MD-80s, MD-90 Development

[IAHM-COL]

I think I'll test.
So many 4 letter acronyms get my brain a hickup

For what I read above, I say MD82 or MD88 (I like analog navigation)

[Octal450]

All can analog navigate, just switch the dial to the left of the pilots seat to "VOR"

[Octal450]

Upgraded EFD MD-90 cockpit has been removed since I can't find enough information to replicate it realistically.

[KL-666]

I tested the one with the steam gauges of course (82). It flew fine manually (did a little circuit, take off and land), and i saw all the instruments i need to fly and navigate. Beautiful plane.

Next i tried to do a normal flight at fl 340 with autopilot of course. There a problem occurred. After changing heading 10 degrees, the autopilot started to roll left-right all the time. Full aileron deflection in 2-3 seconds from the one side to the other, and back and forth all the time. And staying in it, never getting less in the rolls. Not really a way i like to fly for a long time.

Maybe the autopilot plays fine with the route manager, but manual heading inputs are not appreciated by the autopilot.

Kind regards, Vincent

[Octal450]

Thanks for the report. I've never had this problem, but I'll check it out.
The AP shouldn't be allowed to roll the aileron more than 0.5 each way. (max is 1.0).

Josh

[Octal450]

@KL-666
I've tried to solve it, can you give it another try?

Thanks,
Josh

[KL-666]

Yes, now it gets in the same aileron oscillation, but with 50% aileron deflection.

You can try yourself:
- take the 82
- do nothing with route manager, just climb on manual AP inputs
- be sure to be above fl 300 (there i know for sure it happens)
- change heading 10-20 degrees

Then you have your aileron oscillation.

Kind regards, Vincent

[Octal450]

I did this, and it works fine to me.
It was always limited to 50%.
I don't see any terrible roll oscillation. Could you save your FGTAPE or make YT video?

Sure the aileron is not smoothest, due to the FDM having a slight yaw issue. New FDMs will come eventually.

Josh

[KL-666]

I think i found the answer for the oscillating autopilot for some, but not for others. Just read this thread:

As you've guessed, the autopilots oscillate more at low frame rates.

Typically, they will have been tuned on the aircraft developers own machine, and so will work best at whatever frame rate the author had. If you have a significantly lower frame rate, IIRC the autopilot ends up over-correcting, and so oscillates.

https://forum.flightgear.org/viewtopic.php?f=17&t=2974

So if the developer optimizes the autopilot for his 90 fps, and i come along with a meager 20-30 fps, then the autopilot will oscillate for me around the target bank. In bigger turns it has the time to slowly grow in amplitude, until the plane is totally out of control.

The best advise for developers would be to develop while using a low frame rate, so the autopilot works for everybody.

Kind regards, Vincent

[Octal450]

I test on my old PC with 15fps. Not the issue

You could be overspeeding. Keep in mind. The MD-80 has flaps up, then slats retract. In the analog cockpit, there is no indicator for slats (yet).