Answers - Engine Exhaust and Reverser Systems | Aircraft Systems

Answers - Engine Exhaust and Reverser Systems

1. b
Exhaust system parts are subjected to corrosive exhaust gases and large changes in temperature. Therefore, the metals used in these areas must be able to resist corroding and have a low expansion coefficient. One metal that possesses these properties is nickel chromium steel (stainless steel).

2. c
Spring loaded ball/flexible joints and slip joints are commonly used to correct slight misalignments, allow movement and expansion, and simplify installation. Bellows, on the other hand, allow the exhaust components to expand and contract without causing buckling.

3. c
Most light aircraft have a carburetor heat system that draws air from within the cowling and routes it through a shroud that surrounds the exhaust pipe. With this type of system, the hot exhaust gases provide a source of heat that adequately heats the intake air to prevent or remove carburetor ice.

4. c
Because of the high heat encountered in the hot section of a turbine engine, cracks frequently develop on turbine blades, stator vanes, and exhaust system components.

5. a
As an exhaust system heats up, the various system components expand. One way to allow for this expansion so adjacent components do not start buckling against each other is to use slip joints to join different components.

6. c
Metallic sodium is used in some valves because it is an excellent heat conductor. In a metallic sodium valve, the sodium melts at approximately 208 degrees Fahrenheit. When this happens, the reciprocating motion of the valve circulates the liquid sodium enabling it to carry away excess heat and reduce valve operating temperatures.

7. a
Engine manufacturers typically use brass or heat-resistant nuts to fasten exhaust system components to cylinder heads.

8. c
Although repair of exhaust system components can be accomplished, it requires special equipment and techniques that are not typically available in the field. Therefore, it is recommended that exhaust stacks, mufflers, and tailpipes be replaced with new or reconditioned components rather than being repaired.

9. a
To satisfy the minimum braking requirements after landing, a thrust reverser should be able to produce reverse thrust that is between 35 and 50 percent of the full forward thrust for which the engine is capable.

10. c
Most exhaust systems that use a heat exchanger as a source of cabin heat can be inspected visually once the heater air shroud is removed. Although X-ray inspection can detect cracks in exhaust system components, these defects are more easily and economically found by frequent and thorough visual inspection.

11. b
Ceramic coated stacks are typically cleaned using degreasing agents. However, you should always consult the manufacturer's specifications before using any cleaning agents.

12. b
A malfunctioning fuel nozzle or combustion chamber disrupts the normal flow of gases through the turbine and exhaust sections of a turbine engine. These defects can typically be detected by the presence of hot spots on the exhaust duct or tail cone.

13. c
When welding an exhaust stack, the completed weld should have a smooth seam of uniform thickness and the weld should taper smoothly into the base metal.

14. a
A turbocompound engine consists of a conventional reciprocating engine with a set of exhaust-driven turbines, sometimes called power recovery turbines (PRTs), that are coupled to the engine crankshaft through a fluid clutch. With a PRT system, additional power is recovered from the exhaust gases that would otherwise be pumped overboard.

15. c
To prevent dissimilar metal corrosion, corrosion-resistant steel parts should be blast cleaned using sand that has not previously been used on iron or steel.

16. c
Some large reciprocating engines utilize power recovery turbines (PRTs) that are attached to the crankshaft to supplement engine power. A PRT is driven by high velocity exhaust gases and transmits its rotational energy to the engine's crankshaft through a fluid clutch.

17. c
Repairs or sloppy weld beads on exhaust components that protrude into the exhaust gas flow can restrict the exhaust gas flow and cause localized hot spots.

18. c
Flexible ball joints absorb movement between stationary and movable portions of an engine's exhaust system. Therefore, ball joints must be installed with a specified clearance to prevent binding when expanded by hot exhaust gas.

19. b
Exhaust system parts should never be marked with a lead pencil. The lead is absorbed by the metal when heated, creating a distinct change in the metal's molecular structure. This change softens the metal in the area of the mark.

20. a
The airflow coming off the compressor is typically divided into primary and secondary flows. The primary flow is used to support combustion and drive the turbine while the secondary flow is used to cool the combustion and turbine sections.

21. b
Augmenter tubes are exhaust system components that assist engine cooling and provide a source of heat for anti-icing and cabin heating.

22. a
Internal failures in a muffler, such as displaced baffles or diffusers, can restrict the flow of exhaust gases resulting in excessive exhaust back pressure that can lead to a partial or complete engine power loss.

23. a
Engine power loss and excessive back pressure caused by exhaust outlet blockage can be prevented by the installation of an exhaust outlet guard. A typical exhaust outlet guard extends approximately two inches inside the muffler outlet port, thereby preventing any debris from blocking the outlet.

24. a
Cabin heat in most light aircraft is provided by a shroud that routes air over the exhaust system. Therefore, any exhaust system leakage should be regarded as a severe hazard. An undetected exhaust system leak can allow carbon monoxide to enter the cabin and incapacitate the pilot and passengers.

25. c
Prior to any cleaning in an engine compartment, the exhaust system and surrounding areas should be thoroughly inspected. The cowling and nacelle areas adjacent to the exhaust system should be inspected for signs of heat damage or exhaust gas soot, indicating possible exhaust leaks.

26. b
Turbocharged engine exhaust systems extract energy from the exhaust gas flow to compress the intake air before it enters the cylinders. Any time a gas is compressed, its temperature increases. Therefore, turbocharged engine exhaust systems typically operate at higher temperatures and higher pressures than normally aspirated systems.

27. c
Approximately one half of all exhaust system failures are traced to cracks or ruptures in the heat exchanger surfaces used for cabin and carburetor air heat sources. The high temperature of the exhaust system components along with the vibration from the engine promotes thermal and vibration fatigue cracking in areas of stress concentration.

28. a
Turbine engine thrust reversers are typically operated hydraulically, using hydraulic system pressure, or pneumatically using compressor bleed air.

29. a

30. a
Cold stream reversing describes a system that uses bypass air to produce reverse thrust. This is only possible with bypass turbofan engines.

31. c
The two types of thrust reversers in common use are the aerodynamic reversers and the mechanical blockage reversers. Aerodynamic, or cascade, reversers consist of a set of cascade vanes located ahead of the exhaust discharge that turn the escaping exhaust gases forward, which, in turn, produces reverse thrust. Mechanical blockage reversers typically consist of clamshell doors that extend into the exhaust stream and divert the flow of exhaust gases forward to create reverse thrust.

32. c
The most common type of actuators used on thrust reverser systems are pneumatic. However, electric and hydraulic actuators are also used in some applications. Neither fuel pressure nor engine oil pressure is used in thrust reverser systems because the high heat encountered in the exhaust duct could cause either of these to ignite.

33. a
Reversers are capable of producing between 35 and 50 percent of an engine's rated thrust in the reverse direction.

34. a
The thrust reverser systems on some aircraft do create enough reverse thrust to move the aircraft backwards. This is referred to as a power-back operation. However, creating that much reverse thrust burns a great deal of fuel and, therefore, is not very economical.

35. b
Thrust reverse can only be selected with the thrust levers in the ground-idle position. Therefore, to obtain reverse thrust, you must first retard the thrust levers to ground idle, then raise the thrust reverser levers attached to the power levers as required. Once the aircraft has decelerated sufficiently, the thrust reverser levers are returned to the ground idle position.