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aerial engineering

On the right course

Integrated sensors platform will make the flight of light aircraft more precise

The system of navigation for light aircraft is about to gain a new piece of equipment that is going to join the two kinds of system used today to determine the position, trajectory and attitude (angular position) of aircraft. This novelty is an integrated platform of inertial sensors and the Global Positioning System (GPS), which will be bringing more safety to this class of aircraft, just as it already happens with large airplanes. The platform is in the final stage of development by a company called Navcon – Navegação e Controle, from São José dos Campos.

The inertial sensors are regarded as primary instruments for navigation, and they work independently of external signals. They are made up chiefly by two instruments: gyroscopes and accelerometers. The first record all the movements of the aircraft during flight, and they work by means of mechanical principles, with a rotor spinning like a top and recording the movements of the aircraft in relation to the box in which it is installed. They also work with a laser beam emitted through optic fibers. The movement of the plane is felt through the difference in the speed of receipt of the laser beam that runs along the fiber. They provide pilots with information on the attitude of the aircraft on three axes: direction, angle of the nose (upward or downward inclination), and angle of the wings (inclination to the sides), showing if the airplane is flying parallel to the ground. The accelerometers provide data related to the speed of the aircraft.

GPS is a secondary system for helping navigation – its use as a principal system is still being tested. It is made up by a constellation of 24 satellites, in orbit at an altitude of 20,000 kilometers, which sends signals that are captured by receiving apparatus in the aircraft’s cockpit. The signals are used to determine the aircraft’s position and trajectory, through coordinates for latitude and longitude, the imaginary lines that slice the planet. The margin of error of the GPS signals, which in the past was in the order of 100 meters, is today between 1 and 3 meters, thanks to correction by reference stations location on Earth called Differential Global Positioning System (DGPS).

Flying blind
The integrated platform will improve the use of the GPS and of the sensors, and it was conceived correct the deficiencies that may exist in the two systems. Gyroscopes can be unreliable and imprecise, and they may need constant corrections in the course of flight. In the simpler and cheaper models, the margin of error may come to 10 degrees an hour, which would take the plane completely off course. High precision gyroscopes, though, show a deviation of only 1.1 degree an hour, but they are devices that can cost about US$ 300,000.

The GPS system, in turn, only works if signals from four satellites of the constellation are captured simultaneously by the plane. But this is not always possible, which may leave the aircraft flying blind for a few instants. “Failures in the transmission of the signal, geometric limitations on positioning, and even a maneuver by the plane, can mean that the signal from the GPS system is not captured by the antennas located in the aircraft”, Schad explains.

Baptized the Modular System of Attitude and Navigation (Sman in the Portuguese acronym), the platform may also be used by rockets, missiles, satellites, automobiles and ships. After three years of research and development, Navcon’s engineers concluded, in April, a prototype of the equipment, which had support from FAPESP’s Small Business Innovation Research (PIPE). “We are going to use cheaper, less precise, inertial sensors, and, even so, thanks to integration with the GPS receiver, the results obtained have been very satisfactory”, explains electronic engineer Valter Ricardo Schad, a director of Navcon and one of the inventors of Sman.

Sman’s modular form is another great advantage that means it can be used by different vehicles. “Sman is a system with quick prototyping (making up prototypes). This means that, for each application, we can define the level of desired integration”, says Otávio Santos Cupertino Durão, an industrial engineer from the National Institute for Space Research (Inpe) and the coordinator for the project. On account of this characteristic, the platform can be used by automobiles, for navigation or fleet monitoring. In Europe and the United States, there are various vehicle navigation systems in use.

They have the function of showing on a screen on the dashboard of the vehicle the street that the car is going along and showing the best route, or even to show the state of the traffic in the streets and avenues ahead. “In this case, the system will not need to be so complex as in aircraft, as in vehicle navigation we are only interested in projecting the position of the automobile into the map”, says Durão. Another of Sman’s applications is in rockets, satellites and missiles, replacing the expensive components that are currently used to control their orbit and attitude.

Finally, the apparatus can also be used in ships and on oil rigs, helping to position both of them. According to Schad, the use of a low cost integrated platform with GPS and inertial sensors is a target for research and development all over the world. Navcon is the only company in Brazil that has managed to develop an integrated modular system with these two technologies, including determining altitude by GPS and the use of inertial sensors. Other companies have even achieved integration, but focused on just one application.

Sman’s most complex model, for use in aircraft, is made up of six modules, as well as the software. The master sensor unit is made up of gyroscopes, accelerometers and a few circuits needed to make them work, while the sensor and interface unit includes compasses, speed sensors (which measure the miles or kilometers covered per hour) and some additional sensor. The GPS unit may contain one receiver or several. A keyboard and a graphic display, which serve as an interface with the user, will be the basis of the control and visualization unit. Finally, there is the software responsible for making Sman operational.

High technology
Navcon lodged a request for financing the patent for the prototype with FAPESP’s Nucleus for Patenting and Licensing Technology (Nuplitec). In parallel, it is carrying out a few adaptations to Sman, with a view to putting it into the market. Some negotiations are now under way. “We are talking with a company that makes navigation systems for automobiles, and there was an interest on their part to get to know the product better”, says, Schad. The aerospace sector is also being sounded out.

With only three years in the market, Navcon specialized in the development of inertial systems, automation and the control of industrial and laboratory processes. Besides Sman, the company also has another project under PIPE, with its first stage concluded, to develop a GPS receiver for applications in space. With these two projects, new prospects are opening up for Navcon, which gives it greater visibility in the aerospace industry, and is introducing itself to others, like the automotive and nautical sectors.

The Project
Integrated Platform of Inertial Sensors and GPS (nº 97/13014-5); Modality Small Business Innovation Research Program (PIPE); Coordinator Otávio Santos Cupertino Durão – Navcon; Investment R$ 135,374.00 and US$ 67,493.00