Slow Flight / Fast Flight
Chapter 10.2
Objectives
To know the definition of SLOW FLIGHT
To know the behavior of the aircraft in regards to the stability of the speed
To know the adequate corrections in order to respect the tolerances during the SLOW FLIGHT
Definitions
Slow flight is the speed range between V BEST GLIDE and the minimum speed, depending on the mass of the airplane and its configuration
Definitions
Fast flight is the domain beyond V BEST GLIDE.
Definitions
We are in slow flight during:
- FINAL
- LANDING
- TAKE OFF
- INITIAL CLIMB
Definitions
The lowest value of the slow flight is the minimum speed / V stall
The AFM contains a table giving the lower limits of the V STALL slow flight for different configurations and flight attitudes. V stall depends on the following factors:
- Mass of the airplane (load factor, mass x acceleration)
- Position of the flaps
- Engine power for aircraft with engine in front
Stability of Speed During Slow and Fast Flight
For a speed higher than V BEST GLIDE, the airplane is stable at speed.
If the angle of attack is increased by a disturbance in airflow, then lift and drag increase.
This reduces the airspeed. With decrease in airspeed, the drag also decreases.
The airspeed will then be restored.
Stability of Speed During Slow and Fast Flight
For a speed below the VBEST GLIDE, the airplane is not stable.
If the angle of attack of the aircraft flying is below V BEST GLIDE increases due to disturbance, the induced drag increases
The airspeed can not be restored, it will continue to decrease until you reverse this trend by increasing the engine power or by changing the attitude.
Summary
Airspeed, Pressure and its Effects on Flight Controls
Pressure and its effects on flight controls changes with the airspeed:
When the airspeed decreases, the longitudinal static stability is reduced:
- The controls are less efficient and require larger movements
- The pressures on the control surfaces are weaker, thus the flight controls become «sluggish»
- The angle of attack shall be increased in order to obtain the additional lift required.
- Engine power must be increased to overcome the induced drag.