FSXA Altitude lock mode acting weird!

[delivery guy]

My latest project i have noticed that when i am flying low altitude and set the altitude hold mode the VSI needle goes to 0 when i am 40 ft from the desired altitude setting. And then it takes a minutes for the trim wheel to slowly adjust and reach the precise altitude setting. But when i am above 10,000 feet the VSI needle looks good until i get to within 40FT and then instead of it using less VSI it goes from 300 FPM to 500 FPM and passes the desired altitude then Oscillates back and forth.

So my question is what setting is causing this?

And why at low altitude does the ALT hold mode change it's rate at 40FT and take too long but above 10,000 feet it reacts to quickly? And the settings in my cfg under autopilot are the same as my last 2 previous projects and they do not have this issue!

 

[delivery guy]

Okay after a long day i solved my own issue. I also noticed that other aircraft have this oscillating issue and i have found the bug. It's caused by coding that tells the ALT HOLD MODE when to engage and disengage. In my case i had told the AP_VS_VAR_SET_ENGLISH to hold 0 when within 25 ft of desired altitude and by default this is already hard coded to do this action at 40ft. So this is why at 40ft i was having these issues.

I also wanted to have another option to have the ALT HOLD MODE on when your already within 300ft of the desired altitude and this causes the same bug as it would keep trying to engage the mode and causes the oscillation.

 

[Heretic]

Was dealing with the same thing last night, but all I'm telling the AP is to hold the altitude at which it was engaged.

(A:AUTOPILOT MASTER,bool)
  (A:AUTOPILOT ALTITUDE LOCK,bool) !
  and
  if{ (>K:AP_ALT_HOLD_ON) (A:PLANE ALTITUDE, feet) (>K:AP_ALT_VAR_SET_ENGLISH) }

I think I could cut the oscillations down by adjusting elevator trim effectiveness, but I couldn't completely eliminate them.

 

[jx_]

If you are using default autopilot, then you have to much ALTITUDE RATE in your settings.

With 40 feet to go the error is -40;

If rate equals or exceeds -40, the autopilot will stop or reverse it's climb. Rate is probably two variables: Vertical Speed Rate of Change and Altitude Rate of Change. These can be found (through experimentation) in sections 14-25 of table 1199.

Don't believe anyone who tells you 1199 no longer works....

trim/balance settings can also cause the issue.

 

[delivery guy]

Your if statement is giving you the oscillation. It's not the cfg file....

Why do you have a variable in the if statement? Does that method work for getting current altitude? I use a different method!

No need for using the "AP_ALT_VAR_SET_ENGLISH" since this should only be for the pilot to manually adjust and would not be needed for holding current altitude.
To create a way to hold the current altitude i use a code like this:

<!--      ALT MODE         -->

<!--      GET CURRENT ALTITUDE         -->
(L:MODE_ALT, bool) 0 == if{ (A:PLANE ALTITUDE,FEET) (>L:ALT_NODE1,FEET) }
(L:MODE_ALT, bool) 1 == if{ (L:ALT_NODE1,FEET) (>L:ALT_NODE2,NUMBER) }

<!--      AP ALT HOLD         -->
(L:MODE_ALT, bool) 1 == if{ (>K:AP_ALT_HOLD_ON) }


<!--      WITHIN LIMITS          -->
(L:ALT_NODE2,NUMBER) (A:PLANE ALTITUDE,FEET) - ABS -5 &lt;= r 0 &lt;= and (L:MODE_ALT, bool) 1 == and if{ 0 (>K:AP_VS_VAR_SET_ENGLISH) }

<!--      TOLLERANCE 10         -->
(L:ALT_NODE2,NUMBER) (A:PLANE ALTITUDE,FEET) - d -10 &lt;= r -10 &lt;= and (L:MODE_ALT, bool) 1 == and if{ -100 (>K:AP_VS_VAR_SET_ENGLISH) }
(L:ALT_NODE2,NUMBER) (A:PLANE ALTITUDE,FEET) - d  10 &gt;= r  10 &gt;= and (L:MODE_ALT, bool) 1 == and if{ 100 (>K:AP_VS_VAR_SET_ENGLISH) }

<!--      TOLLERANCE 20         -->
(L:ALT_NODE2,NUMBER) (A:PLANE ALTITUDE,FEET) - d -20 &lt;= r -20 &lt;= and (L:MODE_ALT, bool) 1 == and if{ -200 (>K:AP_VS_VAR_SET_ENGLISH) }
(L:ALT_NODE2,NUMBER) (A:PLANE ALTITUDE,FEET) - d  20 &gt;= r  20 &gt;= and (L:MODE_ALT, bool) 1 == and if{ 200 (>K:AP_VS_VAR_SET_ENGLISH) }

<!--      TOLLERANCE 50         -->
(L:ALT_NODE2,NUMBER) (A:PLANE ALTITUDE,FEET) - d -50 &lt;= r -50 &lt;= and (L:MODE_ALT, bool) 1 == and if{ -500 (>K:AP_VS_VAR_SET_ENGLISH) }
(L:ALT_NODE2,NUMBER) (A:PLANE ALTITUDE,FEET) - d  50 &gt;= r  50 &gt;= and (L:MODE_ALT, bool) 1 == and if{ 500 (>K:AP_VS_VAR_SET_ENGLISH) }

 

[Heretic]

Your if statement is giving you the oscillation. It's not the cfg file....

Why do you have a variable in the if statement? Does that method work for getting current altitude? I use a different method!

I'm not even sure if the current altitude gets set for (>K:AP_ALT_VAR_SET_ENGLISH) as the execution of the statement is stopped as soon as the ALT hold mode is engaged.

 

[Roy Holmes]

AP_VS_VAR_SET_ENGLISH.

Sets reference vertical speed in feet per minute according to the SDK.
Roy

 

[delivery guy]

Yep that's what i was saying it just sets reference. The only way to tell the AP or a ALT mode to hold current altitude is to create a way to record the current altitude which is what the code above does. Then it executes and adjusts to hold that specific altitude at the time your pressed the mode. FSX only has wing level code that will hold current altitude but it locks the bank and is hardly ever used. Let me know if this code helps?