the air just before entering the cylinder. This system ensures  a more even fuel distribution between cylinders and better  vaporization, which in turn promotes more efficient use of  fuel. Also, the fuel injection system eliminates the problem  of carburetor icing and the need for a carburetor heat system. The electrical systems, in most helicopters, reflect the  increased use of sophisticated avionics and other electrical  accessories.  [Figure 4-24]  More and more operations in  today’s flight environment are dependent on the aircraft’s  electrical 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-current  electrical system. On small, piston powered helicopters,  electrical energy is supplied by an engine-driven alternator  by means of a belt and pulley system similar to that of an  automobile. 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 rpm. (As a reminder, think of volts or voltage  as the measure of electrical pressure in the system, analogous  to pounds per square inch in water systems. Amperes is the  measure of electrical quantity in the system or available. For  example, a 100-amp alternator would be analogous to a 100  gallon per hour water pump.) Turbine-powered helicopters use a starter/generator system.  The starter/generator is permanently coupled to the accessory  gearbox. When starting the engine, electrical 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 then functions as a generator. 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 incorporated to prevent excessive  voltage, which may damage the electrical components. The  bus bar serves to distribute the current to the various electrical  components of the helicopter. A battery is used mainly for starting the engine. In addition,  it permits limited operation of electrical components, such  as radios and lights, without the engine running. The battery  is also a valuable source of standby or emergency electrical  power in the event of alternator or generator failure. An ammeter (or load meter) is used to monitor the electrical  current within the system. The ammeter reflects current  flowing to and from the battery. A charging ammeter  indicates that the battery is being charged. This is normal  after an engine start since the battery power used in starting  is being replaced. After the battery is charged, the ammeter  should stabilize near zero since the alternator or generator is  supplying the electrical needs of the system.  An ammeter showing a discharge means the electrical load  is exceeding the output of the alternator or generator, and the  battery is helping to supply electrical power. This may mean  the alternator or generator is malfunctioning, or the electrical  load is excessive. An ammeter displays the load placed on the  alternator or generator by the electrical equipment. The RFM  (see page 5-1) for a particular helicopter shows the normal  load to expect. Loss of the alternator or generator causes the  load meter to indicate zero. Electrical switches are used to select electrical components.  Power may be supplied directly to the component or to a  relay, which in turn provides power to the component. Relays  are used when high current and/or heavy electrical cables are  required for a particular component, which may exceed the  capacity of the switch. Circuit breakers or fuses are used to protect various electrical  components from overload. A circuit breaker pops out when  its respective component is overloaded. The circuit breaker  may be reset by pushing it back in, unless a short or the  overload still exists. In this case, the circuit breaker continues  to pop, indicating an electrical malfunction. A fuse simply  burns out when it is overloaded and needs to be replaced.  Manufacturers usually provide a holder for spare fuses in the  event one has to be replaced in flight. Caution lights on the  instrument panel may be installed to show the malfunction  of an electrical component. Most helicopters, other than smaller piston-powered  helicopters, incorporate the use of hydraulic actuators to  overcome high control forces.  [Figure 4-25]  A typical  hydraulic system consists of actuators, also called servos,  on each flight control, a pump which is usually driven by  the main rotor transmission and a reservoir to store the  hydraulic fluid. Some helicopters have accumulators located  on the pressure side of the hydraulic system. This allows for  a continuous fluid pressure into the system. A switch in the  cockpit can turn the system off, although it is left on under  normal conditions. When the pilot places the hydraulic  switch/circuit breaker into the on position, the electrical  power is being removed from the solenoid valve allowing  4-16 Hydraulics Electrical Systems