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oosterlo

Autopilot work with external FMC

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Hi,

 

Would you consider making an option, so the autopilot would be able to work with an external FMC, like Ernie Alston's ISG, or RXP GTN/GNS gauges? These gauges drive the stock heading bug and work with aircraft that use the default AP. I tried to use to use the ISG. It changes the heading bug, but then the heading bug is moved back immediately. 

I am not asking for a way to integrate these gauges in a fancy way, but just an option for the DC8 so that it can listen to standard AP heading bug changes. 

The INS is great of course, just I would like to fly online and I get into troubles as many SIDs and STARS are RNAV based nowadays.

 

Thanks.

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8 hours ago, oosterlo said:

Hi,

 

Would you consider making an option, so the autopilot would be able to work with an external FMC, like Ernie Alston's ISG, or RXP GTN/GNS gauges? These gauges drive the stock heading bug and work with aircraft that use the default AP. I tried to use to use the ISG. It changes the heading bug, but then the heading bug is moved back immediately. 

 

That is normal behavior of the ISG Smiths style FMC (the only one I have experience with), to move the heading bug constantly.  That's how it controls the aircraft when in LNAV mode.

 

8 hours ago, oosterlo said:

I am not asking for a way to integrate these gauges in a fancy way, but just an option for the DC8 so that it can listen to standard AP heading bug changes. 

The INS is great of course, just I would like to fly online and I get into troubles as many SIDs and STARS are RNAV based nowadays.

 

Thanks.

 

You can fly SID's and STAR's using the INS.   Also, you can often fly most SID or STAR using a VOR and DME, and a timer.  It is more difficult than following the magenta line, but I find it a nice break from doing that.

 

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15 hours ago, oosterlo said:

Would you consider making an option, so the autopilot would be able to work with an external FMC, like Ernie Alston's ISG, or RXP GTN/GNS gauges?

 

I'll take a look at this.  Are you sure it doesn't work now in spite of the position of the heading bug? I remember at one point disconnecting the bug from the heading select variable when the autopilot is in turn mode. Turn mode uses heading select, but I didn't want to have the bug cycling around the compass rose when it's in use.  Did you put the autopilot in heading select mode to use the external FMC? I would think you would need to do that.

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13 hours ago, Mace_RB said:

 

You can fly SID's and STAR's using the INS.   Also, you can often fly most SID or STAR using a VOR and DME, and a timer.  It is more difficult than following the magenta line, but I find it a nice break from doing that.

 

 

I am aware that the INS can fly SID's and STAR's. But especially when flying online, these can be assigned and changed dynamically by ATC, leaving no time to look up all the coordinates of the waypoints, let alone keying them into the INS. Also I find that the INS is not well suited when there are sharp turns involved.

Also I know that many SID's and STAR's can be flown conventionally via VOR's and radials. But more and more SID's and STAR's are RNAV based, where the waypoints and legs bear no relation to VOR radials. I fly mainly in Europe where this is the case.

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6 hours ago, Michael2 said:

 

I'll take a look at this.  Are you sure it doesn't work now in spite of the position of the heading bug? I remember at one point disconnecting the bug from the heading select variable when the autopilot is in turn mode. Turn mode uses heading select, but I didn't want to have the bug cycling around the compass rose when it's in use.  Did you put the autopilot in heading select mode to use the external FMC? I would think you would need to do that.

 

I think that is what I tried. But I will give it another try, to explicitly put the autopilot in heading select mode.

Thanks. I will let you know.

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On 11/10/2018 at 1:41 AM, Mace_RB said:

 

You can fly SID's and STAR's using the INS

 

Technically, as far as the sim goes.

 

You shouldn't do that if flying in realistic manner is your goal. INS units did not satisfy requirements for terminal navigation and were banned from being used as such. 

 

For others - try to set your GTN750 to control navigation through heading inputs? It's done via their installer tool. Should work although I haven't tried it. 

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I gave it another try with Ernie Alston's ISG FMC and it wasn't able to drive the heading bug. Not in heading select, turn more or the external mode (the one for using the INS). I can see that upon engaging LNAV, that is tries to move the heading bug, but it's being reset with a split second. I don't have the GTN750 from RXP, but as it also uses the method of driving the heading bug, it won't work either.

 

As far as realism goes, I guess it's not realistic to have an FMC in your DC8-50. Some DC8-70s had an FMC installed (maybe retrofitted), but since this is a 50 series DC8, I can live with the compromise of having an FMC in my DC8-50. This setup will allow me to enjoy this great aircraft online and expand it's usability.

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9 hours ago, oosterlo said:

I gave it another try with Ernie Alston's ISG FMC and it wasn't able to drive the heading bug.

 

Thanks for letting me know -- I will take a look at the issue.

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I have looked at my code and see the problem.  I created a local heading hold variable that controls the sim variable in heading select mode. I did this so you don't the see the heading bug rotating around the compass when using the turn knob to some value other than where you left it.  It's something that I might be able to fix, but I need a little time to figure out the least painful way. 

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I implemented a fix today that should allow external apps to control heading select when the autopilot is in that mode.  The fix will be available in the next update, to be released soon. 

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Thanks for the new 2.0.0 version!

 

I tried it with the new 2.0.0 version. Unfortunately, I didn't get it to work. Did I need to change a setting somewhere to make it work?

I was on AP, in HDG Select mode. But when I engaged LNAV on my ISG gauge, the heading bug is still stuck in place.

 

For reference, I tried the same setup in another aircraft that makes use of the default AP. There the ISG gauge was able to successfully move the heading bug and navigate the plane.

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Sorry for the late reply -- I was away from the computer for a couple of days. 

 

I will look at this again - can you tell me if the third party app appears to control the aircraft's heading, even if the bug doesn't move?

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No problem. I hope you enjoyed your holidays!

 

The third party app is trying to control the heading,as I can see the heading bug on the HSI of the third party app jumping to the desired heading for a split second, but it's being reset immediately as it's not able to change the AP heading bug of the DC8.

In short, same behavior as before.

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I can attest to the fact that the ISG FMC has no effect on autopilot heading. For a moment, however,  when I loaded a P3D flight plan and used the radio switch, the plane was following the FMC route. I inadvertently stalled the plane, and lost control. When I had the plane stable, the plane would no longer follow the fmc heading. It may have been a coincidence, but it might help you in your analysis of the issue.

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I dived into the code of the DC8, and fixed it.

In Aerosoft DC8\SimObjects\Airplanes\DC-8_50\Panel\DC81\logic.xml, I have changed the section in lines 498-501 from:

 

        (L:AP TURN,number) -10 ==         
        if{ (A:AUTOPILOT HEADING LOCK,bool) ! if{ (>K:AP_HDG_HOLD_ON) }
        1 (>L:enable_HS,bool)
        }

 

to:

        (L:AP TURN,number) -10 ==         
        if{ (A:AUTOPILOT HEADING LOCK,bool) ! if{ (>K:AP_HDG_HOLD_ON) 1 (>L:enable_HS,bool) }
        }

That does the trick!

The only thing is that the heading bug is not moving, but the plane turns into the direction that the FMC is commanding, which is good enough.

It would be nice if the heading bug would move as well. If I find the time, I will see if I can make the heading bug move as well. Not sure if I can find a way to do that though.

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