STEADY FLIGHT
Steady flight is the flight with no acceleration. During a steady flight, there is no acceleration of the centre of gravity of the aeroplane. Therefore, all the forces acting on the aeroplane are balanced.
HORIZONTAL STEADY FLIGHT
Horizontal steady flight is the case when aeroplane flies at a constant speed and constant altitude. Thus, it never changes its’ true airspeed and it never changes its’ altitude during a horizontal steady flight. The forces acting on the aeroplane during a horizontal steady flight are balanced as shown in Figure 1.
Figure 1. Forces acting on an aeroplane during a horizontal steady flight.
The force balance along the aeroplane’s flight path:
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(1) |
Thus, the thrust of the aeroplane is equal to the aeroplane’s drag:
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(2) |
The force balance along the axis perpendicular to the aeroplane’s flight path:
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(3) |
Thus, the lift is equal to the aeroplane’s weight:
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(4) |
where, the weight is equal to the aeroplane’s mass times the earth’s gravitational acceleration:
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(5) |
STEADY CLIMBING FLIGHT
Steady climbing flight is the case when aeroplane climbs with a constant true airspeed and with a constant climb angle (g). The forces acting on the aeroplane during a steady climbing flight are balanced as shown in Figure 2.
Figure 2. Forces acting on an aeroplane during a steady climbing flight.
The force balance along the aeroplane’s flight path:
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(6) |
Thus, the thrust of the aeroplane is equal to the aeroplane’s drag plus the component of weight along the flight path axis:
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(7) |
The force balance along the axis perpendicular to the aeroplane’s flight path:
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(8) |
Thus, the lift is equal to the component of aeroplane’s weight perpendicular to the flight path:
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(9) |
STEADY DESCENDING FLIGHT
Steady descending flight is the case when aeroplane descends with a constant true airspeed and with a constant descend angle (g). The forces acting on the aeroplane during a steady descending flight are balanced as shown in Figure 3.
Figure 3. Forces acting on an aeroplane during a steady descending flight.
The force balance along the aeroplane’s flight path:
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(10) |
Thus, the thrust of the aeroplane is equal to the aeroplane’s drag minus the component of weight along the flight path axis:
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(11) |
The force balance along the axis perpendicular to the aeroplane’s flight path:
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(12) |
Thus, the lift is equal to the component of aeroplane’s weight perpendicular to the flight path:
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(13) |
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10 May 2009, (c) kokpit.com
