My Job

Two people asked me to tell more about what I do with airplanes. Here is my cursory description of how I spend the majority of my life.

I am a structural engineer and I am referred to as a "stress engineer", whatever that is. My employer performs modification and maintenance of aircraft. A large portion of the work we do is related to enhancement and maintenance of military aircraft. The majority of the work is on P-3 and C-130 airplanes. Most of the work I do is in support of designers who make drawings of equipment installations and repair for damage.

I spend much of my time using a computer. I write reports, perform calculations, and track labor expenditures and budgets for my efforts and those who help me. During the course of a day I may have several people come to my office for signatures and advice on structural matters.

As a structural engineer I ensure that structural integrity is maintained when we install things on an airplane. The structural integrity depends on strength, endurance, corrosion resistance, stiffness, and resistance to damage. Other people usually provide detailed aerodynamic loading information for the structures I evaluate. I am involved in creating and using finite element models and using classical analysis methods that were developed before digital computers were available.

Stress is defined as force per area. If you were to have a string with an area of 0.01 inches square and applied a load of one pound to it, then it would experience stress of 100 pounds per square inch. Some of the materials used in my work can withstand stresses up to 160,000 pounds per square inch. It is common to see materials that can withstand stresses to 45,000 psi (pounds per square inch). Some exotic materials, like graphite fibers can withstand 1/4 million psi.

Buckling and crippling are two modes of possible failure that must be checked in an aircraft structure. Buckling is seen as waves or curves developed in a component that is in compression. Crippling happens when a thin structure crushes in compression.

There is also another phenomenon that must be detected and eliminated. This phenomenon is known as flutter. Flutter happens when the aerodynamic response and the structural natural frequency are about the same. Any structure has a natural vibration frequency. If you pluck a guitar string you can hear the natural frequency. The aerodynamic response of a structure, like a wing, is how fast it can respond to a change in the flow characteristics. Flutter is bad.

In the end, I work with other engineers to ensure that the airplane can be flown safely. My job is to make sure the installations are strong enough, have the right stiffness, and last long enough.