When writing about aircraft designs, much is made about the wings and engines. After all, these are the components that provide lift and thrust, the two forces that help the aircraft achieve and maintain flight. But on larger commercial aircraft, such as the Boeing 747, the aircraft’s engines are mounted on the wing. What then, is the part that connects the engine to the wing?
That part is the engine pylon, or strut. The strut holds the engine onto the wing and provides a path for all of the engine’s systems, such as fuel and air lines, to connect, and includes the aerodynamic fairing to cover everything. While an engine can be attached and removed freely from the strut for maintenance and replacement, the strut itself is designed to stay attached permanently, with mounts on the strut for the engine. Because engines are so heavy, maintenance personnel will suspend a weight from the strut to balance the aircraft and keep it from tipping over when there is no engine installed.
The strut comes with multiple safety features for both flight and ground operations. For example, in the case of an engine fire, there are multiple fire-prevention measures built into the strut to prevent the fire from spreading to the rest of the aircraft.
Different aircraft manufacturers take different approaches to their strut designs. Boeing, for example, designs its struts to break away from the wing under extreme loads. While this may sound like a terrible idea, it prevents the wing from breaking under the load caused by the engine’s weight, preserving the wing and allowing the aircraft to function like a glider. Airbus engineers its struts to remain attached; this means their structure is less complex and allows their pylons to be narrower than Boeing’s.