Flight Test Engineering Branch
Memo Report No. Eng-47-1734-A
24 April 1944

P-51B-5-NA AIRPLANE, AAF NO. 43-6883

I       Introduction

        Flight tests have been conducted at Wright Field on the P-51B-5-NA airplane, AAF No. 43-6883, at the request of the Fighter Branch, Experimental Engineering Division. These tests were made on the airplane primarily to obtain comparitive performance data with similar tests on a P-47D-10, a P-38J, and a P-39Q-5 airplane. The performance should be that of a typical production model as it was selected at random from airplanes which had been delivered from the factory. From 20 December 1943 to 26 March 1944 approximately 65 hours were flown on the airplane by Captain W. A. Lien and Lt H. A. Johnson. Over fifty per cent of this time was spent in obtaining flight tests investigating the faulty carburation encountered during the performance flights.

II      Summary

        The P-51B is a single engine, low wing, long range fighter. Its long range makes it ideal for escort purposes, and its performance as a fighter aircraft is better or at least equal to that of any enemy fighter that might be encountered. The rate of climb is good and the high speed in level flight is exceptionally good at all altitudes, from sea level to 40,000 feet.

        The airplane is very maneuverable with good controllability at indicated speeds to 400 MPH. The stability about all axes is good and the rate of roll is excellent, however, the radius of turn is fairly large for a fighter. The cockpit layout is excellent, but visibility is poor on the ground and only fair in level flight.

        High speed and climb performances have been completed on this airplane at a take-off weight of 9205 lbs. This loading corresponds to the average P-51B combat weight with full oil, 180 gallons of fuel and specified armament and ammunition.

        The principal results are as follows:

        Maximum speed at critical altitudes. (67" Hg. man. pressure & 3000 RPM)

Low Blower at 16,600 feet430.0 MPH
High Blower at 29,400 feet442.0 MPH

        Maximum speed at sea level (67" Hg. manifold pressure & 3000 RPM)

 371.0 MPH

        Rate of climb at critical altitudes. (67" Hg. man. pressure & 3000 RPM)

Low Blower at 13,800 feet3450 ft/min.
High Blower at 25,500 feet2660 ft/min.

        Time to climb to high blower critical altitude, 25,500 feet.

(67" Hg. pressure and 3000 RPM)8.28 min.
Service ceiling42,000 ft.

III    Condition of Aircraft Relative to Tests

        A.   The configuration of the airplane was normal with all flights at a gross weight of 9205 lbs. with the c.g. at 27.0% MAC, gear down, and 27.3% MAC, gear up. Gross weight included 180 gallons of fuel, 15 gallons of oil, 378 lbs of ballast for ammunition, specified armament, an auto matic observer, complete radio equipment with antenna and 200 lbs. for the pilot. All items affecting the drag of the airplane may be seen in the photographs which are included at the end of the report.

        B.   The airplane was equipped with a Packard V-1650-3 engine with a Bendix PD18-A1 carburetor, and a 11' - 2" dia. hydromatic constant speed Hamilton Standard four blade propeller, blade dwg. No. J-6523A-24. All power figures are based on power curves from Eng. Spec. No. AC-1035b dated 27 September, 1943.

        C.   All flights were made with wing flaps neutral, gear up, oil and coolant shutters automatic, mixture auto rich, canopy closed, and automatic boost control blocked off unless otherwise stated.

        D.   The armament consisted of four .50 caliber machine guns in the wings with ballast corresponding to 350 rounds of ammunition for each inboard gun and 280 rounds of ammunition for each outboard gun. No wing bomb racks were installed on this airplane.

IV    Flight Characteristics

        A.   Taxiing and Ground Handling

               The airplane has good handling characteristics, and directional control is easily maintained.

               The tailwheel, when in a locked position, is steerable through a twelve degree arc which is a desirable feature, and is conveniently unlocked by pushing the stick forward.

               The brakes are satisfactory and may be applied for all rudder pedal positions, however, they become weak if used extensively.

               Visibility forward is obstructed completely by the nose when the airplane is in the three point position and wide S-ing is required when taxiing.

        B.   Take-off

               The airplane has normal take-off characteristics. With rapid application of the throttle the airplane tends to swing slightly to the left, however, sufficient rudder trim is available to compensate for torque at take-off and during climb. The ground roll is short and initial angle of climb steep.

        C.   Stability

               Throughout the entire speed range the airplane is statically stable, but dynamically unstable longitudinally. 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 is exaggerated by rough air.

        D.   Trim and Balance

               The airplane has trim tabs on all of the control surfaces and may be trimmed satisfactorily for all flight conditions. Any variation in airspeed and power requires a slight change in trim. Nose heaviness results when the landing gear is extended, when the oil and coolant shutters are opened, and when the wing flaps are lowered, however, this change in balance is easily corrected by the use of elevator trim control.

        E.   Controllability

               The airplane has very good control charateristics and coordination is very easy throughout the entire speed range. At both high and slow speeds the contros are very effective with moderate control forces. Control throughout the stall is good with the rudder being very effective.

        F.   Maneuverability

               The airplane is very maneuverable with excellent control for acrobatrics. In gentle and steep turns controls are light and very effective. The airplane will stall and tend to snap roll if the turn is pulled in too hard or violently. When pulled in moderately it gives warning of the approaching stall by a slight buffeting of the airplane and vibration of the controls. At slow speeds the airplane will give stall warnings with abrupt use of the controls, however, there is no tendency to spin. The rate of roll of this airplane is especially good with satisfactory control.

        G.   Stalling Characteristics

               The stalling charcteristics of this airplane are good. With power off there is very little warning of the approaching stall and there is a tendency for the right wing to drop, however, the stall is not dangerous and recovery is easily and safely affected.

               Considerable right rudder and aileron is required for power on stalls and the left wing will tend to drop at the stall if the needle and ball are not centered.

        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 forces and the stick force per "g" acceleration is not excessive for pull out from dives. At extremely high speeds a rumble is heard which is caused by the coolant scoop.

        J.   Single Engine Operation

              Not applicable

        K.   High Altitude Trials

               For altitudes up to 41,000 feet there is no noticable change in stability. Handling charateristics are still satisfactory and controls very effective. Trim tab controls freeze above 30,000 feet and are immovable, however, this is not too objectional.

        L.   Approaches and Landing

               The approach is normal for a ship with conventional gear, and with gear and flaps down visibility is good. The airplane has a steep glide angle and fast sinking speed, but is very stable with all controls effective.

               The airplane has satisfactory landing characteristics and there is no tendency to swerve or ground-loop at any time.

        M.   Night Flying

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

               Illumination of cockpit equipment is satisfactory except for the illumination of the fuel gauges and lighting facilities for map reading.

               Landing light installation and operation are satisfactory

               Direct or reflected glare from the instrument board, windshield, inclosure, or propeller arc is not objectionable at anytime.

        N.   Noise and Vibration

               The noise level is not high or objectionable, and very little vibration is noticed at any time.

        O.   Vision and Cockpit Layout

               Visibility for taxiing is vey poor and is only fair for level flight. The horizontal braces on the canopy are too wide and obstruct the vision if the head is too high in the cockpit. The rear vision mirror is poor as too much glare and distortion from the canopy is present.

               The accessibility to the cockpit is satisfactory with the exception that an insufficient number of hand holds is provided.

               The cockpit layout and accomodations are very good, however, the low canopy design is unsatisfactory for tall pilots. All controls are conventional and there is no interference.

               The instruments are marked satisfactorily and easily read, the switches are in good positions, and sufficnet warning lights and emergency systems are installed and operated satisfactorily. The cockpit heating is sufficient, but the ventilation is inadequate for warm weather.

V    Shipboard Tests

        None performed

VI   Performance Data

        A.   Airspeed Indicator and Altimeter Calibration

               The location of the flush static airspeed system and the airspeed and altimeter position are given in Fig. 1 and Fig. 2.

        B.   High Speed

               1.   Curves of Speed vs. Altitude are given in Fig. 3 for a take-off gross weight of 9205 lbs.

               2.   High speed in level flight at 3000 RPM (war emergency power), mixture auto rich with oil and coolant shutters in automatic.

Gr. Wt.
Oil Sh.
Pos. in.
for 75°C
Cool. Sh.
Pos. in.
for 110°C
9150        0370.567.01596LowPart1.26.0
9045*16600 430.067.01618LowW.O0.84.0
8895**29400    442.567.01292HighW.O1.04.2
865040000377.538.1  790HighW.O2.55.0

  *Low blower critical altitude for 67" Hg. and 3000 RPM.
**High Blower Critical altitude for 67" Hg. and 3000 RPM.

        C.   Cruise Data (see Fig. 5)

              Cruising speed at 11,900 feet in low blower with mixture as specified and oil and coolant shutters in automatic. Data corrected to 9080 lbs., the weight at altitude corresponding to a take-off weight of 9205 lbs.

RPMMan. Pr.
Oil Sh.
Pos. in.
for 75°C
Cool. Sh.
Pos. in.
for 110°C
240042.5AR45.5  937349.00.32.2
225037.0AL38.5  763624.00.21.8
195035.0AL26.5  650302.00.11.2
170032.5AL16.5  541273.00.10.9
160025.0AL  8.5  350204.00.10.5

              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 speed points, especially in high blower, is due to inconsistent powers for the same mixture control setting which is caused by malfuntioning of the carburetor.

              The original linkage from the carburetor to the mixutre control on the throttle quadrant was not satisfactory as the carburetor was frequently operating at "full rich" when the mixture control was set at "auto rich". A loss in indicated airspeed of as much as 16 MPH was obtained with this condition. With a different linkage arrangement repetition of this was prevented, however, variation of the fuel-air ratio with the mixture control in auto-rich was still indicated by the erratic speed vs. power data and the corresponding mixture temperatures. This may possibly be due to poor carburetion resulting from high air flows as this condition reached a maximum at critical altitude in high blower.

              The engine data obtained during the speed runs at all altitudes indicated that the actual fuel-air ratio was alway greater than the specified fuel-air ratio for the PD18-A1 carburetor in auto rich, however, the method used in determining the fuel air ratios was not too accurate. Tests are now in progress attempting to determine the cause of this rich mixture and the results will be reported by the Power Plant Laboratory.

        D.   Climb Data (See Fig. 4)

              Climb performance is given below at a gross weight at take-off of 9205 lbs., at war emergency power (67" Hg. and 3000 RPM), mixture auto-rich with oil and coolant shutters in automatic.

BlowerRate of
Oil Sh.
Pos. in.
for 75°C
Cool. Sh.
Pos. in.
for 110°C
  500067.01607Low3282  1.542.08.5
3500046.3  914High130013.303.28.2
4000036.3  725High  50018.973.99.9
* S/C--High  10025.224.511.6  
** A/C  --High      0---

  * S/C Service Ceiling, 42,000 feet.
** Absolute ceiling, 42,600 feet.

        E.   Cooling Shutter Tests

              When in automatic the oil and coolant shutter positions were regulated by thermostats which were set to maintain an oil temperature of 70°C to 80°C and a coolant temperature of 110°C. The average temperatures maintained for all flight conditions was approximately 75°C oil temperature and 110°C coolant temperature, therefore all performance was corrected to shutter positions that would maintain these temperatures on a standard day.

              No standard Air Corps cooling tests were made, however, from all indications the airplane will meet the requirements (125°C coolant temperature and 95°C oil temperature) on a standard day in both level flight and climb at war emergency power.

              On an army hot day the airplane will cool satisfactorily in level flight, however, in climb at war emergency the oil temperature will exceed 95°C at approximately 38000 feet with the shutter wide open. The coolant temperature would be critical throughout the climb and in a range of 120°C to 135°C with the maximum temperatures at sea level and service ceiling.

              The effect of the oil shutter position on indicated airspeed and oil temperature is shown in Fig. 6.

              On this graph, the curve of temperature vs. shutter positions was actually obtained is not a true representation, as at approximately 70°C a valve bypasses the oil around the oil cooler. The dotted line is an estimated curve for a system without a by-pass value.

              The effect of the coolant shutter position on indicated airspeed and coolant temerapture is shown in Fig. 7.

              The effect of the collant shutter position on the rate of climb and coolant temerpature is shown in Fig. 8.

        F.   Stalling Speeds

              Stalling speeds of the airplane, which weighed 9205 lbs. at take-off with the c.g. at approximately 27% MAC, are tabulated below:

Inst. Error Rem.
Inst. Error Rem.
46.5" Hg. & 2700 RPM
UpUpCLosedCLosed94.0 9100
UpUpOpenOpen94.0 9095
DownUpCLosedCLosed93.0 9090
UpDownCLosedCLosed85.0 9085
DownDownCLosedCLosed87.0 9080
UpUpAutoAuto 81.09075
DownUpAutoAuto 80.09065
UpDownAutoAuto 75.09055
DownDownAutoAuto 78.09045

VII   Curves

        All data given in the following curves have been reduced to NACA Standard Atmospheric Conditions.

        Level Fight Data
        Climb Data
        Power Required

VIII   Conclusions

        The performance of the P-51B is very good regardless of the malfunctioning of the carburetor and corresponding loss in high speed and rate of climb, however, this condition should be investigated, and measures should be taken to correct this malfuntioning in P-51B airplanes in the service and to prevent its re-occurrance in later production models. This trouble has been encountered in all production P-51B airplanes at Wright Field and it is believed that considerable improvement in performance can be made in high blower.

        The design, cockpit arrangement, flying characteristics, cooling properties, long range and satisfactory fire power make the P-51B excellent for use as a fighter type aircraft.

IX    Recommendations

        It is urgently recommended that immediate measures be taken to eliminate the carburetor malfunctioning and that provisions are made to positively insure a mixture as selected on the quadrant.

        It is recommended that later production models of the P-51 series have provisions for more satisfactory visibility for both taxiing and flight condition. It is understood that the P-51D is now in production, which essentially is a P-51B with a bubble canopy.

X    General Dimensions and Photographs

        A.   P-51B-5-NA Dimensions:

Span37 ft. - 0 in. 
Length32 ft. - 3 in. 
Height13 ft. - 8 in. 
Tread11 ft. - 10 in. 
Wing Area233 sq. ft. 

        B.   Photographs

Front View
Side view

WWII Aircraft Performance   Mustang Performance Trials