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Why do we care about Engineering Requirements?
When we come up with a new idea for a product or service of some kind, we frequently are motivated by a problem that is bothering us or a notion that inspires our imaginations. The Wright brothers were inspired to create a flying machine that could lift off under its own power and fly from one point to another, something never achieved before. However, the idea was only the beginning of the process of designing and building their revolutionary airplane. Seeing the unsuccessful results of many inventors before them, they quickly realized that they needed to understand what was required to make a machine that could achieve their goals before they could even begin designing it.
The design of all engineered products is driven by the end goal: to fly, to communicate, to enable productivity, etc. However, many other things may need to happen in order to successfully reach that end goal, and if these items are not identified early in the design process, the product may not be successful or may take far longer and consume far more resources than expected to bring to market. Therefore, the first step in determining requirements is to determine the basic things that must be possible in order to succeed.
Begin at the Beginning: Can we do this?
In the case of Orville and Wilbur Wright, the goal was to build a device capable of lifting a man off the ground and allowing him to travel some distance while not being completely subject to the vagaries of the wind (like balloons) or having to start higher than his ending target (gliders). Therefore, the first requirement is that this machine must carry the weight of a pilot, along with all the propulsion system and control elements that drive the machine and allow the pilot to control its flight.
Generally, identifying the core requirement of our new product is the easy part: it must do what we want it to. The more challenging questions that must be answered immediately afterwards are 'Can we do this?' and 'How do we do this?' This is the core of engineering design; we must determine what we must do in order to achieve our goals, including system performance, cost, and appearance. The Wright Brothers, after some research, determined that they would need to use very light and strong materials for their craft, and selected linen and wood as the best candidate materials. However, they did not just start building an airplane, they did more testing in a homemade wind tunnel to determine how much lift they could generate per given area of wing. They did this to understand the total size of their machine, and therefore, how much propulsive power they needed in order to reach flying speed.
Refinement, not just for classy people
So, we have an idea, and have identified what are the essential functions of the device or software we will be building. Now, we must begin to refine our requirements and narrow down the possible options for solving our problem. Therein lies the crux of many engineering projects, and the point at which they either succeed or fail. If we cannot settle on a firm set of requirements and a clear path to achieve them, our chances of creating a workable product are dramatically reduced.
In the early 1900s, gasoline engine technology was primitive at best, and the Wright brothers were unable to find an appropriate power plant for their airplane. Realizing that this was the fundamental technological breakthrough required, they invested much time in creating the first aluminum block internal combustion engine. Though primitive by any standards, their engine design met all of their requirements: it produced enough power while weighing very little and having few moving parts to fail. With this technology in hand, they went on to make history.
Requirements as guiding principles
A well-thought out design should meet one or two core requirements. Keeping it simple is the best way to avoid having a development process that becomes sidetracked by addition of new, but perhaps unneeded features. Furthermore, a well-thought out requirements definition process lets us see how feasible a project might be before investing significant resources into it. For example, if the Wright brothers did not have access to aluminum casting technology, their flyer would probably have been impossible to build. It is far better to learn this while we are still thinking about a project, rather than at the end, when we have constructed an airframe and landing strip that we now cannot use!
