Z longitudinal acceleration provide strange data
Posted 17 August 2012 - 05:22 PM
when programming AP mode using as input offset $3070 (Z (longitudinal, or forward/backward) acceleration in ft/sec/sec) I've found strange behaviour of this offset:
If aircraft is on ground, parking brake set and not moving, this offset oscillate around values 0.57 - 0.58ft/s/s
Such value is not a low deviation - comparing to take-off run or intensive braking when value of this offset is around 10-11ft/s/s
Only in case I shut down both engines, this offset will came close to 0.
Values are from FSinterrogate from Flight1 ATR72 plane, FSUIPC version 4.60a
Could I please get some explanation of this behaviour? Only one possible coming to my mind is vibration from engines.
Thank for any help.
Posted 18 August 2012 - 08:08 AM
- X (lateral, or left/right) and Y (vertical, or up/down) acceleration are NOT affected - when aircraft is parked, then both these are close to 0 as supposed to be
- Used simulator is FSX Acceleration
Posted 18 August 2012 - 07:51 PM
Posted 19 August 2012 - 10:21 AM
I can override output when aircraft is on ground and parking brake is set, that is not an issue.
But problem could be if I can't rely on this offset in flight. I am writing complex autopilot using PID controllers. I would like to use Z acceleration for IAS mode by pitch. This is chain of several controllers first PI setting required acceleration to get to proper IAS and second PID comparing this required acceleration against actual acceleration (this FSUIPC offset) and giving required pitch as its output.
Has anyone used this offset for such in-flight calculations?
There is still possibility to calculate Z acceleration as change in IAS over given time, which is coming to my mind more often now.
Posted 19 August 2012 - 10:29 AM
Posted 19 August 2012 - 10:01 PM
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