Aero Chapter 05/06 (TS) and 05 (ADV & IUT), Thrust and Thrust Curve Review
T-45 Aerodynamics Student Workbook
would decrease with the increase in inlet velocity. However, as inlet velocity increases, airmass flow (Q)
through the engine also increases due to ram effect (Figure 82).
Ram effect, as the name implies, refers to the effect of additional air forced into the engine intake as the
aircraft moves at high speed through the airmass. Inlet velocity increase and ram effect approximately
cancel each other’s effect on thrust available. In practice, there is a slight decrease of thrust with
increasing airspeed at low airspeeds.
(Figure 83) indicates the theoretical and actual effect of increasing airspeed on thrust available in the
T-45. For practical purposes, the T-45’s thrust is the same over the aircraft’s speed range.
Ta = Q (V2 - V1)
6,000
Ta
5,800
5,600
Actual
V2 - V1 EFFECT
Theoretical
5,400
RAM EFFECT (Q)
5,200
AIRSPEED
5,000
0
100
200
300
400
500
600
700
800
Calibrated Airspeed - Knots
Figure 82: T-45 AIRSPEED VS THRUST
Figure 83: T-45 AIRSPEED VS THRUST CURVE
ATMOSPHERIC CONDITIONS
ALTITUDE AND TEMPERATURE
When a turbofan is operated at a constant
50,000
airspeed, the airmass flow through the
45,000
THRUST
engine will depend on the density of the air.
Thrust output, which is directly proportional
40,000
to the airmass flow, will decrease with a
TROPOPAUSE
35,000
A
decrease in air density (Figure 84). There is
L
an appreciable thrust loss with an increase
30,000
T
in altitude. At 30,000 ft, there is a thrust
I
DENSITY
25,000
loss of approximately 40% due to the
T
decrease in density.
U
20,000
D
Actually, the decrease in thrust due to an
E
15,000
altitude increase is not as severe as the
10,000
altitude increase alone would indicate. The
decrease in inlet air temperature as altitude
5,000
increases provides for the addition of more
SEA
combustion energy and, therefore, an
0.4
0.6
0.8
1.0
LEVEL
increase in nozzle velocity. Up to the
Figure 84: T-45 ALTITUDE VS DENSITY
tropopause, approximately 36,000 ft, an
AND THRUST
(7-99) Original
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