Answers - Engine Fire Protection Systems | Aircraft Systems

Answers - Engine Fire Protection Systems

1. c

A typical fire detection system used in reciprocating engine aircraft incorporates a thermocouple system that uses a series of rate-of-temperature-rise detectors. With this type of system a warning will not sound when an engine warms up slowly or when a short circuit develops. However, if temperatures in the engine compartment should rise rapidly, such as when a fire exists, the detectors will sound a warning horn in the cockpit.

2. b

3. c
Since the question specifies a temperature of 75°C you must interpolate between the minimum and maximum limits for both 70°F and 80°F. To interpolate find the difference between the two readings, divide the difference by two and add the quotient to the lower pressure. The minimum container pressure at 70°F is 31 9 psig and 356 psig at 80°F. Therefore, the minimum pressure at 75°F is 338 psig (356 - 319 = 37 ÷ 2 = 18.5 + 319 = 337.5). The maximum pressure at 70°F is 405 psig and 443 psig at 80°F. Therefore, the maximum pressure at 75°F is 424 psig (443 - 405 = 38 ÷ 2 = 19 + 405 = 424).

4. a
In a turbine engine powered aircraft, the fire extinguishing portion of a fire protection system typically includes a cylinder of extinguishing agent for each engine and nacelle area. The container of agent is normally equipped with two discharge valves that are operated by electrically discharged cartridges. The electrical current needed to discharge the cartridges is released by the fire handles in the cockpit.

5. a
When liquid CO, leaves the fire extinguisher nozzle under pressure, it converts into a gas that extinguishes flame by displacing the oxygen around the flame and smothering it.

6. a
The nitrogen charge within a typical high rate of discharge container is retained, or held in by a discharge plug and a safety discharge connection. The discharge plug is sealed with a breakable disk combined with an explosive charge that is electrically detonated to discharge the contents of the bottle. The safety discharge connection, or fusible disk, is capped at the inboard side of the engine strut with a red indication disk. If the temperature rises beyond a predetermined safe value, the disk will rupture, dumping the agent overboard.

7. b
A continuous-loop fire detection system consists of a loop of one or two conductors installed around an engine compartment that, when overheated, sends electrical current to a warning indicator in the cockpit.

8. c
Spot detector fire detection systems consist of a bimetallic thermoswitch installed between two loops of wire. When the thermoswitch is heated to a predetermined temperature, the switch closes and completes the circuit between the two wire loops. With the circuit completed, electrical current flows to the fire warning horn in the cockpit.

9. c
In a typical engine fire extinguishing system, the extinguishing agent is distributed through spray nozzles and perforated tubing. The perforated tubing distribution system is more common with reciprocating engines, while spray nozzles are typically used with turbine engines.

10. c

11. a
Some of the common devices used to detect fires on reciprocating engine aircraft include: overheat detectors, rate-of-temperature-rise detectors, flame detectors, and observation by crewmembers. Smoke detectors, on the other hand, are only effective in relatively still air where materials burn slowly or smolder and, therefore, are not used in reciprocating engine nacelles.

12. b
In a continuous-loop fire detection system, an electrical wire or wires are surrounded by a material with a resistance value that prevents the flow of current at normal temperatures. However, when the material is heated, the resistance decreases and allows current within the wires to find a path to ground. This completes the circuit and allows current to flow to the warning horn in the cockpit.

13. a
Carbon dioxide is the most satisfactory agent to use for a carburetor or intake fire and, when used properly, will not damage the engine.

14. a
The service life of fire extinguisher discharge cartridges is specified by the manufacturer and stated in hours. The service life of a typical discharge cartridge is 5,000 hours.

15. c
The Fenwal fire-detection system utilizes spot detectors that are wired in parallel between two separate circuits so that a short or fault in either leg of the system will not cause a false fire warning. The system is wired so that one leg of the circuit supplies current to the detectors while the other leg serves as a path to ground. If the ground leg should develop a short, a false fire warning will not occur because this portion of the circuit is already grounded. If the powered leg shorts, the rapid increase in current flow will trip a relay which causes the powered leg to become the ground and the grounded leg to become powered.

16. a
The thermocouple fire warning system senses the rate of temperature rise and, therefore, only provides a warning when the temperature increases rapidly. In each thermocouple, there is a cold, or reference junction that is enclosed in an insulated air space and a hot junction which is installed in an uninsulated space. If both of these junctions heat up at the same rate, no fire warning is given regardless of the temperature. However, if the hot junction should be exposed to an extreme amount of heat, a temperature imbalance between the two junctions will exist causing current to flow to the warning horn.

17. b

18. b
The Lindberg continuous-element fire detection system is a continuous-element type detector consisting of a stainless steel tube filled with an inert gas, typically helium. The principle of operation is based on the fact that if the volume of the gas is held constant, its pressure will increase as temperature increases. Thus the helium within the enclosed tube will exert a pressure proportional to the temperature along the entire length of the tube. If the pressure within the tube becomes excessive, it mechanically actuates a diaphragm in a responder unit which sets off the fire alarm.

19. a
The Fenwal fire detection system consists of an Inconel tube with one wire running through it. The wire carries an electrical potential and the tube is the source to ground. The potential and ground are separated by a core material which, when cold, acts as a resistor. However, when the core material is heated to a specified temperature, it acts as a conductor and allows the potential to find a path to ground. When this circuit is completed, it causes a fire alarm to sound.

20. c
The Kidde fire detection system consists of an Inconel tube with two wires running through it. One of the wires has a positive electrical potential while the other is a source to ground. The two wires are separated by a core material which, when cold, acts as a resistor. However, when the core material is heated to a specific temperature it acts as a conductor and allows the potential to find a path to ground.

21. a
Class B fires involve combustible liquids such as gasoline, engine oil, turbine fuel, hydraulic oil, and many solvents and paint thinners used in aviation maintenance.

22. b

23. c
Class C fires are those which involve electrical equipment. When attempting to extinguish a class C fire, special care must be exercised because of the dangers of electricity, as well as those from the fire itself.

24. b
Both the Kidde and Fenwal systems are continuousloop fire detection systems that rely on a complete, unbroken circuit to allow the press-to-test operation to function. However, both systems can experience a break and still give a fire warning.

25. b
In a typical fixed fire extinguishing system, a yellow and a red colored disk are used to indicate the status of the extinguishing agent. The yellow disk blows when the agent has been emptied by a normal discharge (answer B) and the red disk blows when the agent is blown overboard due to an over-temperature condition.

26. b

Carbon dioxide is the most satisfactory extinguishing agent for fires involving electrical equipment. However, halogenated hydrocarbon and dry powder extinguishers may also be used.

27. b

28. a

29. b

30. b
A class D fire is one in which some metal, such as magnesium, is burning. Class D fires are put out using dry powder or halogenated extinguishers and under no circumstances should water be used. The application of water to a class D fire will cause the fire to burn more violently and can cause explosions.

31. b

32. c
begin by locating 50°F at the bottom of the chart. From here, follow the line up to intersect the minimum gauge reading curve. From this intersection, draw a horizontal line to the left that intersects the pressure axis at 475 psig. Next, go back to the 50°F line and follow it up to intersect the maximum gauge reading curve. From this intersection, draw a horizontal line to the left that intersects the pressure axis at 625 psig. Based on this chart, the minimum and maximum container pressure at 50°F is 475 psig and 625 psig respectively.