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# A320 roll function

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# A320 roll function

17th Sep 2023, 14:34

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A320 roll function

Hi,

A320 Normal Law: Side-stick requests a roll rate from 0 to 30 degrees a second.

Question: Is this a linear relationship? 50% side-stick deflection = 15 degrees a second and so on?

A320 Alt/Direct Law: a direct stick-to-surface-position relationship.

Question: Same as above. Does 50% side-stick deflection = ailerons and spoilers 50% extended?

Thanks!
18th Sep 2023, 04:51

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Originally Posted by BoeingDriver99
Hi,

A320 Normal Law: Side-stick requests a roll rate from 0 to 30 degrees a second.

Question: Is this a linear relationship? 50% side-stick deflection = 15 degrees a second and so on?

A320 Alt/Direct Law: a direct stick-to-surface-position relationship.

Question: Same as above. Does 50% side-stick deflection = ailerons and spoilers 50% extended?

Thanks!
Normal law max rate of roll is 15°/sec not 30°. Alternate law goes upto 30°. It is linear. Direct law rate is not mentioned. But may be same as alternate law.
18th Sep 2023, 08:48

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I cannot quote any figures, but I am fairly sure that the rate of roll increases the further out of neutral you hold the side-stick.

e.g. holding 5° side-stick gives a fairly low roll rate. Holding the stick fully over gives a much faster roll rate.

So, no, not linear.

As far as control surface deflection; the FBW will order deflection based on the side-stick demand plus the FBW demand. I don't know if control surface deflection will be linear in terms of deflection versus roll demand, but I would doubt that it is.

I do know from doing the control checks, and observing control checks of other Airbus FBW, that the roll spoilers do not deploy until aileron deflection has already moved a certain amount, but again, I can't quote figures. I have a glitch with my Airbus electronic FCOM, so cannot check.

Last edited by Uplinker; 18th Sep 2023 at 08:58.
18th Sep 2023, 11:12

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vilas; sorry, my mistake on the max roll rate. The FCOM does say that you will achieve a maximum of about 30 degrees a second in clean config in direct Law.

Uplinked; in normal law yes; more side-stick deflection means a higher roll rate demand. But that’s not what I’m trying to get to the bottom of here.

Would you guys have a reference to point to? I wonder if it’s in the AMM?

Thanks
18th Sep 2023, 18:48

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There is very little extra information in the AMM about exact rate vs angular side stick deflection.

Uplinker, you have just described a linear increase, ie demanded rate is proportional to stick deflection.
18th Sep 2023, 22:49

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Hello,

Normal Law:
Roll-rate order is linear to sidestick deflection in Normal Law. Max 15deg/sec except for a few caveats, which I will not go into.
Corresponding maximum Aileron and Spoiler deflection is described by Kinematics, not necessarily linear and different between the different Configs.

Roll Direct Law (=Roll Alternate Law):
Direct stick to surfaces control law does not necessarily mean linear. Kinematics describe actual Aileron and Spoiler deflections as function of both Stick deflection and Config. Still some filters in place…

Hope this helps.

19th Sep 2023, 02:16

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So the answer currently stands at: guesstimates without references
19th Sep 2023, 11:04

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The FCOM I have in front of me (current) says:

The roll rate requested by the pilot during flight is proportional to the sidestick deflection, with a
maximum rate of 15 °/s when the sidestick is at the stop.

DSC-27-20-10-30
19th Sep 2023, 12:48

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For those with access, AMM 27-90-00-00 5. Functions performed in normal configuration describes lateral control.

For further info you will need to go asking Airbus about the exact numbers and Tables populating the matrices in the control law algorithms.
1st Oct 2023, 08:26

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Originally Posted by Boeingdriver999
So the answer currently stands at: guesstimates without references
For normal law:
I can't say if the stick is linear mapped to the 0 to 15 deg/s, but there is a high possibility that it isn't. In SEC alternate law pitch, which is the same c*law as in normal law (mainly gain scheduling relies on different sources and pitch rate feedback is limited) the stick isn't linear mapped. I think it was high sensitivity for small inputs and low sensitivity for larger input. I can look that up if wanted...

For direct law (now roll):
Can't say for ELAC, but no in SEC it depends on the flap/slat position, which look up table is chosen to transfer stick IN to a spoiler deflection command. Though it can be linear... And after rate limiting is applied and keep in mind that normally ELAC sends def commands to the SEC, but I guess LUTs look similar. If not the same... I saw an example of these curves in an accident report, don't ask which. I think it was something with a PIO event with an asian airline?
1st Oct 2023, 14:55

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Bring a protractor and a stopwatch next trip

Last edited by Vessbot; 1st Oct 2023 at 19:51.
1st Oct 2023, 18:42

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Is that a teeth protector or a seat cushion one?

OPEN DES Jwscud : thank you.

1st Oct 2023, 19:52

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Originally Posted by FlightDetent
Is that a teeth protector or a seat cushion one?

OPEN DES Jwscud : thank you.
I should read my posts before submitting. Lame joke fixed.

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