wind and standard atmosphere
Take off run 330 yds.
Distance from rest to clear 50 foot screen 530 yds.
Under conditions of test: i.e. 14.1 mph wind, +2 deg.C temp and 29.96 Hg pressure
Take-off run: 250 yds .......Time 12.4 seconds.
* Full throttle height

[ FIG. 1 RATE OF CLIMB TIME TO HEIGHT AND BOOST]
[ FIG. 2 LEVEL SPEEDS & BOOST AT HEIGHTS]

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