Tools of Aeronautics

Tools of Aeronautics

The Four Tools

       Researchers in the field of Aeronautics primarily use four "Tools" to test their hypotheses: Computational Fluid Dynamics, Wind Tunnel Testing, Flight Simulation and Flight Test. Each of these four "Tools" consists of unique and specialized equipment and experts trained in the development, management and operation of the Tools. These Tools were developed only within the last 100 years and have evolved in parallel with technology in other areas. On one hand their evolution was dependent on the development of technology and on the other hand, their evolution pushed the technology faster and to greater heights. Each Tool has its own niche in the design cycle of a new airplane or in the modification of an existing one. Data from one Tool can feed into the tests performed using another Tool. Oftentimes, research will be completed using one Tool and proceed on to another, only to return to the previous Tool because of a new question generated during tests using the second Tool. Selecting which Tool to use is based on the question being asked. A Tool that can provide excellent data on, say, the aerodynamics of a wing may not be able to give any information about how that wing affects the controllability of the entire airplane.

Wind Tunnels
        Wind Tunnels were the first Tool to be developed and have been used since the time of the Wright brothers. The name "Wind Tunnel" isvery appropriate. A wind tunnel is basically a long tube or tunnel through which air is blown at controlled speeds. A scale model of an airplane, or part of an airplane is mounted in the tunnel and measurements are taken of the forces and pressures that the model experiences when the air is blown. The basic idea of a wind tunnel is to move wind past a stationary airplane, instead of flying the airplane through the air. This is safer, cheaper, and provides a more controlled environment in which to test. It has been proven that data gathered in this way is able to accurately predict forces and pressures generated during real flight.

The models mounted in the tunnel can either be a scaled version of the real airplane, or a scaled version of part of the airplane. Note that the scaling must be extremely accurate or the prediction of forces and pressures will be in error. Measurements are made by sensors which are embedded in the model and mounted throughout the tunnel. Examples of sensors are strain gauges, balances and pressure sensors. Examples of sensors mounted within the tunnel are floor balances (much like bathroom scales), barometers, thermometers, anemometers, pressure sensors and microphones. Data from all of these sensors are fed into computers. Researchers and engineers then display the data in numerical form (lists of numbers) or graphical form (graphs and plots). Some tunnels have the capability to inject oil, smoke or water into the airflow so that photographs may be taken. Other visualization techniques using lasers, paint that changes color in response to changes in pressure, and other high technology tools are currently being used.

	Wind tunnels come in all shapes and sizes, from small hypersonic tunnels (3000+ miles per hour) to very large low-speed (115 miles per hour) tunnels which can test full-sized models. Many wind tunnels exist throughout the world. The largest wind tunnel can be found at NASA Ames Research Center in California. The test section - where the model is mounted - is 80 feet high by 120 feet wide. A full-size model of a Boeing 737 airplane can be mounted in this test section. Wind tunnel testing is critical during the design of a new airplane or when making modifications to an existing airplane. A common usage of wind tunnel testing is to gather data to help build a mathematical representation of an airplane that can reside in a computer - called a mathematical model. This type of information is invaluable to researchers and enables them to more fully utilize the other Tools. Cars, trucks, parachutes and rotorcraft are also tested in wind tunnels.</p>
	Computational Fluid Dynamics      Wind tunnel tests can be very expensive. Wind tunnels themselves use massive amounts of electricity to generate the airflow. The maintenance of machinery, equipment and tunnels the size of multiple football fields is also very expensive. Airplane models with their rigorous requirements for precision and durability take much time and money to build. In the early 1960s the idea was conceived to run wind tunnel tests in a computer. In those days, computers were large, slow and cumbersome compared to the computers of today. However, given a mathematical model of an airplane, they were able to accurately predict forces and pressures in support of research in fluid dynamics. The real beauty of this technique, however, was the ability of the computer to display graphical pictures and representations of the data which allowed researchers to almost instantaneously perceive and analyze what was happening to a particular model. This visualization was only available in crude forms in the wind tunnel. The field of fluid dynamics was thus able to perform research computationally, inspiring the moniker Computational Fluid Dynamics or CFD.
	In the early days, however, computers had not evolved enough to handle the huge amounts of data and computations needed to accurately model modern airplanes. In an excellent example of research needs pushing the evolution of another technology, aeronautical researchers cried out for faster computers that could handle huge amounts of data. With the advent of the supercomputers, their dreams were realized. Supercomputers can easily perform over one billion calculations per second. It would take a person solving one equation every second, 24 hours a day, over 32 years (or a whole career) to solve what a supercomputer can in one second. As fast as today's computers are, however, many aeronautical models are so complex that hours are needed for these analyses. However, the results are well worth the wait! Modern computer graphics that can present data in three-dimensions give a researcher information about the aerodynamics of an entire airplane on one computer screen. While the graphics are visually striking and artistically beautiful, their most valuable contribution to aeronautical engineering is their ability to present an incredibly large amount of very complex information in a manner that enables researchers to quickly and accurately draw conclusions from their data. The capabilities of CFD will continue to expand and grow as computer and visualization technology continue to evolve.

Flight Simulation

The previous two Tools have not included one very important aspect of flight - the pilot. Flight Simulation incorporates the ability of a human to subjectively observe and analyze his or her experiences. As in CFD, a mathematical model of the research airplane is programmed into a computer. Instead of providing graphical images of the model, a flight simulation computer controls a cockpit mock-up designed to look like the interior of an airplane, a motion system to simulate the movements of an airplane, visual computers to create out-the-window scenes for the pilot, sound systems, and instruments all working together to provide the pilot with an extremely realistic flying environment. Again, the evolution of computers has greatly influenced the ability of flight simulators to accurately simulate real flight. There are twoprimary uses of flight simulators: training and research. Training simulators now enable pilots to learn to fly new airplanes on the ground. They are able to perfect their skills prior to taking off in the real airplane. Flight simulators are particularly adept at training pilots to handle emergency situations. Engine-out, loss of hydraulics, blown tires, and a host of other life-threatening situations can be accurately simulated and effective pilot responses learned, all without the possibility of loss of life or airplane.

Research flight simulators are used extensively to examine the handling qualities of an airplane. As drivers of cars we are intimately familiar with, and often critical of, how our vehicles handle. The same holds true with pilots and airplanes. Modern high performance airplanes (such as the X-29) are very difficult to "handle." Complex computer-based control systems are used to help the pilot fly. In some cases the airplane could not be flown without the aid of a control system. These control systems must be extensively tested and fine-tuned before they are incorporated into a real airplane. Much of this testing takes place in flight simulators. Research simulators are flown by test pilots. Test pilots are trained how to provide accurate and technically sound subjective evaluations of an aircraft's handling qualities. On some occasions, test pilots will fly a set of maneuvers in a simulator in the morning and fly the same set of maneuvers in the real airplane in the afternoon.

The Vertical Motion Simulator (VMS) at NASA Ames Research Center in California is the largest motion-base simulator in the world. It is known as a six-degree-of-freedom simulator. This means that the cockpit can move in the three translational directions (forward/back, up/down, side to side) and generate the three rotational movements (roll, pitch and yaw). The simulator cockpit can travel vertically over 60 feet and can experience accelerations close to 32 feet per second per second (or "1 g"). The VMS is one of the most technically advanced flight simulators in the world. Because simulators are so cost effective and can so accurately mimic the motion and environment of flight, they have become critical in the development of new airplanes and modifications to existing ones.

Flight TestAfter all the above three Tools have been used and used again, the true test of any airplane is real flight. This is where the Tool of Flight Test becomes critically important.

A new airplane, or a newly modified airplane, is not built and immediately pressed into service. It must undergo rigorous flight testing. All the predictions made using the other three Tools are only that - predictions. Flight Test is when those predictions are finally proved or disproved.

Flight Tests require much advance planning and preparation. Instruments are placed in the airplane to record forces, pressures, control surface movements, pilot movement of controls, and radio communications. Every possible bit of information about the flight is recorded.

On the ground, tracking stations are set up. Microphones and cameras are readied. Barometers, thermometers and anemometers are installed to record the environment during the flight.

A precise and exhaustive list of all maneuvers that researchers want the pilot to fly are compiled in a test plan. Every action of the pilot is prescribed in this test plan - from takeoff to landing.

A test pilot receives hours of training, not only on how to fly and how to handle emergency situations, but how to accurately report what he or she is seeing, feeling and hearing throughout the flight. Test pilots wear a flight suit that has snaps and straps that allow them to strap the test plan to one leg and a notepad on the other. Everything the pilot says is recorded and analyzed. A test pilot must be able to follow the flight plan precisely. And, if something goes wrong the test pilot must be able to quickly determine the cause of the problem and its severity. It is a point of honor for all test pilots to land their airplane. One of the most difficult but also the most challenging decision a test pilot must make is whether or not, when a problem arises, the airplane is still flyable. Unfortunately, history has seen test pilots who have "stuck it out" thinking they could successfully land the airplane, when in fact they couldn't. Being a test pilot is an incredibly demanding and dangerous occupation! The advent of flight simulators and CFD has helped reduce the risks of flight test by making sure the design is more mature before testing.

Based on the results of a flight test, an airplane may be tested further using one of the other three Tools, more flight tests may be recommended or it could be determined that the research questions have been adequately answered.