How many times have you booked a flight, perhaps deciding on a window seat so that you could see the view from 10,000 metres away? Maybe even the window right next to the wings? If so, have you ever noticed that there are moving parts attached to the wings of the aircraft? Well, you have noticed the hypersostenters. You will certainly have noticed the presence of two different parts in opposing positions in the wings. If the flaps are on the trailing edge, they are called flaps, or slats if they are on the leading edge.

What are hypersostenters and what are they used for?

Hypersostenters are moving parts attached to the wings, which, by modifying the aerodynamic characteristics of the wing, optimise its geometry in relation to a specific flight condition, in order to increase lift during take-off and landing, a phenomenon known as hypersostentation. This phenomenon is obtained by diverting the fluid current downwards or accelerating it on the back of the airfoil. In the first case, an increase in upward aerodynamic reaction is generated on the wing; in the second case, the separation of the fluid stream from the back of the wing is delayed.

Since, for assigned values of wing loading and air density, the speed of an aircraft is inversely proportional to the square root of its lift coefficient, it is evident that any aircraft with a high wing loading, as is typically the case with all high-speed aircraft, can only sustain itself in flight at relatively low speeds if its maximum lift coefficient can be greatly increased, when necessary, by using flaps.

An important feature of hypersupervisors, besides increasing lift, is the substantial reduction of the aerodynamic stall phenomenon. Stall represents a (critical) reduction in the aircraft’s lift coefficient due to an increase in the angle of attack of an airfoil. The most commonly used flaps are of two basic types: those made up of trailing edge elements (flaps) and those made up of leading edge elements (slats).

FLAP

The flaps, with their downward rotation, exert a hypersostentative action, essentially based on the increase in curvature of the midline of the airfoils, which considerably changes both the incidence of null lift and the aerodynamic moment. Let us describe some types:

Plain flap or Hypersostentator

It represents the simplest hypersostentation, hinged at the rear of the wing. It rotates downwards when extended, with a maximum range of 40°/50°. We see the variation in the curvature of the airfoil in a convex concave, which makes the wing ideal for slow flight, i.e. in take-off and landing situations, causing an increase in lift of up to 50%. While in flight, the plain flap is retracted to give the ideal airfoil for fast flight.

Split flap or soffit flaps

They consist of a flat surface, hinged to the wing at the ventral surface. Split flaps increase the lift coefficient by approximately 60%, with a 10% increase in the coefficient compared to plain flaps, at the same angles. This is achieved by increasing the curvature of the profile, which is different due to the fact that the dorsal wing surface is not modified.

Slotted flap or hyperslots 

Apparently the same as plain flaps, slotted flaps are the most widely used flaps today. When extended, they create a slot of a specific shape between the trailing edge of the wing and the leading edge of the flaps, which allows a ventral flow passage with increased energy to the back of the flaps. This flow deviation adds energy to the boundary layer on the dorsal surface of the flaps, delaying the separation of the airflow and substantially reducing resistance, increasing the lift coefficient by about 70%.

Fowler flap or sliding hypersupporter

This type of hypersostenters have the particularity that their movement does not employ a single degree of freedom, but two, rotation and translation. This privilege first causes translation backwards, thus increasing the wing surface area, and only then lowering, thus leading to greater efficiency in terms of controllability of the aircraft in particular flight configurations.

Slat

The slats, or fins, thanks to the effect produced by the gap that forms between them and the wing, increase the stall incidence of the wing, and therefore also the value of the maximum obtainable lift coefficient, without however determining appreciable variations in the incidence of zero lift. They do this by increasing both the surface area and the curvature of the wing, deploying outwards and lowering downwards from the leading edge. In contrast, Krueger flaps increase the curvature of the wing by extending the panels forward from the lower surface of the wing.

Slats are often extended and retracted using hydraulically or electrically operated actuators. In some more simplistic designs, however, they are held in the retracted position by aerodynamic forces and use springs or counterweights for automatic extension at low speeds.

In addition to hypersupervisors, you will certainly have seen aircraft with and without winglets in your lifetime!