18 September 1943
Wright Field, Dayton, Ohio, USA
Kelsey saw the manila envelope on his desk before he even took off his jacket. It was stamped with a bold red “CONFIDENTIAL” and addressed directly to him from the Army Air Forces Air Technical Services Command. Although they were at Wright Field and he always worked closely with them the chain of command and Army procedures dictated he gets the report no different than if it had come from Materiel Command down in Florida. He was waiting for several performance testing reports from them but one in particular had him itching: the tests of the XP-38J.
They had received the initial manufacturer’s trials from Lockheed’s in-house development of P-38G-10-LO #42-12869 back in April. The Lockheed report indicated that they had fitted the experimental Allison V-1710-F15R/L engines, which the Army had later accepted as V-1710-75/77, and matched these engines with a new high-activity propeller form Hamilton Standard. The performance gains were impressive enough for the AAF to place a formal order for an official version of the P-38 with this engine/propeller combination as the XP-38J.
Lockheed built up P-38G-10-LO #42-13558—which had been one of the P-38H development planes and was already upgraded to H-5 standards—to the new P-38H-10 standards then fitted the F15 engines, high activity propellers, and new B-33 Turbo-chargers from GE. After an initial few shake-down flights, Lockheed pilot Tony LaVier had delivered this heavily modified airplane to Wright Field in mid-June.
Almost as soon as it arrived, though, the Army—fearing Allison’s inability to produce them—decided they did not want the F15 engines and ordered that they be replaced from the airplane with more readily available Allisons. The first temptation had been to put in the less extremely modified F17 Engines, which Allison was already testing with Lockheed, but Allison intervened with a rather interesting proposition.
They had developed a new engine intended for the P-63 which they called the E27. The E27 was originally designed to use an externally mounted auxiliary supercharger in order to give the P-63 high altitude performance on par with aircraft using Two-Stage Superchargers. More intriguing, was that Allison had designed the engine to withstand extremely high boost pressures with the aid of Water Injection. In the original configuration it was tested at over 1,800 horsepower under War Emergency Power using the Water/Methanol Injection.
Since the P-63 had been canceled and Allison was already tooling up to produce several thousand of these E27 engines, they had proposed to modify the engine to F-Series standards (which simply required changing the front crank-case cover and adding the appropriate gear-box) and remove the auxiliary supercharger so that it could be fitted into the P-38 as the F27. The Technical Services branch agreed and the Army officially accepted the F27R as the Allison V-1710-117 and the F27L as the V-1710-119.
It took them a few weeks to get the engines modified and installed properly in the XP-38J but by June 27th they were ready to begin ground runs with the new plane. They had looked at several possible installation locations to place the Water/Methanol tanks but finally settled the otherwise unoccupied section of the outer wing leading edges between the engine nacelle and the first rib. This allowed about 12 gallons of solution per engine which was calculated to be enough for five to seven minutes of Water Injection time. The plane was finally ready to fly on July 5th and for the next six weeks it had undergone extensive performance and reliability tests. It was the report on these tests for which Kelsey had been anxiously waiting.
After hanging his Service jacket and cap on the rack he sat down at the desk and opened the envelope…
Flight Test Engineering Branch
Memo Report No. Eng-47-1406-A
12 September 1943
FLIGHT TESTS
OF XP-38J AIRPLANE
I Introduction
Flight tests have been conducted at Wright Field on the XP-38J Airplane, AAF, No. 42-13558, at the request of the Fighter Branch, Experimental Engineering Division. These tests were made on this airplane primarily to obtain comparative performance data with existing production P-38 airplanes. The performance is that of an experimental model as it was modified to XP-38J standard at the factory and received additional modifications at the Flight Test Engineering Branch at Wright Field. From 5 July 1943 to 21 August 1943 approximately 30 hours were flown on this airplane by Capt. G. E. Lundquist, Capt F. C. Bretcher, and Capt J. W. Williams.
II Summary
The XP-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 high but when reached may cause 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 16,847 lb. This loading corresponds to the average P-38 combat weight with full oil, 410 gallons of fuel and specified armament and ammunition.
The principal results are as follows:
Max speed at critical altitude, 28,800
(60.0" Hg. Man. Pr. & 3000 rpm) = 460.0 mph
Max speed at sea level
(60.0" Hg. Man. Pr. & 3000 rpm) = 388.0 mph
Rate of climb at sea level
(60.0" Hg. Man. Pr. & 3000 rpm) = 5,090'/min.
Rate of climb at critical altitude, 25,800 ft.
(60.0" Hg. Man. Pr. & 3000 rpm) = 3,545'/min.
Time to climb to critical altitude, 25,800 ft.
(60.0" Hg. Man. Pr. & 3000 rpm) = 5.83 min.
Service Ceiling = 45,000'
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 16,847 pounds with the c.g at 24.75 m.a.c., gear down; and 28.5% m.a.c. , gear up. Gross weight included 410 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, complete radio equipment and antenna, and 200 pounds for the pilot. All items effecting 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 Allison V-1710-117 & 119 engines, type B-33 turbo superchargers with A-13 turbo regulators and Hamilton Standard three blade high-activity propellers. All power figures are based on a power curve from Eng. Spec. No. 198, dated 20 June 1943.
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.
B. Take-off
The take-off characteristics of the XP-38J are normal for a tricycle gear airplane except for the absence of any noticeable 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.
C. Stability
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% which was the maximum allowable rearward c.g. position at the time of the test. Recent tests on other P-38’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.
E. Controllability
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.
F. Maneuverability
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 noticeable 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 in excess of Mach 0.78 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.
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. It should be noted, however, that this landing light has been replaced with a streamlined leading edge light in current production airplanes.
N. Noise and Vibration 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. Most controls in the cockpit are easily accessible to the pilot and in general the cockpit layout is satisfactory, however, it can be difficult for the pilot to reach the Propeller Feathering switches in certain conditions.
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
Airspeed indicator 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.
B. High Speed
High speeds in flight at 3000 rpm, oil flaps flush, coolant flaps automatic, and intercooler shutters closed. Tests were performed at both War Emergency Power at 60”Hg and with use of Water Injection at 70”Hg.
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.
D. Climb Data
Climb performance at 3000 rpm with oil and coolant flaps automatic, and intercooler shutters wide open.
E. Cooling Flaps Tests
The average temperatures maintained by the thermostatic controls on the oil and coolant flaps were 85°C and 105°C respectively; therefore, all performance was corrected to flap positions that would maintain these temperatures on a standard day with the exception of the oil flaps, which were corrected to the flush position for level flight.
No standard Air Corps cools tests were made, however, from all indication 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.
F. Stalling Speeds
G. Remarks
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 4 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.
Both engine failures were attributed to carburetor icing resulting from condensation caused by vaporizing action of the Water/Methanol solution on humid days. See Section IX.B.
VII Curves
A. Speed vs. Altitude
B. Rate of Climb and Time to Climb
VIII Conclusions
It is concluded that the reported high speed and climb performance, and the service ceiling of the tested airplane is superior to current production P-38 airplanes in normal conditions, as the subject airplane was flown at combat weight.
IX Recommendations
A. It is recommended that immediate action be taken to begin production and procurement of the XP-38J airplane with the specified engines and propellers.
B. It is also recommended that if the V-1710-117/119 engines are adopted with Water Injection that a method for maintaining solution temperature and for de-icing the carburetors be developed.
