Aero Chapter 05/06 (TS) and 05 (ADV & IUT), Thrust and Thrust Curve Review
T-45 Aerodynamics Student Workbook
Maximum horizontal airspeed for an aircraft
is where the thrust available (Ta) line
6,000
Ta at Sea Level
intersects the thrust required (Tr) curve
5,000
(Figure 90).
SEA LEVEL
STANDARD DAY
4,000
Tr
(CLEAN)
REGION OF NORMAL COMMAND/
3,000
REGION OF REVERSE COMMAND
(L/D)max divides the “Region of Normal
2,000
Command” and the “Region of Reverse
(L/D )
Command” (Figure 91). Flight in the region
MAX
VH
1,000
of normal command involves velocities
0
greater than maximum endurance airspeed,
0
100
200
300
400
500
600
in which an aircraft is in stable equilibrium.
TRUE AIRSPEED - KNOTS
That is, if disturbed (slowed down), it tends
Figure 90: T-45 MAXIMUM HORIZONTAL SPEED
to return to equilibrium. At speeds greater
than (L/D)max, more power is required to fly
faster.
6,000
A pilot cruising in the region of normal
Region of
Region of
command at 88% rpm increases the throttle
Reverse
Normal
5,000
Command
Command
Tr
to 95% rpm; the aircraft would accelerate as
4,000
thrust exceeds drag. The aircraft would
accelerate and parasite drag would increase
Total Drag
3,000
until total drag equaled thrust. Throttle
2,000
reduction would cause the aircraft to
(L/D)
MAX
decelerate until parasite and total drag
1,000
decreased sufficiently that total drag
equaled thrust.
0
TRUE AIRSPEED - KNOTS
In the region of reverse command, speeds
Figure 91: REGIONS OF NORMAL COMMAND
less than maximum endurance airspeeds,
AND REVERSE COMMAND
more power is required to fly slower due to
the increased induced drag. To fly at a
slower speed, a pilot would be required to add thrust to overcome the additional drag. Takeoff and landing
may venture into this region, also called the “back side of the power curve.” In the region of reverse
command, a pilot on an approach might raise the nose of the aircraft in an attempt to reduce the rate of
descent.
The large increase in induced drag and rapid reduction in airspeed could cause an increase in the rate of
descent and a stalled condition. In the region of reverse command, airspeed must be controlled with
angle-of-attack or nose position and rate of descent must be controlled with thrust. During a normal on-
speed approach, the T-45 is approximately 13 kts above the region of reverse command.
THRUST CURVE VARIABLES
A thrust-required curve is based on the variables of weight, altitude, and aircraft configuration. If any of
these variables change, the thrust-required curve would also change.
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