General Question Falcon 9 - the autopilot can't never reach proper inclination

vojtas

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Hello,
when using autopilot off Falcon 9 addon, I can never get correct inclination after getting to orbit in compares to what I set in to the autopilot. The difference seems to be always atleast about 3° at the end. Am I doing something wrong or this is proper behavior? I have one more question related to this. When trying to manually reduce relative inclination of orbit by using NML+/NML- buttons, Falcon 9 starts to rotate and never getting correct position. So my question is what I'm doing wrong?
 

BrianJ

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Hello :welcome:
Hello,
when using autopilot off Falcon 9 addon, I can never get correct inclination after getting to orbit in compares to what I set in to the autopilot. The difference seems to be always atleast about 3° at the end. Am I doing something wrong or this is proper behavior?
The ascent autopilot usually gets better accuracy for me - could you post a launch scenario that shows this?

I have one more question related to this. When trying to manually reduce relative inclination of orbit by using NML+/NML- buttons, Falcon 9 starts to rotate and never getting correct position. So my question is what I'm doing wrong?
The upper stage has weak RCS compared to mass - might be better to roughly line-up manually and then let NML autopilot take over.

Cheers,
Brian
 

vojtas

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Hi Brian,
thank you for quick reply.
The ascent autopilot usually gets better accuracy for me - could you post a launch scenario that shows this?
Scenario in the attachment. Hopefully this is what you were asking for. :)

The upper stage has weak RCS compared to mass - might be better to roughly line-up manually and then let NML autopilot take over.
It makes sense what you said, thanks for the explanation. But to be honest, it's not a big deal to do it manually. It's even more fun. :) I just wanted to know, if I'm doing something wrong. By the way, this Falcon 9 addon is fantastic!
 

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  • DM2 Launch 30 May 2020.scn
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BrianJ

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Hi,
thanks for posting the scenario - ascent autopilot is working normally for me.
Autopilot inclination is set for 54.00 at launch. OrbitMFD shows 54.00 after orbit insertion (52.10 in ecliptic frame).
Changing autopilot inclination to 51.65 (for ISS) after booster stage separation gives 51.65 after orbit insertion (48.98 ecliptic frame).

Could you be confusing equatorial and ecliptic frames?
(Ascent autopilot uses equatorial frame).

Cheers,
Brian
 

vojtas

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Thank you Brian so much, you solved my problem. For the autopilot I was taking the inclination value from the Align Planes MFD and I was not aware, that it shows ECL value. Now everything works just fine. I was quite sure, that this is my fault and I was right. :) Thank you!
 
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