Tanks, every boy loves 'em whether he admits it or not.
I was just starting my technical training at SEME when everything changed for me. I had to sign in to the 'heavy A' hanger and there I saw my first tank close up. It was a Chieftain, it had a 19 litre stroke diesel engine and it SHRIEKED when it was revved up. I ought to explain, a big 4 stroke diesel engine roars, its all bass. A 2 stroke Diesel shrieks, the noise is unworldly. I was hooked. The following day I went in to the chief instructor and told him I wanted to be an 'A' Mech. He wasn't happy, told me it would be the end of my career. Oh well. I did it anyway.
After waiting for an 'A' mech course to come through I was in. Mostly they did the same curriculum as 'B' mech courses like my original one but where a B mech course restricted themselves to 'little' armoured vehicles like the 432, 'A' mech courses worked on Chieftain. I can still remember the thrill of my first day with Chieftain, standing on the engine. It weighed 3 tons and was 5 feet long! the gearbox alone weighed 2 tons. Everything about tanks was big. The cooling fans were made of metal and were heavy enough to slice and dice anything that got near them. The blower was 3 feet long and required 100 hp just to drive it!!. All this paled into insignificance when we were told about ......"CRITICAL SPEED"!!
Critical Speed
It even sounded dangerous!. There were a few things we learned about the L60 tank engine. We learned its idle speed, we learned its maximum governed speed....and finally in hushed tones we were told all about critical speed. So, what happens at critical speed? in short everything!. Remember those cooling fans I told you about? the big heavy ones?. Well they're made up of individual fan blades all bolted to a common hub. They are VERY heavy, each individual blade weighs at least a kilo and there are 10. They are held on by 2 bolts each. Problem is, when the fan is going round REALLY fast, faster than its design speed, centrifugal force acts on it to make it even heavier. It makes it so heavy that the 2 bolts there to hold it on aren't really up to it. Whats worse than that is it only takes one blade to shear, then the fan is out of balance and a chain reaction occurs. All the blades then come off and bounce round inside the armoured engine bay of the tank. They rip off all the exposed pipes, they sever cables and generally destroy whatever gets in their way. In my years since training I have seen the results of a few engines reaching 'critical speed'. While I was attached to 1 RTR, all of the tanks in our squadron were named after battle honours held by the regiment. All except 1. That one was called Vesuvius. It got its name because when it reached critical speed there was a bang and a fireball 30 feet high flew out of the engine bay. It took months to complete repairs and when the tank came back to us some wag at base workshops had written Vesuvius on it in chalk. The name stuck and it was soon rechristened.
