While I was routinely reading the FCOM normal procedures I came across a note with regard to the speedbrakes retraction time going up to 25 seconds when we use them at speeds at or over 315 knots / .75 Mach.
Why is this ?
$\begingroup$
$\endgroup$
6
-
4$\begingroup$ Presumably the speedbrakes cause a significant change in flight characteristics, and you want that to happen gradually at higher speeds. $\endgroup$– DJClayworthCommented May 13, 2019 at 13:53
-
1$\begingroup$ @DJClayworth Yes, they cause quite a change in pitch moment balance as far as I know. Not sure whether that’s the only reason, though. $\endgroup$– Cpt ReynoldsCommented May 13, 2019 at 14:28
-
$\begingroup$ Other possibilities are that there is some kind of noise that scares ppl if they are retracted quickly, or there is a ballooning effect from having significant lift restored at that high a speed that creates an unpleasant G load. When we used flight spoilers on the CRJs you were supposed to retract them in steps. You'd have to get lucky and find someone on here that is associated with AB engineering to get a definitive answer I expect. $\endgroup$– John KCommented May 13, 2019 at 15:39
-
1$\begingroup$ Suggest you ask your flight ops management about the process for sending questions to Airbus's Liaison Pilot organization (they may call it something else). LPs are the primary interface between the operator flight ops community and AB's engineering organization, and one of their jobs is answering these sorts of questions submitted by flight crews. $\endgroup$– John KCommented May 13, 2019 at 15:52
-
1$\begingroup$ note that "25 seconds" is not a "rate of retraction", it is a time. a rate of retraction would be, for example "1°/sec" $\endgroup$– FedericoCommented May 27, 2019 at 8:12
|
Show 1 more comment
1 Answer
$\begingroup$
$\endgroup$
Please read the entire answer to understand the matter even if the answer goes a bit beyond the question.
On the A320 wings you have panels that may open upward and that could be used to fulfill 3 different functions: ground spoilers, speed brakes, roll spoilers.
The outer panels are used in addition to the ailerons for roll function, that is helping the ailerons only on one of the wing according to the turn direction.
The central panels are used in flight for the speed brake function as follows: when the pilot order is beyond a limit the Fly By Wire will provide protections because an excessive drag might damage the wing structure, so the higher the speed the lower will be their maximum angle of deployment and their speed of deployment even if the pilot gives a full order of deployment.
The drag produced by the air brakes causes a mechanical torque on the wings roots, a sudden removal of the drag would be similar to a stress cycle, therefore deployment and retraction are managed to protect the wing structure. Any pitching effect of these surfaces in flight is automatically compensated by the FBW through the elevators.
At landing the ground spoilers function is as follows; all the surfaces are deployed fully if the function is armed.
