Mixed auto coordination

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it0uchpods
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Re: Mixed auto coordination

Postby it0uchpods » Fri Nov 25, 2016 4:38 am

But you aren't coordinating it.
Your just dividing your input in half. I always wondered when I watched you fly why your turns had so much yaw movement. Now I know if that much input you use!

The 777 has a Yaw Damper anyways (I think)

It's still an odd way to fly in my opinion.
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sanhozay
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Re: Mixed auto coordination

Postby sanhozay » Fri Nov 25, 2016 7:45 am

it0uchpods wrote:But you aren't coordinating it. You're just dividing your input in half.

Correct. Hence "auto" coordination. It's a compromise for pilots using the keyboard, mouse or joysticks with jittery twist axes. Not ideal but better than no coordination at all.

I haven't seen an autopilot that implements a yaw damper, but until I tried Richard's Aero VSP FDM for the Beagle Pup, I hadn't experienced dutch roll in a Flightgear FDM either.

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Re: Mixed auto coordination

Postby Richard » Fri Nov 25, 2016 8:32 am

A fair few aircraft have an aileron rudder interconnect (ARI) usually as part of a stability augmentation system (SAS); the F-15 definitely does, some research aircraft (M2F2) had a configurable version of ARI where you can set the gain via a cockpit control. The gain on the F-15 is a function of elevator and flaps (at elevator -24 the gain is -0.9, 0 is -0.105, 15 is 0.406); flaps adds roughly 0.1 to these figures. The F-15 has also got a yaw damper - but this is part of the SAS and can be turned off. You can notice that the yaw damper is off often at M>0.8 where you can get yaw oscillation (it's a feature of the airframe).

The built auto coordination is a very simplistic ARI - it's not a yaw damper.

All of the Boeing 7xx series have a yaw damper; since 1959 when they fitted it to the 707; pretty certain that all of the Airbus have it as well.

It's fairly easy to add an effective yaw damper as it's really just a function on the angular velocity r ; this is the F-15 version.

Code: Select all

        <scheduled_gain name="fcs/yaw-damper-sum">
            <input>velocities/r-aero-rad_sec</input>
            <table>
                <independentVar>velocities/vc-kts</independentVar>
                <tableData>
                    0   0
                    80  0
                    120   3.6251
                    650 1.65
                    890 1.00
                    1000 0.5
                </tableData>
            </table>
            <clipto>
                <min>-0.2000</min>
                <max>0.2000</max>
            </clipto>
        </scheduled_gain>

        <scheduled_gain name="fcs/yaw-damper-dmd">
            <input>fcs/yaw-damper-sum</input>
            <table>
                <independentVar>aero/qbar-psf</independentVar>
                <tableData>
                    2.9900   0.0000
                    3.0000   1.0000
                </tableData>
            </table>
            <gain>fcs/yaw-damper-active</gain>
        </scheduled_gain>

        <summer name="Rudder Sum">
            <input>fcs/rudder-command-sum</input>
            <input>fcs/yaw-damper-dmd</input>
            <clipto>
                <min> -1.1 </min>
                <max>  1.1 </max>
            </clipto>
        </summer>

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it0uchpods
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Re: Mixed auto coordination

Postby it0uchpods » Fri Jan 27, 2017 4:19 am

On my IT autopilots, I now block "auto"coordination while the AP is on, because it causes problems with the roll control. I might end up adding a YD to it using the slip/skid indicator, outputting to rudder, which would engage whenever one or more APs is on.

But I still think autocoord is useless except for taxiing. It might cause issues during flight.

J
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