I      Introduction

       Flight tests have been conducted at Wright Field on the P-51B-15 airplane, AAF No. 43-24777, using 44-1 fuel, at the request of the Power Plant Laboratory, Engineering Division. These tests were made to determine the performance of the airplane at the higher powers allowable with 44-1 fuel as compared with the performance at powers allowable for standard aviation fuel. From 24 March to 24 April 1944 approximately 25 hours were flown on the airplane by Major G. E. Lundquist.

II     Summary

       The P-51B-15 airplane, AAF No. 43-24777 is a low wing fighter equipped with a Packard V-1650-7 engine. Equipped with an additional fuselage tank and wing racks to which may be attached fuel tanks the airplane has long range for a fighter.

       The airplane is very maneuverable with excellent controllability at all speeds up to slightly over 400 MPH indicated, the highest speeds attained in level flight. Stability is good about all axes, and recovery from stalls is normal. The airplane has a fairly short radius of turn and an excellent rate of roll. Visability is poor in taxing and only fair in level flight. The cockpit layout in general is good.

       All tests were made at a gross weight at takeoff of 9335 lbs. which included full oil and 265 gallon of fuel. Level flight and climb performance were completed with wing racks. In addition level flight speeds were obtained at the critical heights without wing racks.

       In level flight the high blower critical altitude for 75 in. Hg. manifold pressure and 3000 RPM was 20,800 ft. At this altitude the airplane attained a maximum true speed of 444.0 MPH at 75 in. HG. manifold pressure without wing racks, a high speed of 431 MPH at 75 in. Hg. manifold pressure with wing racks, and a high speed of 417 MPH at 67 in. Hg. manifold pressure with wing racks. At 24,000 ft., high blower critical altitude for 67 In. Hg. manifold pressure and 3000 RPM, a maximum true speed of 426 MPH was attained.

       In climb the low blower critical altitude for 75 in. HG. manifold presure and 3000 RPM was 2,200 ft. At this altitude the airplane attained a maximum rate of climb of 4380 ft/min. at 75 in. Hg. manifold pressure and 3,820 ft/min. at 67 in. Hg. manifold pressure. The service ceiling of the airplane was 40,500 ft. and the absolute ceiling was 41,200 ft.

III    Condition of Aircraft Relative to Tests

       A.   All tests were flown at a gross weight at take-off of 9335 lbs. with the c.g. at 31.07% gear down. This weight included 265 gals. of gasoline (85 gals. in fuselage tank), full oil, and 200 lbs. for the pilot. The weight as flown was 125 lbs. heavier than the combat weight with 1260 rounds of .50 caliber ammunition (378 lbs.) and the fuselage tank empty.

       B.   The airplane was flown throughout the tests at normal configuration with wing racks, gear and wing flaps up, mixture auto rich, and oil and coolant shutters automatic unless otherwise specified. It was equipped with four .50 caliber guns, two in each wing, with the gun ports covered with fabric patches. The aluminum skin of the airplane was unpainted.

       C.   The airplane was equipped with a Packard V-1650-7 engine and a 11 ft ft. 2 in. diameter Hamilton Standard hydromatic four blade propeller, blade dwg. No. K-6523A-24 Serial No. 403196. Horsepowers reported obtained from Packard Motor Car Co. altitude performance chart for V-1650-7 engine dated 12-3-43.

IV    Flight Characteristics

       A.   Taxiing and Ground Handling

              The airplane had good handling characteristics but visibility over the nose is poor, necessitating wide weaving while taxiing.

              A tail wheel lock incorporated on the stick makes directional control very good as it allows turning the tail wheel through a twelve degree arc by use of the rudder pedal.

              Brakes are satisfactory and are readily applied for all positions of the rudder, however, they become weak if used extensively.

       B.   Take-off and Initial Climb

              The airplane has a short ground roll with no tendency to swing to either side. The initial angle of climb is steep and there is adequate rudder trim available to correct for torque during take-off and climb.

       C.   Stability

              The airplane is statically stable and dynamically unstable longitudinally throughout the entire speed range. The degree of dynamic instability becomes slightly less with the fuselage fuel tank empty. Lateral stability is neutral, and the airplane is both statically and dynamically stable directionally. The airplane has a slight tendency to hunt longitudinally, and this condition becomes more exaggerated in rough air.

       D.   Trim and Balance

              Trim tabs are provided for all control surfaces and the airplane is readily trimmed for all normal conditions. The changes in longitudinal trim resulting from the operation of landing gear, wing flaps, and oil and coolant shutters are slight and can be easily corrected by use of the elevator trim control.

       E.   Controllability

              The airplane has excellent control characteristics. The controls are well coordinated and are highly effective at all speeds with moderate control force.

       F.   Maneuverability

              The airplane is very maneuverable and response to the controls in aerobatics is excellent. It has a fairly short radius of turn, and there is no tendency to tighten up in steep turns. However, if the turn is pulled in too violently, the airplane will stall abrubtly with little warning. Abrupt use of the controls at slow speeds will cause the airplane to stall predeeded by sharp elevator buffeting, but there is no tendency to spin. It has an exceptionally fast rate of roll with excellent lateral control at all speeds.

       G.   Stalling Characteristics

              The stall is gentle with the airplane rolling slowly to the right; there is no tendency to spin. In the power off stall, some warning is given about 3 to 4 MPH above the stalling speed by slight elevator buffeting. The controls remain effective throughout the stall, and recovery is immediate upon release of back pressure on the stick and application of rudder and aileron opposite the dropping wing. Considerable right rudder and aileron is required for power on stalls. See paragraph V E for stalling speeds at various configurations.

       H.   Spinning Characteristics

              See Memo Report No. Eng-47-1737-A, dated 30 April 1944, for tests made on P-51B, AAF No. 42-12136.

       I.   Diving Characteristics

              At indicated airspeeds slightly over 500 MPH the controls are still highly effective with only moderate force. The stick force per "g" acceleration is normal for recovery at this speed. In trimmed dives there is no tendency for the airplane to recover automatically once the recovery has begun. At indicated airspeeds over 450 MPH a rumble is heard emanating from the coolant scoop.

       J.   Single Engine Operation

              Not applicable

       K.   High Altitude Trials

              Handling characteristics and stability of the airplane are satisfactory up to 40,000 ft., and the controls are still very effective. The aileron trim tab freezes at altitudes over 30,000 ft., however, this is not too objectional.

       L.   Approaches and Landing

              Approach and landing characteristics are normal for an airplane with conventional gear. The airplane has a steep glide angle and vision during the approach is good. A three point landing is easily made and there is no tendency to ground loop.

       M.   Night Flying

              The airplane is satisfactory for night operation with the exception of poor vision in the tail low attitude during take-off and landing.

              The illumination of cock pit equipment is satisfactory except for the illumination of fuel gages and lighting facilities for map reading.

              Direct or reflected glare from the instrument board, windshield, enclosure, or propeller arc is not objectionable at any time.

       N.   Noise and Vibration

              The noise and vibration level in the cockpit is low and not objectionable at any time.

       O.   Vision and Cockpit Layout

              Visibility for taxiing is poor and is only fair for level flight. The metal framework around the canopy is too wide and obstructs vision to the side greatly. Vision to the rear is poor, and the rear view mirror is of little use.

              Cockpit layout is very good. Instrument arrangement is satisfactory and all controls are well located and within easy reach of the pilot.

V    Performance Data

       A.   Airspeed and altimeter calibration (see Fig. 1 and 2.)

       B.   High Speed

               1.   Curves of speed vs. altitude are given in Fig. 3 and curves of power vs. altitude are given in Fig. 4.

               2.   High speed in level flight at 3000 RPM, mixture auto rich, and oil and coolant shutters in automatic.

              The high speeds reported are from a faired curve which was the average speed obtained from all the level flight tests.

              The wide scatter of points in high blower is due to inconsistent powers obtained for the same mixture control setting, caused by malfunctioning of the carburetor.

              Throughout the level flight tests the oil shutter position to maintain 80°C on a standard day did not exceed 1.5 in. open from the full closed postion. The coolant shutter position to maintain 110°C on a standard day did not exceed 7.4 in. open from the full closed position.

              Data was corrected to a weight at altitude for a normal power climb given by the curve in Fig. 4.

       C.   Cruise Data

              Cruise data at 22,400 ft. corrected to a weight of 9240 lbs. corresponding to a weight at take-off of 9335 lbs.

       D.   Climb Data

              Climb data at 3000 RPM and 75 in. Hg., 67 in., and 61 in. Hg. manifold pressure is given in Fig. 6 and 7.

       E.   Stalling Speeds

              Stalls were made at 8000 ft. at the following configurations.

VI   Curves

       The data given in the following curves have been reduced to NACA standard conditions.

       Fig. 1    Airspeed Calibration
       Fig. 2    Altimeter Calibration
       Fig. 3    Speed vs. Altitude
       Fig. 4    Power vs. altitude in level flight
       Fig. 5    Power required for level flight at 22,400 ft.
       Fig. 6    Rate of climb vs. altitude
       Fig. 7    Power vs. altitude for Climb
       Fig. 8    Speed vs. altitude (P-51B-5, AAF No. 43-6883 with Packard 1650-3 engine vs. P-51B-15, AAF No. 43-34777 with Packard 1650-7 engine)

VII   Conclusions

       A.   Operation of the airplane at 75 in. Hg. manifold pressure in low blower increased speed in level flight 16 MPH over the high speed at 67 in. Hg. manifold pressure at altitudes from sea level to 7400 ft. A 14 MPH increase was obtained at altitudes from 16,000 ft. to 20,800 ft. in high blower.

       B.   The rate of climb was increased 560 ft/min. from sea level to 2,200 ft. by 75 in. Hg. manifold pressure operation. At 15,700 ft. in high blower the rate of climb was increased 580 ft/min.

       C.   From sea level to 10,000 ft. in low blower the 1650-7 engine gave increases in speed from 2 to 11 MPH over the 1650-3 engine. From 16,600 ft. to 24,000 ft. in low blower the 1650-3 engine was approximately 20 MPH faster than the 1650-7 engine. In high blower from 18,000 to 24,200 ft. the 1650-7 gave an increase in speed of approximately 10 MPH but at 29,200 ft. the 1650-3 engine was 6 mph faster. This increase of the 1650-3 engine over the 1650-7 engine should continue at altitudes above 29,200 ft. as is shown in Fig. 8 by the dash line. Due to malfunctioning of the carburetor, however, speeds of the 1650-3 fell off above this altitude and were as much as 12 miles slower than those obtained with the 1650-7 engine.

VIII  Recommendations

       A.   It is recommended that the war emergency rating of the V-1650-7 engine as installed on the P-51B airplane and using 44-1 fuel be increased to 75 in. Hg. manifild pressure and 3000 RPM.

IX    General Dimensions and Photographs

        A.   P-51B-15 Dimensions: