An engine pylon is a streamline-section, rigid pillar-like structure that projects from the wing, fuselage, or tail to serve as the connecting device between the powerplant and the airframe. By providing the primary mounting point, it transmits engine thrust and external loads into the aircraft structure while distributing the engine's weight evenly across the airframe.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is an aircraft engine pylon?
An engine pylon is a structural unit that connects an aircraft engine and provides a mounting point for the engine, while it connects to the wing or fuselage and provides a means of transferring the engine's thrust to the airframe. A pylon is a streamlined aircraft structure that connects the airframe to the engine pod. The part is a hard-point provided with aircraft fastening points disposed symmetrically relative to a median vertical longitudinal plane. These upper and lower aircraft fastening points, including the left aircraft fastening point and the right aircraft fastening point, are spaced apart in the transversal direction so that the pylon is joined to the wing or fuselage.
The primary structure comprises a load-bearing mounting bracket and structural assemblies to which the engine is fastened. Engine mounts are also found in the nacelle. It includes an upper fitting, a thrust link that transmits engine forces, and a spherical joint in the pylon aft bulkhead that attaches to a clevis mounted on the underside of the wing. A stainless or titanium bulkhead contains any fire within the nacelle, and some designs use specific points designed to fail if there is excessive force, preventing the entire wing from being ripped apart. The pylon holds the streamlined enclosure that houses the engine, and its aerodynamic design reduces drag.
What is the function of an airplane engine pylon?
The function of an airplane engine pylon is to create a structural bridge between the wing and the engine. The pylon provides the primary mounting point and maintains the engine's position beneath the wing. At the same time, it bears the weight of the engine and distributes that weight evenly across the airframe, reducing stress on both wing and fuselage. A thrust link, called a thrust strut or thrust rod, transmits the engine's thrust forces to the pylon and on to the aircraft structure, while a forward mount transmits thrust, vertical, and lateral loads into the pylon. These elements guarantee that the forces generated during flight and reverse thrust are safely transferred without risking structural failure.
The pylon acts as a conduit for multiple systems, routing fuel, oil, and hydraulic lines between aircraft and engine, and it accommodates engine thermal expansion as temperatures change. Aerodynamically, the pylon reduces drag by streamlining the airflow around the engine and wing intersection, and it creates a gap between the wing's forward section and the pod to smooth the flow further. To protect the airframe, the pylon creates a fireproof barrier between engine and wing, preventing damage to the wing-enclosed fuel tank and fuel lines in the event of an engine fire and providing fire protection for the fuselage.
Maintenance is simplified because the pylon often provides convenient access points, including servicing doors and inspection panels, and incorporates secondary structure for mounting multiple systems. The design absorbs engine vibrations, reducing stress on both wing and fuselage and further lowering the risk of structural failure. Thus, the pylon unites load bearing, thrust transmission, system routing, aerodynamic smoothing, vibration absorption, fire protection, and maintenance access in a single, cohesive structure.
How many bolts hold an aircraft engine?
The number of bolts holding an aircraft engine are only a few, arranged at three points that usually include two forward and one aft. At each of these points, one or two bolts are used. Specifically, the forward mount uses four bolts, while the aft mount also uses four bolts. Together, these eight bolts sustain 560 kN. The bolts attach to the pylon structure, connecting the engine pods at the top of the fan frame and the top of the turbine frame. Bolts used for CFM56-7B on B737NG have part number BACB30PN14-32M (14 mm - 32 in) in Boeing nomenclature. These bolts are manufactured according to Air Force-Navy specs, assuring their reliability and strength in securing the engine to the aircraft.
