As aircraft have increased in gross weights with higher landing airspeeds, the problem of stopping an aircraft after landing has greatly increased. In many instances, the aircraft brakes can no longer be relied upon solely to slow the aircraft within a reasonable distance, immediately after touchdown. Most thrust reverser systems can be divided into two categories: mechanical-blockage and aerodynamic-blockage.

Mechanical blockage is accomplished by placing a removable obstruction in the exhaust gas stream, usually somewhat to the rear of the nozzle. The engine exhaust gases are mechanically blocked and diverted at a suitable angle in the reverse direction by an inverted cone, half-sphere, or clam shell. [Figure 3-48] This is placed in position to reverse the flow of exhaust gases. This type is generally used with ducted turbofan engines, where the fan and core flow mix in a common nozzle before exiting the engine. The clamshell-type or mechanical-blockage reverser operates to form a barrier in the path of escaping exhaust gases, which nullifies and reverses the forward thrust of the engine. The reverser system must be able to withstand high temperatures, be mechanically strong, relatively light in weight, reliable, and “fail-safe.” When not in use, it must be streamlined into the configuration of the engine nacelle. When the reverser is not in use, the clamshell doors retract and nest neatly around the engine exhaust duct, usually forming the rear section of the engine nacelle.

Figure 3-48. Engine exhaust gases are blocked and diverted in a reserve direction during thrust reversal.

Figure 3-48. Engine exhaust gases are blocked and diverted in a reserve direction during thrust reversal.

In the aerodynamic blockage type of thrust reverser, used mainly with unducted turbofan engines, only fan air is used to slow the aircraft. A modern aerodynamic thrust reverser system consist of a translating cowl, blocker doors, and cascade vanes that redirect the fan airflow to slow the aircraft. [Figure 3-49] If the thrust levers are at idle position and the aircraft has weight on the wheels, moving the thrust levers aft activates the translating cowl to open closing the blocker doors. This action stops the fan airflow from going aft and redirects it through the cascade vanes, which direct the airflow forward to slow the aircraft. Since the fan can produce approximately 80 percent of the engine’s thrust, the fan is the best source for reverse thrust. By returning the thrust levers (power levers) to the idle position, the blocker doors open and the translating cowl closes.

Figure 3-49. Components of a thrust reverser system.

Figure 3-49. Components of a thrust reverser system.

A thrust reverser must not have any adverse affect on engine operation either deployed or stowed. Generally, there is an indication in the flight deck with regard to the status of the reverser system. The thrust reverser system consists of several components that move either the clam shell doors or the blocker door and translating cowl. Actuating power is generally pneumatic or hydraulic and uses gearboxes, flexdrives, screwjacks, control valves, and air or hydraulic motors to deploy or stow the thrust reverser systems. The systems are locked in the stowed position until commanded to deploy by the flight deck. Since there are several moving parts, maintenance and inspection requirements are very important. While performing any type of maintenance, the reverser system must be mechanically locked out from deploying while personnel are in the area of the reverser system.

Exhaust Systems With Turbocharger (Part Two)

Induction and Exhaust Systems

Convergent Exhaust Nozzle As the exhaust gases exit the rear of the engine, they flow into the exhaust nozzle. [Figure 3-46] The very first part of the exhaust nozzle and the exhaust plug form a divergent duct to reduce turbulence in the airflow, then the exhaust gases flow into the convergent component of the exhaust […]

Read the full article →

Exhaust Systems With Turbocharger (Part One)

Induction and Exhaust Systems

When a turbocharger or a turbosupercharger system is included, the engine exhaust system operates under greatly increased pressure and temperature conditions. Extra precautions should be taken in exhaust system care and maintenance. During high-pressure altitude operation, the exhaust system pressure is maintained at or near sea level values. Due to the pressure differential, any leaks […]

Read the full article →

Reciprocating Engine Exhaust Systems (Part Two)

Induction and Exhaust Systems

Radial Engine Exhaust Collector Ring System Figure 3-40 shows the exhaust collector ring installed on a 14-cylinder radial engine. The collector ring is a welded corrosion-resistant steel assembly manufactured in seven sections, with each section collecting the exhaust from two cylinders. The sections are graduated in size. [Figure 3-41] The small sections are on the […]

Read the full article →

Reciprocating Engine Exhaust Systems (Part One)

Induction and Exhaust Systems

The reciprocating engine exhaust system is fundamentally a scavenging system that collects and disposes of the high temperature, noxious gases being discharged by the engine. Its main function is to dispose of the gases with complete safety to the airframe and the occupants of the aircraft. The exhaust system can perform many useful functions, but its […]

Read the full article →

Turbine Engine Inlet Systems (Part Three)

Induction and Exhaust Systems

Bellmouth Compressor Inlets A bellmouth inlet is usually installed on an engine undergoing testing in a test cell. [Figure 3-30] It is generally equipped with probes that, with the use of instruments, can measure intake temperature and pressure (total and static). [Figure 3-31] During testing, it is important that the outside static air is allowed […]

Read the full article →

Turbine Engine Inlet Systems (Part Two)

Induction and Exhaust Systems

Divided-Entrance Duct The requirements of high-speed, single- or twin-engine military aircraft, in which the pilot sits low in the fuselage and close to the nose, render it difficult to employ the older type single-entrance duct, which is not used on modern aircraft. Some form of a divided duct, which takes air from either side of […]

Read the full article →

Turbine Engine Inlet Systems (Part One)

Induction and Exhaust Systems

The engine inlet of a turbine engine is designed to provide a relatively distortion-free flow of air, in the required quantity, to the inlet of the compressor. [Figure 3-24] Many engines use inlet guide vanes (IGV) to help straighten the airflow and direct it into the first stages of the compressor. A uniform and steady […]

Read the full article →

Turbocharger Controllers and System Descriptions (Part Two)

Induction and Exhaust Systems

Variable Absolute Pressure Controller (VAPC) The VAPC contains an oil control valve similar to the other controllers that were discussed. [Figure 3-21] The oil restrictor is actuated by an aneroid bellows that is referenced to upper deck pressure. A cam connected to the throttle mechanism applies pressure to the restrictor valve and aneroid. As the […]

Read the full article →