The U.S. Army impulse cartridge M-796 and U.S. Air Force BBU-35B are used to eject countermeasure stores (flares and chaff) from aircraft dispensers (XM-130, ALE-40, ALE-45, ALE-47) of military aircraft (F-16, F-15, A-10, C-130, AH-64, MH53E, and CH-47). Both the M-796 and BBU-35B impulse cartridge are of the same general configuration with different part numbers for the Army and Air Force. Both are used to eject a M-206 Infrared Flare.
The M-796 and BBU 35B are subjected to temperature-altitude conditions and aircraft flight, ground and maintenance environments (-62°C/-80°F to 95°C/203°F) during qualification and acceptance tests.
The M-796 and BBU-35B use a double base NC/NG propellant for producing gas pressure against the countermeasure piston for ejection (and to ignite a Mg-Teflon flare) from the aircraft dispenser. In 1978 the double base propellant (Bullseye), U.S. Army drawing 9326769 (USAF drawing 7829435), was used in the impulse cartridges M-796, USA 9311660 and BBU-35B, USAF 7729436.
During qualification testing, the M-796 impulse cartridge had experienced inconsistent function time and pressure rise time (psi/ms slope) failure mode. The failure occurred after exposure to Temperature–Altitude test per the customer’s procurement specification tailored from MIL-STD- 810, Method 504.1.
Failure investigation identified decomposition of the Nitrocellulose/Nitroglycerine (NC/NG) double base propellant which occurred during temperature cycling where the temperature was held at +95°C (+203°F) for 16 hours.
This paper describes an empirical investigation test method used to determine the failure mode and discusses the test results.