Aerial navigation

The aerial navigation is the whole of the techniques making it possible a pilot of aircraft to control its displacements. In general, this road begins and finishes on an aerodrome.

History

The aerial navigation is largely heiress of sea transport and the terminology used is identical. It is characterized some by the fact that the plane can fly over maritime zones as well as terrestrial zones which comprise obstacles. The speed of the planes is much higher than that of the ships and autonomy is limited; it results from it that the calculation of the position, then of the route to follow, must be carried out more often and more quickly.

The aerial navigation, during second half of the 20th century, developed thanks to the radionavigation, helped by the fact that the propagation of the radio waves is easier between the ground and the air that on the level of the ground. The development and generalization, to the beginning of, the satellite means of navigation tend to remove any specificity with the aerial navigation.

Necessary tools

The watch

The practice of navigation requires the use of a Montre for the calculation of the hours estimated of passage with the points of carryforward and of the hour of arrival to destination. It as makes it possible to determine the Ground speed of the plane by measuring the time necessary to traverse a Distance and by comparing this result with time as it would have been necessary without Vent. The watch was used as from 1956 in the aerial navigation.

The Rapporteur

It is essential to be able to measure the angles on the Carte to sail. Our Trajectoire in the horizontal plane is indeed characterized by a Route, which one expresses by a Angle compared to the Northern truth.

The rule

There are several types, the most adapted to the Cockpit of the planes being the rules of small size. They allow, in addition to the , road alignment Mesurer the Distances to be traversed.

The log book

The pencil and the gum

The pencil and the gum make it possible to trace the road on the aeronautical chart for a given flight. It will be preferable to use a fatty mine to make it possible to erase without traces.

Navigation at sight

VFR: Visual Rules Flight.

Navigation at sight is practiced since the origins of aeronautics and remains still the means more used by light aviation. The pilot knows his position while seeking on the ground of the reference marks which are reproduced on its chart. He follows a trajectory while moving of one benchmark to the other, or even while following a continuous reference mark such as a highway or a river.

Navigation at sight does not require any instrument but it is not practicable that when the weather conditions make it possible to see the ground.

There are two methods of navigation:

The advance

To walk on consists in following the characteristic natural lines good visible since a plane. This method can be used each time part of the course brings to skirt a natural or artificial reference mark (highway, important river) during a certain time.

It is important to choose of good Repère S, easily visible and recognizable, like the rivers, the highways, the coasts, the important railways.

One calls also advance makes it move, at sight, of a point known with a Repère identified, then this one with another identified reference mark.

One can finally walk on of VOR out of VOR, by using the means of Radionavigation.

Navigation with the regard

The principle of the regard is simple: knowing a starting position, it is a question of determining the course to take and HEA to arrive on a characteristic point or a Aérodrome. It can also be a question, after a time of flight to a given course, to determine the position of the plane.

The regard is the technique of adapted navigation when one wishes to join two points by the way more direct : the straight line.

The method is the suivante : at the beginning, being in possession of weather information, you have an estimate of the wind envisaged on your way. You can thus estimate the drift roughly and from the beginning post it. In flight, the first section makes it possible to test this drift and to possibly make of it a new estimate for the following section.

In addition, you estimated, during the preparation of the flight, the time necessary to traverse the distance between two reference marks. In flight, the difference between the estimated hour and the real hour of passage of the first Reference mark, had with the wind possibly met, makes it possible to more finely estimate the hour of passage with the Repère according to: if you spent more time than designed to join this first Repère, you increase Proportionnellement time estimated to join the Repère according to.

With the passage on this last Reference mark, the difference between the real hour of passage and the estimated hour enable you to recompute the hour of passage to the following reference mark. This technique is repeated in the passing of each Repère.

Navigation by systematic error

Combination of the two preceding methods. It consists in easily sailing with the regard in direction of a reference mark " cheminable" (maritime coast for example, river etc) but very upstream (systematic error) of the reference mark which one really wishes to reach, the destination for example. It is then enough to walk on along the first reference mark, the coast in our example. The systematic error makes it possible to know undoubtedly the direction to be taken starting from this first remarkable reference mark.

Navigation with the instruments

IFR: Instrument Rules Flight

It is based on the follow-up of axes radioelectric, or located between two waypoints RNAV. In this case, equipment RNAV is necessary (GPS, case RNAV, inertial Centrale)

Astronomical navigation

For very the long distances, this type of navigation, used in the marine , was also used in the plane. For the astronomical Navigation the planes were equipped with a bubble on the back of the fuselage to allow the use of a Sextant.

Inertial navigation

Inertial navigation uses an instrument, the inertial power station, which has a whole of accelerometers and Gyroscope S able to measure accelerations and the number of revolutions according to the three axes of space. The integration of these measurements during time makes it possible to calculate the speed and the attitude of the plane and thus its trajectory. This technique is completely independent of average outsides, discrete since it does not use the radio and remains most precise for the military needs (circular error about the kilometer per hour of flight).

Inertial navigation uses a very expensive instrument and is used more only for the military needs. It was used by the commercial aviation in the areas deprived of infrastructure radioelectric before the appearance of the satellite means. The drift of the power stations requires to carry out a retiming from time to time when one must carry out a precise navigation.

Correlation of altitude or image

The plane is equipped with a calculator which carries in memory a numerical chart of altitudes, echoes radars or images of the ground. It uses a radioaltimeter, a radar or a camera “to read” altitudes or the topography of the ground flown over. The calculator carries out a correlation between information in memory and information read to deduce the position from it.

The navigation systems by correlation are autonomous but are not discrete. Their precision is very good, even excellent, but their cost is very high. They are used only for the military applications and allow the retiming of the systems inertia, in particular near the objective.

Radionavigation

It is a help with navigation used to fly in level, to control a navigation with the regard, to carry out VFR one signal (flight with the top them clouds), to carry out IFR

Satellite navigation

Starting from 1990, the the United States set up a navigation system, GPS, using beacons on satellites. The basic principle is identical to that of the radionavigation. By receiving the emission coming from a beacon the receiver calculates its distance; it is thus on a sphere centered on the satellite. The intersection of two spheres gives a circle; the intersection with a third sphere gives two points and finally a single point with the reception of a fourth emission.

The advantage of the satellite systems on the traditional systems of radionavigation is its accessibility and its constant precision on the unit of the terrestrial sphere.

The principal defect of the GPS is that it belongs to the ministry for the defense of the United States and that it is likely to be made inalienable on simple political decision. The Soviet Union had begun the deployment of an equivalent system, the Glonass, but the future of this system is dubious. The European Union develops another system, Galileo.

On the technical plan, the satellite systems of navigation are currently most precise. Very the low costs of the receivers make it possible to consider the equipment of all the types of aircraft.

The thorniest problem of the GPS relates to the integrity of the system, in particular for the future use at the time of precision approaches. The integrity of a system is its capacity to detect a degradation beyond fixed threshold and to inform the user without exceeding a time of alarm. One must be sure that the signal used for a precision approach is absolutely reliable. In the case of THEY for example, one should not radiate false-signals more than 1 second for example for the cat 3 and 6 seconds for category 1. An automated control system causes the stop of the station in the event of bad radiation.

Probable evolution

On a technical plan the satellite systems of navigation combine the advantages of the systems of radionavigation at a cost much weaker. The reduction of the cost of the calculators makes it possible to develop whole of navigation which superimposes the data on a chart, thus simplifying, if not eliminating, the function of navigation. These systems exist for the aviation of leisure and are largely used by the other flying activities.

The pilot must however have permanently of the access to another technology in the event of breakdown or stop of the satellite system.

The radionavigation makes it possible to follow only trajectories made up of segments of right-hand side (with the approximations close to the systems of projection used in cartography). The satellite systems make it possible to follow unspecified trajectories; in the long term, this capacity should revolutionize air control by multiplying the number of “roads” available, including for the approach and the landing. Moreover, the precision of these systems should make it possible to decrease spacings between planes all while maintaining a level adequate of safety. Experiments or projects are in hand on the roads and the zones charged: the North-East of the United States, Atlantic-North and Western Europe.

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