Aircraft Take off Technical Explanation

Aircraft take off is a critical phase of flight where an aircraft transitions from a stationary position on the ground to sustained flight in the air. The takeoff process involves several key stages and factors to ensure a safe and successful departure. Here we will explain technical aspects of Aircraft take off.

What is Aircraft Take off?

The takeoff maneuver encompasses the stages of flight from the initial acceleration at the beginning of the runway until the aircraft reaches a specified altitude and velocity, as defined by aviation regulations. During takeoff, the aircraft operates at maximum engine thrust, with flaps and landing gear in the appropriate positions.

In the initial phase of the takeoff maneuver, the aircraft undergoes two main stages: rolling on the ground and ascending into the air. These stages can be further divided into sub-phases to better understand the sequence of events and performance characteristics.

1. Rolling on the Ground (0 ≤ V ≤ VLOF):
   • a. Rolling with All Wheels on the Ground (0 ≤ V ≤ VR): During this phase, the aircraft accelerates along the runway with all wheels in contact with the ground. It continues to build speed until it reaches a critical velocity known as the rotational velocity (VR).
   • b. Rolling with Aft Wheels on the Ground (VR ≤ V ≤ VLOF): After reaching VR, the nose of the aircraft is rotated upward, and it continues to accelerate, but now only the aft wheels remain in contact with the runway. This phase leads up to the takeoff velocity (VLOF), where the aircraft becomes airborne.
2. Path in the Air (VLOF ≤ V ≤ V2):
   • a. Track of Curve Transition (V ≈ VLOF): Immediately after becoming airborne, the aircraft undergoes a transition phase to establish the desired ascent flight path angle. This involves adjusting the pitch attitude and flight controls to achieve the desired climb trajectory.
   • b. Straight Accelerated Track (VLOF ≤ V ≤ V2): Once the aircraft has transitioned to the desired climb angle, it enters a phase of accelerated ascent. The aircraft continues to climb at a constant flight path angle until it reaches a specified velocity (V2) at a predetermined altitude (typically 35 feet or 10.7 meters above the runway).

For detailed analysis and approximation of takeoff distances and times, a simplified model assuming uniform acceleration and only thrust force acting on the aircraft can be employed. According to Newton’s second law, the acceleration (a) of the aircraft is directly proportional to the thrust force (T) divided by its mass (m):

T=ma​

This simplified approach provides initial estimates for takeoff performance metrics, which can then be refined using more detailed aircraft performance data and calculations.

Aircraft Take off Equations

Following equations are very useful to understand aircraft take off for engineers, technicians and scientists.

Forces during taking off.

During takeoff, several forces act on the aircraft, each playing a crucial role in the process of accelerating and lifting off from the runway. Here are the main forces involved:

1. Thrust (T): Thrust is the forward force generated by the aircraft’s engines. It propels the aircraft forward along the runway and provides the necessary acceleration to overcome drag and achieve takeoff speed.
2. Drag (D): Drag is the aerodynamic resistance that opposes the aircraft’s forward motion. During takeoff, drag increases as the aircraft accelerates, requiring more thrust to overcome it. Pilots aim to minimize drag by maintaining a streamlined configuration and reducing parasite drag from factors like landing gear and flaps.
3. Weight (W): Weight is the force exerted by gravity on the aircraft. It acts vertically downward through the aircraft’s center of gravity (CG) and represents the aircraft’s mass. During takeoff, the aircraft’s engines must produce enough thrust to overcome its weight and achieve lift-off.
4. Lift (L): Lift is the aerodynamic force generated by the wings that opposes the aircraft’s weight. As the aircraft accelerates along the runway, the wings generate lift through the airflow over their surfaces. Lift increases as airspeed increases, eventually exceeding the aircraft’s weight and allowing it to become airborne.

During takeoff, the balance between thrust and drag determines the aircraft’s acceleration along the runway, while the balance between lift and weight governs its ability to become airborne. Pilots carefully manage these forces by adjusting engine power, controlling the aircraft’s pitch attitude, and configuring aerodynamic surfaces to achieve a safe and efficient takeoff. Additionally, factors such as runway length, aircraft weight, air density, and environmental conditions influence the effectiveness of these forces during the takeoff phase.