Aero Chapter 05/06 (TS) and 05 (ADV & IUT), Thrust and Thrust Curve Review
T-45 Aerodynamics Student Workbook
AERO CHAPTER 05/06 (TS) AND 05 (ADV & IUT), THRUST AND THRUST CURVE
REVIEW
OVERVIEW
This lesson discusses the factors that affect the thrust output of a turbofan engine and how changes in
weight, altitude, and configuration affect the thrust-required curve and aircraft performance, relevant to the
T-45.
JET PROPULSION THEORY
The thrust of a turbojet or turbofan engine comes from taking a large mass of air in and pushing it out the
exhaust nozzle at a much higher velocity. This is a direct application of Sir Isaac Newton’s Third Law that
states “for every action, there is an equal and opposite reaction.” Jet engine thrust is the result of reaction
to the acceleration of an airmass created by the engine and not, as is sometimes supposed, the effect of
exhaust gases pushing against the outside air.
Understanding the HOW of thrust production requires familiarity initially with the construction of the
turbojet engine (Figure 77). The forward or input part of the turbojet engine is the compressor section.
Through a series of stationary vanes and rotating blades, the incoming air is compressed and passed to
the combustion section where nozzles spray fuel and mix it with the highly compressed air. The burning
fuel/air mixture adds energy to the airflow through the engine. From the combustion section, the gases
enter the turbine section. Power is produced in the turbine section to drive the compressors, accessories,
etc. In the exhaust section, following the turbine section, the pressure forces the gases at very high
velocities through the jet nozzle at the rear of the engine.
Turbine
Compressor
Combustion
Exhaust
Section
Section
Vin
Vexh
or
or
V1
V2
Figure 77: JET PROPULSION THEORY
In the turbofan (Figure 78), power is also
Turbines
N1
N2
provided from the turbine to drive the fan
N2
N1
Compressor
Compressor
at the front of the engine. Where a
Exhaust
Afterburner
Combustion
turbojet engine derives its thrust by the
Section
Section
Section
large acceleration of a relatively small
airmass, a turbofan derives its thrust by
imparting less acceleration to a relatively
larger airmass. A turbofan version of a
similar turbojet engine will have more
static takeoff thrust, more climb thrust,
Variable
Exhaust
more cruise thrust, lower specific fuel
Figure 78: TURBOFAN ENGINE WITH AFTERBURNER
(7-99) Original
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