12.64 Descending Flight

12.64.2 Identify and name the forces acting in a glide.

In a glide, the four forces acting on the aircraft are lift, weight, and drag. Thrust is absent (engine at idle or failed).

Forces Acting:

• Lift (L): Acts perpendicular to the flight path
• Weight (W): Acts vertically downward
• Drag (D): Acts opposite to the flight path
• Thrust (T): Zero or negligible in a glide

Force Relationships in a Glide:

• The aircraft descends because weight is not balanced by lift alone
• Weight can be resolved into two components:
  • One component balances drag (along the flight path)
  • The other balances lift (perpendicular to the flight path)
   

Summary

In a steady glide:

• Lift acts perpendicular to the flight path
• Drag opposes motion
• Weight provides the driving force for the descent
• No thrust is present

The aircraft glides forward and downward under the action of weight balanced by lift and drag.

12.64.4 Explain how the forces in a glide become modified in a constant speed power on descent.

In a glide, there is no thrust, and weight provides the driving force for the descent. In a power-on descent at constant speed, the introduction of thrust changes the balance of forces.