Which is true regarding the forces acting on an aircraft in a steady-state descent? The sum of all forward forces is equal to the sum of all rearward forces.

Which is true regarding the forces acting on an aircraft in a steady-state descent? The sum of all forward forces is equal to the sum of all rearward forces.

• A. The forward forces exceed the rearward forces.
• B. The rearward forces exceed the forward forces.
• C. The net force is directed downward only.
• D. The sum of all forward forces is equal to the sum of all rearward forces.

Answer: (D)

In steady-state descent, the aircraft passes through the air with constant speed and a constant flight-path angle, so there’s no acceleration. To understand this, separate the forces into components parallel and perpendicular to the flight path. Along the flight path, the forward force is thrust and the rearward force is drag. Since there’s no acceleration along that path in steady flight, these forces must balance, making their sums equal. The forces perpendicular to the flight path—lift and weight—also balance so the aircraft maintains its angle of descent. If forward forces exceeded rearward ones, the aircraft would accelerate forward; if rearward exceeded forward, it would slow or descend differently. The statement that the sums are equal reflects the zero-acceleration condition along the direction of motion in steady descent.

In steady-state descent, the aircraft passes through the air with constant speed and a constant flight-path angle, so there’s no acceleration. To understand this, separate the forces into components parallel and perpendicular to the flight path. Along the flight path, the forward force is thrust and the rearward force is drag. Since there’s no acceleration along that path in steady flight, these forces must balance, making their sums equal. The forces perpendicular to the flight path—lift and weight—also balance so the aircraft maintains its angle of descent.

If forward forces exceeded rearward ones, the aircraft would accelerate forward; if rearward exceeded forward, it would slow or descend differently. The statement that the sums are equal reflects the zero-acceleration condition along the direction of motion in steady descent.