3 January 1942
Wright Field
Dayton, Ohio, USA
Major Ben Kelsey, chief of the Pursuit Branch of the Army Air Forces’ Production Engineering Section, the P-38’s original test pilot and biggest proponent, completed reviewing the latest performance test memorandum reports from Lockheed. The three reports were delivered the previous week and with the Army building up to Maximum Effort for the newly joined war the 34 year old aviator was wasting no time digesting the data.
The first report was a supplement to the preliminary report he had received in early November regarding the Performance Acceptance Tests carried out by Lockheed using a production block P-38E (#41-1983). The tests were cut short after the left engine ingested some debris from somewhere in the ducts, forcing a shut down. The data which was obtained prior to the failure, however, was acceptable if underwhelming.
The current production airplane—while still faster than anything else in the current Air Corps inventory—had been unable to meet the specified airspeed of 400 miles per hour at any altitude and the climb to 20,000 feet was over a minute slower than expected. The problem stemmed from the increased weight of armor and armament and limited power production from the F2 engines. Of particular note was that the climbing test had to be abandoned at 26,000 when the Carburetor Air Temperature exceeded 60 degrees Celsius and that Louis H. Siblisky, who prepared the report, indicated the inter-cooling was insufficient even in level flight at 20,000 when under Military and Rated Power settings.
The other two reports were the results of the modified P-38E #41-2009 test flight; one was the test flight data and pilot notes, the other was the report from the investigation of the turbo failure which ended the flight.
The flight did not follow the full acceptance test profile but instead focused on general handling characteristics with the new wing, radiator installations, and center nacelle changes including the temporary canopy. The pilot--Kelsey assumed it was probably Virden--noted all the aircraft handling to be positive and equal to the standard P-38E in most respects but that full performance and stall tests would need to be completed to make a direct comparison.
The results of the dive tests were fantastic. In a series of four powered dives the airplane achieved progressively faster maximum speeds and according to the test pilot never experienced any indication of the diving tendency and tail flutter of the standard airplanes. The maximum speeds, when corrected for atmospheric conditions and compressibility errors were calculated for each dive as follows:
1) 532 mph (0.745 Mach)
2) 546 mph (0.760 Mach)
3) 549 mph (0.760 Mach)
4) 551 mph (0.761 Mach)
The pilot noted that at around approximately 0.64 Mach the ailerons responded poorly and that prior to 0.7 Mach lost their effectiveness. This was neither a surprise nor a real problem as the 4412 outer wings had a lower critical speed than the new inner wing section and the P-38 already had a “No Spins” restriction in place so pilots were ordered to avoid large aileron deflection during dives anyway.
Although Lockheed had intended the tests to continue until the final dive speed limit was attained the flight was cut short after the left turbo-supercharger catastrophically failed in flight. The pilot made a successful recovery and landed #009 on a single engine but the airplane was badly damaged and needed extensive repairs.
The accident report revealed that one of the ducting seals in the left leading edge inter-cooler channels failed. They exact reason for the failure was unknown but the post-accident examination led the investigators to suspect that poor initial fitment was exacerbated by High-G pullouts after the dives which further weakened the seal. A sudden change in load due to turbulence during a climb finally caused the seal to fail which resulted in a sudden drop in manifold pressure. The automatic pressure regulator attempted to compensate by increasing the exhaust pressure to the turbine, which in turn caused an over-speed condition and subsequent turbo failure and explosion.
Pieces of the exploded turbo were found throughout a large portion of the aircraft. There was indication that several pieces had ricocheted off the armored plate behind the pilot. If the armor had not been installed it is likely that the pilot would have been killed and the aircraft lost.
The investigation concluded with several recommendations:
1) New inter-cooler installations be investigated; and/or
2) Better duct joining methods be developed and used
3) An automatic turbo-supercharger over-speed regulator be installed which will automatically open the waste-gate in the event of turbine run-away.
4) That the turbo-supercharger wells in each boom be integrally armored to protect the pilot and aircraft in the event of catastrophic failure.
5) Installation of a backup electrical generator, preferably on the right side engine, to ensure continued power in the event of left-engine failure.
In light of both the 009 accident and the inadequate charge air cooling noted in the reports on 983, Maj. Kelsey drafted an order to the effect that examination of alternate inter-cooler installations be immediately added to the scope of the P-38 Improvement Program under High Priority with provision that it only be included in the P-38F development so long as it does not delay the scheduled production start date. The other recommendations from the accident report he included on the order under Normal Priority—that they be investigated if practicable in current production timelines without impacting High and Urgent items.
With the order drafted and signed, he sent it on to his superiors for Approval and dissemination.
(As witness my adoration for the projected F4U-1D with them, the P-80, & at least one homebuilt {name of which I can't recall
