Airplanes are exposed to extreme stress during flight, including lift, drag, weight and thrust. Lift is an upward force generated by an airplane’s lifting surface. Drag is air resistance that counters an airplane’s forward motion. Weight is the gravitational pull that an airplane experiences. Finally, thrust is a force generated by an airplane’s propulsion system (e.g. jet engines).
Airplanes are meticulously designed with structural members to overcome these forces. While most passengers are familiar with visible structural members like the wings and landing gear, stringers often go unnoticed. Here’s everything you need to know about stringers and how they affect airplanes.
What Are Stringers?
Stringers are long and narrow structural members that form an airplane’s skeletal body. They typically run lengthwise along the fuselage or wings. Collectively, stringers help to reinforce the airplane’s outer skin, allowing the airplane to withstand the extreme forces to which it’s exposed during flight.
How Stringers Work
Stringers work by protecting the airplane’s outer skin from damage. Without them, the skin may flex or buckle under extreme forces. Over time, this can lead to direct damage. Stringers protect the skin from damage by providing reinforcement.
Most airplanes are designed with a thin outer skin. Consisting of aluminum or composite, it covers the airplane’s skeletal body. Stringers reinforce the skin by serving as a skeleton. Located directly behind the skin, they add stiffness to adjacent structural members, thereby protecting the airplane from damage caused by flight-related forces.
Most stringers are made of the following materials:
- Aluminum alloy
- Titanium alloy
- Carbon fiber composite
- Fiberglass-reinforced composite
Do All Airplanes Have Stringers?
Stringers are an essential part of most modern airplanes. Airplanes today typically use a semi-monocoque design consisting of stringers to reinforce their skin. With that said, not all airplanes use stringers. Ultra-light and glider airplanes, for instance, don’t use stringers, nor do they use a semi-monocoque design,
Stringers vs Longerons
Many people assume that stringers and longerons are the same. While they both form an airplane’s skeletal body — and provide reinforcement — they are two different types of components.
Longerons are generally longer than stringers. Most airplanes also have significantly fewer longerons than stringers. A typical airplane may only have a dozen or so longerons but may have hundreds of stringers.
Longerons are considered major structural members. Because they are longer, they carry heavier loads. Stringers still carry loads, but their primary job is to provide reinforcement.