Airbus minimum selected speed (a320-340s)
Hi Goldenrivett,
"Although I can find no reference to your statement in FCOM, I think they must be affected in the same way they move with changes in delta g."
It seems logical that they would, so my memory may well be wrong. Perhaps vilas, or someone else with access to the FCOM, etc., will find a reference.
Quote from Microburst2002:
"...speedbrakes reduce stall AoA
therefore V alpha max should increase accordingly, and VLS, too"
Yes. My tentative understanding of aerodynamics suggests that the airbrakes would, as you say, reduce the stall AoA because of the disruption to airflow. That would obviously increase the stall IAS/EAS. But the loss of lift resulting from the disrupted airflow would increase the stall IAS still further for a given weight.
The combination of these two factors may explain the great effect that use of "speedbrakes" has on VLS, which IIRC is simply a function of Vs-min.
"Although I can find no reference to your statement in FCOM, I think they must be affected in the same way they move with changes in delta g."
It seems logical that they would, so my memory may well be wrong. Perhaps vilas, or someone else with access to the FCOM, etc., will find a reference.
Quote from Microburst2002:
"...speedbrakes reduce stall AoA
therefore V alpha max should increase accordingly, and VLS, too"
Yes. My tentative understanding of aerodynamics suggests that the airbrakes would, as you say, reduce the stall AoA because of the disruption to airflow. That would obviously increase the stall IAS/EAS. But the loss of lift resulting from the disrupted airflow would increase the stall IAS still further for a given weight.
The combination of these two factors may explain the great effect that use of "speedbrakes" has on VLS, which IIRC is simply a function of Vs-min.
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,407
Likes: 0
Received 0 Likes
on
0 Posts
Goldenrlvett
Speed brakes effect incidence opposite of flaps so AoA actually reduces. VLS can be seen increasing with SB. When flying manually reversion to speed mode can occur at VLS-2 KTS but with full speed breaks it occurs at VLS-19(increased VLS). FCOM doesn't say much on this.
Speed brakes effect incidence opposite of flaps so AoA actually reduces. VLS can be seen increasing with SB. When flying manually reversion to speed mode can occur at VLS-2 KTS but with full speed breaks it occurs at VLS-19(increased VLS). FCOM doesn't say much on this.
Join Date: Jan 2014
Location: N5109.2W10.5
Posts: 720
Likes: 0
Received 0 Likes
on
0 Posts
vilas
Please explain why speed brakes actually reduces AoA.
I thought speed brakes spoil the lift over part of the wing effectively reducing the lifting Wing Area, thus requiring an increase in AoA to maintain the same lift.
Speed brakes effect incidence opposite of flaps so AoA actually reduces.
I thought speed brakes spoil the lift over part of the wing effectively reducing the lifting Wing Area, thus requiring an increase in AoA to maintain the same lift.
Quote from Goldenrivett's last-but-one post:
"Use of speed brakes will result in increased AoA."
Did you mean that use of speedbrakes will require an increase in AoA? If so, that would explain your misunderstanding with vilas...
"Use of speed brakes will result in increased AoA."
Did you mean that use of speedbrakes will require an increase in AoA? If so, that would explain your misunderstanding with vilas...
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,407
Likes: 0
Received 0 Likes
on
0 Posts
Goldenrivett
Microburst is talking about stalling AoA. With flaps that reduces. You are talking about actual angle AoA. Flaps being under the wing the change in effective chord will increase the AoA. Speed brakes are above the wing the chord will reduce the angle of attack. However the pitching moment with flaps is down and speed brakes is up.
Microburst is talking about stalling AoA. With flaps that reduces. You are talking about actual angle AoA. Flaps being under the wing the change in effective chord will increase the AoA. Speed brakes are above the wing the chord will reduce the angle of attack. However the pitching moment with flaps is down and speed brakes is up.
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes
on
0 Posts
With spoilers deployed, the airflow separates at a lower AoA (in those sections where there are spoilers deployed).
Not the whole wing, but if you are extending speedbrakes you can have a significant part of the wing in a stalled condition at speeds well above clean VS1G. Those stalled sections will give control problems and the margin to a totally unacceptable situation is reduced. I guess that is why the VLS increases with the speedbrakes extended.
There was an incident of a 320 where a spoiler remained deflected due to a mechanical failure. The VLS remained the same, but the AP had some trouble maintaining lateral control during approach, when speed was VAPP. If I recall correctly. It was that small section of the wing that was creating the problem, probably.
Not the whole wing, but if you are extending speedbrakes you can have a significant part of the wing in a stalled condition at speeds well above clean VS1G. Those stalled sections will give control problems and the margin to a totally unacceptable situation is reduced. I guess that is why the VLS increases with the speedbrakes extended.
There was an incident of a 320 where a spoiler remained deflected due to a mechanical failure. The VLS remained the same, but the AP had some trouble maintaining lateral control during approach, when speed was VAPP. If I recall correctly. It was that small section of the wing that was creating the problem, probably.
