30 tons of aircraft, 3 tires can support, why 30 tons of trucks but 20?
Have you ever wondered if the same 30-ton weight, why can an airplane support 3 wheels while a truck needs 20 wheels?
In fact, this description is not very accurate, in order to balance the gravity of the aircraft, the simplest layout of the landing gear supporting the weight of the aircraft is: a three-point structure with two main starts.
For small tonnage aircraft, the installation of 3 wheels is enough to support its weight, while the large tonnage aircraft will be installed in the front and two main starting 3 groups of positions each 4 to 8 wheels.
For example, the 3 sets of wheels of the Boeing 737 and The Airbus A320 actually contain two tires in each group, so there are 6 tires in total.
The largest number of tires on the passenger aircraft is the Airbus A380, which has 2 tires from the front, 4 sets of wheels on the left and right main starts, and 6 tires per set of wheels, so the Airbus A380 has a total of 22 wheels.
The greater the number of tires, the heavier the weight of the aircraft, the maximum takeoff weight of the A380 can reach 560 tons, and the pressure per tire can be up to 25 tons on average.
However, heavy trucks have 20 or more tires when the maximum load capacity does not exceed 100 tons.
Why is this difference?
First, junior physics tells us that the greater the weight of an object, the greater its inertia. If we increase the number of wheels, we can increase the contact area with the ground, so that when braking, the truck's speed can be reduced more quickly.
Secondly, we must also take into account that the working environment of the truck is on the road, and once a tire bursts, it is difficult for the truck to maintain its balance, and even may roll over. Therefore, increasing the number of truck tires is to ensure the safety of the truck itself.
Finally, the quality of car tires and aircraft tires is still not comparable. In the process of taking off and landing, tires have to go through various "life and death tests".
When taking off, the speed will reach a speed of 300 to 400 kilometers per hour, and when it flies to a height of 10,000 meters, the temperature of the tire will plummet to minus 50-60 degrees; when landing, the aircraft tire will collide violently with the ground at a speed of 200 kilometers per hour, and once again withstand the 150-degree heat test brought by the deceleration brake.
Radial tires for aviation purposes
The car tire naturally can not withstand this test, so according to these special conditions, engineers designed aviation-specific radial tires, the production process is very complex, harsh, can be described as full of "black technology".
This tire is made of rubber, nylon wire, steel wire, three basic materials, through vulcanization bonded together a composite structure. Take the tread of an airplane tire, which is made of steel wire and special rubber and is about 2 centimeters thick.
In order to ensure that the tire can withstand the strong impact force, two special curtain towels called "reinforcing cord layer" are also added inside the rubber.
Even for small air nozzles, engineers designed them with high-temperature fluoroplastics, which are just enough to ensure tire stability and load performance.
Airplane tires are not filled with air, but with nitrogen
Because the tire pressure of the car is usually 220 to 280 MPa, the air pressure of the aircraft tire is often as high as 1500-1600 MPa.
For example, the tire pressure of the Boeing 737 aircraft is 1378 MPa, which is six times the air pressure of the car tire, so the pressure is so high that only nitrogen can be filled to ensure the safety of the tire.
The chemical properties of nitrogen are extremely inactive, and the deformation amplitude of this nitrogen in the face of changes in heat and cold is smaller than that of oxygen, and compared with air, the speed of nitrogen penetrating the tire wall is only 60-70%, which can continuously stabilize the tire pressure.
In this way, the quality of the aircraft tire is indeed not ordinary, but it also has a disadvantage that cannot be hidden, that is, it is not durable.
After 250 consecutive flights, a tire needs to be retreaded, and after 5 to 6 retreads, the second layer of the cord layer will be exposed, which means that the tire is time to be scrapped. In this way, a tire can only use 1500 flights.