Monday, 17 October 2016

Fatal misconceptions

This is actually not a bad video, albeit a bit light on detail, what it does illustrate though is the power of ill conceived notions. There's a process through which information is disseminated and acquired that is a bit like Chinese whispers: send three and fourpence we're going to a dance. It occurs where there's a common exchange of information that is generally accepted as fact but the information of concern, was acquired without sufficient insight or context to apply it effectively. Generally the consequences of such activity are insignificant, people just go around with a bunch of notions in their head that are not connected to reality. Big deal, that happens all the time, read a newspaper or watch the a television news bulletin and you'll find a bunch of folk making their living ensuring that condition is maintained. This particular notion though, the Spitfire's fatal flaw, is an exception; unfortunately it's been implicated as a contributory factor in an accident that lead to the death of two people. I call this process of flawed information exchange, eavesdrop acquisition, which seems to aptly summarise it because the information of concern is often overheard during a casual encounter and the peril of eavesdropping is the lack of relevant context.

The details of the early iteration of the Spitfire's fuel system and its performance during negative g relayed here are essentially correct, it's just that the implications drawn are misleading. Weapons like the Spitfire are essentially solutions to engineering problems, because they're used in conflict the effectiveness of such solutions is subject to an intense imperative. Practical engineering is a process involving compromise and trade off, the fastest aeroplane you can make, wont be the one with the highest climb rate so you settle upon a compromise between those two goals. In the meantime, you do your best to ameliorate any negative impact of such compromise. When it came to designing the Spitfire their solution was, let's get as much power out of this engine as we possibly can. Maybe as a consequence of this urgent imperative, the negative g performance of the Merlin's fuel system, seems to have been overlooked or even placed on the back burner, it being seen as not of immediate significance. Unfortunately that all changed rather catastrophically when Johnny French adopted waving white flags as his national past time.

When Fritz spanked Frenchy and sent him to work in the cheese factory, one of the consequences was they captured a number of intact Hawker Hurricanes. The Hurricane's engine and fuel system were essentially identical to the Spitfire's and what did Fritz find when he put this booty through flight test? Yep, look what happens when you put the thing into negative g. So the flaw in the Spitfire wasn't so much the compromised fuel system, it was the fact that the Germans knew about it and were able to exploit it. They also found a number of other significant flaws with the Hurricane, not least its header tank situated on the cockpit side of the engine firewall, just behind the pilot's instrument panel. They must've laughed their nuts off when they found that howler. Incidentally, after testing the Hurricane, the German opinion was almost universally derisive. Which must've been a great relief to them because the Me 109 had been, rather hastily, rebuilt into a much larger aeroplane after a panic at the German air ministry prompted by the Hurricane's introduction.

So why didn't the Germans win The Battle of Britain then? Well although the negative g performance of the early Spitfire's and Hurricane is a significant flaw, it's only really exploitable in a head on confrontation or against an inexperienced pilot. It doesn't work while you're being chased by a Spitfire because your opponent has ample opportunity to avoid negative g, all he has to do is bank his aeroplane and pull back the stick. It works head on because you can just gently nose down your 109, the Spitfire can't bring his weapons to bear and goes sailing over your head. The flaw caused enough concern though, to prompt hasty remedial action. The video's account is reasonably accurate in this regard, Miss Shilling's orifice, followed by successive more effective solutions. So in short measure, poor ol' Fritz found himself sauntering through the sky thinking he'd dive to safety, only to find himself facing eight angry machine guns, that must've been a bad day.

So how does eavesdrop acquisition prove to have fatal consequences in this case? Well the misconceptions around this topic aren't just related to the means by which the Germans acquired knowledge of this issue and were able to exploit it. Perhaps because of the rather colourful term associated with Miss Shilling, the tale of the Spitfire, negative g and the orifice in question had become a bit of common banter; raised whenever the topic of conversations turns to The Battle of Britain, the Spitfire, the Merlin engine or aerial combat in general. And so 'knowledge' of the Spitfire's and Merlin's negative g flaw, permeates the broader collective consciousness. So when two pilots noted intermittent problems with one of the engines on their Merlin engined Mosquito bomber, they drew upon their common understanding to attribute it to this flaw. The simple fact that the negative g flaw had been diligently and systematically eradicated from all Merlin engines by a process of managed and recorded modification, as is standard practice in the aerospace industry, was lost upon them. As a consequence they missed a vital clue to the condition of the engine after faulty maintenance.

And so I'm afraid, that's how the fatal consequences followed. I suppose there's a lesson there; be careful of the wisdom you bestow, make sure it is actually wisdom.

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