Fuel Trimmers (2)
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What is it?
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The most important system that has been added is the Fuel Trimmers (2). You will use these controls to set the correct fuel/air mixture for engine start and for landing. Additionally, you will use these controls to set the correct cruise parameters of 14200 RPM and the TGT of 770 degrees. Basically, these controls regulate the TGT. This gauge has been set up in such a way that if you load a situation with engines already running, the fuel trim will be automatically set to a correct position. This is to prevent a case where upon loading the plane the engines would overheat instantly. In this kind of a situation, you will have no manual control over the fuel trim for 10 seconds or so.
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Controls
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There are two parts in this instrument. Above, you'll see two gauges, each ranging from 0% to 100%. One gauge per engine, and the tick marks are at 10% intervals. Below the gauges are two momentary switches, that are used to set the needle in the gauges to a correct figure. Also one per engine.
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Before engine start, you should set the fuel trim appropriately. The fuel trim can be in any position for the engines to be started. Each operator has their own guidelines for what settings are to be used for engine start, but here's a rule of thumb. If the outside air temperature is above 15 degrees centigrade, set the fuel trim for 50% or so. If it is colder, use a setting of 100%. After ignition takes place, you will have to constantly monitor the TGT gauge for the engine being started, and as the TGT rises, you will need to adjust the fuel trim to prevent overheating. You should be able to keep the TGT below the red area.
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Once the engines are running, adjust the fuel trim so, that both engines, with throttles idle, are running at 8500 RPM.
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Once you reach cruise state, you should work with throttles/fuel trim to set the correct cruise parameters. This will require some trial and error by adjusting both, the throttles and the fuel trim. You should aim for a cruise RPM of 14200 and a TGT of 770 degrees. As the fuel trim setting is depedent on the outside air temperature, you'll need to adjust these whenever the conditions change.
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Before landing, you should set the fuel trim to a pre-calculated value. This value can be found from a table that is included in the checklists (see the image below). The purpose of this is to have a correct value set up for a possible go-around situation. When you add full power in a go-around, you'll already have the fuel trim set up so that engines won't overheat. Please remember, that full the power is 15000 RPM, not firewalling the throttles!
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