Operational Liaison Meeting Fly-By-Wire aircraft
2004
Take off rotation
Some additional issues
Customer Services
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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Takeoff rotation
Page 2
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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Takeoff rotation
Page 3
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 spoilers extended increase the pitch required at lift off, thus reduce the tail strike margin (lift reduction) a large lateral stick input may cause a lateral control problem at lift off.
4 Since
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4 Since
Takeoff rotation
Page 4
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.
Direct law
Pitch rate
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A320
Gain
Tail distance protection
+ A319/321
A330/340
Pitch RA
Gain integrator
Pitch rate target max 2.5/sec
A340-500 A340-600
Pitch rate
Takeoff rotation
Page 5
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 (12.5 o 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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Takeoff rotation
Page 6
Reminder of various recommendations
Regarding the pitch control of the aircraft:
4Avoid 4Avoid
aggressive and sharp stick inputs
shy initial stick inputs and further aft stick inputs just prior lift off chasing FD bar during initial rotation
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4Avoid
Takeoff rotation
Page 7
T/O Rotation some additional issues
In order to minimize tail strike risks, following
recommendations apply:
4Avoid
premature rotation 4Avoid excessive rotation rate, over rotation 4Apply proper THS setting 4Avoid improper use of FD pitch bar during rotation
and also
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4Properly
choose T/O configuration 4Check Landing Gear shock absorbers
Takeoff rotation
Page 8
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 2 nd segment climb gradient, more particularly in hot weather high T/O CONF (e.g. 3) is preferable
4A
To improve tail clearance at lift off To lower T/O speeds on rough runways
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Takeoff rotation
Page 9
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) configuration allowing for Lower Take off Speeds
4The 4The
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Preferred Configuration for comfortable Aircraft handling (e.g. tail strike)
Takeoff rotation
Page 10
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
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Select the highest possible flap configuration, up to
CONF3, provided it does not induce a Flex Temp greater than 5o.
Takeoff rotation
Page 11
Landing gear shock absorbers
There are 2 types of gears regarding the kinematics of the
shock absorbers (oleos) and wheels:
4The 4The
conventional gears with conventional oleos
shock absorbers associated to Rocking Bogie via a Pitch Trimmer
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Takeoff rotation
Page 12
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 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 rotation of the bogie around rear wheels added to the oleo extension allows for such max pitch attitude
4The
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4The
Takeoff rotation
Page 13
Comparison Conventional Gear with Rocking Bogie
A340 ROTATION LAW
Attitude(o)
Lift Off
2)
3)
4)
Time (sec) Rotation VR
13 A340 ROCKING BOGIE CHARACTERISTICS 12 Conventional Landing Gear 11 10 Materializes Additional Stroke Required 9 8 7 6 Landing Gear Fully Extended 5 Start of Rocking Bogie Mechanism 4 (400 mm shock absorber closure) 3 2 Start of Bogie rotation 1 Lift Off 0 1 2 3 4 5 6 7 8 9 Time (sec)
Takeoff rotation
Page 14
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Tail Clearance ()
A340 Rocking Bogie Simplified Principle
1) Aircraft at VR+ - Beginning of rotation Oleo has started to extend
At VR+
2o
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Pitch Trimmer
Takeoff rotation
Page 15
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.
At VR+ Between VR and VLOF
2o
6o
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400 mm
Pitch Trimmer
Takeoff rotation
Page 16
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 absorber remains at 400 mm. Since pitch increases, tail clearance decreases and reaches minimum prior lift off.
At VR+ Between VR and VLOF
2o
6o
9o
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400 mm
Pitch Trimmer
Takeoff rotation
Page 17
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+
Between VR and VLOF
Close to VLOF
2o
6o
9o
12o
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Pitch Trimmer
Takeoff rotation
Page 18
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
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? This is an additional reason to positively initiate
rotation, and avoid further aft stick inputs during rotation (Pitch 8o )
Takeoff rotation
Page 23
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A340 / A330 Rotation Law Technique
Takeoff rotation
Attitude (o)
GOOD
Time (sec) POOR
LIFT OFF
Page 24
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 bottomed 4A low pressure oleo delays the time where the bogie starts to rotate
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Typically, a 10 bars low pressure in oleo, leading to a 60 mm oleo reduction, decreases the tail clearance by approximately 1 ft (or 1o)
Takeoff rotation
Page 25
A340 Tail Clearance During Take Off
16 14 12 10 8 6 4 2 0 -2 0 1 2 3
A340 Rotation Law
Lift Off
Attitude (o)
10
Time (sec)
18 16 14
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A340 Rocking Bogie Characteristics
Maximum Pitch Attitude / Ground (o)
Start of Bogie rotation
Landing Gears Fully Extended
12 10 8 6 4 2 0
Takeoff rotation
Start of Rocking Bogie mechanism (400 mm shock absorber closure)
Nominal pressure Nominal 10 bars
Tail Clearance (o) (ft) Lift Off 0 1 2 3 4 5 6 7 8 9 10 Time (sec)
Page 26
Conclusions
This presentation actually enhances 3 issues:
4All
present recommendations in SOPs and FCOM supplementary techniques are unchanged configuration must be judiciously determined. Amongst others, higher CONF is preferable provided that FLX TEMP is not penalized by more than 5o C absorbers must be adequately pressurized. Crews shall check consistency in between both MLG shock absorbers length, and report any suspected anomaly.
4But
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4Shock
Takeoff rotation
Page 27
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.
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AN EADS JOINT COMPANY WITH BAE SYSTEMS
Takeoff rotation
Page 28
