All About Universal Joints

Functions of A Universal Joint On An Aircraft

universal joints are used to connect two shafts that are not directly in line with one another. They are coupled so that it flexes in two separate planes that are 90 degrees apart. In other words, the U-joint flexes both up-and-down and from side to side.

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The U-joint that is the subject of the service bulletin is a bendable connection between the Y-shaped control yoke assemble and the control wheel shaft under the instrument panel. Each aircraft has two U-joints installed, one of the pilot side and the other on the co-pilot side. A breakdown and subsequent detachment of either U-joint would render the control wheel on the side with the failed joint defective. Depending on which side failed, either the pilot or co-pilot would no longer have control of the ailerons or elevator.

Universal joints used in aircraft handled temporary torsional overloads as high as 80% of rated ultimate without harmful binding. The overloads reach up to 150% more than estimated ultimates that have been required without binding. These features guarantee high safety factors under the most challenging operating conditions. A U-joint is also used in 'crash test dummies' to help determine the extent of physical harm caused by the collision. With a length of 0.937 inches and outside diameter of 0.375, this small component is capable of bending in any direction. Some of the U-joints used in aircraft include:

Cessna Control Yoke Universal Joint

This is designed with two yokes that provide the attach points for connecting the control yoke shaft and control wheel shaft; a centre bolt and two half-bolts that the yokes pivot around; and a centre block used as a support for mounting the bolts. In order to tighten the bolts and yokes to the base, a rivet is used. If not done properly and the rivet was to separate and slip out, the entire mechanism could come apart.

A Single Universal Joint

It is designed from high-grade metal steel for enhanced durability and better performance than standard industrial-grade designs. All components are heat-treated, accuracy machined and ground to close tolerances. The Heavy Duty, High Strength universal joint offers an excellent service life in the most demanding applications.

The Double Universal Joint

It provides similar safety and service life as the single universal joint with a maximum joined working angle of 90°. Double universal joints offer precise positioning and versatility under higher operating angles.

Needle-Bearing Universal Joints

They come with roller bearings that lessen friction. These high-precision joints are produced to manage minimal backlash at higher angles for crucial applications, such as instrumentation and robotics. They produce excellent lifetime at constant controls and high RPM at working angles of up to 45°. They can be restored when wear and tear happens


Universal Joints allow positive device of alternating energy at a larger angle than is allowed with a flexible coupling and it can dispatch energy and motion. They can be widely used in all types of power transmission systems and have a diversity of applications.