Aircraft Performance and Altitude

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Questions and Answers

What is the main reason for the increased acceleration of the unit trying to exit the exhaust nozzle?

The entry of the new unit into the inlet

The decrease in the acceleration of the unit

The decrease in the mass of the unit

The increase in the volume of the unit (correct)

What is the force that acts on an object in Earth's gravitational field?

Weight (correct)

Thrust

Mass

Acceleration

What is the equation that relates force, mass, and acceleration?

F = m - a

F = m + a

F = m/a

F = ma (correct)

What is the purpose of the turbine in a gas-turbine turbojet engine?

To perform work and generate thrust Signup and view all the answers

What is the result of burning fuel in a turbojet or turbofan engine?

A forward reaction called thrust Signup and view all the answers

What is the relationship between mass and weight on Earth?

Mass is equal to weight Signup and view all the answers

What determines engine operating limitations in a gas turbine engine?

Turbine and nozzle materials used Signup and view all the answers

Where are engine operating limitations typically found?

Engine Maintenance Manual and Aircraft Type Certificate Data Sheet Signup and view all the answers

What is the approximate bypass ratio in a low-bypass engine?

1:1 Signup and view all the answers

What advantage do full fan ducts provide in low-bypass engines?

Reduce noise emissions Signup and view all the answers

What is an additional limiting factor for all gas turbine engines?

Vibration Signup and view all the answers

What is the primary purpose of the International Standard Atmosphere (ISA)?

To compare the performance of similar engines Signup and view all the answers

What is the temperature lapse rate in the International Standard Atmosphere (ISA)?

1.98 °C per 1000 ft Signup and view all the answers

What determines the bypass ratio in a medium-bypass engine?

Fan diameter Signup and view all the answers

What is included in the engine operating limitations for a turboprop engine, such as the Allison 250 Series?

Maximum thrust settings, fuel and oil pressures, engine oil temperatures, and torque Signup and view all the answers

What is the typical range of bypass ratios in a high-bypass turbofan engine?

4:1 to < 9:1 Signup and view all the answers

Why may borescope inspections need to be performed?

If engine operating limitations are exceeded Signup and view all the answers

At what altitude is the temperature constant in the International Standard Atmosphere (ISA)?

36 089 ft to 65 617 ft Signup and view all the answers

What is the advantage of high-bypass turbofan engines over low- or medium-bypass turbofan engines?

Higher propulsive efficiencies and better fuel economy Signup and view all the answers

What is the unit of measurement for atmospheric pressure in the International Standard Atmosphere (ISA)?

Pounds per square inch (psi), inches of mercury (inHg), or millibars (mbar) Signup and view all the answers

What is not a typical engine operating limitation for a gas turbine engine?

Engine acceleration rate Signup and view all the answers

What is the factor that affects the mass airflow through an engine?

Density of the air entering the inlet Signup and view all the answers

What type of engines are typically used on large airliners used for long flights?

High-bypass turbofan engines Signup and view all the answers

What is the primary mechanism by which an engine produces thrust?

By accelerating the mass airflow through the engine Signup and view all the answers

What is the effect of a reduction in pressure on air density?

It reduces air density Signup and view all the answers

What is the primary factor affecting engine performance at high altitudes?

Pressure Signup and view all the answers

What happens to temperature at the tropopause?

It remains constant Signup and view all the answers

What is the principle behind the operation of a gas turbine engine?

Continuous combustion Signup and view all the answers

What is the effect of an increase in temperature on air density?

It reduces air density Signup and view all the answers

What is the nature of the reactive force of thrust in a turbine engine?

It is created by the acting forces within the engine Signup and view all the answers

Study Notes

Gas Turbine Engine Performance

At sea level, the ISA value is 14.7 psi, and pressure decreases with altitude, affecting engine performance.
Temperature also decreases with altitude, but at the tropopause (36,089 ft), it remains at -56°C.
Both pressure and temperature affect density, which impacts engine performance, with pressure having a greater effect.
Density reduction is more significant due to pressure than temperature.

The Reactive Force of Thrust

Thrust is not created by pushing outside air, but rather by the reacting force within the engine.
Continuous flow cycle is utilized to create the acting force within a turbine engine.
Gas turbine engines operate on a principle of continuous combustion, with one unit of mass airflow in and one unit out.
Thrust is transmitted to the aircraft through the engine mounts.

Newton's Second Law

Force is proportional to the product of mass times acceleration (F = ma).
Mass and weight are different quantities, but in Earth's gravity, they can be treated as similar.
Weight is mass with gravity applied (W = mg).

Turbojet and Turbofan Engines

These engines burn fuel to accelerate a mass of gas rearwards, creating a forward reaction called thrust.
Bypass air flow and fan duct design can affect engine performance.

Engine Types and Bypass Ratios

Low-bypass engines have a bypass ratio of approximately 1:1.
Medium-bypass engines have a bypass ratio of 2:1 to 3:1.
High-bypass turbofan engines have a bypass ratio of 4:1 to <9:1 and offer higher propulsive efficiencies and better fuel economy.

Engine Ratings and Limitations

International Standard Atmosphere (ISA) is used to standardize engine performance comparisons.
ISA defines a temperature lapse rate of 1.98 °C per 1000 ft, resulting in a fall from 15 °C at sea level to -56.5°C at 36,089 ft.
ISA standard pressure at sea level is 1013.2 mbar, 29.92 inHg, or 14.69 psi.

Engine Thrust in Flight

Net thrust is determined by in-flight variables, including mass airflow, altitude, air temperature, humidity, airspeed, ram effect, ram drag, engine rpm, and engine conditions.

Engine Operating Limitations

Engine operating limitations are determined by turbine and nozzle materials used.
If limits are exceeded, borescope inspections may need to be performed.
Engine operating limitations include maximum thrust settings, fuel and oil pressures, engine oil temperatures, engine operating temperature limitations, and engine maximum operating rpm.

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Description

Learn how altitude affects aircraft performance, including the impact of pressure and temperature on air density and thrust.