Flight Test Engineering Branch
Memo Report No. Eng-47-1706-A
4 February 1944
OF A P-38J AIRPLANE
Flight tests have been conducted at Wright Field on the P-38J Airplane, AAF, No. 42-67869, at the request of the Fighter Branch, Experimental Engineering Division. These tests were made on this airplane primarily to obtain comparitive performance data with similar tests on a P-47D-10, a P-39Q-5 and a P-51B 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 2 December 1943 to 21 January 1944 approximately 30 hours were flown on this airplane by Capt. G. E. Lundquist, Capt F. C. Bretcher, and Capt J. W. Williams.
The P-38J is designed as a high altitude fighter interceptor. This airplane has a fast rate of climb and performs well at high altitude, however, caution must be used in acrobatics and diving maneuvers at all altitudes to keep below limiting airspeeds. These airspeed limitations are low due to tail buffeting which may eventually cause structural failure and are definitely objectionable and hazardous from a combat viewpoint. The stability about all axis is good, the radius of turn is fairly large for a fighter and the rate of roll is fair at medium speeds, but slow at high speeds because of heavy aileron forces. The single engine operation, visibility on the ground and in the air and cockpit layout is good.
High speed and climb performance have been completed on this airplane at a take-off weight of 16,597 lb. This loading corresponds to the average P-38 combat weight with full oil, 300 gallons of fuel and specified armament and ammunition.
The principal results are as follows:
Max speed at critical altitude, 25,800'
(60.0" Hg. Man. Pr. & 3000 rpm) = 421.5 mph
Max speed at sea level
(60.0" Hg. Man. Pr. & 3000 rpm) = 345.0 mph
Rate of climb at sea level
(60.0" Hg. Man. Pr. & 3000 rpm) = 4000'/min.
Rate of climb at critical altitude, 23,400 ft.
(60.0" Hg. Man. Pr. & 3000 rpm) = 2900'/min.
Time to climb to critical altitude, 23,400 ft.
(60.0" Hg. Man. Pr. & 3000 rpm) = 6.49 min.
Service Ceiling = 40,000'
III Condition of Aircraft Relative to Tests
A. The airplane was equipped with wing racks, otherwise the configuration was normal with all flights at a gross weight at take-off of 16,597 pounds with the c.g at 24.75 m.a.c., gear down; and 28.5% m.a.c. , gear up. Gross weight included 300 gallons of fuel, 26 gallons of oil, 457 lbs. of ballast for ammunition, 100 pounds of ballast in the nose to locate the center of gravity within the allowable range, and automatic observer, complet radio equipment and antenna, and 200 pounds for the pilot. All items effecting the drag of the airplane may be seen in the photgraphs which are included at the end of the report.
B. The airplane was equipped with Allison V-1710-89 & 91 engines, type B-33 turbo superchargers with A-13 turbo regulators and Curtiss Electric three blade propellers, blade design numbers 89303-18 and 88996-18, left and right respectively. All power figures are based on a power curve from Eng. Spec. No. 162, dated 30 November 1942.
C. The armament consisted of four 50 caliber machine guns and one 20 mm. cannon in the nose with 457.5 lb. of ballast corresponding to the weight of 1200 rounds of 50 caliber and 150 rounds of 20 mm. ammunition.
D. All flights were made with flaps neutral, gear up, air filter off, coolant and oil shutters automatic, and mixture automatic rich unless otherwise stated.
IV Flight Characteristics
A. Taxiing and Ground Handling
The airplane is easy to taxi and vision is excellent. Response to throttles in turning is good and brakes are readily applied for all positions of the rudder making directional control easy.
The take-off characteristics of the P-38J are normal for a tricycle gear airplane except for the absence of any noticable torque effect due to the opposite rotating propellers. The airplane takes off after a short ground run and has a steep initial angle of climb. Vision during take-off and climb is good.
The airplane has good longitudinal, directional and lateral stability at all normal speeds, however, there is a slight tendency to hunt directionally in rough air or when flown with external wing tanks. It must be noted, however, that all stability tests were run with full ammunition and an additional 100 lbs. of ballast in the nose to keep the c.g. ahead of 28.5% whcih was the maximum allowable rearward c.g. position at the time of the test. Recent tests on other P-38J's show that it is permissible to move the c.g. back to 32% of the m.a.c.
D. Trim and Balance
The airplane is readily trimmed for all normal flight conditions. Due to the opposite rotating propellers, rudder and aileron trim tab settings do not require adjustment with changes in speed and power. The airplane becomes very noticeably nose heavy when flaps and landing gear are extended, but this change in balance can be easily corrected by use of elevator trim tab.
Handling qualities of this airplane are generally good. Control forces are moderate and controls are responsive to a high degree at all normal speeds. However, at extremely high speeds beyond the P-38's dive speed limits, the airplane tends to become rapidly nose heavy and elevator effectiveness decreases, making it difficult to pull out.
The airplane is highly maneuverable considering the high wing loading. It has a fairly large radius of turn for a fighter but this is greatly improved by the use of maneuvering flaps. Response to controls in rolls, loops, immelmans is good and these maneuvers are easily executed.
G. Stalling Characteristics
In either power on or power off stalls with flaps and landing gear up the airplane stalls straight forward in a well controlled stall. With flaps and gear down there is a slight tendency for a wing to drop, but there is no tendency to spin. Ailerons remain effective giving adequate control throughout the stall. Warning of the approaching stall is given by a noticable buffeting and shaking of the airplane and controls. See Part IV F. for stalling speeds for different configurations.
H. Spinning Characteristics
No spin tests were performed.
I. Diving Characteristics
At extremely high speeds in dives the airplane rapidly becomes nose heavy and starts to buffet as if it were about to stall. If this condition is allowed to develop the nose heavy condition becomes more pronounced making the pull out difficult.
J. Single Engine Operation
The airplane has excellent single engine performance. The indicated speed for best climb on one engine is approximately 145 mph and the minimum indicated airspeed at which control can be maintained at rated power is 110 mph. Normal single engine procedure is used.
K. High Altitude Trials
The general operation of the airplane and all controls at high altitudes and low temperatures is satisfactory, however, tail buffeting is experienced even at maximum speeds in level flight at altitudes over 30000 feet. Although the buffeting causes an uneasy feeling, controls remain effective, and it is not dangerous if the dive speed limits are not exceeded.
L. Approach and Landing
The airplane has a normal glide angle and landing technique used is similar to that for airplanes with tailwheels. Vision is excellent on the approach and landing and the tricycle gear reduces the hazards from landing in a cross wind.
M. Night Flying
The cockpit lighting in general is good. Direct or reflected glare from the instrument board lights is not objectionable, however, considerable glare is caused by the cockpit lamps. A retractable landing light is mounted under the left wing and provides adequate lighting for landing, but causes considerable buffeting when fully extended.
N. Noise and Virbration Level Tests at Crew Stations
The noise level of the airplane is low and is not objectionable at any time.
O. Pilot's report on vision and cockpit layout
The vision from the cockpit is good except to the side and down where the engine nacelles interfere. All controls in the cockpit are easily accessible to the pilot and in general the cockpit layout is satisfactory.
V Ship Board Tests
No tests performed.
VI Performance Data (War Emergency Power, 60.0" Hg. Man. Press. & 3000 rpm and 16,597 lb.)
A. Airspeed indicator and altimeter calibration (See Fig. 1 &2)
Airspeed indiator error with Kollsman type D-2 ship's standard pitot head located 8' 1-1/2" inboard left wing tip, 14-5/16" below the wing with the static holes 25-3/4" aft of the leading edge of the wing.
Error - Feet
B. High Speed (see Fig. 3)
High speeds in level flight at 3000 rpm, oil shutters flush, coolant shutters automatic, and intercooler shutters closed.
Pos for 105°C
*Critical altitude for 26,400 limiting turbo speed and 60.0" Hg. manifold pressure.
C. Cruise Data
Cruising speed at 11,850 feet with mixture as specified, oil shutters flush, coolant shutters automatic, and intercooler closed. This cruise data was obtained on the original right engine and the new left engine and is not comparable to the other reported (see part VI. Sec. G) speed data.
|Coolant pos. for|
D. Climb Data (See Fig. 4)
Climb performance at 3000 rpm with oil and coolant shutters automatic, and intercooler shutters wide open.
|Time of |
Sh. Pos. for
*Critical altitude in climb for 26400 limiting turbo speed and 60.0" Hg. manifold pressure.
E. Cooling Shutter Tests
The average temperatures maintained by the thermostatic controls on the oil and coolant shutters were 85°C and 105°C respectively; therefore, all performance was corrected to shutter positions that would maintain these temperatures on a standard day with the exception of the oil shutters, whixh were corrected to the flush position for level flight.
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) in both level flight and climb with the exception that the oil temperature would be critical in climb above 35000' on an army hot day.
(1) Oil and coolant shutter calibrations in level flight at 5000 feet altitude with 50" Hg. manifold pressure and 3000 rpm.
|Constant coolant shutter position||Oil shutters flush|
|Intercooler closed||Intercooler closed|
|Oil shutter as specified||Coolant shutter as specified|
From W.O. position
From W.O. position
|5.55 W.O.||0.0||13.55 W.O.||0|
F. Stalling Speeds
Correctedfor instrument error
|Landing gear||Flaps||Power Off||Power on*|
*Power on was at 54" Hg manifold pressure and 3000 rpm
The high speeds reported were obtained with the original engines in the airplane. The left engine failed during a critical altitude power run and after replacement several high speed checks were made. The high speeds obtained with this new combination of engines were approximately 7 mph slower than on the original combination.
Climb performance was obtained with the original right engine and the new left engine. The right engine also failed during a critical altitude power run and high speed checks made after this engine was replaced showed the airplane to be approximately 5 mph slower than the original combination. The high speeds obtained on the two original engines was reported because more speed data was available, less time was on the airplane and engines, and the surfaces of the airplane were less worn at the time this data was obtained.
No war emergency rating was available on the engine when performance tests were commenced at Wright Field, however, after several test flights were made, 60" Hg. manifold pressure was selected as the maximum power at which the engines should be operated for five minutes. It may be stated here that the performance reported cannot be obtained unless strict attention is given to maintaining a minimum duct leakage by keeping the entire duct system tight.
Speed vs Altitude
Rate of Climb and Time to Climb
It is concluded that the performance reported is representative of the P-38J airplane, as the subject airplane was flown at combat weight and was also selected at random from P-38J airplanes delivered from the factory.
It is recommended that this method of selection of airplanes for flight test be adopted, and that hereafter all airplanes be test flown at the specified combat weight.
X General Dimension and Photographs
A. P-38J Dimensions
|Wing Area||328 sq. ft.|