Flying West or East: How Geographical Direction Affects Airliner Speed

The age-old question of whether airliners traveling east or west at 10,000 feet experience different speeds has always intrigued aviation enthusiasts. While prevailing winds and weather conditions are typically the dominant factors, the subtle effects of centrifugal force and gravitational pull can play a role.

Centrifugal Force and Airliner Speed

When an aircraft is flying at an altitude of 10,000 feet over the equator, the direction of flight can indeed influence the effective weight the wings need to support. This is due to the centrifugal force created by the Earth's rotation. The centrifugal force is a result of the aircraft's motion in combination with the Earth's rotation.

Calculating Centrifugal Force

To better understand the impact, let's calculate the centrifugal force in two different scenarios: one where the aircraft is flying east and another where it is flying west.

Eastbound Flight at 10,000 Feet

For an aircraft flying due east at 10,000 feet over the equator, its centrifugal force is determined by the following formula:

Aircraft weight: 800,000 pounds Centripetal force: (aircraft weight) * (true groundspeed) / (32.2) * (speed of the Earth's surface due to rotation)^ 2

The speed of the Earth's surface at the equator is approximately:

3963.252802 * (3.1416/24) * 3600 1,521 feet/second

For an airliner flying at a true groundspeed of 585 mph (858 feet/second), the centrifugal force is:

800,000 * 858^2 / 32.2 * 1,521^2 6,725 pounds

Westbound Flight at 10,000 Feet

For an aircraft flying due west at 10,000 feet over the equator, its centrifugal force is:

800,000 * 858^2 / 32.2 * (1,521 - 858)^2 523 pounds

From these calculations, it can be inferred that the eastbound aircraft would experience a reduced effective weight of 6,725 pounds, while the westbound aircraft would experience a reduced effective weight of 523 pounds. This reduction translates to a difference of 6,672 pounds, which represents 0.84% of the aircraft's total weight.

As a result, the eastbound aircraft might indeed move faster than the westbound aircraft due to the reduced gravitational pull. However, this difference is so small that it is negligible in practical applications.

Jet Stream and Airliner Speed

While the centrifugal force effect is minute, another significant factor is the jet stream. This high-speed 'stream' of air can shift constantly at velocities above 100 KTS, depending on altitude. Jet streams are often used by airlines to create new point-to-point speed records, especially over long distances where climb and descent represent a smaller proportion of total flight time.

Jet Stream Utilization

To take advantage of jet-stream activity, airlines plan their routes accordingly. For example, a UAL 747 has achieved over 600 KTS from Asia or Hawaii to the US, flying far above the aircraft's VNE (Ventiespeed). These routes, which optimize tailwinds, can significantly reduce flight times and fuel consumption.

Conversely, to avoid severe headwinds, airline meteorologists help pilots steer clear of areas with strong jet streams. This requires meticulous planning and a deep understanding of weather patterns.

Airline Meteorology: An Arcane Art

Airline meteorology is an intricate field, greatly assisted by modern data collection and observation methods, including weather satellites. These satellites provide crucial information to pilots and meteorologists, allowing them to make informed decisions. Additionally, the International Space Station provides stunning videos of jet streams and other atmospheric phenomena, offering a unique perspective on these air currents.

Nonetheless, pilots often rely on their experience and observations, as they say, "If all else fails, look out of the window." This mantra highlights the impermanence of weather patterns and the importance of real-time observations.

Conclusion

While the centrifugal force effect is a fascinating aspect of airliner speed, the more significant factor is the jet stream. With modern technology, airlines can optimize their routes and take advantage of favorable wind conditions to maximize speed and reduce fuel consumption. Understanding these factors is crucial for efficient airline operations and safe, speedy flights.