<p>I have to write a paper involving a career in a science field that I find interesting. I have always loved airplanes and spaceships but I really have no knowledge of any of the more technical sides of the field. Can anyone tell me things that an aerospace engineer would do/build? What kinds of scientific principles would they use on a daily basis? Any good or bad things about the job? Any and all help would be absolutely wonderful, thanks!</p>
<p>I’m an aerospace engineering student, so I’ll give it a shot. There are three basic areas within aerospace engineering: gas dynamics, structures, and controls. An aerospace engineer (at least one doing research) typically chooses one of these fields to specialize in.</p>
<p>Gas Dynamics</p>
<p>This branch primarily deals with aerodynamics and propulsion. In aerodynamics, the goal is usually to optimize the shape of an aircraft to obtain the most amount of lift for the least amount of drag. There are three main types of drag: induced drag, pressure drag, and skin friction. Induced drag is caused by the fact that an aircraft generates vortices (most visible near the wingtips) as it flies; pressure drag is caused by flow separation, which occurs when an aircraft is not adequately streamlined; and skin friction is caused by the roughness of the aircraft’s skin, which slows down the fluid passing by and turns its energy into wasted heat. The goal is to minimize these different types of drag, and to find an optimum balance between them. </p>
<p>To do this, both analytical models of fluid flow (for example, the “potential flow” model) and exact descriptions of fluids obtained from conservation of mass, energy, and momentum (e.g. the Navier-Stokes equations) are used. The former are mathematical approximations of simple flows (for example, 2D flows around thin airfoils) that allow flow properties to be calculated quickly and analytically. The latter equations, which represent the exact physics, are typically very difficult to work with due to their size and complexity. Various simplifications of these equations are used in Computational Fluid Dynamics to predict the flow around more complicated objects such as an entire 3D aircraft.</p>
<p>Currently, the aerodynamics associated with the flight regime of general aviation aircraft is relatively well established, and ongoing research in this area typically consists of trying to optimize the entire aircraft as a system to squeeze out a few more percentage points of efficiency.</p>
<p>However, most research in aerodynamics today focuses on flight at very high or very low speeds (or more technically, Reynolds Numbers). These regimes include hypersonic flight on one end of the spectrum and insect flight on the other. Hypersonic flight includes complicated effects such as the dissociation of air molecules, heat transfer between this dissociated gas (called plasma) and the aircraft, and the presence of strong shockwaves in the flow. The flapping-wing flight of insects, on the other hand, deals with viscous and unsteady phenomena that are difficult to model analytically. The production of lift at these low Reynolds numbers is completely different than for general aircraft, and the exact nature of how insects achieve efficient flight is still not understood. The ultimate goal is to build mechanical micro-UAVs that mimic the flight of insects and that could be used for military reconaissance, search and rescue, and other operations.</p>
<p>The fundamental nature of turbulence, which still remains largely a mystery, is also a topic of study within gas dynamics, and is important in both aerodynamics and propulsion.</p>
<p>Structures</p>
<p>In addition to aerodynamics, aerospace engineers are also concerned with the structure of an aircraft. The goal is here is typically to build things as light and strong as possible, since the lighter the structure, the lower the fuel consumption. Typically, structural optimization is done using Finite Element Analysis on a computer. </p>
<p>One way to make things lighter and stronger is to use composite materials such as carbon fiber, fiberglass, and kevlar - as opposed to the aluminum that is currently used on most aircraft. Since composite materials are relatively new, their performance has not been well documented, and current research focuses on designing new materials and documenting their relevant characteristics. Another area of interest is in shape memory alloys such as Nickel Titanium. These alloys are basically materials that alter their shape when an electric field is applied to them. For example, if a wing was made of a shape memory alloy, the wing shape itself could be adjusted in flight to optimize the lift/drag ratio in a certain flight condition. </p>
<p>Finally, aeroelasticity, which deals with the interaction between aerodynamics and structures, is a third area of interest. The aeroelastic properties of a wing must be predicted accurately to ensure in-flight forces don’t cause it to become unstable and oscillate uncontrollably (this is called “flutter”). Aeroelasticity is also important in insect flight, where the insects’ wings experience large deformations due to the forces caused by the surrounding flow. </p>
<p>Controls</p>
<p>Controls mainly deals with making sure the aircraft behaves stably in flight. The main focus within controls is on creating robust flight software and autopilot systems that can maintain control of the aircraft in a variety of circumstances. Control laws incorporated into an autopilot system dictate, for example, how much (and how quickly) the rudder is deflected in response to a gust encountered in flight. The deflections of control surfaces need to be precisely tuned to ensure that the aircraft remains stable; this is done by adjusting the “gains” of the controller, which is typically a PID type (Proportional, Integral, Derivative). PID control basically means that the aircraft’s control surface deflections depend on the magnitude of the error between desired and actual states (proportional), the rate at which this error is changing (derivative), and the total amount of error accumulated over time (integral).</p>
<p>Control systems are important in general aviation aircraft, which typically operate on autopilot for a majority of their flight, and it is absolutely critical on fighter jets. Fighter jets are purposely made unstable in order to have greater maneuverability, but this means that they can only be flown safely when a computer is dictating the control surface movements. If the autopilot on a B-2 or F-16 fails, the aircraft will crash, regardless of what the pilot does.</p>
<p>A current area of interest in controls is in “adaptive controls”, which roughly deals with having the control laws themselves change in response to a change in the flight environment.</p>
<p>That’s basically a general summary of the field, though I probably left some important things out. I’m not too sure of the pros/cons of having a full-time job in the aerospace engineering field, since I don’t have experience with that. One con is that in the commercial industry, new aircraft are designed only once every couple decades. This means that if you work for Boeing, for example, you could be stuck on the same project for years. In addition, many projects in the aerospace field are subject to the whims of the government, which means that a project you’ve spent years of your life on could be canceled if the funding dries up. </p>
<p>A pro to working in the aerospace industry is that it sounds (and is) cool :)</p>
<p>Hope you find some of this useful; let me know if I can answer anything else.</p>
<p>Good post Kastsm! To clear up a thing or two, though, with the fighter jets it’s not the autopilot that would make the airplane crash. The aircraft uses a fly-by-wire system which just means that the on board computer system is responsible for getting the control inputs from the pilot, doing all the calculations and then moving the control surfaces to fly the jet.
If this onboard computer were to fail, the jet would become unflyable. The autopilot is a whole different thing.</p>
<p>Thanks Josh. I’m not a controls guy, and I guess “autopilot” was the wrong word to use for what I meant, but I wasn’t just referring to the fact that they are fly-by-wire. The fly-by-wire is, like you said, just converting the inputs from the pilot into electrical signals and then determining how to best move the control surfaces. But many fighter jets are statically unstable, which means even if the pilot is not making any inputs, the onboard computers are actively moving the control surfaces in order to create an artificially stable aircraft. If this system were to fail, even if the rest of the fly-by-wire continued working somehow, the aircraft would become unstable and uncontrollable. This isn’t technically an autopilot I guess, but it’s something that’s happening automatically and independent of the pilot. I think the correct term for it is “control configured vehicle.” Correct me if I’m wrong though.</p>
<p>but dont computer science/engineering type people develop the controls system for any airplanes? or can aerospace engineers do that all on their own?</p>
<p>It’s done by CSE/CS and CE people. That’s actually the major I’m currently in and the path I’d like to go down; developing avionics systems for aircraft/avionics companies.</p>
<p>There are people/labs within the aerospace department that specialize in control - Professors Atkins, Bernstein, and Girard, for example. They typically have backgrounds in computer science/engineering as well though.</p>