getting to grips with aircraft performance 如何掌握飞机性能 2(18)

1.3.2. Temperature Effect
As temperature increases, thrust decreases due to a lower air density. As a result, the effect is the same as for altitude.
Temperature . . climb gradient . rate of climb .
1.3.3. Weight Effect
As seen in the previous section:
Thrust -Drag
. (5) .
γ
rad =
Weight Thrust -Drag
RC = TAS .
. (9) .
Weight
Therefore, at a given engine rating, altitude, and climb speed (TAS), any increase in weight leads to a decrease in the climb gradient and rate of climb.
Weight . . climb gradient ì rate of climb .
1.3.4. Wind Effect
A constant wind component has no influence on the rate of climb, but changes the flight path.

GS = Ground Speed
TAS = True Air Speed
γg = Ground climb gradient
γa = Air climb gradient

As shown in Figure G3, the air climb gradient remains unchanged, whatever the wind component. So, the fuel and time to the Top Of Climb (T/C) remain unchanged.
Headwind .
.  Rate of climb . 
Fuel and time to T/C . 
Flight path angle (γ
g) .
 
Ground distance to T/C .
 
Tailwind .
 .  Rate of climb . 
Fuel and time to T/C . 
Flight path angle (γ
g) .
 
Ground distance to T/C .
 

2. CLIMB IN OPERATION
2.1. Climb Management
2.1.1. Thrust Setting
The standard climb rating is called “Maximum Climb Thrust”. At the reduction altitude, pilots have to reduce thrust from takeoff power to climb power by setting the thrust throttles to the climb (CL) gate (Figure G4). This must be done prior to a maximum time of 5 minutes after brake release.

2.1.2. Energy Sharing
Aircraft energy is provided by the engines. To fly, an aircraft needs:
.
Kinetic energy : Energy necessary to maintain speed and accelerate.

.
Potential energy : Energy necessary to maintain altitude and climb.

The sum of the kinetic energy and the potential energy cannot exceed the total aircraft energy. Consequently, the total energy has to be shared between the need for speed and the need for altitude.
The FMGS manages this energy sharing during the climb (70% for speed, 30% for altitude). As a result, when:
.  
TAS increases: The climb gradient and the rate of climb decrease, as potential energy is converted into kinetic energy.

.  
TAS decreases: The climb gradient and rate of climb increase, as kinetic energy is converted into potential energy.

2.1.3. Climb Ceiling
The climb could continue until leveling off (i.e. when the rate of climb is close to zero). Nevertheless, as it would be both time and fuel consuming to reach the desired flight level, so the FMGS limits the climb to a maximum altitude. This maximum altitude is generally obtained when the rate of climb is equal to 300 feet per minute.
　
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