1.     Introduction.
 
        Measurements of climb and level speed performance and position error have been made on Corsair F.Mk.II JT.259 at a take-off weight of 11,865 lb. representing the Service load for short range fighter duties, and form the subject of this Part of the Report.
 
2.     Condition of aircraft relevant to tests.
 
        2.1   General.   The aircraft was a standard Corsair F.Mk.II with the following principal features:-

Double Wasp R.2800-8 engine.
Hamilton hydromatic 3-blade 134 diameter propeller, type 23ESO-495.
Air intakes for engine, oil-cooler, and intercooler in leading edge of wings.
3 stub exhausts on each side of engine forward of wing.
Anti-CO contamination scoops on fuselage sides and extractor underneath.
"Clipped" wing tips.
3 x 0.5 in. guns in each wing with leading edge ports and ejection chutes sealed.
Wireless mast forward of cockpit with aerial to fin.
I.F.F. aerials between fuselage and tailplane.
Retractable tail wheel with arrestor hook.
Kollsman 5816-2 pitot-static head on leading edge of port wing.

        Details of the pitot-static installation are given in Fig.1.
 
        2.2.   Loading.   The aircraft was flown throughout the tests at a take-off weight of 11,865 lb. with the centre of gravity position 100.1 ins. aft of the horizontal reference line (undercarriage down).
 
        This represents the typical load for short range fighter duties.
 
        2.3.   Engine numbers and limitations.   The aircraft was fitted with a Double Wasp R.2800-8 engine Nos. 8544/52239B, and the following operating limitations were applicable throughout the tests:-

 RPMManifold pressure
Maximum for climb255044 ins.Hg.
Maximum for combat270052 ins.Hg.

3.     Tests made.
 
        (1)     The position error was measured by the aneroid method with flaps and undercarriage up over the speed range 120 mph to 320 mph ASI.
 
        (2)     Partial climbs to determine the optimum climbing speed were made at 5000 ft. and 14,500 ft. using normal climbing power, and at 5000 ft., 14, 500 ft., 20,500 ft. and 30,500 ft. using power.
 
        (3)     Using the optimum climbing speed determined in test (2) climbs were made at normal climbing power to 33,000 ft. with the engine cowling gills 2/3rds open, the intercooler shutter open, and oil cooler shutter fully open. Similarly, climbs were made using combat power in Main supercharger to 12,000 ft., in Auxiliary Low supercharger gear from 10,000 ft. to 23,000 ft., and in Auxiliary High supercharger gear from 16,000 ft. to 32,000 ft.
 
        (4)     Maximum level speeds were measured at heights up to 33,000 ft. with the engine cowling gills, intercooler shutter, and oil cooler shutter closed.
 
        (5)     In view of the high propeller tip speeds obtaining during the level speed measurements further level speed tests were made in Auxiliary High supercharger gear at 17,000 ft. and 30,000 ft. reducing engine rpm in stages of 100 while using maximum permissible or obtainable manifold pressure. These tests were for convenience made on another aircraft. JT.257.
 
4.    Results of tests.
 
        The results of the climb and level speed performance tests have been corrected to standard atmospheric conditions by the methods of Report No. A.& A.E.E./Res/170, using a supercharger constant of 0.002, and the results of the level speed tests have also been corrected to 95% of the take-off weight, viz. 11,270 lb. by the method of the same Report. The compressibility correction used has been calculated by the methods of the Addendum to Report No. A.& A.E.E/Res/147.
 
        The position error correction is given in Fig.2 and the correction to be applied to the altimeter when connected to the static of the airspeed system is given in Fig.3. The results of the climb performance under normal climbing power are given in Table I and Fig.4, and the results of the climbs made at combat power are given in Table II and Fig.4. The results of the level speed tests are given in Table III and Fig.5, and the results of the speed measurements at reduced rpm are given in Table IV and Fig.6.
 
        4.1.   Summary of results.
 
                  (i)   Position error correction:- The position error correction varied linearly from +2.6 mph at 120 mph ASI to +10.1 mph at 320 ASI.
 
                 (ii)   Partial climbs:- The best climbing speed using either normal climbing power or combat power was found to be 140 mph ASI up to 21,000 ft. decreasing by 2 mph per 1,000 ft. thereafter.
 
                (iii)   Climb performance:-
 
                        (a)   At normal rating:- Table I gives the climb performance as it would be on a normal climb, changing the supercharger gear at the optimum manifold pressures, but in Fig.4 the performance is more fully illustrated to indicate the vagaries on the performance, particularly in Auxiliary High supercharger gear.

Max. rate of climb at  2,000 ft. = 2060 ft/min.
    "      "    "     "     "   4,600 ft. = 2050     "     F.T. ht. in Main gear.
    "      "    "     "     " 10,000 ft. = 1700     "    
    "      "    "     "     " 19,600 ft. = 1600     "         "        "  Aux. Low gear
    "      "    "     "     " 24,600 ft. = 1200     "         "        "  Aux. High gear
    "      "    "     "     " 30,000 ft. =   625     "    
Service ceiling (100 ft/min) 34,900 ft.
Estimated absolute ceiling. 35,800 ft.

        For the optimum climb performance the supercharger gear should be changed thus:-

Main to Aux. Low gear when the manifold pressure had fallen to 39 ins. Hg.
Aux. low to Aux. High gear 42 ins. Hg.

                        (b)   At combat power:- The climb performance as it would be on a continuous climb at combat power is given in Table II, though in practice combat power is only permitted for 5 mins. Fuller details of the combat power climb performance are shown in Fig.4.

Max. rate of climb at  2,000 ft. = 2470 ft/min.
    "      "    "     "     "   5,000 ft. = 2140
    "      "    "     "     " 15,300 ft. = 2140     "     F.T. ht. in Aux. Low gear.
    "      "    "     "     " 20,600 ft. = 1640     "         "        "  Aux. High gear.
    "      "    "     "     " 32,000 ft. =   250     "    
Service ceiling (100) ft/min.) 33,200 ft.
Estimated absolute ceiling. 34,000 ft.

(iv)   Maximum level speed performance:-
 
Max. level speed at   3,400 ft. = 334 mph TAS. F.T. ht. in Main gear
    "      "         "     "  12,000 ft. = 350    "      "     F.T. ht. Aux. Low gear
    "      "         "     "  17,800 ft. = 373    "      "     F.T. ht. Aux. Low gear
 
    "      "         "     "  22,600 ft. = 382    "      "     F.T. ht. Aux. High gear
    "      "         "     "  32,000 ft. = 351    "      "     F.T. ht. Aux. High gear

        For the optimum maximum level speed performance the supercharger gear should be used as below:-
 
        Use Aux. Low gear if the manifold pressure in Main gear is less than 44 ins. Hg.
        Use Aux High gear if the manifold pressure in Aux. Low gear is less than 47 ins. Hg.
 
        4.2.   Correction of results to nominal manifold pressure:- It will be seen that owing to inaccurate functioning of the boost control the full value of controlled manifold pressure was not realized when using the auxiliary gears during both the climb performance tests at combat power and during the level speed performance tests. If corrected to the nominal value of manifold pressure the results would be:-
 
        (a) Climb performance at combat power:-
 
        Max. rate of climb at F.T. ht. in Aux. Low gear = 2230 ft/min at 14,600 ft.
        Max. rate of climb at F.T. ht. in Aux. High gear = 1750 ft/min. at 19,800 ft.
 
        (b) Level speed performance:-
 
        Max. level speed performance at F.T. Ht. in Aux low gear = 373 mph TAS at 17,700 ft.
        Max. level speed performance at F.T. Ht. in Aux High gear = 382 mph TAS at 22,500 ft.
 
        4.3.   Propeller tip Mach number. In level flight at 22,500 ft. (Full throttle height in Aux. High gear) the propeller tip Mach number reached a value of 1.07 and at 33,000 ft. the value was 1.165. No corrections for any consequent effects of the propeller efficiency have been made in correcting the results to standard temperature conditions. The range of air temperature difference from standard above 20,000 ft. during the tests was from +5°C to -7°C.
 
        In consequence of these high tip speed level speeds were measured at 17,000 ft. and 30,000 ft. in Auxiliary High supercharger gear to investigate the effect of operating at reduced engine rpm. The results of this investigation are given in Table IV and Fig.6. These tests were done on another aircraft JT.257, which accounts for the speed at 2700 rpm differing from that given in Fig.5.
 
5.    Discussion of results.
 
        In Fig.4 it will be seen that above 23,000 ft. the rate of climb at combat power is less than the rate of climb at normal power, and that if combat power is employed above this height the Service ceiling is reduced by about 2,000 ft.
 
        From Fig.6 it will be seen that at 17,000 ft. and increase of about 4 mph TAS in level speed can be obtained by reducing the engine speed from 2700 rpm to 2500 rpm, and that a similar effect is produced at 30,000 ft.
 
        From Fig.4 it should also be noted that in Auxiliary High supercharger gear the manifold pressure at full throttle is approximately 1 in.Hg. less at 2700 rpm than at 2550 rpm.
 
        The precise explanation of these unusual effects is not known, but it seems that at high engine speeds at altitude there is a reduction in both propeller and supercharger efficiencies.
 
        The measurement of climb and speed performance on this aircraft was found to be difficult owing to the experimental points being considerably more scattered than is usual. This may be due in part to the reduction methods being less dependable for aircraft with this unusual supercharger arrangement, allied to the fact that the propeller and supercharger efficiencies fell off at high engine speeds at altitudes, but it is also probably due to the fact that the auxiliary and main superchargers are linked by ducting containing many potential sources for air leaks and consequent errors. In these tests every effort was made to reduce errors due to the latter cause to a minimum.

TABLE I
Climb performance at normal rating

Engine cooling gills 2/3rds open, intercooler shutter ½ open,
oil cooler shutter fully open

Standard
height
ft
Rate of climb
(ft/min.)
Time to height
(mins)
ASI
mph
Manifold
Pressure
(ins. Hg.)
RPMS/C
gear
02065  0.0014044   2550Main
  20002060  0.95
     4600 *2050  2.25
  60001920  2.9542.2
  80001720  4.0539.5
1000017005.244   Aux.
low
1200016806.4
1400016607.6
1600016408.8
18000161510.05
   19600 *160011.05
20700146511.7542.1
22000139512.6513844   Aux.
high
   24600 *120014.6513244   
26000105015.9  13041.5
28000  84018.0512638.4
30000  62520.7512235.7
32000  41024.6511832.9
33000  31027.4  11631.6
        * Full Throttle height.
 
        Service ceiling (100 ft/min.) 34,900 ft.
        Estimated absolute ceiling     35,800 ft.
 
        For optimum climb performance the supercharger gear should be changed as follows:-
 
        Max. to Aux. low when the manifold pressure has fallen to 39½ ins. Hg.
        Aux. low to Aux. high when the manifold pressure has fallen to 42 ins. Hg.

TABLE II
Climb performance at combat power

Engine cooling gills 2/3rds open, intercooler shutter ½ open,
oil cooler shutter fully open

Standard
height
ft
Rate of climb
(ft/min.)
Time to height
(mins)
ASI
mph
Manifold
Pressure
(ins. Hg.)
RPMS/C
gear
02600014052.52700Main
       800 *26000.352.5
  200024700.850.3
  40002250  1.6546.8
  500021402.145.1
  800021403.550.2Aux.
low
100004.4
12000  5.35
   15300 *6.9
1850016758.645.4
   20600 *1640  9.8550.4Aux.
high
22000146510.8513847.6
24000122012.2513444.0
26000  97514.1   13040.5
28000  72516.4512637.4
30000  49019.7512234.7
32000  25025.3   11832.0
        * Full Throttle height.
 
        Service ceiling (100 ft/min.) 33,200 ft.
        Estimated absolute ceiling     34,000 ft.
 
        For optimum climb performance the supercharger gear should be changed as follows:-
 
        Max. to Aux. low when the manifold pressure has fallen to 45 ins. Hg.
        Aux. low to Aux. high when the manifold pressure has fallen to 45½ ins. Hg.

TABLE III
Maximum level speed performance

Engine cooling gills, intercooler shutter, and oil cooler shutter closed
corrected to 95% of take-off weight, viz 11,270 lb.

Standard
height
ft
TAS
mph
ASI
mph
Corrections
mph
Manifold
pressure
(ins. Hg)
RPMS/C
gear
PECE
     3400 *334309+9.7-1.352.52700Main
  6000334298+9.3-1.747.1
  8000334290+8.9-2.244   
10000333280+8.6-2.440.8
12000332271+8.3-2.738.1
14000330261+7.9-2.735.6
10000342288+8.9-2.752.4Aux.
low
12000350286+8.8-3.2
14000358284+8.7-3.7
16000366281+8.6-4.2
   17800 *373278+8.5-4.7
20000370267+8.1-4.848.1
22000367256+7.7-4.744.8
24000362244+7.2-4.441.7
26000356232+6.8-4.238.8
20000367264+8.0-4.352.2Aux.
high
   22600 *382264+8.0-5.452.2
24000381257+7.7-5.349.4
26000377246+7.3-5.245.7
28000371234+6.8-4.942.3
30000363220+6.4-4.439.2
32000351205+5.7-4.036.3
33000343196+5.4-3.635   
*Full throttle height

TABLE IV
Effect on level speed of reducing RPM

Engine cooling gills, intercooler shutter,
and oil cooler shutter closed.
Corrected to 95% of take-off weight, viz 11,270 lb.
Auxiliary high supercharger gear

Height
ft
RPMManifold
pressure
(ins.Hg)
ASI
mph
TAS
mph
17000270052    275365   
260052    278368   
250051.4279369   
240050.2279 369   
230048.8276365½
30000270038.3224368   
260037.7225370½
250036.8227372½
240035.8226371½
230034.6223367½
220033    218359   

Climb Performance
Maximum Level Speed Performance

WWII Aircraft Performance