直升机飞行员手册直升机操作手册 The Helicopter Pilot’s Handbook

时间：2011-04-05 11:37来源：蓝天飞行翻译 作者：航空 点击：次

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In IFR, journeys are split into specific phases, such as start, checks, and taxi (that is, before take off), take-off and climb (another phase), cruise and descent (yet another), approach and landing, plus 10%, plus missed approach and diversion to the alternate. Then there's holding at the alternate, unuseable and contingency fuel, which covers errors in forecast winds, navigation, ATC restrictions and individual variations from standard fuel consumption. By arrangement, block figures can be used which ignore the take-off and climb. Fuel flow will have to be adjusted if you plan to use specialised equipment in flight, such as heaters, or not use anything essential, such as an engine.
By day, use the IFR figures as above, but without missed approach and loiter fuel, and the contingency fuel can be 5% if over non-hostile terrain, and 10% otherwise (non-hostile in this context means where fuel is available). By night, add loiter fuel as well. Whatever happens, you need 20 minutes’ worth at the destination.
Jet and piston fuels mix differently with contaminants (particularly water), which is due to variations in their specific gravities and temperature. The s.g. of water, for example, is so close to Avtur that it can take up to 4 hours for it to settle out, whereas the same process may take as little as half an hour with Avgas. As a result, there is always water suspended in jet fuel, which must be kept within strict limits, hence two filtration stages, for solids and water. The latter doesn’t burn, of course, and can freeze, but it’s the fungi that gather round the interface between it and the fuel that is the real problem – it turns into a dark-coloured slime which clings to tank walls and supporting structures, which not only alters the fuel chemically but will block filters as well. Not much water is required for this – trace elements are enough, although, in reduced temperatures, dissolved water will escape as free water, and look like fog. Aviation fuel is “clean” if a one-quart sample is clear of sediment when viewed through a clean, dry, clear glass container, and looks clear and bright.
Note (again): It has been found that when visible water is present in jet fuel containing anti-icing additive, the additive will separate from the fuel and be attracted to the water. After a certain amount, thought to be about 15%,the density of the new liquid changes so much that it is not identified as water, and will therefore pass through water filters, and not be detected by water finding paste. Where the ratio becomes 50%, as much as 10% of whatever is going through the filter could actually be water, which is very likely to get to the engine, since the filters on the airframe itself are not as restrictive.
Drums are also flushed with a solution containing sodium that passes through filters.
While on the subject of filters, they work on a certain psi, which may be less sometimes, if you use a manual pump, or more if you use an electrical one. In other words, if the pressure is not as designed, they will not do their job properly.

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