Slowing down the aircraft in x wind!!
Join Date: Mar 2009
Location: pre-dep area
Posts: 163
Likes: 0
Received 0 Likes
on
0 Posts
@scotbill:
you surely are gonna get a kick out of this: Airbus prohibits a "controlled sidelip" technique.
however, guess how to perform the "de-crab" maneuver accdg to Airbus?
a rose is a rose...
you surely are gonna get a kick out of this: Airbus prohibits a "controlled sidelip" technique.
however, guess how to perform the "de-crab" maneuver accdg to Airbus?
a rose is a rose...
Thanks for that Cpt S!
Is any Airbus pilot prepared to admit he has found controlled slip works? I'm told the problem is that the sidestick sets an aileron input which is maintained till it is cancelled - but that may be too simplistic?
1) Avoid deflecting the stick into wind. It has practically no efficiency, but has adverse side effects on braking. Indeed, it creates a differential down force on the wheels into the wind side due to the aileron deflection, and it creates a differential drag effect due to spoiler retraction on the out-of-wind side. These differential effects favor the natural "into the wind" turn tendency of the aircraft."
What "into the wind" tendency is that? Taildraggers yes - which is why the pros used controlled slip. But you can crash a tricycle into the ground fully crabbed (as some have suggested on this thread) and the machine automatically tries to straighten up. The important thing on a slippery runway is the aircraft line of inertia - which is why a controlled flare along centre line is preferable to a late adjustment due to (all-too-common) misjudgement of the KOD point.
Surely (sorry - mustn't call you Shirley) the "down force on the wheels into the wind side" is actually what you need to ensure maximum brake/anti-skid efficiency? And the "differential drag ...on the out-of-wind side" would counter any into the wind tendency.
Is any Airbus pilot prepared to admit he has found controlled slip works? I'm told the problem is that the sidestick sets an aileron input which is maintained till it is cancelled - but that may be too simplistic?
1) Avoid deflecting the stick into wind. It has practically no efficiency, but has adverse side effects on braking. Indeed, it creates a differential down force on the wheels into the wind side due to the aileron deflection, and it creates a differential drag effect due to spoiler retraction on the out-of-wind side. These differential effects favor the natural "into the wind" turn tendency of the aircraft."
What "into the wind" tendency is that? Taildraggers yes - which is why the pros used controlled slip. But you can crash a tricycle into the ground fully crabbed (as some have suggested on this thread) and the machine automatically tries to straighten up. The important thing on a slippery runway is the aircraft line of inertia - which is why a controlled flare along centre line is preferable to a late adjustment due to (all-too-common) misjudgement of the KOD point.
Surely (sorry - mustn't call you Shirley) the "down force on the wheels into the wind side" is actually what you need to ensure maximum brake/anti-skid efficiency? And the "differential drag ...on the out-of-wind side" would counter any into the wind tendency.
Join Date: Jul 2006
Location: USA
Posts: 451
Likes: 0
Received 0 Likes
on
0 Posts
Captain Solipsist:
You are to be commended for quoting an authoritative document.
Your point #1, however, refers to the aircraft when it is already on the
ground....not the flare and touchdown.
The Flight Crew Training Manual describes the situation....everyone have a
look, please.
Tires have cornering capability and stopping ability....but as Mu
decreases, one cannot expect tires to do both very well. In other,
words, as braking action decreases, you're going to have to accept
one or the other (cornering or braking)....and with less and less
braking action, the trade-off becomes more pronounced.
When wheel are 'crooked' (landing in a crab), you're already
at at disadvantage....cornering and braking.....
This is why the Airbus (and Boeing) procedure is to use
the rudder to align the aircraft with the runway centerline
as you begin the flare. Use some aileron to counteract
any drift downwind.
In 'strong' crosswinds, there may a problem with the above.
There may be geometric limits to 'putting a wing down'. In
that case, some crab at touchdown is to be accepted.
For the Airbus, a maximum of 5 degrees of crab, maximum of
5 degrees of wing down at touchdown. (Reference the FCTM
and the document by Captain Thierry Bourges, Experimental
Test Pilot, Airbus, entitled "Crosswind Landings"....presented
at an OLM FBW conference in 2006.)
The problem with landing in a crab is that, when you grab a
handful of reverse, you will, as Captain Solipsist so correctly
quotes, 'destabilize' the approach. In other words, the reverse
thrust vector is not aligned with the runway....and, it (the thrust
vector) will 'pull' you to the downwind side of the runway. This,
coupled with the fact that, because of the tires not being aligned
(which handicaps their ability to 'corner'), is a prescription for
a runway excursion.
Actually, in this case, Airbus hints that maybe less reverse and
more autobrakes is a better solution.
Landing with more than 5 degrees of crab, for the Airbus, risks
damaging the gear. Further, too much bank risks scraping some
metal. Again, "five and five" is the recommended max. (Ref: ibid)
Good luck, everyone.
Your point #1, however, refers to the aircraft when it is already on the
ground....not the flare and touchdown.
The Flight Crew Training Manual describes the situation....everyone have a
look, please.
Tires have cornering capability and stopping ability....but as Mu
decreases, one cannot expect tires to do both very well. In other,
words, as braking action decreases, you're going to have to accept
one or the other (cornering or braking)....and with less and less
braking action, the trade-off becomes more pronounced.
When wheel are 'crooked' (landing in a crab), you're already
at at disadvantage....cornering and braking.....
This is why the Airbus (and Boeing) procedure is to use
the rudder to align the aircraft with the runway centerline
as you begin the flare. Use some aileron to counteract
any drift downwind.
In 'strong' crosswinds, there may a problem with the above.
There may be geometric limits to 'putting a wing down'. In
that case, some crab at touchdown is to be accepted.
For the Airbus, a maximum of 5 degrees of crab, maximum of
5 degrees of wing down at touchdown. (Reference the FCTM
and the document by Captain Thierry Bourges, Experimental
Test Pilot, Airbus, entitled "Crosswind Landings"....presented
at an OLM FBW conference in 2006.)
The problem with landing in a crab is that, when you grab a
handful of reverse, you will, as Captain Solipsist so correctly
quotes, 'destabilize' the approach. In other words, the reverse
thrust vector is not aligned with the runway....and, it (the thrust
vector) will 'pull' you to the downwind side of the runway. This,
coupled with the fact that, because of the tires not being aligned
(which handicaps their ability to 'corner'), is a prescription for
a runway excursion.
Actually, in this case, Airbus hints that maybe less reverse and
more autobrakes is a better solution.
Landing with more than 5 degrees of crab, for the Airbus, risks
damaging the gear. Further, too much bank risks scraping some
metal. Again, "five and five" is the recommended max. (Ref: ibid)
Good luck, everyone.
Join Date: Sep 2005
Location: Denmark
Posts: 58
Likes: 0
Received 0 Likes
on
0 Posts
Airbus FCTM
Hi,
Just to add to Pantlords excelent post. A few quotes from the Airbus FCTM.
FLARE:
"In crosswind conditions, a crabbed-approach should be flown.
During the flare, rudder should be applied as required to align the aircraft with the runway heading. Any tendency to drift downwind should be counteracted by an appropriate input on the sidestick.
In the case of a very strong cross wind, the aircraft may be landed with a
residual drift (maximum 5°) to prevent an excessive bank (maximum 5°).
Consequently, combination of the partial de-crab and wing down techniques may
be required."
ROLL OUT:
"Additionally, the pilot will avoid setting stick into the wind as it increases the weathercock effect. Indeed, it creates a differential down force on the wheels into the wind side and differential drag due to spoiler retraction.
The reversers have a destabilizing effect on the airflow around the rudder and thus decrease the efficiency of the rudder. Furthermore they create a side force, in case of a remaining crab angle, which increases the lateral skidding tendency of the aircraft. This adverse effect is quite noticeable on contaminated runways with crosswind.
In case a lateral control problem occurs in high crosswind landing, the pilot will consider to set reversers back to Idle.
At lower speeds, the directional control of the aircraft is more problematic, more specifically on wet and contaminated runways. Differential braking is to be used if necessary. On wet and contaminated runways, the same braking effect may be reached with full or half deflection of the pedals; additionally the anti skid system releases the brake pressure on both sides very early when the pilot presses on the pedals. Thus if differential braking is to be used, the crew will totally release the pedal on the opposite side to the expected turn direction."
Just to add to Pantlords excelent post. A few quotes from the Airbus FCTM.
FLARE:
"In crosswind conditions, a crabbed-approach should be flown.
During the flare, rudder should be applied as required to align the aircraft with the runway heading. Any tendency to drift downwind should be counteracted by an appropriate input on the sidestick.
In the case of a very strong cross wind, the aircraft may be landed with a
residual drift (maximum 5°) to prevent an excessive bank (maximum 5°).
Consequently, combination of the partial de-crab and wing down techniques may
be required."
ROLL OUT:
"Additionally, the pilot will avoid setting stick into the wind as it increases the weathercock effect. Indeed, it creates a differential down force on the wheels into the wind side and differential drag due to spoiler retraction.
The reversers have a destabilizing effect on the airflow around the rudder and thus decrease the efficiency of the rudder. Furthermore they create a side force, in case of a remaining crab angle, which increases the lateral skidding tendency of the aircraft. This adverse effect is quite noticeable on contaminated runways with crosswind.
In case a lateral control problem occurs in high crosswind landing, the pilot will consider to set reversers back to Idle.
At lower speeds, the directional control of the aircraft is more problematic, more specifically on wet and contaminated runways. Differential braking is to be used if necessary. On wet and contaminated runways, the same braking effect may be reached with full or half deflection of the pedals; additionally the anti skid system releases the brake pressure on both sides very early when the pilot presses on the pedals. Thus if differential braking is to be used, the crew will totally release the pedal on the opposite side to the expected turn direction."
ROLL OUT:
"Additionally, the pilot will avoid setting stick into the wind as it increases the weathercock effect. Indeed, it creates a differential down force on the wheels into the wind side and differential drag due to spoiler retraction.
I'm sorry guys, this still makes no sense.
I repeat - what "weathercock effect" with tricycle gear?
The only weathercock effect you might get is if the aircraft is already crabbing on a slippery surface - with reverse thrust therefore giving a component across the runway. This is the situation where it might be necessary to cancel reverse.
The danger of not having into-wind aileron is that, for example, it has been shown to delay automatic lift dump on aircraft like the 757. On one swept wing aircraft I remember it was shown that the upwind wing was still giving significant lift at 80 knots - thereby disabling the anti-skid.
Opposite aileron is essential with KOD to avoid any risk of touching wingtip or pod on the downwind side. The controlled slip merely advances that a 100' or so up the glideslope
Could an airbus pilot comment on whether the real reason for their philosophy is a risk of overcontrolling with the sidestick?
"Additionally, the pilot will avoid setting stick into the wind as it increases the weathercock effect. Indeed, it creates a differential down force on the wheels into the wind side and differential drag due to spoiler retraction.
I'm sorry guys, this still makes no sense.
I repeat - what "weathercock effect" with tricycle gear?
The only weathercock effect you might get is if the aircraft is already crabbing on a slippery surface - with reverse thrust therefore giving a component across the runway. This is the situation where it might be necessary to cancel reverse.
The danger of not having into-wind aileron is that, for example, it has been shown to delay automatic lift dump on aircraft like the 757. On one swept wing aircraft I remember it was shown that the upwind wing was still giving significant lift at 80 knots - thereby disabling the anti-skid.
Opposite aileron is essential with KOD to avoid any risk of touching wingtip or pod on the downwind side. The controlled slip merely advances that a 100' or so up the glideslope
Could an airbus pilot comment on whether the real reason for their philosophy is a risk of overcontrolling with the sidestick?
