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Roll Trim


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34 minutes ago, midlifeflyer said:

I know what it does - allows the PC system to compensate for asymmetrical loading - but how does it work? Is there a hidden trim tab? Is it adjusting the PC vacuum system? Release gerbils to ad symmetry? Something else entirely?

 

Thanks.

It biases the vacuum to the appropriate side.  Think of it as a calibrated, variable leak to apply less vacuum ot one side than the other.

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17 hours ago, takair said:

It biases the vacuum to the appropriate side.  Think of it as a calibrated, variable leak to apply less vacuum ot one side than the other.

Thanks. I guess I need to take a step back to make sure I understand how the system itself works (simplistically) — 

The unit detects changes in the turn coordinator indicating change from level coordinated flight. Based on that, it uses vacuum to operate servos attached to the [edit] ailerons and rudder controls to return to level flight. The Roll Trim allows the pilot to manually favor one side or the other.

Is that pretty much it?

Edited by midlifeflyer
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6 minutes ago, midlifeflyer said:

Thanks. I guess I need to take a step back to make sure I understand how the system itself works (simplistically) — 

The unit detects changes in the turn coordinator indicating change from level coordinated flight. Based on that, it uses vacuum to operate servos attached to the elevator and rudder controls to return to level flight. The Roll Trim allows the pilot to manually favor one side or the other.

Is that pretty much it?

pretty much.  Even the TC is a valve that biases vacuum one way or other. 

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My 20C had the PC system removed prior to me.  In it's place is an electric trim with a rocker switch and indicator on the panel.  The left aileron has a 3/4" by 5" tab on the trailing edge with a thin wire pushrod that goes into the aileron.  So far, albeit the plane new to me, the system is not really necessary, it barely gets an imbalance.  I've operated the system to make sure it works, it's pretty effective and does not impact speed at all.  Then again, I have not looked for the Gerbils.  :-)

 

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2 hours ago, midlifeflyer said:

Thanks. I guess I need to take a step back to make sure I understand how the system itself works (simplistically) — 

The unit detects changes in the turn coordinator indicating change from level coordinated flight. Based on that, it uses vacuum to operate servos attached to the elevator and rudder controls to return to level flight. The Roll Trim allows the pilot to manually favor one side or the other.

Is that pretty much it?

ailerons not elevator and rudder.

Hence the self test on the ground.

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Tcraft,

expect that the wings get heavy... one side or the other, as fuel burns off...

Actually one is getting lighter, but it feels as though you are lifting the heavy wing with the yoke...

This happens with either 52gallons useable or 100+ gallons....

Left untended, the heavy wing dips slowly at first...

In 65, the M20C had its own gyro in the tail to operate the wing leveler....

Later models have a panel mounted TC that does the job.

Not sure where your electric trim tab style wing leveler came about....

The Mooney Miser had such an aftermarket device available on his site.

Got any pics?

PP thoughts only, not a mechanic...

Best regards,

-a-

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