How do pilot know the speed of plane

 

With the help of modern radio tech, the ground bases can send the planes’ velocity to the pilots. But do you wander how pilots knew the velocity before the radio tech developed. I want to introduce the general idea of the devices which were used to measure the velocity. So people use other methods to measure the speed.

People know that we can measure the angular velocity of wheels which linearly proportion to the velocity. But the plane flies without wheels. They take advantage of the pressure of air.

Pitots.This is the device which can measure the speed of the plane.(photo by Baidu)

 

 

It is pitots that pilots can use to know the speed. Even modern planes have advanced radio devices, most planes still have pitots. It means that the pitots are practical devices.

The device has a hole on the front of the plane. When the plane flies, air will flow into the hole and hit the inductor inside the devices. The inductor can measure the force of crash. The faster the plane flies, the bigger the force is. They have some kind mathematical relation. So pilots can figure out the velocity by knowing the force.