Aircraft Wing Structure - Ribs, Stringers, Spars Functioning

Just like our body has a skeleton, the complex structure of wings are manufactured in the same way and since wings of an aircraft are responsible for lifting the aircraft off the ground, the wings must adhere to the aerodynamic shape.

So the wing skeleton must be made in such a way so that not only it does not change the aerodynamic characteristics of the wing but also the skeleton is able to provide the required strength in order to withstand different loads in air and/or ground and is able to sustain itself without causing any damage.

Typically the wings of a fixed wing aircraft generally consist of ribs, stringers, spars and skin.

We know that aerofoil is cross section of the wing. The chief component for providing the shape of an aerofoil are the Ribs.

These are structural members which are shaped like an aerofoil, and are responsible for giving the shape to the wing. The ribs are usually made of aluminum alloys, carbon steel and corrosion resisting steel but now these days emphasis is being given on composite material ribs since composite materials have a higher strength to weight ratio. The ribs are placed at small intervals and their numbers depend from wing to wing.

The stringers which are basically a stiffening members and goes through these ribs and are mainly there to transmit the aerodynamic loads. The aerodynamic loads get transmitted from the wing skin or the surface of the wing to the ribs and spars via the stringers.

Spars are the main structural members along the span of the wing. Their role is to take the aerodynamic loads which are imposed on the wings when in air and also support the weight of wings while on ground. Bending loads, drag loads, torsional loads etc. are some loads which this member must hold. For withstanding the loads effectively, 2-3 spars namely the Front Spar, Mid Spar and Rear Spar or just the Front and Rear spar must be placed inside the wing. Following figure shows the placement of the Front and Rear Spar.

The ribs, stringers and spars mainly make up the internal structure of the wing just like different type of bones make up the skeleton. 

To cover the internal structure of the wing, a skin must be put over it to keep the surface smooth which will minimize the drag produced and make the aircraft fuel efficient. The skin is riveted to the rib flanges and longitudinal stiffeners. 

At the leading edge of the wing, the curvature is large. In order to preform the aluminum sheets into correct shape, they are passed through “rolls”. Moreover, for delaying the transition from laminar to turbulent flow in the forward chord-wise section, countersunk rivets are used in these sections as opposed to dome-headed rivets.