Destructive Forces Acting on an Aircraft in Flight

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Aircraft in Peril. Photo Credit: Rocklin Lyons

Though aircraft are engineered to take advantage of the required forces in an efficient manner, an excess of these forces has a devastating effect on the plane’s flight.

The aircraft requires a productive manipulation of lift, weight, thrust and drag; the four primary forces acting on an aircraft in flight.

An imbalance between these forces that exceeds the airplane limitations, be it positive or negative, severely affects the performance of an aircraft in flight.

Forces Which Can Destroy an Aircraft in Flight

Although these forces work to benefit the plane, they can also destroy it – so exercise caution.

Lift: All vertical movement of the aircraft in terms of altitude gain and loss, is in relation with the force of lift. You need lift to fly, and airplane wings are the basic airfoils required to create lift. The wings of an aircraft in flight tend to bend upwards during flight, a phenomenon commonly termed as Aero-elasticity.

All are aware of the positive effects of the creation of lift, but in some cases, it is actually a destructive force. What does lift doto the wings of an aircraft in flight?The upward bending of the aircraft wings subject the upper surface to compressional forces, and the lower surface to tension, a common cause of wear and tear in airplane wings.
Torsional forces tend to twist the wing structure, acting downwards from the leading edge and upwards from the trailing edge of the wing, creating additional stress.

Drag: The force of drag is fundamentally created as a reactional force to the creation of lift and thrust. Drag basically seeks to retard the forward motion of an aircraft as follows:All surfaces through which the force of drag acts tend to bend backwards, or in the direction of the force of drag. This exposes the airplane components under consideration to compression, tension and bending.
The undercarriage may experience severe deformation due to compression and tension, if deployed at airspeeds exceeding limitations.

Inertia and Momentum: An aircraft in flight develops significant momentum due to its motion through the air, trumped by its enormous mass. The combination of these two factors create the following issues for the aircraft:As an airplane approaches to land, at touchdown, the weight of the plane is transferred from the wings to the landing gear.
Inertial forces pull the airplane wings downwards, thus exerting compressional forces on the lower surface of the wing and tension on the upper surface of the wing.

This spontaneous transfer of momentum onto the landing gear exposes the landing gear to forces of compression.

Friction: Frictional forces acting on the tires must also be kept in check. Uncontrolled friction between the tires and the runway at higher-than-recommended speeds may lead to a nose-down moment, and subsequent crash.

Destructive these forces may be, nonetheless their positive aspects trump their negative affects. In other words, as long as the pilot follows appropriate regulations, and uses control to keep these forces under check, they can be used to produce and prolong the aircraft’s flight. Despite this, the forces continue to exert stress on the airplane. This means that airplane parts must be regularly inspected to maintain their serviceability and prevent in-flight damage.

Failsafe measures are adopted to ensure that a component, even if it errs within its safe life, is accompanied by a backup or secondary component. The use of aluminum alloys and the introduction of new composite materials, all seek to negate the unwanted properties of these forces faced by modern aircraft in flight.

Resources:

S. M. Rizvi. Basic Airframe Precis. PIA Training Centre.

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