The words "aviation" and "aeronautics" until the 20s. 20th century were synonyms. Everything changed at the beginning of the last century. Aeronautics began to be called movement with the help of devices that are lighter than air, and aviation - flying on airplanes. That is, ships that are heavier than air. In the article we will consider in detail the history of aeronautics, the physics of the process.

## Why does the balloon take off

Recall under what conditions a body immersed in a liquid floats. If its density is less than the density of the liquid. The same applies to gas, in particular air. A balloon (aerostat) will take off if there is a lighter (compared to air) gas inside its shell. The balloon also "floats" up, although it is hindered by the force of gravity acting on the shell.

Let's list the forces acting on the ball. First, it is the gravity of the shell. The second is the gravity of the gas. The gas inside the ball also has mass, which means that it is also affected by gravity. Let us assume that these two forces together are not inable to overcome the Archimedean force, which acts on the gas from the air. If so, then the balloon can take off and lift the load.

## Lift

Let's consider the key provisions of the physics of aeronautics. If we tie the balloon to the ground, it will pull up, pulling the rope with a force called lift. To calculate it, you need to subtract the weight of the gas along with the shell from the Archimedes force. Weight is the sum of the gravity of the shell and the gravity of the gas. The Archimedes force is equal to the product of the density of air, the acceleration of free fall, and the volume of the ball.

The lifting force is greater, the lighter the shell. It is the greater, the larger the volume of the ball and the greater the difference between the density of air and the density of gas. So, if you want to get maximum lift, the balloon must be filled with the lightest gas. This is hydrogen. However, there is one problem: it is very flammable, especially when mixed with oxygen. Therefore, most often balloons are inflated with helium.

## Balloon

A balloon is an apparatus that is filled with light gas. The photo shows a hot air balloon used to study the weather. This is the so-called balloon-probe. It is filled with helium, a radio transmitter is suspended from below, transmitting information about temperature, pressure, air humidity at different heights. Balloons are used in meteorology.

It is possible to create aeronautic vehicles that are both relatively safe and very cheap, requiring neither hydrogen nor helium.Instead of these gases, the shell is filled with ordinary air, but hotter. Such a balloon was invented by the French, the Montgolfier brothers. This event was great! The figure shows the first hot air balloon. A fire was lit from below, hot air filled the shell, and the ball soared upwards. At a certain height, he stopped rising. To continue the ascent, ballast was dropped from the apparatus. If it was necessary to go down, they lowered the fire.

## Stratostat

At very high altitudes, the air density decreases. Consequently, the lifting force also decreases. How can it be increased? It is necessary to increase the volume, so those aeronautic vehicles that rise very high into the stratosphere are huge. Such ships are called stratostats.

Recently, one extreme athlete set a record: he climbed on a stratospheric balloon to a height of 39 km and in free fall exceeded the speed of sound. This is Felix Baumgartner. The photo shows the stratostat he used. Its dimensions are about 100 m, which is commensurate with the height of the Statue of Liberty. The aircraft is filled with 85 thousand m33 helium, the so-called gondola is suspended below, where the passenger is located.

## Airship

Consider the physics of aeronautics. The balloon and stratosphere balloon move where the wind blows. Experienced aeronauts know that the wind is different at different heights. So they adjust the height of the balloon so that the wind blows where they want. If you need to sail from point A to point Bregardless of the wind, then a special propeller should be adapted to the apparatus, as in an airplane, which will help to move in the right direction. Such a device is called an airship. As a rule, these are very large systems. The device is filled with helium, a gondola is attached below, and a propeller is located under its bottom. The cables that hang from the bottom of the airship are used to secure it to the ground.

One of the most famous airships in the world was built by the Germans in the early 30s. XX century, it was called "Gendenburg". The fate of this apparatus is somewhat similar to the fate of the Titanic. She was an unusually comfortable ship. Its length was about a quarter of a kilometer. About 100 people were placed on board. The airship was powered by 4 engines.

May 6, 1937, the ship suffered an accident. It had to be filled exclusively with helium, and at that time helium was only available in the United States. Since this was the time of Hitler's rule, the Americans flatly refused to sell gas to the Nazis. The airship was filled with hydrogen. Extraordinary precautions were taken to avoid a fire. During the landing, the weather was pre-stormy, and there was a strong electric field in the air. The airship made a flight from Germany (Frankfurt) to New York, across the Atlantic Ocean. When he was planted, a spark arose, due to a leak of hydrogen, the airship caught fire. Of the 97 passengers, 35 died, and another person was killed on the ground.

## The first steps of aeronautics in our country: a bit of history

About aeronautics in Russialearned in the time of Catherine II. Her envoy in France announced the invention of the Montgolfier brothers.

The sensation was replicated by Russian newspapers, and later a book was published that explained the principle of the balloon. It was read by Euler, a member of the Academy of Sciences in St. Petersburg. He studied the physics of aeronautics and designed the first balloon. After the only flight of this apparatus, Catherine II, by her decree, banned aeronautics due to the risk of fire. For violation of the decree, a fine of 20 rubles was provided.

Under Catherine II, no one violated the decree, but when Alexander I ruled the country, the balloon flew again. This happened in Moscow, the balloon was controlled by a man named Terzi. He promoted ballooning like a circus and made a lot of money from it.

In 1803, the famous aeronaut Garnerin and his wife were invited to Russia. They demonstrated the capabilities of the balloon to an astonished audience, among which was Emperor Alexander I.

## The use of the apparatus in science and military affairs

Garnerin made more than one demonstration flight before scientists became interested in aeronautics. The Academy of Sciences sent one of its members, Zakharov, on a flight to make atmospheric observations. The academician took with him on board a lot of measuring instruments and reagents. Due to the fact that the balloon was not too big, in order to gain height, it was necessary to drop not only the ballast, but also many appliances, food andeven a tailcoat.

In 1812, at the court of the emperor, they were sure that Napoleon would nevertheless go to war against Russia. We decided to use the aircraft for military purposes. Work began on the construction of the airship. 150 carpenters and blacksmiths created the gondola, while seamstresses worked to create the shell. The airship had a rudder for changing the flight altitude, as well as oars for maneuvering. The gondola had a hatch for dropping land mines on the enemy. Unfortunately, the aircraft never saw action.