SUBJECT: Flight Tests

SECTION: Flight

SERIAL No. Eng-47-1656-A

A.   Purpose

      1. To report results of flight tests on P-38J airplane, AAF No. 43-13563, and P-38J-10 airplane, AAF No. 43-67570.

B.   Factual data.

       1.   P-38J airplane, No. 43-13563 was delivered to Wright Field in July of this year for performance tests to be run at war emergency power at 60" Hg. manifold pressure and 3000 RPM and loaded with full combat equipment. With the airplane loaded to this condition the gross weight at take off was 16,163 pounds with the c.g. at 25.7% m.a.c. gear down and 27.96% m.a.c. gear up as reported by the Wright Unit of the Airplane Labortory.

       2.   Considerable delay was encountered during the tests since it was necessary to change the left engine and also revise the exhaust systems to prevent burning the cowling. Previous to changing the left engine the level flight data which appears in paragraph 8 of this report was obtained.

       3.   When it was determined that the critical altitude for war emergency power was 20,300 feet it was deemed advisable to investigate the induction systems for leaks. Both intercoolers were removed and checked by the Power Plant Laboratory who reported that both intercoolers were leaking badly. New intercoolers were obtained, checked, found to be within specifications and installed. The entire induction systems were then checked and found to be leaking at all joints.

       4.   An attempt was made to correct this condition by filing the joints smooth to provide a better fit and sealing them by glazing compound in addition to external rubber seals used by the manufacturer. A check of critical altitude with the refitted systems gave an observed critical altitude of 21,800 feet for the left engine and 24,000 feet for the right. It was decided that since this airplane was a very early model and the induction systems had been retrofitted here, a more representative test of the airplanes being delivered to the service would be obtained if a later production model were tested.

       5.   P-38J airplane, AAF No. 43-67570, was delivered to Wright Field on 24 October 1943. A preliminary check of the induction systems of this airplane disclosed that both systems had severe leaks at the joints.

       6.   Prior to instrumentation a preliminary check of the critical altitude was made. The results of this check gave an observed critical altitude of 19,000 feet for the left engine and 20,500 feet for the right engine. Severe detonation was also encountered at war emergency power.

      7. The Lockheed Company's representatives stated the critical altitude in level flight at a manifold pressure of 59.5" Hg. and 26,400 turbo RPM, is 27,500 feet for the P-38 J tested at the factory.

      8. Level flight results of the P-38J, AAF No. 43-13563 were obtained with wheels up, wing flaps neutral, intercooler flaps flush, coolant flaps automatic and carburetor auto-rich.

      *Critical altitude for 60" Hg. manifold pressure and 26,400 turbo RPM.

C.   Conclusion

       1.   Results of flight tests on two P-38J airplanes at Wright indicate that these airplanes are unsatisfactory for tactical use above 20,000 ft. Considerable induction system leakage was encountered in both airplanes resulting in a loss of critical altitude of approximately 7500 ft. Additional trouble was encountered while testing the first of these airplanes at war emergency power in that one engine had to be changed and several revisions were required in the exhaust system before test could be continued. It is believed that the P-38J airplanes at Wright Field are representative production airplanes and it is recommended that immediate action be taken to correct the leakage in the induction system, either through redesign or better production control of the manifold leading from the turbo to the engine.