直升機飛行員手冊直升機操作手冊 The Helicopter Pilot’s Handbook

時間：2011-04-05 11:37來源：藍天飛行翻譯 作者：航空 點擊：次

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The reason the temperature cools either side of the peak reading is that on the one hand (rich), there is too much fuel and, on the other (lean), there is too much air (having said that, the hottest CHT is between 25-50° rich of peak EGT, because that's where the peak cylinder pressure occurs, with a high rate of heat transfer to the cylinder head, so you need to lean past it). However, although being lean of peak works, there is much more potential for causing damage to the engine if it is mismanaged – it needs more monitoring to be used effectively, as the temperature at the exhaust will still be high, which is not good for the valves, particularly acute with high performance turbocharged engines – Australian authorities found that leaning causes lead oxybromide deposits to cling to various parts inside the combustion chamber, which could become hotspots and cause detonation (the lead appears as a result of chemical changes in avgas as it burns). At richer settings, the lead either doesn't form or is swept out of the cylinder (this may be true for lower performance engines, too).
Don't forget to enrich the mixtures before increasing power when at peak EGT or when increasing to more than 75% power. Move the engine controls slowly and smoothly, particularly with a turbocharged engine. Harsh movements that (on older engines) will result in a cough and splutter and having no power can be embarrassing.
Although many flight manuals state that as soon an engine is running without stuttering it's safe to use it to its fullest extent, try warming up for a few minutes before applying any load, at least until you get a positive indication on the oil temperature (and pressure) gauges. This ensures a film of oil over all parts.
Even better, warm it before you start it, because the insides contract at different rates – in really cold weather the engine may have the grip of death on the pistons and cause some strain when you turn the starter. Equally important is not letting an engine idle when it's cold, as it must be fast enough to create a splash (about 1,000 RPM is fine).
After flight, many engines have a rundown period which must be strictly observed if you want to keep it for any length of time. As engines get smaller relative to power output, they have to work harder. Also, in turbines, there are no heavy areas to act as heat sinks, like the fins on a piston engine, which results in localised hotspots which may deform, but are safe if cooled properly, with the help of circulating oil inside the engine (75% of the air taken into a turbine is for cooling purposes). If you shut down too quickly, the oil no longer circulates, which means that it may carbonise on the still-hot surfaces, and build up enough to prevent the relevant parts from turning. This coking up could sieze the engine within 50 hours or less.
If the starter light remains on after you release the starter button on a piston engine, you should shut it down, as it indicates that the starter is still engaged with the engine and is being driven by it.

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