Turbine Aircraft Systems - Electrical Flashcards
Describe some of the advantages of NiCad batteries.
Nickel-cadmium batteries are used frequently in turboprop aircraft.
Advantages:
- Long service life and excellent reliability.
- Can maintain sustained voltage until almost completely discharged.
- Deliver large amounts of current.
- Short recharge time after heavy use.
Describe some of the disadvantages of NiCad batteries.
Nickel-cadmium batteries are used frequently in turboprop aircraft.
Disadvantages:
- Relatively expensive.
- Temperature sensitive.
- Thermal runaway problem.
- Battery memory can prevent battery from fully recharging.
What is thermal runaway?
Basically, “thermal runaway” is an uncontrollable rise in battery temperature that will ultimately destroy the battery. This condition can occur when a nickel-cadmium battery is operated at above normal temperatures and is subjected to high charging currents associated with constant voltage charging. As the temperature of the battery increases, the effective internal resistance decreases and higher current is drawn from the constant voltage charging source. The higher current increases the battery temperature, which in turn results in even higher charging currents and temperatures.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 17). Aviation Supplies & Academics, Inc.. Kindle Edition.
Describe lead-acid batteries.
A common type of battery used in small aircraft as well as some turbine aircraft. The cells of the battery are connected in series. In discharging, the chemical energy stored in the battery is changed to electrical energy; in charging, the electrical energy supplied to the battery is changed to chemical energy and stored. Each cell of a lead acid battery normally develops 2 volts. The most common lead acid batteries are 12 or 24 volt and are rated in amp hours. An amp-hour equals 1 amp delivered for 1 hour.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 18). Aviation Supplies & Academics, Inc.. Kindle Edition.
What is a generator?
Any device that converts mechanical energy into electrical energy by electromagnetic induction. AC and DC generators are the most common types; both operate by inducing an AC voltage in coils varying the amount and direction of the magnetic flux cutting through the coils.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 18). Aviation Supplies & Academics, Inc.. Kindle Edition.
Describe the function of a starter-generator unit.
Many gas turbine aircraft are equipped with starter-generator systems that use a combination starter-generator, which operates as a starter motor to drive the engine during starting, then operates as a generator to supply the electrical system power after the engine has reached a self-sustaining speed.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 18). Aviation Supplies & Academics, Inc.. Kindle Edition.
Describe generator control units (GCUs).
GCUs are mulitfuctional electrical components that provide electrical system control and protective functions such as:
- Voltage regulation
- Over-voltage protection
- Load paralleling between generators
- Automatic cancellation of start cycle
- Reverse polarity protection
What are inverters?
Inverters are used in some aircraft systems to convert a portion of the aircraft’s DC power to AC power, which is used mainly for instruments, radio, radar, lighting, and other accessories. There are two types of inverters, rotary and static; they are usually designed to supply current at a frequency of 400 cps. Some are designed to provide more than one voltage; for example, 26 volt AC in one winding and 115 volts in another.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (pp. 18-19). Aviation Supplies & Academics, Inc.. Kindle Edition.
Why do most large aircraft us AC power rather than DC power?
Alternating current has largely replaced direct current in commercial power systems for a number of reasons:
- It can be transmitted over long distances more readily and more economically than direct current, since AC voltages can be increased or decreased by means of transformers.
- Space and weight can be saved, since AC devices, especially motors, are smaller and simpler than DC devices.
- In most AC motors, no brushes are required so commutation trouble at high altitude is eliminated.
- Circuit breakers operate satisfactorily under load at high altitudes in an AC system, whereas arcing is so excessive in DC systems that circuit breakers must be replaced frequently.
- Most airplanes using a 24-volt DC system have special equipment that requires a certain amount of 400-cycle AC current, making it necessary to convert with inverters.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 19). Aviation Supplies & Academics, Inc.. Kindle Edition.
What is an electrical bus bar?
A common electrical system component that interfaces power from a common source, such as a generator, to a variety of electrical components connected to the bus. Most transport category aircraft use multiple bus systems, allowing for a certain degree of redundancy in the event of a failure of any one component.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 19). Aviation Supplies & Academics, Inc.. Kindle Edition.
What are electrical bus ties?
A bus tie is an electrical switch that connects (or disconnects) different electrical buses. Bus ties provide a means of isolating a powered bus from one that has failed. They can also redirect power to buses that have lost their primary power source.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 19). Aviation Supplies & Academics, Inc.. Kindle Edition.
What is a rectifier?
A rectifier is a device that transforms alternating current (AC) into direct current (DC) by limiting or regulating the direction of current flow. Rectifiers provide a simple and efficient method of obtaining high voltage DC at low amperage. They can also be an excellent source of high amperage at low voltage, depending on the type of rectifier used.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 20). Aviation Supplies & Academics, Inc.. Kindle Edition.
What is a diode?
A two-element electrical device that allows current to travel in one direction only. Sometimes thought of as an electronic check valve.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 20). Aviation Supplies & Academics, Inc.. Kindle Edition.
What is a hot battery bus?
An electrical bus that is directly connected to the battery. Usually contains items that might be needed in a complete electrical system failure, such as emergency lights, communication radio, engine fire extinguishing, etc.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 20). Aviation Supplies & Academics, Inc.. Kindle Edition.
Describe the function of a transformer and transformer rectifier unit.
A transformer changes electrical energy of a given voltage into electrical energy at a different voltage level. A transformer rectifier unit (TRU) is a component used to reduce the AC voltage and change it into DC for charging the battery and for operating DC equipment in an aircraft.
Hayes, Michael D.. Airline Transport Pilot Oral Exam Guide (Oral Exam Guide Series) (p. 20). Aviation Supplies & Academics, Inc.. Kindle Edition.
