takeoff rotation[1]
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Take off rotationSome additional issues
Operational Liaison Meeting – Fly-By-Wire aircraft 2004
Customer Services
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Introduction
• Why do we talk again about Take Off Rotation?
It has been addressed in 2002 OLMs and in 2003 Performance & Operations Conference in Rome.
Some recent incidents call for some additional explanations.
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Reminder of various recommendations
• The Rotation flying techniques are outlined in FCOM SOPs and supplementary techniques
• They address the lateral and the pitch control of the aircraft.
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Reminder of various recommendations
• Regarding the lateral control of the aircraft:
? Do not apply large roll inputs in case of crosswind
4 Since they favor the natural “into the wind turn tendency” of the aircraft
4 Since spoilers extended increase the pitch required at lift off,thus reduce the tail strike margin (lift reduction)
4 Since a large lateral stick input may cause a lateral control problem at lift off.
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Reminder of various recommendations
• Regarding the pitch control of the aircraft:? The T/O normal law is adapted to each aircraft model
so as to ensure a similar pitch rotation technique on all FBW models.
Gain Pitch rate
+- A319/321A330/340
A320Direct law
PitchRA
-
A340-500A340-600
Tail distanceprotection
Pitch rate targetmax 2.5°/sec
Pitch rate
Gainintegrator
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Reminder of various recommendations
• Regarding the pitch control of the aircraft:
? At VR initiate rotation – with a positive side stick input for A330/A340, to achieve a continuous rotation of about 3o/sec, towards a pitch attitude of:
4 AOE: 15o (12.5o on A340-200/300)
4 OEI: 12.5o
NOTE: this pitch target is the average pitch which will be commanded by the FD pitch bar, once A/C is airborne and SRS available
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Reminder of various recommendations
• Regarding the pitch control of the aircraft:
4Avoid aggressive and sharp stick inputs
4Avoid shy initial stick inputs and further aft stick inputs justprior lift off
4Avoid chasing FD bar during initial rotation
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T/O Rotation some additional issues
• In order to minimize tail strike risks, following recommendations apply:
4Avoid premature rotation4Avoid excessive rotation rate, over rotation4Apply proper THS setting4Avoid improper use of FD pitch bar during rotation
and also4Properly choose T/O configuration4Check Landing Gear shock absorbers
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Properly Determine the Take Off Configuration
• CONF 1+F / CONF2 / CONF3 / are available for T/O As a general rule:
4A low T/O CONF (e.g. 1 + F) is preferable to optimize the 2nd
segment climb gradient, more particularly in hot weather
4A high T/O CONF (e.g. 3) is preferable– To improve tail clearance at lift off– To lower T/O speeds on rough runways
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Properly Determine the Take Off Configuration
• The criteria used to determine the best T/O CONF are:
4The configuration allowing the Highest Flex Temp(Engine saving)
4The configuration allowing for Lower Take off Speeds
4The Preferred Configuration for comfortable Aircraft handling (e.g. tail strike)
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Properly determine the Take off Configuration
• Some airplanes are more prone to tail strikes due to their geometry (e.g. A321, A340-500/600, …)
• For a given stick input at rotation, the tail clearance is reduced at lower configuration (e.g. 1+F), because the rotation rate is higher
• A compromise is to be done in between Flex Temp, lower T/O speed and preferred configuration for aircraft handling
⇒ Select the highest possible flap configuration, up to CONF3, provided it does not induce a Flex Temp greater than 5o.
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Landing gear shock absorbers
• There are 2 types of gears regarding the kinematics of the shock absorbers (oleos) and wheels:
4The conventional gears with conventional oleos
4The shock absorbers associated to Rocking Bogie via a Pitch Trimmer
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Landing gear shock absorbers
• The A330/A340 are fitted with Rocking Bogies
4The Rocking Bogie allows a greater pitch attitude at lift off than a conventional gear with the same stroke
4The shock absorber stroke is physically limited to about 750 mm. A conventional gear would need 1000 mm additional stroke on A340, for the same attitudes at rotation, than with Rocking Bogies
4The rotation of the bogie around rear wheels added to the oleo extension allows for such max pitch attitude
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Comparison Conventional Gear with Rocking Bogie
131211109876543210
1 2 3 4 5 6 7 8 9
Conventional Landing Gear
A340 ROCKING BOGIE CHARACTERISTICS
Landing Gear Fully Extended
Start of Bogie rotation
Start of Rocking Bogie Mechanism(400 mm shock absorber closure)
Tai
l Cle
aran
ce (°
)
Time (sec)
Materializes Additional Stroke Required
Lift Off
Lift Off
Att
itude
(o)
Time (sec)
A340 ROTATION LAW
2) 3) 4)
Rotation VR
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A340 Rocking Bogie Simplified Principle
1) Aircraft at VR+ - Beginning of rotationOleo has started to extend
At VR+
PitchTrimmer
2o
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A340 Rocking Bogie Simplified Principle
2) Aircraft between VR and VLOF, with pitch increasing and A/C accelerating.Typically when pitch about 5°/6°, shock absorber is 400 mm and pitch trimmer bottomed. Front wheels and MLG leg are mechanically interlocked.
PitchTrimmer
Between VR and VLOF
6o
At VR+
2o
400 mm
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A340 Rocking Bogie Simplified Principle
3) The shock absorber cannot extend, the rocking bogie cannot rotate as long as A/C lift has not reached a certain value. Shock absorberremains at 400 mm. Since pitch increases, tail clearance decreases and reaches minimum prior lift off.
At VR+
PitchTrimmer
2o
Between VR and VLOF
6o 9o
400 mm
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A340 Rocking Bogie Simplified Principle
4) The lift has increased; the oleo can further extend and the bogie can rotate; the tail clearance slightly decreases, while the A/C pitch increases.
At VR+
PitchTrimmer
2o
Between VR and VLOF
6o 9o 12o
Close to VLOF
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Landing Gear with Rocking Bogie
• The Rocking Bogie allows to fly greater pitch attitude at lift off
• The Rocking Bogie kinematics are such that the minimum tail clearance is actually reached before lift off, at initial bogie rotation
? This is an additional reason to positively initiate rotation, and avoid further aft stick inputs during rotation (Pitch ≈ 8o …)
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A340 / A330 Rotation Law Technique
LIFT OFF
POORPOOR
GOOD
Time (sec)
Att
itu
de
(o )
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Landing Gear with Rocking Bogie
• On any type of Landing Gear, servicing shall ensure that oleos are properly pressurized.
• The effects of low pressure in oleos are somehow increased with the Rocking Bogie system, indeed:4A low pressure oleo delays the time where pitch trimmer is
bottomed4A low pressure oleo delays the time where the bogie starts to
rotate
? Typically, a 10 bars low pressure in oleo, leadingto a 60 mm oleo reduction, decreases the tail clearance by approximately 1 ft (or 1o)
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A340 Tail Clearance During Take Off1614121086420-2
0 1 2 3 4 5 6 7 8 9 10
0 1 2 3 4 5 6 7 8 9 10
18
16
14
12
10
8
6
4
2
0
A340 Rotation Law
A340 Rocking Bogie Characteristics
Lift Off
Lift Off
Landing GearsFully Extended
Start of Rocking Bogie mechanism(400 mm shock absorber closure)
Maximum Pitch Attitude / Ground (o)Start of Bogie rotation
Att
itude
(o)
Tail Clearance (o) (ft)
Nominal pressureNominal – 10 bars
Time (sec)
Time (sec)
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Conclusions
• This presentation actually enhances 3 issues:
4All present recommendations in SOPs and FCOM supplementary techniques are unchanged
4But configuration must be judiciously determined.Amongst others, higher CONF is preferable provided that FLX TEMP is not penalized by more than 5o C
4Shock absorbers must be adequately pressurized.Crews shall check consistency in between both MLG shock absorbers length, and report any suspected anomaly.
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This document and all information contained herein is the sole property of AIRBUS S.A.S. No intellectual property rights are granted by the delivery of this document or the disclosure of its content. This document shall not be reproduced or disclosed to a third party without the express written consent of AIRBUS S.A.S. 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 S.A.S. will be pleased to explain the basis thereof.
AN EADS JOINT COMPANYWITH BAE SYSTEMS
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