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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To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. The "LL" in 100LL stands for low lead, but there is still about four times more than is needed. As well as the lead (in the form of TEL— Tetra-Ethyl Lead), a scavenging agent (Ethylene DiBromide, or EDB) is also added to ensure that the lead is vapourised as far as possible, ready to be expelled from the cylinder with other gases. Unfortunately, this is not 100% successful, but the results are best at high temperatures and worst at low ones - the unwanted extras result in fouling of spark plugs, heavy deposits in the combustion chamber, erosion of valve seats and stems, sticking valves and piston rings and general accumulation of sludge and restriction of flow through fine oil passages, so it makes you wonder which is worse (in fact, petrol is not the only fuel you can use – Japanese Zeros used to outfly American aeroplanes because they used ethyl alcohol). TEL, by the way, is actually a liquid gas, which was developed by a subsidiary company (Ethyl, Inc) belonging to General Motors and I G Farben sometime before WWII. In June, 1940, just before the Battle of Britain, it could only be obtained through the Anglo-American Oil Company, or Esso - when the fuel was changed from 87 octane to 100, German pilots got a real surprise, because the Spit could suddenly climb a whole lot quicker. Oil An engine that is not used enough develops corrosion very quickly on the inside, and rust flakes, which are very abrasive, will circulate when the engine is started, which is why you have to change the oil even when you don’t fly a lot. Another reason is an increased water content, which will have an acidic effect once it mixes with the byproducts of combustion. The most wear takes place in the first seconds of a cold start, after the oil has been allowed to settle. Priming will wash whatever is left off the cylinder walls, so don't do too much, and maintain the minimum RPM to let it circulate. Synthetic oils have come from turbine oil development, but they have one drawback, in that the sludge in tends to centrifuge out inside the dome of a constant speed propeller and make cycling a bit difficult. They also hold contaminants longer. Many Flight Manuals recommend not changing brands of oil (e.g. the JetRanger), but if you check with the engine manufacturer’s manual (in this case Allison), you may find that it is permitted on a top-up basis, that is, if you already have one brand in there, just start using the new stuff until eventually the contents change completely. Do not drain your present oil, and replace it in one go, because oils have different cleaning characteristics—your new brand may be more efficient and you get bits of coke and carbon floating around that could cause a seizure. However, this is something you should discuss with your maintenance people. Carburettor Icing |
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