M.B.138

           

1.   Introduction.

               The climb and speed performance has been measured on Seafire F. Mk. IIC M.B.138, fitted with a Merlin 32 engine. The climb performance was measured using normal and combat power ratings.

2.   Condition of aircraft relevant to tests.

      2.1.  General. The principal features of the aircraft are given below:-

A Merlin 32 engine
A 4-blade propeller, type V.P RF/4F5/4
Triple ejector exhaust stubs with fishtails and heater stubs.
The heater tubes were not connected at the rear of the exhausts.
Ice guard over air intake which was of the temperate type.
Universal wings as on Spitfire VC.
Armament:- 2 x 20 mm. guns, 4 x 0.303" machine guns; relevant ejection chutes open; 20 mm gun muzzles and 0.303" gun ports sealed. Hemispherical blanks over remaining 20 mm. gun stubs.
Catapult spools beneath and on the sides of the fuselage.
Rear view mirror above windscreen.
Internal bullet proof windscreen.
Wireless mast behind cockpit.
W/T aerial.
No I.F.F. aerials
A 30 gallon auxiliary drop tank was not fitted during these tests.

      2.2.  Propeller details.

Type of propellerRotol Hydraulic V.P. RF/4F5/4. 
Diameter10'9" 
Number of blades4 
Direction of rotationR.H. 
Serial number38964 
Serial No. Blade No. 1.S.P.60863 
Serial No. Blade No. 2.S.P.61267 
Serial No. Blade No. 3.S.P.61351 
Serial No. Blade No. 4.S.P.61688 
Blade Drawing numberR.A.10046 
Coarse pitch setting63° 00' 
Fine pitch setting26° 20' 
MaterialWood 

      2.3.  Loading. The tests were made at a take-off weight of 6,995 lb. with the C.G. 7.0" aft of the datum (undercarriage down).

              This represents typical Service load without the 30 gallon auxiliary drop tank.

      2.4.  Engine numbers and limitations.   The aircraft was fitted with a Merlin 32 engine No. 66033/253722. The engine limitations relevant to tests were:-

     R.P.M.Boost
lb/sq.in.
Maximum for take-off, all-out level flight or combat (5 minute limit)3000+18
Maximum for continuous climbing2850+12

3.   Scope of tests.

              The following tests were made:-

      (i)    Partial climbs at heights of 5,000 ft. and 29,500 ft. at combat rating and at 6,000 ft. at normal rating to determine the best climbing speed.
      (ii)   One climb at combat rating using the best climbing speed from test (i) with the radiator exit duct flap fully open.
      (iii)   One climb at normal rating using the best climbing speed from rest (i) with the radiator exit duct flap fully open.

              It was found necessary to increase the climbing speeds in order to obtain satisfactory cooling results at normal rating, and the climbs were therefore repeated using the speeds as follows:-

      (iv)   Two climbs at combat rating at increased climbing speed with the radiator fully open.
      (v)    Two climbs at normal rating at increased climbing speed with the radiator fully open.

              (Combat rating is normally permitted for periods of 5 minutes only, but for test purposes full climbs were allowed at this rating).

      (vi)    Level speeds at heights between ground level and 27,000 ft. with the radiator exit duct flap in the minimum drag position.

4.   Results of tests.

              The results have been corrected to standard atmospheric conditions by the methods given in Report No. A.& A.E.E./Res/170. The level speeds have been corrected to 95% of the take-off weight, i.e. 6,645 lb. by the method given in the same Report.

              The position error used was that given in the 38th Report No. A.& A.E.E./692,i. for a Spitfire V. A.A.878, which had the same type of wing, armament and pressure head installation as this aircraft.

              In correcting the speed measurements a "strut correction" has been applied in addition to the usual position error and compressibility corrections, the source of this correction being the A.R.C. Report 6420.

      (i)   The best climbing speed found from the partial climbs was 160 m.p.h. A.S.I. up to 6,000 ft. (approximately full throttle height at normal rating) decreasing by 1 1/2 m.p.h. per 1,000 ft. thereafter, for both normal and combat rating.

              In view of the adverse cooling results obtained at this climbing speed, the climbing speed was increased to 180 m.p.h. A.S.I. up to 6,000 ft., decreasing by 2 m.p.h. per 1,000 ft. thereafter.

              The decrease in rate of climb obtained by increasing climbing speed was small and within the experimental scatter observed for the rate of climb curves given in this Report.

      (ii)   Results of the climb performance at combat rating are given in full in Table I and Fig. 1. Briefly they are:-

HeightRate of climbTime from S.L.
2,700 ft. (F.T. height)4680 ft./min0.6 min.
10,000 ft.3360 ft/min.2.4 min.
20,000 ft.1890 ft/min.6.4 min.
30,000 ft.660 ft/min.14.95 min.
Service ceiling - 34,600 ft.Estimated absolute ceiling - 35,600 ft.

      (iii)   Results of the climb performance at combat rating are given in full in Table I and Fig. 1. Briefly they are:-

HeightRate of climbTime from S.L.
6,250 ft. (F.T. height)3560 ft./min1.85 min.
10,000 ft.2920 ft/min.3.0 min.
20,000 ft.1500 ft/min.7.75 min.
30,000 ft.470 ft/min.19.25 min.
Service ceiling - 33,700 ft.Estimated absolute ceiling - 34,800 ft.

      (iv)   The level speed performance is given in full in Table III and Fig. 2. Briefly the results are:-

Maximum true airspeed at ground level315 m.p.h.
Maximum true airspeed at 5,100 ft.339 m.p.h. (full throttle height)
Maximum true airspeed at 27,000 ft.312 m.p.h.

TABLE I
Performance on climb (combat rating)
Take-off weight 6,995 lb.Radiator flap open
 
Height
(ft)
Time
from
start
mins.
Rate of
climb
ft/min.
T.A.S.
m.p.h.
ASI
mph
P.E.C.C.E.CBoost
lb/sq.in.
R.P.M.
00       
*2,700.64680188.51810-0.1+183000
4,000.8544301921810-0.2+16.6"
6,0001.354060197.51810-0.3+14.6"
8,0001.853700199.5177+0.2-0.4+12.7"
10,0002.43360201.5173+0.5-0.5+10.9"
12,0003.053030203.5169+0.8-0.6+9.1"
14,0003.752730206165.5+1.0-0.7+7.5"
16,0004.52430208.5162+1.3-0.8+5.9"
18,0005.42160210157.5+1.7-0.9+4.4"
20,0006.41890211153+2.0-1.0+2.9"
22,0007.51640212148.5+2.3-1.1-1.6"
24,0008.851380213143.5+2.7-1.1-0.2"
26,00010.41140214.5139+3.0-1.1-1.0"
28,00012.4900217135.5+3.3-1.2-2.1"
30,00014.95660220132+3.5-1.2-3.2"
31,00016.55530221130+3.6-1.2-3.6"
32,00018.65410221.5128+3.8-1.3-4.0"
33,00021.65290222.5126+3.9-1.3-4.2"
34,00026170224.5124.5+4.0-1.3-4.4""
* Full throttle height
Service ceiling 34,600 ft.
Estimated absolute ceiling 35,500

TABLE II
Performance on climb (normal rating)
Take-off weight 6,995 lb.Radiator flap open
 
Height
(ft)
Time
from
start
mins.
Rate of
climb
ft/min.
T.A.S.
m.p.h.
ASI
mph
P.E.C.C.E.CBoost
lb/sq.in.
R.P.M.
00       
2000.63370186.51810-0.1+122850
40001.234601921810-0.2+12"
6,2501.853560198180.50-0.3+12"
8,0002.353250199.5177+0.2-0.4+10.3"
10,0003.02920201.5173+0.5-0.5+8.5"
12,0003.72590203.5169+0.8-0.6+6.8"
14,0004.552290206165.5+1.0-0.7+5.3"
16,0005.452000208.5162+1.3-0.8+3.8"
18,0006.551740210157.5+1.7-0.9+2.5"
20,0007.751500211153+2.0-1.0+1.2"
22,0009.21270212148.5+2.3-1.10"
24,00010.91070213143.5+2.7-1.1-1.2"
26,00013.0870214.5139+3.0-1.1-2.3"
28,00015.65670217135.5+3.3-1.2-3.3"
30,00019.25470220132+3.5-1.2-4.3"
31,00021.65370221130+3.6-1.2-4.7"
32,00024.8270221.5128+3.8-1.3-5.2"
33,00029.35170222.5126+3.9-1.3-5.6"
* Full throttle height
Service ceiling 33,700 ft.
Estimated absolute ceiling 34,800

TABLE III
Level speed performance
Take-off weight 6995 lb.
Results corrected to 95% of take-off weight i.e. 6645 lb.
Radiator flap in minimum drag position
Height
feet
(ft)
T.A.S.
m.p.h.
A.S.I.
m.p.h
P.E.C.C.E.C. StrutBoost
lb/sq.in.
RPM
0315325-10.200+183000
2,000324.5325.5-10.2-0.6+0.4+18"
5,100339.5326-10.2-1.6+0.4+18"
8,000338.5311-9.2-2.2+0.5+14.3"
12,000336.5290-7.6-2.9+0.5+10.2"
16,000*334270-6.3-3.5+0.4+6.6"
20,000328.5248-4.8-3.7+0.4+3.5"
24,000320.5225-3.1-3.5+0.4+0.6"
27,000312206.5-1.8-3.3+0.3-1.1"
* Full throttle height

Fig 1. Climb Performance    Fig 2. Level Speed Performance

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