Early jet engines needed a way to turn the motor over to start the engine going. Many propeller driven aircraft had relied on a man swinging the propeller to turn the engine to kick it into life. This was obviously not an option with a jet engine so a large blank starter cartridge was used. Made of brass, this cartridge looks very much like an artillery shell:It was in effect a large blank cartridge and the gasses from this cartridge expanded and turned the engine over allowing it to start. The top of the case has bent over lips and originally when it was full these would have held a large disc made of a material that would have been consumed by the explosion, such as cardboard:The base of the cartridge is marked up and we can tell this is an Electric Starter Cartridge No9 Mk I and was manufactured in 1952. The ‘K’ indicates it was produced by Kynoch:These cartridges were used on a number of early RAF jets including the Canberra and the Hunter. One American technician who worked on the Canberra bomber recalls using these cartridges:
Tech question: yes, the starter cartridge in the older marks of Canberra was just a huge shotgun shell, albeit without the shot. There was an explosive release of gases which was channelled to the turbine to wind the thing up. The earliest marks B2, T4, TT18 had only 1 fitted per engine, so, after a failed start, it would take several minutes for the area to cool enough for the cartridge to be replaced, often resulting in a delay of 20 minutes or more.
The latter (early) marks, PR7, E15, T17, T22 had 3 per engine, 2 as spares. The last mark, PR9, used a really nasty explosive fuel called AVPIN, which was volatile in the extreme. One of our jeeps carrying the stuff through a small town, fortunately in an unpopulated area, caught fire spontaneously, the driver bailed, and the resultant conflagration melted the concrete of the sidewalk. You can imagine the effect this had on the local populous – we were thereafter banned from transporting it through residential areas.
The explosion from the starter cartridge was impressive: 4-foot flames would leap from 3 vents in the engine casing, the whole area would be wreathed in pungent cordite smoke, and pilot and supervising technician would watch the engine and each other nervously in case of engine fire. In 3 years, I only had to evacuate once because of a suspected fire, which turned out to be a false alarm. However, you can imagine that when the plane was fully fuelled, we were out of there in a flash and up and running!
The gas release should take the engine up to about 2000 RPM, which was enough to energize the igniters and allow the engine to work with the start inertia to get it up to normal idling RPM (I forget the figure). The main thing you were watching at this stage was either for an internal fire, in which case the EGT gages would leap off the scale, or compressor surge, usually accompanied by a lot of popping and banging. In both cases, the actions would be the same: throttle closed, HP cock closed, LP pump off; for a fire of course, additional actions would be fire extinguisher shot through the engine (only 1 available) and evacuate (run for the hills!).