Aircraft Engineering

In aircraft engineering, a universal joint is a spatial mechanism. It allows users to transmit the motion between two rotating axes whose extensions are joined at a point. universal joints are classifiable as transmission components.

Learn more about universal joints

It consists of two rotary pairs fitted on the same component bent at 90 degrees on one side that is connected to an axis. This central element is known as a cross.

The universal joint is not homokinetic and the average rotation speeds of the two shafts are equal. This causes the obvious disadvantage of a non-fluid transmission, which can cause problems related to vibrations.

A homokinetic transmission can be obtained by using two universal joints in series between them. The universal joint is widely used in mechanics for its properties. It also favoured for the relative simplicity and economy compared to other types of connections between trees of the aforementioned type.

When it comes to an aircraft, it is generally used in steering shafts and transmission. The use of the universal joint is necessary where the axis that transmits the motion is not perfectly coincident with the trailing axis, or when the latter is susceptible to even minimal misalignments.

A telescopic shaft may be used with two joints to transmit the rotary motion from the power take-off of the tractor to the connected tools.


Inspection mirrors allow an aircraft technician to see the universal joint remotely, particularly in places where normal vision is limited. These mirrors should be mounted using universal joints so that they can be positioned at various angles.

The development of this device allows users to change the angle of the mirror with remote control. A rack and pinion mechanism passes through the stem and is controlled by a knob on the handle.

This allows a range of angles to be obtained after inserting the instrument into the structure. Some instruments are equipped with non-dazzling integral lighting.

Magnifying glasses are more useful tools, to help with the closed inspection of a wing section. Experts can clarify the details when a normal visual inspection produces only the suspicion of a crack or corrosion.

The magnifying glasses are of different styles, from the type of pocket, with a magnification factor of 'twice' (x2), to the stereoscopic type with a magnification up to x32.


The magnification factor refers to the size of an object, seen through the magnifying glasses, concerning the size of the object, seen with the naked eye, at a distance of 250 mm (10in).

For day-to-day inspection of the structures, a hand-held instrument with an 8x magnification and integral lighting could be used. Magnification above this value should not be used unless specified, as the limited observation area does not reveal the surrounding area. A higher magnification factor can be used, once a smaller magnification has identified a problem.

Magnifying glasses and similar inspection tools can provide the best results only when the area under control is well lit. These tools have a variety of different names, although all of them essentially operate on similar principles.

If they are called endoscopes or fiberscopes, (or videoscopes), they are optical instruments used to control isolated areas of structures, components or motors, which would otherwise not be directly viewable.