ELEC PT1 Flashcards
Define electrostatic force. (021.09.01.01 - Calculation)
The relationship between 2 positive or negative ions.
It is proportional to the quantity of charge (from both ions) and inversely proportional to the square of the distance between the charges. Opposite ions attract, same charges repel. This is known as Coulomb’s law.
Explain static electricity and where it is most likely to affect an aircraft. (021.09.01.01)
The friction of air and ice molecules on the aircraft ionise the airframe negatively. This is concentrated on sharp edges, such as trailing edges of wings or antennas. It builds up more in dry air, such as in winter.
Describe a static discharger including its use and location. What should a pilot do on their pre-flight inspection? (021.09.01.01)
Static dischargers or wicks use cotton wires or carbon fibre (low conductivity), and fitted to reduce static build up on the airframe, and are fitted to the trailing edges of control surfaces, tips of wings, or stabilisers.
A pilot must check the number and condition of static discharges, and should refer to the configuration deviation/minimum equipment list (CDL/MEL) if any are missing or damaged.
How is ensured there is no electrical charge remaining on an aircraft when it has landed? (021.09.01.01)
The main bond is brought into instantaneous contact with the ground as the aircraft touches down. This is done by the the tyres being in contact with the main bond via the wheel bearing, and containing a high proportion of carbon. This dissipates all the static energy as it lands.
Why and how is an aircraft grounded during fuelling? (021.09.01.01)
It is grounded to avoid a risk of fire or explosion due to static electricity build up.
The aircraft should be earthed and bonded to the refuelling equipment using dedicated wires and clips, which should also be earthed.
Explain what electrical bonding is and why it is necessary. (021.09.01.01)
Bonding is the process where each piece of the metal structure is joined to another by flexible wire strips, which provide an easy path for electrons to move around. It also allows the electrons to travel to static dischargers.
An aircraft will pick up a static charge while flying, and bonding prevents any part of the aircraft building up a different charge with surrounding parts to avoids sparks.
What is the difference in atomic structure that affects conductivity, and give an example of conductors, semiconductors, and insulators. (021.09.01.02)
Conductors contain few (1,2, or 3) electrons in the outer layer, which can easily leave the atom and become free electrons. Example is copper or aluminium.
Semiconductors contain 4 electrons in outer layer. They can possess some free electrons at room temperature. Example is silicon or germanium.
Insulators contain many (5,6, or 7) electrons in outer layer. Example is nitrogen or air.
Explain direct current. (021.09.01.02)
The generators polarity remains the same, so the current always flows in the same direction.
Describe the difference in the following mechanical switches, and how to observe their state: toggle switch, rocker switch, pushbutton switch, rotary switch. (021.09.01.02)
Define voltage and current, including their units. (021.09.01.02)
Voltage is the difference in electric potential between 2 points. Is also known as potential difference or electromotive force (EMF). Symbol V, measured in volts v.
Current is the flow of electrons through a conductor. Symbol I, measured in ampere A. 1A=1coulomb/second. A=Q/t.
Explain Ohm’s law and state the equation. (021.09.01.02)
The current in the circuit is proportional to the voltage and inversely proportional to resistance. V=I*R. V in volts(v), I in amps (a), R in ohms(Ω).
Explain the affect on total resistance when resistors are connected in series or parallel, and state their equations. (021.09.01.02)
In series, the current is constant, and the voltage is the sum of the individual voltages. Hence resistance is the sum of the resistances. Rt=R1+R2+…
A failure of one resistance would mean a failure of the rest of the circuit.
In parallel, the voltage is constant, so the current is the sum of the individual currents. Hence inverse resistance is the sum of the inverses. 1/Rt=1/R1+1/R2+…
Failure of one resistor will not affect the others.
How does temperature affect resistances? (021.09.01.02)
The resistivity of a material is valid for a given temperature. The changes in temperature will change the value of resistivity. Generally, there is a PTC, however semiconductors, some aircraft temperature measurement systems, and some battery types have a NTC.
Positive temperature coefficient (PTC): resistivity increasers with temperature rise.
NTC: Resistivity decreases with temperature rise.
Define electrical power, including its unit and calculation. (021.09.01.02)
P=IV, P=power(w), I=amperes(A), V=voltage(v).
P=(I^2)*R
P=(V^2)/R
Explain alternating current. (021.09.01.03)
The generators polarity switches over continuously at a given frequency, therefore the current changes direction at the same frequency.
