Answers - Aircraft Electrical System

Fill in the Blanks

1. mathematical, electricity
2. semiconductors, transistors
3. generators, alternators
4. conductor movement/force, magnetic field current
5. inverter, HZ (cycle) AC
6. Inductive, capacitance, phase
7. Inversely, reduced, half
8. impedance, resistance
9. lead‐acid, ni‐cad, plates
10. essential, thirty
11. potassium hydroxide, discharge, manufacturer’s instructions
12. increases, greater, greater
13. generator control units (GCU), output
14. armature, field, electromagnetic, bus, loads
15. voltage/current, field
16. solid state, AC power, bus
17. alternator housing, integrated drive generator
18. bus power control unit, generator control unit
19. throttle, activated
20. flexing, stranded
21. mega‐ohmmeter, condition
22. derating, %
23. voltage drop, satisfactory
24. one, staggered
25. switches, close


1. 1‐c, 2‐d, 3‐b, 4‐d, 5‐a, 6‐b
2. 1‐a, 2‐b, 3‐b, 4‐c, 5‐a, 6‐c
3. 1‐c, 2‐d, 3‐c, 4‐b, 5‐a, 6‐d, 7‐c, 8‐a, 9‐b, 10‐d
4. 1‐c, 2‐a, 3‐b, 4‐d, 5‐b, 6‐a, 7‐c
5. 1‐e, 2‐c, 3‐a, 4‐f, 5‐d, 6‐b
6. 1‐f, 2‐c, 3‐a, 4‐d, 5‐b, 6‐e

Knowledge Application

1. 2.4A
2. 4 ohms
3. 24V
4. 24 x .707 = 17V
5. 112 x 1.41 = 158V
6. XL=2π (60) (.175) XL=66Ω

10. T.P. = I2 x 6

11. Watts

13. A.P. = E x 1
14. Volt amps (VA)
15. T.P.= 52 x 5.6 T.P.= 140 Watts, A.P.= 50 x 5 A.P.= 250VA, PF= (140/250) X 100 PF=56%
16. in between 14 and 12, choose bigger size of 12.
17. size 20 wire
18. size 18 wire (in between 20 and 18)
19. 26.5A
20. 17.2A

Multiple Choices

1. b
One method for reversing the direction of rotation of electric motors is to employ two field windings wound in opposite directions on the same pole. A single-pole, double-throw switch makes it possible to direct current through either of the two windings.

2. c
For testing armatures, a device called a growler is used. This device can be used for shorts, opens, proper grounds, and continuity.

3. a
The ring-type terminal is less likely to fail than slide-on type terminals.

4. b
If high starting torque is needed under heavy load conditions. the series wound motor is the best one to use.

5. b
When an added load is applied to a generator using a vibrator-type voltage regulator, the field rheostat is shorted for a longer period of time, which causes the solenoid armature to vibrate more slowly. The vibrating solenoid armature is what opens and closes the points.

6. a
Excessive pressure on generator brushes will cause rapid wear, but too little pressure will cause "bouncing" of the brushes which results in arcing and burned and pitted surfaces.

7. c
Synchronizing, or paralleling, of AC generators (alternators) is somewhat similar to paralleling DC generators, except that there are more steps with the alternators. In order to synchronize (parallel) two or more alternators to the same bus, they must have the same phase sequence as well as equal voltages and frequencies.

8. c
Because of the low resistance in the windings, the series motor is able to draw a large current in starting. This starting current, in passing through the field and armature windings, produces a high starting torque.

9. c
When a motor needs to have a precise point at which it will stop, an armature brake is utilized. A landing light retraction motor is an application where a precise stopping point is needed.

10. b
An interpole is a pole placed between the main poles of a generator. Interpoles may be used to counteract the effects of armature reaction.

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