Retractable Landing Gear - Landing Gear - Airframes & Aircraft Systems #15

Summary

This lesson delves into the design and construction of retractable main landing gear systems in aircraft, which are crucial for aerodynamic performance by reducing drag. It discusses various systems like hydraulic, pneumatic, and electrical that power the gear. The gear includes mechanical locks for secure positioning, indicators for crew awareness, and emergency lowering mechanisms. Wheel wells are typically sealed by doors for aerodynamic efficiency. The lesson also covers the geometric arrangement and physical location of landing gear, influenced by factors like aircraft size, role, and wing position. It highlights the importance of shock absorbers, steering mechanisms, and the various loads the gear must withstand during operation.

Takeaways

• 🔧 Retractable landing gear is designed to improve aerodynamic performance by reducing drag during flight.
• ⚙️ The operation of retractable landing gear is typically powered by hydraulic systems, but pneumatic or electrical systems are also used in some cases.
• 🔒 Mechanical locks are essential to ensure that each landing gear leg is securely in place when retracted or extended.
• 📡 Indicators are provided to the crew to confirm the position of each landing gear leg, ensuring safe operation.
• 🚫 Systems are in place to prevent gear retraction when the aircraft is on the ground, and warning devices prevent landing with the gear retracted.
• 🛫 Wheel wells are normally sealed by doors that close after the gear is retracted, contributing to the aerodynamic design.
• 📏 The placement and design of landing gear are determined by factors such as aircraft size, weight, intended role, and wing configuration.
• 🔄 Some aircraft feature steerable body gear to reduce turning circles and minimize tire scrubbing effects on the runway.
• 🔩 The main landing gear on larger aircraft is often attached to the wing, with some designs incorporating both wing and body gear.
• 📐 The design of the landing gear must accommodate various loads, including compressive, bending, and side loads experienced during different phases of flight and operation.

Q & A

What is the primary purpose of retractable landing gear on aircraft?

The primary purpose of retractable landing gear on aircraft is to improve aerodynamic performance by reducing drag during flight.

What are the common systems used to operate retractable landing gear?

Hydraulic systems are commonly used to operate retractable landing gear, but pneumatic or electrical systems are also sometimes used on smaller aircraft.

Why are mechanical locks important for retractable landing gear?

Mechanical locks are important to ensure that each leg of the landing gear is securely locked in either the up or down position for safety.

How does the landing gear system indicate its position to the flight crew?

The landing gear system includes indicators that inform the crew about the position of each leg, ensuring they know whether it is up or down.

What is the purpose of the wheel wells on an aircraft with retractable landing gear?

Wheel wells are where the wheels are housed when the landing gear is retracted. They are normally sealed by doors to reduce drag for aerodynamic reasons.

Why are some aircraft designed with high wing monoplane type landing gear?

Some aircraft are designed with high wing monoplane type landing gear to allow the floor of the aircraft to be as close to the ground as possible for ease of freight loading, despite the height of the wings.

How does the main landing gear attach to the wing on most modern aircraft?

On most modern aircraft, the main landing gear attaches to the wing with the leg being attached to the wing spars by a cylindrical beam or trunnion, allowing it to rotate laterally.

What is the function of the drag strut in the landing gear system?

The drag strut supports the leg of the landing gear in the fore-and-aft direction, helping to manage loads during takeoff and landing.

How does the jury strut contribute to the locking mechanism of the landing gear?

The jury strut geometrically locks the gear down by being pulled over center by the down lock actuator, ensuring the gear is securely in the down position.

What are the various loads that a landing gear unit must withstand during its life?

A landing gear unit must withstand compressive loads during landing, rearward bending loads during braking, side loads during crosswind landings and takeoffs, and longitudinal loads during pushback and towing.

Outlines

00:00

🛫 Design and Function of Retractable Landing Gear

This paragraph discusses the design and construction of retractable landing gear systems in modern aircraft. The primary purpose of these systems is to enhance aerodynamic performance by reducing drag during flight. The operation of the landing gear is typically powered by hydraulic systems, but pneumatic or electrical systems are also used in some cases. Retractable landing gear features mechanical locks to secure the gear in both the up and down positions, indicators for crew awareness, and backup systems for lowering the gear in the event of power failure. The paragraph also covers the necessity of wheel wells and doors for aerodynamic sealing and the variability in the geometric arrangement and physical location of landing gear units, which are determined by factors such as aircraft size, role, and wing configuration. The text describes how the main landing gear is attached to the wing and how it functions during takeoff and landing, including the use of talk links, drag struts, and jury struts for support and locking mechanisms.

05:01

🔩 Forces and Components of Aircraft Landing Gear

The second paragraph delves into the forces that landing gear must withstand and the components designed to manage these loads. It explains that gear mechanisms in aircraft with landing gear built into the fuselage may require alternative locking provisions due to space constraints. The paragraph outlines the various types of loads that the landing gear experiences, such as compressive loads during landing, rearward bending loads during braking, side loads during crosswind operations, and longitudinal loads during pushback and towing. It also details the functions of different components like the talk links, which handle torsion loads during ground maneuvers, and the drag strut, which manages rearward bending loads. The paragraph concludes by emphasizing the understanding of the main landing gear components and their purposes, including the role of the geometric lock produced by the jury strut in securing the gear down.

Keywords

💡Retractable Landing Gear

Retractable landing gear is a system used in aircraft to improve aerodynamic performance by reducing drag during flight. It involves the gear being able to be pulled up into the aircraft when not in use for landing or taking off. This is a key concept in the video as it explains the primary reason for the design and use of such systems in modern aircraft.

💡Aerodynamic Performance

Aerodynamic performance refers to how efficiently an aircraft moves through the air. In the context of the video, improving aerodynamic performance is a main reason for using retractable landing gear, as it helps to reduce drag and thus enhances the aircraft's overall efficiency in flight.

💡Hydraulic System

A hydraulic system is a method of transferring power in which fluid power is used to transmit energy. In the video, it is mentioned that operating power for retractable landing gear is normally provided by a hydraulic system, highlighting its importance in the functioning of the gear mechanism.

💡Mechanical Locks

Mechanical locks are devices that secure each leg of the landing gear in either the up or down position to ensure safety and proper function. The video emphasizes the importance of these locks for the secure operation of the landing gear.

💡Position Indicator

A position indicator is a device that signals to the crew the current position of each leg of the landing gear. This is crucial for safe operation, as the crew must be aware of the gear's status at all times, as mentioned in the video.

💡Emergency Lowering

Emergency lowering refers to the procedure by which the landing gear can be lowered in the event of a failure of the normal power system. The video discusses the necessity of having such a system to ensure the aircraft can land safely even in the case of a malfunction.

💡Wheel Wells

Wheel wells are the compartments in an aircraft where the wheels are housed when the landing gear is retracted. The video explains that these are normally sealed by doors to maintain aerodynamic efficiency, which is essential for the aircraft's performance.

💡Geometric Arrangement

The geometric arrangement refers to the physical layout and positioning of the landing gear units on an aircraft. The video mentions that this arrangement is not standard and is decided during the design stage, taking into account various factors such as the aircraft's size, weight, and intended use.

💡Steerable Body Gear

Steerable body gear is a feature on some aircraft where the main landing gear attached to the body of the aircraft can be steered. This helps to reduce the turning circle and the effect of wheel sideways movement, as discussed in the video, particularly beneficial for larger aircraft.

💡Olio Pneumatic Strut

An olio pneumatic strut is a type of shock absorber used in landing gear systems. It helps to cushion the loads experienced by the gear, especially during landing and when the aircraft's weight is on the ground. The video explains its role in absorbing these compressive loads.

💡Drag Strut

A drag strut is a component of the landing gear that supports the leg in a fore-and-aft direction. It is mentioned in the video as being responsible for handling rearward bending loads during braking, which is a critical function for the stability and control of the aircraft.

Highlights

Retractable landing gear improves aerodynamic performance by reducing drag in flight.

Hydraulic systems commonly power retractable landing gear, but pneumatic or electrical systems are also used.

Mechanical locks ensure the secure positioning of landing gear legs in both up and down positions.

Indicators inform the crew about the position of each landing gear leg.

Backup systems allow for landing gear lowering in the event of a normal power system failure.

Systems prevent retraction when the aircraft is on the ground.

Warning devices are installed to prevent landing with retracted gear.

Wheel wells are sealed by doors for aerodynamic efficiency.

The geometrical arrangement and physical location of landing gear are determined during the design stage.

Main considerations for landing gear design include aircraft size, weight, role, and wing configuration.

Some aircraft have both wing and body gear, with body gear being steerable for reduced turning circles.

High-wing monoplane designs have the floor close to the ground for ease of freight loading.

Landing gear in the fuselage is used for aircraft with high wings, due to strength and reach limitations.

The leg of the landing gear is attached to the wing spars by a trunnion, allowing lateral rotation.

The drag strut supports the gear in the fore-and-aft direction, while side struts handle lateral support.

The jury strut geometrically locks the gear down and is pulled over center by a down lock actuator.

In fuselage-mounted gear, alternative locking provisions are necessary due to potential geometric limitations.

Landing gear must withstand various loads, including compressive, rearward bending, and side loads.

The talk links take torsion loads during ground maneuvering, and larger aircraft may have a steerable body gear.

The gear is normally locked down by a geometric lock produced by the over center movement of the jury strut.

Transcripts

in this lesson we will look at the

design and construction of retractable

main landing gear the majority of modern

transport aircraft and an increasing

number of light aircraft are fitted with

a retractable landing gear for the

simple purpose of improving aerodynamic

performance by helping to reduce drag in

flight operating power is normally

provided by a hydraulic system but

pneumatic or on some small airplanes

electrical systems are sometimes used a

retractable landing gear is provided

with mechanical locks to ensure that

each leg is locked securely in the up or

down position it will have a means to

indicate to the crew the position of

each leg and a means by which the

landing gear can be lowered in the event

of the failure of the normal power

system in addition a system is provided

to prevent retraction with the aircraft

on the ground and warning devices are

fitted to help guard against landing

when the gear is retracted for

aerodynamic reasons wheel wells which is

where the wheels are housed are normally

sealed by doors which close after the

gear is up

for the same reason some of the doors

may also close after the gear is locked

down this picture here shows the closed

main gear doors on a Boeing 747

the geometrical arrangement and physical

location of landing gear units on

aircraft is by no means standard the

type size and position are decided at

the design stage having already taken

into account the many factors that must

be considered the main considerations

are the size and weight of the aircraft

the role the aircraft will fulfill

whether it has a high or low wing and

any associated gear stowage problems

most modern aircraft will have the main

landing gear attached to the wing with

some of the larger types having both

wing and body gear the body gear itself

may actually still be steerable this

helps to reduce the turning circle and

reduces the effect of wheel sideways

movement or tire scrubbing which affects

multiple wheel landing gear systems a

number of aircraft are designed to

operate in the jewel freight and

passenger carrying roles especially from

airports with limited resources this has

resulted in high wing monoplane type

aircraft where the floor of the aircraft

is as close as possible to the ground

for ease of afraid loading however with

some wings being as high as six or more

meters off the ground it is impossible

to build a landing gear of sufficient

strength to reach this far so these

aircraft incorporate the main gear in

the fuselage

the diagram here shows a typical large

aircraft retractable wing gear the leg

is attached to the wing spars by a

cylindrical beam or trunnion on which

the leg is free to rotate laterally the

upper part of the leg forms the outer

cylinder of the earlier pneumatic strut

the strut inner cylinder is connected to

the wheel bogie or truck beam the truck

beam is able to pivot about its central

point in a controlled way as you see

here this allows all main wheels to be

on the ground with the fuselage in the

take-off or landing attitude there is an

axle connected to a pair of brake wheels

at each end of the truck beam

the wing gear talk links prevent

rotation between the shock strut inner

and outer cylinders without affecting

their reciprocating action during normal

operation of the strut the drag strut as

shown here supports the leg in a

fore-and-aft direction the upper and

lower side struts support the leg

laterally they fold out when the gear is

lowered and are then held in place by

the jury strut which also folds out

during extension the jury strut is

pulled over center by the down lock

actuator geometrically locking the gear

down if the gear is lowered without

hydraulic power then the over centering

action will be performed by an internal

spring in the down lock actuator to

review the purpose of any of the

components we've just mentioned click on

the appropriate label

for aircraft with the landing gear built

into the fuselage the requirements are

basically the same as those for

wing-mounted landing gear except that

often the gear mechanism may not be long

enough for geometric lock to be

available so an alternative provision

has to be made for locking the gear both

up and down depending on wheel layout

each wheel may require its own shock

absorber unit and possibly even a

steering motor

a landing gear unit has to withstand

various loads during its life these

loads are transmitted to the mountings

in the aircraft structure so these two

have to be very strong a landing gear is

also subject to compressive loads

particularly during landing but also

whenever the weight of the aircraft is

on the ground the olio pneumatic strut

helps to cushion these loads the gear is

also subject to rearward bending loads

during braking these loads are taken by

the drag strut there are also side loads

during crosswind landings also during

takeoffs and taxiing these loads are

taken by the side struts the nose gear

is subject to longitudinal loads during

pushback and towing again these loads

are taken by the track strut assembly

you should now be able to identify the

various components of the main landing

gear as well as understand their purpose

you should know for instance that the

talk links take the main landing gear

torsion loads during ground maneuvering

and that some larger aircraft have a

steerable body gear and that lastly the

gear is normally locked down by a

geometric lock produced by the over

center movement of the jury strut