LG Design and Integration into Aircraft - ingaero.uniroma1.it presentation - LG... · Landing Gear...

LG Design and Integration into Aircraft

November 2016Landing Gear Design and Integration into Aircraft

Sapienza University, Adriano Argiolas

LG Flight Physics Integration

© AIRBUS Operations LTD. All rights reserved. Confidential and proprietary document.

What’s a Landing Gear?


“The essential intermediary between the aeroplane and the catastrophe”Conway, H. G., Landing Gear Design, Chapman & Hall, London, 1958


A bit of terminology


Nose landing gear Main landing gear


What does a landing gear do

Airbus A380

MTOW 575 tT/O speed: 277 km/hLanding speed: 240 km/h

Landing distance 1900m @ 386tOperating Temperature -50˚C to +70˚C


US Class 8 truck

MTOW 36 t Stopping distance 102 m @ 96 km/h:

F1 car

ZFW 0.702 tTop speed in 2016: 372.54* km/hOperating Temperature +5˚C** to +38˚C***

* 2016 Mexico Grand Prix – V Bottas

**1978 Canadian Grand Prix

***1984 Dallas Grand Prix


Landing gear design



LG design objectives


• Safety• Landing gear is designed to be safe life • Max strength & min weight

• High reliability & low cost

• A/C integration & airport compatibility

• Low maintenance

The final scope is not to design the best landing gear, but to design the best overall aircraft


Configuration definition

TailwheelPros• Simplicity

• A/C is tilted to high AoA, providing improving lift at TO and higher clearance for propeller engine

Cons• Intrinsically instable


Nose wheel tricyclePros• Fuselage (and cabin/cargo floor) are nearly level

• Improved stability during braking and manoeuvres

• Pitch-down moment at landing, reduces AoA and lift

Cons• Gears locations are more constrained


Tailwheel gear ground loop


Video: tailwheel gear ground loop


Where to put the LG?

• NLG and MLG must be placed far enough from the A/C CG such that there is no risk of tipping back or turning over under any static or dynamic condition

• In order to guarantee the braking performance, MLG should support between 85% and 92% of the A/C weight

• A/C loadability must be taken into account


Components cg envelopes



Aircraft loadability

Loadability issue on cargo aircraft


Geometry definition


• The available pitch at TO and Landing must be ≥ the value imposed by A/C performance requirement. If this is not respected, the consequence would be a reduction in minimum liftoff speed and/or operations in crosswind

• The A/C height on the groundline is also determined by the engine to ground clearance and the LG doors to ground clearance

Tail clearance Wing clearance


Crosswind landing – Low speed takeoff


Crosswind one-wheel landing

Video: A340 low-speed takeoff


Flotation

• Airports charge airlines based on ACN (Aircraft Classification Number)

• ACN takes in account MTOW, LG configuration, CG position and runway pavement type

• Modifying the number of tyres and the wheelbase has an effect on ACN, and can do the difference on whether an A/C can or cannot land in a specific airport




Runway (in)compatibility

Aircraft/runway loading incopatibility


Tyres

• Tyres are not tailored to a specific A/C. Tyre selection is based on the simple requirement that its load and speed rating must be compatible with the AC characteristics

• Load transfer between LG and ground is heavily dependent from tyre characteristics

• Tyre behaviour is highly nonlinear

• LG design must cater for the possibility to have a non homogeneous set of tyres on any gear




Side loads on tyres

Brake pivot turn


Brakes and wheels

• Brakes are used to stop and steer the AC

• Brake sizing depends directly upon the AC performance

• Wheel design is driven primarily by its requirement to accommodate the required tyre and to house the brake while retaining minimum weight and maximum life


Wheel and brake cutout


“Square” tyre


Buckled deflated tyre


Brakes instabilities

• Squeal vibration is characterized by torsional motion of stators, torque tube, and piston housing. Typical frequency range is between 100 Hz and 20 kHz

• Whirl vibration shows up as out of plane "wobble" motion involving the brake disks, torque tube and piston housing. Whirl frequency range is 100 Hz to 300 Hz

• Chatter mode of vibration involves torsional motion of rotors and wheel, typically coupled with fore-aft motion of the landing gear. Chatter is largely controlled by tire stiffness and it can occur at the end of taxi stops. The frequency of chatter vibration is in the range between 10 Hz and 100 Hz.



Shock Absorber definition


• The basic function of the shock absorber is to absorb and dissipate the impact kinetic energy to the extent that accelerations imposed upon the airframe are reduced to a tolerable level

0

Aircraft Shock Absorber


Spring curve definition


• SA starts moving once the breakout load is reached

• WoW signal triggers full lift dump

• MRW static load

• MRW bump load

Shock absorber spring curve at different temperatures


Reaction factor


0 2 0 3 0 4

• Hydraulic peak load

• Gas peak load

• 1 g load case

• Max peak

Static vs Dynamic loads on a shock absorber


Kinematics


LGs must be able to fold back into the A/C to minimise drag on cruise.

Design objective is to have the simplest possible (i.e. with the minimum amount of moving parts) extension/retraction system that:

• takes up the least amount of stowage volume

• avoids interferences between the landing gear and surrounding structures

• in case of emergency, safely extends and locks using only gravity

LG extension/retraction cycle


Structural preliminary sizing

Preliminary sizing of landing gear can be carried out considering a rigid aircraft and approximating the LG itself with a beam.

Landing and on ground manoeuvre load cases are analysed as simple static equilibrium cases


turning

lateral drift landing

1-wheel landing

Braked rollTail down landing

3 point level landing


Ground loads calculation


At a later stage, the dynamic FEM of the gear becomes available, and it is then integrated into the AC Dynamic Master Module (DMM)

This allows a full load loop to be calculated, this time fully taking into account

• AC flexibility

• LG flexibility

• Tyres behaviour

• SA characteristics

• AC control logic

Ground loads so generated are then used to fine tune the AC and LG design

MLG beam modelA/C dynamic model with LGs embedded

A/C dynamic model with LGs embedded


Do LGs size the aircraft?


Dynamic landingTaxi

Landing braked rollTowing

Dynamic brakingTaxi

Steering

Dynamic landingTaxi

Loads can be controlled using:

• Spring/damping curve

• LG geometry

• Unsprung mass

• Brake logic

• Lift dump logic

• Gear/Aircraft stiffness

Fuselage/wing sizing cases influenced by LG


LG stability


The dynamic LG models are also used to analyse the stability of the LG while steering, or when excited by Out Of Balance loads, and shimmy

Out of balance accelerations spectrogram Video: Hawker Siddeley 125 NLG shimmy


Resources

Videos:

• MD80 hard landing: https://youtu.be/C74ZXW2NlSY

• Ground loop: https://youtu.be/Dz2_QJpfqXI

• Airbus YouTube channel: https://www.youtube.com/user/airbus

Further readings:

Norman S. Currey, Aircraft Landing Gear Design: Principles and Practices (AIAA Education)




© AIRBUS Operations LTD. All rights reserved. Confidential and proprietary document. This document and all information contained herein is the sole property of AIRBUS Operations LTD. No intellectual property rights are granted by the delivery of this document orthe disclosure of its content. This document shall not be reproduced or disclosed to a third party without the express written consent of AIRBUS Operations LTD. This document and its content shall not be used for any purpose other than that for which it is supplied.The statements made herein do not constitute an offer. They are based on the mentioned assumptions and are expressed in good faith. Where the supporting grounds for these statements are not shown, AIRBUS Operations LTD. will be pleased to explain thebasis thereof. AIRBUS, its logo, A300, A310, A318, A319, A320, A321, A330, A340, A350, A380, A400M are registered trademarks.

LG Design and Integration into Aircraft - ingaero.uniroma1.it presentation - LG... · Landing Gear...

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