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I was reading in the FCOM about the speedbrakes and ground spoilers when I came across the below lines.

The maximum speedbrake deflection in manual flight is:

  • 40° for spoilers 3 and 4
  • 20° for spoiler 2.

The maximum speedbrake deflection with the autopilot engaged is:

  • 25° for spoilers 3 and 4
  • 12.5° for spoiler 2.

Why is there a difference?

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  • $\begingroup$ @ymb1 I understood the reason for the question you have linked. In the above answer you stated single slotted flaps are usually thicker. I read about how Airbus uses high lift wing planforms specifically also how the A320 wing was chosen through the paper you linked. If I posted a question could you answer it ? On the A380 also they had to redesign the wings and high lift devices as mentioned but one point kept coming up to increase flap thickeness and I couldn’t understand why? $\endgroup$ – Jai Jan 26 '18 at 15:54
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Airbus prefers simpler single-slotted flaps, which offer a weight advantage, but require higher-lift wing, which in turn slows the cruise speed. This is covered in a paper by an Airbus engineer, which I've used to answer a question about why the Airbus wide-bodies use different flaps when compared to the competition.

The single-slotted flaps are usually thicker as well, which in turn lead to thinner spoilers (so both can fit when retracted). Here's what the paper says:

However, the reduction of the spoiler thickness increases the deformation tendency of the spoiler and the necessary higher stiffness would then result in higher weight of the spoiler parts.

The inboard flaps/wing generate more lift because the wing is thicker there, and the flaps are generally longer there. Which in turn is more suction behind the inboard [thin] spoilers. So a solution is to decrease the inboard deflection angle.

In comparison, this question about the 777 spoilers, shows that for all but one panel on each side, the deflection is uniform. This is a deductive answer. So kindly keep that in mind.

The following side drawing from an unrelated patent may help visualize the interaction better:

enter image description here

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  • $\begingroup$ could you please explain the advantage of having thicker TE flaps I have read about it many articles and publications but can't seem to understand the benefits $\endgroup$ – Jai Jan 26 '18 at 13:20
  • $\begingroup$ I understood the reason for the question you have linked. In the above answer you stated single slotted flaps are usually thicker. I read about how Airbus uses high lift wing planforms specifically also how the A320 wing was chosen through the paper you linked. If I posted a question could you answer it ? On the A380 also they had to redesign the wings and high lift devices as mentioned but one point kept coming up to increase flap thickeness and I couldn’t understand why? $\endgroup$ – Jai Jan 26 '18 at 15:53
  • $\begingroup$ got it sorry about the invalid tag. I'm still relatively new here $\endgroup$ – Jai Jan 26 '18 at 16:19

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