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Why is the plane so fast? Does the plane fly in a straight line

For long-distance travel, most people will choose to take a plane, because the plane is fast and comfortable. Why is the plane so fast? Use elementary knowledge: is the plane flying in a straight line? In fact, on the sphere, between two points, there is a shorter line than the line segment, which is the great circle arc. Please see the global route map below

Specific to a certain flight, it is like this

The route from Shanghai to Fuzhou is not a straight line, but close to an arc.

Why is the flight path curved?

Can't the plane fly in a straight line? A: Yes

When looking at a map, such as from Shanghai to Fuzhou, the nearest distance must be a straight line. However, the earth is a sphere rather than a plane. A plane is made between the starting and destination places and the center of the earth. The major circle and minor arc intersecting the plane and the earth's surface is the shortest distance. Therefore, the shortest distance between two points on the earth is an arc, not a straight line. We call the shortest path between the two points along the earth's surface as the "great circle route.".

The plane does not fly strictly along the great circle route

In principle, the flight distance of the plane is the shortest, the most time-saving, the most fuel-saving and the most efficient. Unfortunately, the ideal is plump, but the reality is very skinny. The plane does not fly strictly along the great circle route, which is mainly restricted by the following four factors:

Navigation technology limitations: however, there are GPS navigation technology, but many civil aircraft flight still rely on the combination of inertial navigation (IR) and VOR / DME, so as to ensure the aircraft navigation accuracy to a very high degree. However, one disadvantage of VOR navigation technology is that navigation needs to rely on the navigation station, and the aircraft can obtain high precision only when facing or backing the navigation station Therefore, the flight path of the aircraft is essentially flying from one navigation station to another, so it is impossible to achieve straight-line flight.

Airworthiness regulation restriction (ETOPS restriction): due to the low reliability of the early aircraft engine, it was easy for the double engine aircraft to have an engine failure during the flight, which caused serious safety hazards. Therefore, the International Civil Aviation Administration stipulated that the distance from any point in the aircraft's whole route to the nearest alternate airport should not exceed the 60 minute flight distance of a single engine, Be able to land safely before the plane is out of control.

Now, with the improvement of engine reliability, the flight time of this single engine to the nearest alternate airport has been extended to 120 minutes, which enables the aircraft to choose a closer route. The routes that the dual engine aircraft could not fly are no longer restricted. Airbus's newly developed A350XWB has been certified as long as 370 minutes, which means that even if one engine fails, the A350 can still fly for up to 6 hours on another engine.

ATC restriction: the command and deployment of each aircraft from takeoff to landing by the air traffic controller (which can be considered as traffic police). The two aircrafts flying in the air should keep a certain altitude difference and horizontal distance difference, otherwise they will be affected by each other and even dangerous. And these vertical and horizontal intervals have specific numerical provisions, and depend on the command of the controller to ensure.

Terrain and climate constraints: different geographical environment will produce different weather conditions, and the aircraft will be restricted by weather conditions in flight. For example, there are more foggy weather in basins and valleys, thunderstorms in temperate zone, typhoons and hurricanes in tropical and subtropical waters. These weather has obvious regional and seasonal characteristics, so the flight route will try to avoid dangerous weather prone areas.

Concave line

The plane does not fly in a straight line, but in a zigzag circle. In the case of bad weather, there will be flying around, alternate landing and so on. At this time, the route is all kinds of concave shape.

In the face of severe weather, frequent cancellations or delays are normal.