technical basis for reducing bank angle at high atlitutde

[realmanofgenius]

why change the bak angle in swept wing jet to 15 from 30 at high alt or above the transition zone 260. it is for passenger comfort? is it to minimize a stall in a turn due to the buffet margin from high atl flight. I've been taught this but couldn't really say why when I was asked. mainly for pax comfort I would think...

 

[ultrarunner]

Depends on the plane. In the aircraft I fly, the AP automatically does this just below FL420, and it's a buffet-margin issue.

I think some airlines do it for comfort...not sure, but I seem to remember going to 1/2 bank at 100 or 180 in the airlines...and I don't believe it was buffet margin related as it was at such a low altitude.

Ultra--

 

[svcta]

At my own peril I'll hazard a guess that it is simply because:

A: bank angle increases load factor--load factor increases stall speed and swept wing a/c shed lift fast with increased angles of bank.

B: yaw dampers are probably less effective at high alt., as well, exacerbating the vulnerabilities of swept wing a/c with regards to blanking out wings by the fuselage. So there is likely an increased likelihood of dutch roll at altitude with higher bank angles or, more directly, larger aileron or spoiler inputs at those speeds and altitudes.

 

[climbhappy]

the turn with 10 or 15 sure feels smoother at 370 than 30. the boeing TOLD cards say that the buffet margin limit is 39 degrees of bank. I'd hate doing a turn liie that with a full boat at 370

 

[great cornholio]

What I've always wondered was why in heading mode the EMB 145 is limited to 14 degrees bank above FL260, but in LNAV mode it will still go beyond that bank angle if needed to stay on the airway.