A320 Positive Static Spiral Stability in Turbulence
 

Anybody know or can check when they are in the sim the following:

Below 33 degrees Angle of Bank the A320 provides Neutral Static Spiral Stability when stick free.

However if there is a gust, does it then change to Positive Static Spiral Stability.

i.e. you have 15 degrees of bank and the gust temporarily banks you to 17 degrees, does it return to 15 degrees.

I think it doesn't, but can't find any reference to back this up.

Cheers.

It does not return to or maintain a bank angle - stick free it tries to maintain zero roll rate.

FIS - do you mean 'lateral stability' aka stability in roll?

TP. Thanks for that. It's exactly as I thought.
BOAC. Wording is from Airbus docs, but I do mean lateral/roll stability.

It's just typically vague airbus information regarding this subject. I've found the following statements in various google searches:

"Even in turbulent conditions, the control law resists the
disturbances well without pilot inputs." http://www.smartcockpit.com/data/pdf...ing_Manual.pdf

"Resists" is pretty vague, in my view this means that it immediately counters any uncommanded rolling moment, whilst the rolling moment is present. i.e. "neutral static spiral stability".

But I found this other reference:
Babylon 9 Translation Software and Dictionary Tool

ON A320:
.neutral spiral stability as commanded by the pilot but positive spiral stability in case of external disturbance.
.positive spiral stability beyond 33° bank angle.
.in case of engine failure contenaining the bank angle into a safe limit

I take it that the "in case of external disturbance" statement means that the "positive static spiral stability" occurs only because the disturbance has rolled the aircraft past 33 degrees.

Hi Field In Sight,

TyroPicard is correct.

From FCOM 1.27.20. Lateral Control
"If high speed protection is operative, the system maintains positive spiral static stability from a bank angle of 0°, so that with the sidestick released, the aircraft always returns to a bank angle of 0°."

"positive static spiral stability" is to prevent the spiral dive. Simply pulling the nose up may not reduce the speed when beyond a certain bank angle, so a "level the wings" command is made when high speed protection is operative.

The main question was regarding normal bank angles i.e. less than 33 degrees.

I had a discussion with someone from work who said that in turbulence the FCS would try to maintain the bank angle.

I disagreed and said it would only try to initially stop any non-commanded roll but would not return to the bank angle that existed before the turbulence.

I was looking for confirmation that I was correct.

Thanks.