1. Pitot-Static Tubes:
* How it works: This classic method utilizes the difference in pressure between the total pressure (stagnation pressure) measured at the tip of the tube and the static pressure measured at the side of the tube.
* Calculation: The velocity is calculated using the Bernoulli's equation and the known density of air.
* Limitations: Accuracy is affected by factors like shock waves, turbulence, and the angle of attack.
* Common applications: Used on aircraft for airspeed indication (airspeed indicators).
2. Doppler Radar:
* How it works: This method measures the change in frequency of radar waves reflected off the moving object.
* Calculation: The Doppler shift is directly proportional to the velocity of the target.
* Advantages: Can measure velocity from a distance, works well for high-speed objects, and can track multiple targets.
* Limitations: Weather can affect accuracy, requires specialized equipment.
3. Laser Doppler Velocimetry (LDV):
* How it works: A laser beam is split into two beams. One beam is directed towards the target, and the other beam is used as a reference. The frequency of the light scattered back from the target is measured, and the difference in frequency between the scattered light and the reference beam is proportional to the target's velocity.
* Advantages: Highly accurate, can measure velocity at specific points.
* Limitations: Requires precise alignment, expensive equipment.
4. GPS:
* How it works: Global Positioning System (GPS) can be used to determine the position of a jet at various points in time. The velocity can then be calculated by dividing the distance traveled by the time elapsed.
* Advantages: Easy to use, can measure velocity over long distances.
* Limitations: Less accurate than other methods, can be affected by atmospheric conditions.
5. Flight Data Recorders (FDRs):
* How it works: FDRs capture various parameters, including airspeed, which is measured using pitot-static tubes.
* Advantages: Provides a detailed record of the aircraft's flight, including velocity data.
* Limitations: Provides data after the flight.
Considerations:
* Mach Number: For supersonic speeds, velocity is often expressed as Mach number (ratio of aircraft speed to the speed of sound).
* Calibration: All instruments used to measure velocity need to be calibrated regularly to ensure accuracy.
Important Note:
* Most modern supersonic jets are equipped with a combination of these methods to ensure accurate and reliable velocity measurements.
* The specific methods used will depend on the application and the desired level of accuracy.
