Aircraft Takeoff: When Do The Wheels Stop Spinning?

There are various mechanisms used to stop the spinning wheels so they can be stowed.

As a bystander, have you ever been intrigued by the continuous spinning of aircraft wheels after takeoff? Do they stop spinning in time for the “gear up” position, or do the pilots apply brakes before stowing the landing gears? The answer depends on the type of aircraft and the systems installed in the landing gears. This article explores various manual and automated mechanisms that ensure safe stowaway of wheels after takeoff and during flight.

A typical landing gear retraction system utilizes pressurized hydraulic fluid to actuate various linkages to raise and lower the gear. When the pilot commands the landing gear in the "up" position, hydraulic fluid is directed into the gear line. The fluid flows through sequenced valves and down-locks to the gear-actuating cylinders.

The system also incorporates a hydraulic reservoir to contain excess fluid and to provide a means of determining the system fluid level. Each gear has two limit switches installed, one dedicated to extension and one to retraction.

Aircraft wheels are heavy, and on larger aircraft, the wheels are heavy spinning items that act as gyroscopes. Based on the principle of conservation of angular momentum, it is the tendency for the spin of a system to remain constant unless subjected to external torque. When the pilot commands the gear up on most large aircraft, the main landing gears turn sideways for stowing.

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Think about trying to turn a fast-spinning gyroscope sideways (changing its orientation). The centripetal and centrifugal forces generated through the spin would cause wobble, leading to uncontrollable vibrations throughout the aircraft. The wobble may also damage the internal systems of the landing gears, which comprise many electrical and hydraulic links.

In some aircraft, the pilots must briefly apply brakes to the main landing gear before activating the gear up in the cockpit. The application of the disk brakes stops the spinning of the wheel before they are stowed sideways. Smaller aircraft with lighter retractable landing gear systems may require manual brake application.

Large modern airliners will auto brake and stop the spinning of wheels when the gear up is commanded. For example, on a Boeing 747, The requirement from the pilots is to pull the gear level and let the aircraft do the rest. The aircraft uses auto brakes as part of the gear-up process. Similarly, on a Boeing 737, the main gear gets retract-braking pressure when the gear-up position is commanded.

The nose wheels are free to spin up into the wheel bay, where they contact a friction brake that drags to the tires before slowing and stopping the spin. Snubber units (friction brakes) are generally installed within the nose gear compartment since there is no braking system on the nose gear.

There are also cylindrical brushes installed within the bay, which clean the tires as they slow down. The brushes around the periphery of the wheel bay housings also reduce aerodynamic drag and noise by closing off the gap between the tires and the bay walls.

What are your thoughts on the mechanisms to stop wheels spinning after takeoff? Tell us in the comments section.

Writer - Omar is an aviation enthusiast who holds a Ph.D. in Aerospace Engineering. With numerous years of technical and research experience under his belt, Omar aims to focus on research-based aviation practices. Apart from work, Omar has a passion for traveling, visiting aviation sites, and plane spotting. Based in Vancouver, Canada