On 6. Jan 2021, Michael S. wrote
(in article <
i5mfqm...@mid.individual.net>):
> > Sprich. Man konnte damit auch in 10’ nur einen Reverser öffnen. Dabei
> > bitte bedenken. Ausser High Idle Reverse Schub war vor dem Touchdown nicht
> > möglich.
>
> Ich habe keine Vorstellung, wie stark ein Reverser im Idle bremst und ob
> so ne Asymmetrie schlimmer als z.B. ein Triebwerksausfall im Startlauf ist.
>
> Beim Startlauf dürfte das aber unkritischer sein (man möge mich
> korrigieren):
> So lange man noch auf der Bahn ist, hat man Seitenführung und ein gut
> wirksames Ruder. Nach dem Abheben ist es erstmal egal, wenn man 10-20°
> auf ne Seite driftet, wichtiger ist, dass man steigt.
>
> Im Flare wären 10° wegdriften ungesund.
Ich glaube, Du überschätzt jetzt die Kraft von Idle Reverse Thrust.
Der Bobby hatte keinen starken Idle Schub. Nur bei ganz leichten Gewichten
rollte dieser von alleine los.
Bsp: STR taxi zur RWY25 von der Rampe.
Aufgrund des starken Gefälles wurde man ständig schneller. Ohne
gelegentliches runterbremsen ging es nicht.
Man konnte dies vermeiden, in dem man einen der Reverser öffnete. Nun ja,
gemäß Procedure war Reverse during Taxi nicht erlaubt, gelegentlich sah man
aber den ein oder anderen dies machen. Ein Reverser kompensierte in dem Fall
gerade soviel, das man nicht schneller wurde.
Das ganze wäre beim flare nur kritisch, wenn durch den idle Reverser
Steuerflächen nicht mehr angeströmt wären. Da aber diese Logik zugelassen
wurde, wurde sie auch getestet...
Darüberhinaus hat so einen Bobby ja nun auch hydraulische Controls die
einmotorigen TakeOff Thrust kompensieren kann. Also sehr effektive
Flightcontrols.
Das Fahrwerk kann eine Landung mit 15 Kts Seitenwind im Crab problemlos ab.
--
Grüße Steffen
PS: Auszug aus dem OM-B 2005
OPERATION
Each engine is equipped with a hydraulically operated thrust reverser,
consisting of left and right translating sleeves. Aft movement of the
reverser sleeves causes blocker doors to deflect fan discharge air forward,
through fixed cascade vanes, producing reverse thrust. The thrust reverser is
for ground operations only and is used after touchdown to slow the airplane,
reducing stopping distance and brake wear.
Hydraulic pressure for the operation of engine No. 1 and engine No. 2 thrust
reversers comes from hydraulic systems A and B, respectively. If hydraulic
system A or B fails, alternate operation for the affected thrust reverser is
available through the standby hydraulic system. When the standby system is
used, the affected thrust reverser deploys and retracts at a slower rate, and
some thrust asymmetry can be anticipated.
The thrust reverser can be deployed when either radio altimeter senses less
than 10 feet altitude, or when the air/ground safety sensor is in the ground
mode. Movement of the reverse thrust levers is mechanically restricted until
the forward thrust levers are in the idle position.
When reverse thrust is selected, the isolation valve opens, and the thrust
reverser control valve moves to the deploy position, allowing hydraulic
pressure to unlock and deploy the reverser system. An interlock mechanism
restricts movement of the reverse thrust lever until the reverser sleeves
have approached the deployed position. When either reverser sleeve moves from
the stowed position, the amber REVERSER UNLOCKED light on the center
instrument panel illuminates. As the thrust reverser reaches the deployed
position, the reverse thrust lever can be raised to detent No. 2. This
position provides adequate reverse thrust for normal operations. When
necessary, the reverse thrust lever can be pulled beyond detent No. 2,
providing maximum reverse thrust.
Downward motion of the reverse thrust lever past detent No. 1 commands the
reverser to stow. Once the thrust reverser is commanded to stow, the control
valve moves to the stow position allowing hydraulic pressure to stow and lock
the reverser sleeves. After the thrust reverser is stowed, the isolation
valve closes.
The REVERSER light, located on the aft overhead panel, illuminates when the
thrust reverser is commanded to stow and extinguishes 10 seconds later when
the isolation valve closes. Any time the REVERSER light illuminates for more
than approximately 12 seconds, a malfunction has occurred, and the MASTER
CAUTION lights and the ENG annunciator illuminate.
When the reverser sleeves are in the stowed position, a hydraulically
operated locking actuator inhibits motion to each reverser sleeve until
reverser extension is selected. Apart from that, an electrically operated
mechanic Sync Lock is installed which, in the locked position, prevents
movement of the hydraulic actuators. This lock is spring loaded to the locked
position and solenoid operated to the unlocked position when energized. When
reverse thrust is selected, power is send to a latch relay, which energizes
the sync lock to move to the unlocked position. Moving the reverse thrust
levers to the stow position, power is removed from the solenoid after a time
delay of two minutes, releasing the sync lock to the locked position.
Additionally, an auto– restow circuit compares the actual reverser sleeve
position and the commanded reverser position. In the event of incomplete
stowage or uncommanded movement of the reverser sleeves toward the deployed
position, the auto–restow circuit opens the isolation valve and commands
the control valve to the stow position, directing hydraulic pressure to stow
the reverser sleeves. Once the auto–restow circuit is activated, the
isolation valve remains open and the control valve is held in the stowed
position until the thrust reverser is commanded to deploy or until corrective
maintenance action is taken.
Warning: Actuation of the thrust reversers on the ground without suitable
precautions is dangerous to ground personnel.
----
@SteffenA380