Aero Chapter 05/06 (TS) and 05 (ADV & IUT), Thrust and Thrust Curve Review
T-45 Aerodynamics Student Workbook
SUMMARY OF ATMOSPHERE TO TURBOFAN PERFORMANCE
The following chart (Figure 87) summarizes the relationship between atmospheric changes and turbofan
engine performance. Assume the change of one or more atmospheric conditions listed in the left column.
The engine performance will be affected as stated in the right column. Sequential changes are connected
by the symbol “->”. The first situation below translates “an increase of temperature produces a decrease
of density, mass flow, and thrust available.”
INCREASE OF BELOW CONDITION(S)
CAUSES BELOW TO DECREASE
Temperature
Humidity
Density -> Mass flow -> Thrust Avail
Altitude
DECREASE OF BELOW CONDITION(S)
CAUSES BELOW TO INCREASE
Temperature
Humidity
Density -> Mass flow -> Thrust Avail
Altitude
WHEN ALTITUDE INCREASES
CAUSES FOLLOWING DECREASES
(Up to 36,000’)
Density
Temperature (partially compensates for
decrease in density)
Mass flow
Thrust available
Drag
Summary:
WHEN ONE OF DENSITY OR MASS
THRUST AVAILABLE
FLOW OR (Vexh-Vin) CHANGES>
ALSO CHANGES DIRECTLY
Figure 87: SUMMARY OF ATMOSPHERE TO TURBOFAN PERFORMANCE
JET ENGINE ANOMALIES
COMPRESSOR STALLS
The rotating blades of the engine compressor have airfoil profiles and act like little wings. Just like a wing,
they can stall if the airflow over them is disrupted or exceeds the stall angle of attack. When this happens,
the smooth flow of compressed air to the combustion section is interrupted and a compressor stall occurs.
Effects and indications of a compressor stall can be a loss of thrust; rising EGT; stagnant or falling rpm; or
audible bangs, pops, and vibrations. Compressor stalls can lead to engine damage if not cleared quickly
(mostly through excessive internal temperatures). For specific T-45 compressor stall characteristics, read
T-45A or T-45C NATOPS.
FLAMEOUT
Flameout refers to the inadvertent shutdown of burning in the combustion chamber. Usually an
interruption of fuel flow or misadjustment of the fuel control is the cause of a flameout induced by
mechanical failure. Pilot-induced flameouts caused by inadvertently pulling the throttle lever past idle
while airborne are common enough to be a real hazard. Indications of flameout are low and falling EGT
and low and falling rpm. Flameouts are not usually damaging to the engine, but obviously are undesir-
able. Pilot-induced flameouts caused when the engine is quickly reduced to idle from a high power setting
may not be immediately recognized by the pilot since the engine and aircraft “feel” the same until the
engine rpm drops below idle. The NATOPS airstart procedure is the pilot’s action following a flameout.
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