Flight Test Engineering Branch
Memo Report No. Eng-47-1771-A
5 July 1944
Flight Tests on the Lockheed
P-38J Airplane, AAF NO. 43-28392
Using 44-1 Fuel
Flight test have been conducted at Wright Field on the P-38J-15 Airplane, AAF, No. 28392 at the request of the Power Plant Laboratory, Engineering Division. These tests were made to determine the increased performance of the airplane using the higher powers allowable by the use of 44-1 fuel as compared with the powers allowable with the standard fuel, grade 100/130, Spec AN-F-28. From 6 April to 24 June 1944 approximately 30 hours were flown on the airplane by Major F. A. Borsodi, Major G. E. Lundquiest, Captain Z. D. Fountain, Jr., Captain E. W. Lesch, and Captain J. D. Onerem. Approximately 18 hours were flown on the original engines, the remainder with a new right engine.
The P-38J-15 is a twin-engine, high altitude interceptor-fighter. The airplane performs well at high altitude, having a good maneuverability and radius of turn when using maneuvering flaps. The rate of roll is fair at medium speeds and slow at high speeds because of high aileron forces. This is improved in later models by the use of aileron boost.
The principal results are summarized in the following paragraphs.
In level flight at 19800 ft., the critical altitude for 70" hg. manifold pressure, 3000 RPM, and 26,300 limiting turbo RPM, a maximum speed of 419 MPH was attained. At this altitude a high speed of 402.5 MPH was attained at 60" Hg. manifold pressure. At 24000 ft., the critical altitude for 60" Hg. manifold pressure, 3000 RPM, and 26,300 limiting turbo RPM, a high speed of 413 MPH was attained.
At sea level a maximum rate of climb of 4040 ft/min was attained at 70" Hg. manifold pressure and a rate of climb of 3570 ft/min at 60" Hg. manifold pressure and 3000 RPM. The service ceiling of the airplane was 39,000 ft.m, and the absolute ceiling was 39,700 ft.
III Condition of Aircraft Relative to Tests
a. All tests were flown at a gross weight at take-off of 17,363 lbs. with the c.g. at 26.72% MAC, gear up, and 23.86% MAC gear down. This weight which corresponds to the combat weight of the airplane included 416 gallons of gasoline, full oil, 457.5 lbs. of ballst for 1500 rounds of .50 caliber ammunition, and 200 lbs. for the pilot.
b. The airplane was equipped with Allison V-1710-89 and 91 engines, type B-33 turbo superchargers with type A-13 turbo regulators and CUrtiss Electric three bladed propellers, blade design numbers 89303-18 and 88996-18, left and right respectively.
c. All tests were flown at a normal configuration with oil and coolant shutters automatic. Five .50 caliber machine were installed in the nose with the gun ports covered. The metal surface of the airplane was unpainted.
IV Flight Characteristics
a. Taxiing and Ground Handling
While taxiing the airplane responds readily to the throttles and brakes, but application of the brakes requires considerable pressure. The nose wheel action on rough and smooth ground is satisfactory. The taxiing qualities of the airplane are effected very little by crosswinds.
b. Take-off and Initial Climb
Take-off is normal for an airplane with tricycle gear in that the airplane will not fly itself off but requires back pressure on the control column. No trim is necessary as there is no noticable torque due to the opposite - rotating propellers. Flaps are not necessary for take-off except for a very short ground roll. The angle of attack is steep and the tare of climb good.
Only qualitative stability tests were run on the airplane. Longitudinally and directionally it is statically and dynamically stable. Laterally the airplane is statically stable.
The airplane has a tendency to hunt longitudinally in turbulent air.
d. Trim and Balance
There are small load changes in the aileron and rudder for attitude changes with wheels or flaps lowered and there is nose heaviness at high speeds, but these conditions can be trimmed out readily. The action of the oil cooler flaps opening and closing continuously causes yawing of the airplane.
Handling qualities in general are good. The ailerons are effective at all speeds down to the stall, but aileron control is heavy at high speeds. The rudder is very effective at all speeds, and the elevator is well balanced and controllable at moderate speeds but loses effectiveness at very high speeds.
The airplane is very maneuverable, although the forces for executing turns is high. The radius of turn is fair without maneuvering flaps and good with flaps. The rate of roll is fair. Response to the controls in making side slips, loops, and rolls, is positve and effective.
g. Stalling Characteristics
The airplane stalls straight forward with power-off but tends to fall off on either wing with power on. There is no tendency for the airplane to go into a spin.
h. Spinning Characteristics
No spin tests were performed.
i. Diving Characteristics
Dives in this airplane are critical and caution has to be taken to prevent exceeding speeds at which the nose becomes extremely heavy and violent elevator buffeting develops. The airplane handles well for normal dives, and all controls respond readily.
j. Single Engine Operation
Single engine operation is very good in this airplane. The minimum indicated airspeed at which control can be maintained at rated power on one engine is 115 MPH. The indicated airspeed for best climb is from 145 to 150 MPH. Normal feathering procedure is to be used on this airplane.
k. High Altitude Trials
General operation at high altitude is satisfactory. At high speeds vibrations develop in the cockpit and there is tail buffeting. Controls are effective at altitudes, but the trim tabs become stiff making trim at altitude difficult.
l. Approaches and Landing
The tricycle gear gives excellent landing characteristics. Strong crosswing landings can easily and safely be accomplished. WIth wing flaps and landing gear extended the nose becomes heavy. With full trim 18 degrees to the rear and power off, the aifplane handles well. The airplane has a normal glide of 125 to 130 MPH indicated.
m. Night Flying
The landing light switch is extremely hard to see and reach due to the position of the control column. The landing light causes buffeting when extended but gives sufficent lighting. The instrument panel lights are satisfactory, but the cockpit lamps cause excessive glare. Sufficient control of light intensity is given by rheostats.
n. Noise and Virbration Level Tests at Crew Stations
The noise level of the airplane is low and not objectionable. A vibration develops at very high speeds at 2600 engine RPM.
o. Vision and Cockpit Layout
Vision during taxiing, take-off, climb, and landing is very good, although the engine nacelles cut out vision to the side somewhat. Rear vision through the mirror on top of the canopy is very good, but the seat must be lowered enough to give head room to look up. The bullet proof glass in the front panel is very clear, and there is no noticable distortion in any panel.
The recognition light box and bomb and gas tank release box interfere with the use of the hand hydraulic pump. The parking brake doesn't stand under moderate usage. When full rudder is applied an obstruction presses down in the instep of the opposite foot; a greater clearance is needed. Knee room under the control column is cramped when wearing winter flying clothes. The switches in front of the control column should be relocated where they can be seen and within easy reach. The engine primer in its present location is awkward to operate. The fuel selector valves are placed in reverse from what they should be. The shoulder harness should not be locked for small pilots as they cannot reach the emergency controls at the feathering switch.
V Performance Data
a. The curve showing the airspeed postion correction and location and type of airspeed head is given in Fig. 1.
b. Curves of speed vs. altitude are given in Figure 2. The high speeds reported are those obtained with the original left engine and new right engine. The oil shutters in automatic averaged from 2.5 to 3 inches open throughout the level flight tests.
c. Power data for level flight and weight at altitude are given in Figure 3 and Figure 4. The horsepowers reported were calculated from T.O. 02-15AB-1C power chart for V-1710-89 and 91 engines.
d. Figure 5 shows the rate of climb and time to climb.
e. Power data for climb and coolant shutter position are given in Figure 6.
e. Stalling Speeds
Flaps Manifold Pressure RPM IAS, MPH Up Up Power-Off 97.5 Down Up Power-Off 99.5 Up Down Power-Off 86.0 Down Down Power-Off 80.5 Up Up 33.0" Hg. 2400 90.5 Down Up 33.0" Hg. 2400 94.0 Up Down 33.0" Hg. 2400 65.0 Down Down 33.0" Hg. 2400 60.0
Speed vs Altitude
Rate of Climb and Time to Climb
a. In level flight operation a gain of 17 MPH can be obtained by increasing the allowable power from 60 to 70" Hg. (W.E.R.).
b. In climb operation a gain of 500 ft/min can be obtained by increasing the allowable power from 60 to 70" Hg.
c. Cooling the airplane can be easily maintained at 70" Hg. However, maximum performance can only be maintained by strict maintenance on the duct system to prevent possible leakage.
c. The maintenance difficulties experienced throughout the tests were considerable. These consisted mainly of induction, exhaust system, and spark plug failure. However, these difficulties could not be attributed directly to any action of the 44-1 fuel.
a. It is recommended that the Allison V1710-89 and 91 engines be rated at 70.0" Hg. when using 44-1 fuel or its equivalent. Because of the mechanical and maintenance characteristics of the engine and the P-38J installation this rating should be limited to a very short time. Periods between overhaul should be shortened for the engines using this power.
Main P-38 Performance Trials