NIFE Engines 3-4-1 Engine Types

Question 1

Describe a turbojet engine

Answer 1

Constructed by the addition of a inlet and an exhaust section to the basic gas generator. Derives its thrust by highly accelerating a small mass of air through the engine. It is the simplest form of gas turbine engine.

Question 2

Turbojet engine advantages

Answer 2

• Lightest specific weight (weight per pound of thrust produced)
• Higher and faster than any other engine

Question 3

Turbojet engine disadvantages

Answer 3

• Low propulsive efficiency at low speeds
• Relatively high TSFC at low altitudes and low airspeeds
• Long takeoff roll required

Question 4

Describe a turbofan engine

Answer 4

A cross between the turbofan and the turboprop. Combines the propulsive thrust of the exhaust gases from the gas generator with additional thrust that is generated by a duct enclosed fan. The duct enclosed fan partially compresses air that is then channeled around the turbojet and produces 30 to 60 percent of the thrust. The exhaust from the turbo jet generates the remaining thrust.

Question 5

Turbofan engine advantages

Answer 5

• Higher thrust at low aiirspeeds
• Lower TSFC
• Shorter takeoff sidtance
• Quieter

Question 6

Turbofan engine disadvantages

Answer 6

• Higher specific weight
• Larger frontal area
• Inefficient at higher altitudes

Question 7

Define thrust specific fuel consumption

Answer 7

Is the amount of fuel required to produce one pound of thrust.

Question 8

Compare the thrust specific fuel consumption of turbojet engines

Answer 8

Higher TSFC than a turbofan at low altitude and airspeeds due to lower bypass ratios

Question 9

Compare the thrust specific fuel consumption of turbofan engines

Answer 9

Turbofans have higher bypass ratios, which yields a lower TSFC

Question 10

Compare the propulsive efficiency of airplane engines

Answer 10

Turbojets have higher propulsive efficiency at high speeds. Turbofans convert more fuel into pressure energy (static pressure), requiring less energy to turn the turbine while also accelerating large masses of air with its fans. The large mass of airflow is only accelerated to moderate speeds, limiting high-end airspeeds and altitudes.

Question 11

Describe the effect of bypass ratio on turbofan performance

Answer 11

As the bypass ratio increases, the TSFC decreases because a larger mass of air can be accelerated for the same amount of fuel. The goal is to maximize the bypass ratio while still meeting mission requirements.

Question 12

Describe a turboprop engine

Answer 12

A turboprop engine is a gas generator that connects a propeller to the turbine section through a reduction gear box. The propeller gives it high propulsive efficiency by imparting a small amount of acceleration to a large mass of air.

Question 13

Turboprop advantages

Answer 13

• High thrust at low airspeeds
• Excellent take-off, slow speed, and low altitude characteristics
• Superior for lifting heavy loads off short runways

Question 14

Turboprop disadvantages

Answer 14

• Heavy
• More complicated
• Limited speeds

Question 15

Describe a turboprop propeller assembly

Answer 15

Essentially a rotating wing or airfoil. The prop converts the power output of the engine into forward thrust to move the aircraft through the air. The majority of the thrust, approx 90%, is a result of the large air mass being accelerated by the propeller.

Question 16

Describe the operation of the reduction gear box in a turboprop engine

Answer 16

Located between the gas generator and the propeller assembly, it prevents the propeller blades from reaching supersonic speeds. Converts high RPM low torque of the generator into low RPM high torque for the prop.

Question 17

Propeller assembly

Answer 17

• Blades
• Hub/barrel assembly
• Pitch change/dome assembly

Question 18

Torque meter assembly

Answer 18

• Torque shaft (inner) transmits

- Reference shaft (outer) measures

Question 19

Describe the torquemeter assembly in a turboprop engine

Answer 19

A set of shafts located between the generator and reduction gear box. It is used on some turboprop engines to transmit and measure the power output from the generator to the gear box.

Question 20

List operations of the propeller of a turboprop engine

Answer 20

1. Alpha

2. Beta

Question 21

Alpha range

Answer 21

(flight range) In this range, the power control lever (PCL) sends signals to the FCU for fuel flow. The FCU also works with the prop governor to ensure a constant prop RPM by adjusting the blade angle

Question 22

Beta range

Answer 22

Can only be used during ground operations, where the PCL can be positioned from flight idle to max reverse by changing the prop blade angles (T-6B does NOT have beta)

Question 23

Describe a turboshaft engine

Answer 23

Same as a turboprop except the power shaft is connected to something other than a propeller and the shaft is only connected to a free/power turbine. 100% of thrust is mechanical

Question 24

Describe the operation of the free/power turbine of a turboshaft engine

Answer 24

Is mechanically independent from the gas generator. Driven by gas generator exhaust. connected to the main transmission through a coaxial main drive shaft

Question 25

Describe basic light civilian aircraft reciprocating engine

Answer 25

Arrangements are inline, opposed, or radial. Props can be directly driven by a crankshaft or through a reduction gear box. A governor is used to control the blade angle and propeller speed. Props can be controlled hydraulically or by oil pressure.