routing air across a heat source, such as an exhaust manifold, before it enters the carburetor. [Figure 5-11]. driven alternator. These alternators have advantages over older style generators as they are lighter in weight, require lower maintenance, and maintain a uniform electrical output even at low engine r.p.m. [Figure 5-12] In a fuel injection system, fuel and air are metered at the fuel control unit but are not mixed. The fuel is injected directly into the intake port of the cylinder where it is mixed with the air just before entering the cylinder. This system ensures a more even fuel distri- bution in the cylinders and better vaporization, which in turn, promotes more efficient use of fuel. Also, the fuel injection system eliminates the problem of carbu- retor icing and the need for a carburetor heat system. The fuel control system on the turbine engine is fairly complex, as it monitors and adjusts many dif ferent parameters on the engine. These adjustments are done automatically and no action is required of the pilot other than starting and shutting down. No mixture adjustment is necessary and operation is fairly simple as far as the pilot is concerned. New generation  fuel controls incorporate the use of a full authority digital engine control (FADEC) computer to control the engine’s fuel requirements. The FADEC systems increase efficiency, reduce engine wear, and also reduce pilot workload. The FADEC usually incorpo- rates back-up systems in the event of computer failure. The electrical systems, in most helicopters, reflect the increased use of sophisticated avionics and other elec- trical accessories. More and more operations in today’s flight environment are dependent on the aircraft’s elec- trical system; however, all helicopters can be safely flown without any electrical power in the event of an electrical malfunction or emergency. Helicopters have either a 14- or 28-volt, direct-cur- rent electrical system. On small, piston powered  helicopters, electrical energy is supplied by an engine- Current from the alternator or generator is delivered through a voltage regulator to a bus bar. The voltage regulator maintains the constant voltage required by the electrical system by regulating the output of the alternator or generator. An over-voltage control may be Turbine powered helicopters use a starter/generator system. The starter/generator is permanently coupled to the engine gearbox. When starting the engine, elec- trical power from the battery is supplied to the starter/generator, which turns the engine over. Once the engine is running, the starter/generator is driven by the engine and is then used as a generator. ELECTRICAL SYSTEMS TURBINE ENGINES FUEL INJECTION 5-8 Figure 5-12. An electrical system scematic like this sample is included in most POHs. Notice that the various bus bar accessories are protected by circuit breakers. However, you should still make sure all electrical equipment is turned off before you start the engine. This protects sensitive compo- nents, particularly the radios, from damage which may be caused by random voltages generated during the starting process. Figure 5-11. When you turn the carburetor heat ON, normal air flow is blocked, and heated air from an alternate source flows through the filter to the carburetor. Filter To Carb Carb HeatGLYPH<.notdef> Collector Manif oldGLYPH<.notdef> Pipe Door Filter To Carb Carb HeatGLYPH<.notdef> Collector ManifoldGLYPH<.notdef> Pipe Door Heated Air Carb Heat Off Carb Heat On AvionicGLYPH<.notdef> BusGLYPH<.notdef> Bar AvionicGLYPH<.notdef> Bus Avionics Relay On Off Avionics MasterGLYPH<.notdef> Switch Lights PanelGLYPH<.notdef> PositionGLYPH<.notdef> Beacon TrimGLYPH<.notdef> InstrGLYPH<.notdef> Lndg LtGLYPH<.notdef> RadioGLYPH<.notdef> XpdrGLYPH<.notdef> Clutch Ammeter Mag Switch LeftGLYPH<.notdef> Magneto RightGLYPH<.notdef> Magneto StarterGLYPH<.notdef> Relay EngineGLYPH<.notdef> Starter Bus Bar BatteryGLYPH<.notdef> Relay Battery BatteryGLYPH<.notdef> Switch StarterGLYPH<.notdef> Switch M/R GearboxGLYPH<.notdef> Press Switch Release Hold Engage ClutchGLYPH<.notdef> Switch Alternator AlternatorGLYPH<.notdef> Switch AlternatorGLYPH<.notdef> Control Unit Clutch ActuatorGLYPH<.notdef> (Internal Limit SwitchesGLYPH<.notdef> Shown in FullGLYPH<.notdef> Disengage Position) 24V – + F1 F2 – + StartingGLYPH<.notdef> Vibrator R R Both L L Off Ret Adv Adv G (Optional Avionics)