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Autopilot Dips In Turns


Lanzfeld113

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I thought I would give this its own thread.
About the autopilot I would like to bring up one issue that I have confirmed does NOT happen in the real F-16.
When I have altitude hold mode on (with attitude bank) it will hold altitude just fine BUT when I put the jet into a banking turn (lets say 20 or 30 degrees) the jet will lose about 200 to 300 feet and will stay low until I come back to wings level. At wings level the jet will climb back up to the original altitude and hold. We are not talking about any steep bank angles here just normal mild turns.
Just yesterday my first officer was a viper pilot (block 40's) and he confirmed the real jet does NOT do this at all.

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1 hour ago, Lanzfeld113 said:

I thought I would give this its own thread.
About the autopilot I would like to bring up one issue that I have confirmed does NOT happen in the real F-16.
When I have altitude hold mode on (with attitude bank) it will hold altitude just fine BUT when I put the jet into a banking turn (lets say 20 or 30 degrees) the jet will lose about 200 to 300 feet and will stay low until I come back to wings level. At wings level the jet will climb back up to the original altitude and hold. We are not talking about any steep bank angles here just normal mild turns.
Just yesterday my first officer was a viper pilot (block 40's) and he confirmed the real jet does NOT do this at all.

Hi, 

we would need to see a source data, not that I don't believe you, it is just we have to have the data to back it up. 
 

Thank you

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You have data that says the autopilot loses 200-300 feet in a 20 to 30 degree banked turn?

My source data is viper pilot with 1800 hours or so in type. Why would he lie? He was actually laughing when I told him about this quirk in DCS.

Respectfully, you have to let logic creep in at some point. Do you really believe they would build such a system and find it acceptable? 

 


Edited by Lanzfeld113
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Forgive me, we get many people who claim to have knowledge of an issue, but without verified data we can not change anything. 

Please also supply a track replay showing this behavior, we will take a closer look. 

You can save a track replay when you exit a mission during the debrief screen. 

thanks

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The aircraft manuals state that the PITCH switch in the ALT HOLD position generate command that result in the aircraft maintaining a constant altitude.

If you need proof stating that it will continue doing that in a 20 to 30º AOB or any other sensible aircraft state, then you are not going to find it explicitly written as such, because we in the aviation industry give for granted that when something is labeled altitude hold it holds altitude and don't need specifying that kind of information.

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Pitch AP has limited authority. It starts the trimmed state I think +1.0/-0.5g. If trim is bad then AP authority window is shifted. At high AOA AP pitch authority may be unable to supply enough pitch up command to keep altitude even wings level. With sufficient speed the AP will handle constant altitude banked turns just fine. Presumably that would be up to 60 degrees AOB if in the strictly G-based envelope. Since the AP roll-commanded turns are much less than that (30 AOB?) as long as the pitch AP can pull 1.15g (+0.15 over 1g trim) it should maintain altitude.

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Positioning the PITCH switch to ALT HOLD enables the FLCS to use CADC information to generate commands to the horizontal tails which result in the aircraft maintaining a constant altitude. The FLCS limits the pitch command to +0.5g to +2g. Engagement of altitude hold at rates of climb or dive less than 2000 fpm selects an altitude within the pitch command g limits. Engagement above rates of 2000 fpm causes no unsafe maneuvers; however, the engaged altitude may not be captured. Control accuracy of +-100 feet is provided to 40,000 feet pressure altitude for normal cruise conditions. The altitude reference may be changed by depressing the paddle switch, changing altitude, and releasing the paddle switch. ALT HOLD in the transonic region may be erratic.


T.O. GR1F-16CJ-1

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We will continue to try and verify with our SME's and sources but unless you can provide the evidence for us this isnt going to go anywhere.

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I'm not quite sure what more information needs to be given. As @TEOMOOSE wrote, the T.O. GR1F-16CJ-1 states that +/- 100 feet can be maintained up to FL400 PA utilizing pitch commands up to +2.0 Gz. Both the HDG SEL and STRG SEL roll modes command a maximum of 30 degrees bank, which is ~+1.15 G, which gives the AP an additional +0.85G to maintain altitude in turns (up to 15 degrees alpha mind you, at which point the AP should disengage). 

The only mention of inaccuracies in ALT HOLD mode are in the transonic region (due to shock errors in CADC input) as well as attempting engagement beyond +/-2000 fpm; and even then, the AP should attempt to maintain the given altitude within the -.5/+2.0 pitch command limits, it's just noted that the intended altitude may not be captured. 


Edited by Mikaa
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