AFCS mode capture/tracking conditions question
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Join Date: May 2012
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AFCS mode capture/tracking conditions question
Hello,
first I am not a pilot, more aviation enthusiast, with avionics programming for simulators as a hobby. I would like to ask here for help of professional pilots community. I currently try to simulate Honeywell GP-300 / IC-800 AFCS components, as used in Do-328 and probably ATR planes as well. But IMHO same principles, I am searching for, applies to other autopilots / AFCS as well.
For some lateral (VOR, LOC, BC..) and vertical (ALT SEL, GS..) modes AFCS has two phases, the capture and tracking. The capture mode is normally identified by star i.e. VOR*, ALT* The conditions when AFCS will switch from capture into tracking phase differs for each mode, but mostly are based on current error and error rate (for example for ALT SEL could be altitude error and vertical speed).
Once mode is in tracking phase, AFCS will optimize its guidance to keep error on minimum level, together with lowering controllers gains and setting lower pitch and rolls limits.
Now here is my question: Lets assume, that you are in track mode, flying manually following FD. What will happened, if you intentionally stops to follow FD guidance and fly away from the target? Will increase of the error and/or error rate (when reaching some threshold) switch AFCS back from tracking to capture phase? Or once given mode is in tracking phase, it will never switch back to capture, even if capture phase could be faster to return on target? (as capture phase is typically more aggressive - higher gains and roll/pitch limits and rates).
Hopefully I described my theoretical problem well enough.
I would welcome any help or hint, thank you.
first I am not a pilot, more aviation enthusiast, with avionics programming for simulators as a hobby. I would like to ask here for help of professional pilots community. I currently try to simulate Honeywell GP-300 / IC-800 AFCS components, as used in Do-328 and probably ATR planes as well. But IMHO same principles, I am searching for, applies to other autopilots / AFCS as well.
For some lateral (VOR, LOC, BC..) and vertical (ALT SEL, GS..) modes AFCS has two phases, the capture and tracking. The capture mode is normally identified by star i.e. VOR*, ALT* The conditions when AFCS will switch from capture into tracking phase differs for each mode, but mostly are based on current error and error rate (for example for ALT SEL could be altitude error and vertical speed).
Once mode is in tracking phase, AFCS will optimize its guidance to keep error on minimum level, together with lowering controllers gains and setting lower pitch and rolls limits.
Now here is my question: Lets assume, that you are in track mode, flying manually following FD. What will happened, if you intentionally stops to follow FD guidance and fly away from the target? Will increase of the error and/or error rate (when reaching some threshold) switch AFCS back from tracking to capture phase? Or once given mode is in tracking phase, it will never switch back to capture, even if capture phase could be faster to return on target? (as capture phase is typically more aggressive - higher gains and roll/pitch limits and rates).
Hopefully I described my theoretical problem well enough.
I would welcome any help or hint, thank you.
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Join Date: May 2012
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200 views and no answer?
No one ever left ALT SEL mode, manualy flying from given altitude (as it is easiest way to find answer to my question)?
Please any hint is welcome...
No one ever left ALT SEL mode, manualy flying from given altitude (as it is easiest way to find answer to my question)?
Please any hint is welcome...
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I don't think this info is usually in the scope of most pilots. That's more up to the designers.
eg. The B737 will give pretty large pitch corrections in "speed on elevator" scenarios when you're outside of 10kts from the requested speed. But this is all relatively behind the scenes from the pilot perspective.
Pilots I fly with like to be smooth and so will often override the F/D or pick a smoother mode simply from experience rather than thinking of gain per se.
eg. The B737 will give pretty large pitch corrections in "speed on elevator" scenarios when you're outside of 10kts from the requested speed. But this is all relatively behind the scenes from the pilot perspective.
Pilots I fly with like to be smooth and so will often override the F/D or pick a smoother mode simply from experience rather than thinking of gain per se.
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I think you are being a bit cheeky suggesting that we fly out if the director for you. Big Brother is now watching all of us and excursions from the glideslope, altitude and tracking might generate "unwanted calls" from the spies who perform our FDM functions. This is the sort of thing that should be done in the sim.
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Hello,
thank you for answers. I didn't meant any offence to anyone.
To be honest I do not know much about bigger planes. But with ATR it should not be big deal to fly raw data, just switching FD off, disconnecting AP and for example leaving ALT SEL by just pushing the yoke forward, when starting descent is required. (and yes watching AFCS screen how/if ALT SEL mode changes) Or is it forbidden today to do such thing?
The simulator thing, well that is really tricky. I have experience with few different ATR FFS and at least regarding AFCS and GNSS there are discrepancies in theirs functions. Especially in these, which are not described in documentation exactly (like the one I am asking). Anyway it will be probably last call to test it in simulator, even if this will be only copy of copy.
Anyway than you for help.
thank you for answers. I didn't meant any offence to anyone.
To be honest I do not know much about bigger planes. But with ATR it should not be big deal to fly raw data, just switching FD off, disconnecting AP and for example leaving ALT SEL by just pushing the yoke forward, when starting descent is required. (and yes watching AFCS screen how/if ALT SEL mode changes) Or is it forbidden today to do such thing?
The simulator thing, well that is really tricky. I have experience with few different ATR FFS and at least regarding AFCS and GNSS there are discrepancies in theirs functions. Especially in these, which are not described in documentation exactly (like the one I am asking). Anyway it will be probably last call to test it in simulator, even if this will be only copy of copy.
Anyway than you for help.
