Editing Gear Retraction System


'''Gear Retraction System'''

[[File:AV_F-16_Emergency_3117x4000.jpg|thumb|right|517x517px|F-16 gear retraction at Red Flag – Image: Al Clark]]
[[File:Gear_retract.png|thumb|right|Conventional landing gear retraction system.|401x401px]]

A gear retraction system, or '''retractable landing gear''', allows aircraft to stow their landing gear wheels and struts into the body of the aircraft during flight, reducing drag and improving fuel efficiency. These systems typically use hydraulic or electric actuators, with manual systems used on smaller aircraft.

== Types of Retractable Landing Gear ==

'''Manual:'''
: The simplest type, used on small, low-performance aircraft, where the pilot manually raises or lowers the gear.

'''Electrical:'''
: Uses an electric motor to raise and lower the gear, common in smaller, high-performance aircraft.

'''Hydraulic:'''
: Uses pressurized hydraulic fluid to actuate the gear, common in larger, heavier aircraft such as airliners.

== How Retractable Landing Gear Works ==

'''1. Actuation:'''
: When the pilot selects "gear up," the system activates the actuators (hydraulic or electric).

'''2. Downlocks:'''
: Releases the locks that keep the gear extended.

'''3. Retraction:'''
: Actuators move the gear struts and wheels into the retracted position inside the wing or fuselage.

'''4. Up-locks:'''
: Once fully retracted, up-locks secure the gear in place.

'''5. Door Operation:'''
: Landing gear doors open/close automatically as part of the gear cycle.

'''6. Sequence:'''
: Doors open before gear retracts, and close after retraction is complete.

'''7. Safety:'''
: Systems are designed to be fail-safe. If power is lost, the gear defaults to the extended, locked position.

== Benefits of Retractable Landing Gear ==

* '''Reduced Drag:''' Stowing the gear reduces drag and improves fuel efficiency.
* '''Aerodynamic Efficiency:''' Streamlining improves overall performance.
* '''Weight and Space Savings:''' More efficient internal configuration.

== Design Considerations and the Four-Bar System ==

Most modern retraction systems are based on the '''four-bar linkage mechanism'''. This complex yet effective system allows for:

* Favorable actuator positioning and moment arms
* Minimal actuator stroke length
* Strong over-center locking
* Compact stowage within limited wing/fuselage volume

A simple hinge mechanism is insufficient because it lacks locking, demands higher actuator force, and doesn’t fit within the confined space. The four-bar system balances all these requirements efficiently.

For deeper insight into the kinematic principles of landing gear design, including actuator dynamics and structural integration, see the resources below.

== References ==

* [https://aviation.stackexchange.com/questions/60169/why-are-landing-gear-retraction-mechanisms-mostly-based-on-the-four-bar-syste Aviation Stack Exchange]
* [https://www.eaa.org/eaa/aircraft-building/builderresources/while-youre-building/building-articles/landing-gear-wheels-and-brakes/gear-retraction-details EAA – Gear Retraction Details]