On 11/17/2020 2:59 PM, Samuel Spanovich via KRnet wrote:
I took a look at my trim last time I was up at the hangar, and even with full
up trim, the trim tab moves a lot. I understand it is supposed to move
slightly as the elevator travels down and up, but this feels way more “loose”
than anything; I can basically move the trim tab full deflection up and down at
all times, even with full up trim.
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If you have your pitch trim set in the cockpit your trim tab should not
move at all when you grasp it on the elevator and try to move it. If it
moves at all you have a problem and I'd get it corrected before next
flight. It was trim tab flutter / failure that brought down the P51 at
Reno.
I started with a trim tab lever in the cockpit and model airplane steel
cables to the tab on the elevator. I wasn't comfortable with the slop /
looseness in the tab at the elevator. I installed the Ray Allen servo
in the elevator with a short rod to actuate the tab. It is rock solid
with no movement from where it is set. That is the only acceptable mode
of operation. No slop. If you get rid of the slop in the system your
trim will work.
Here is a shot of my install.
https://www.dropbox.com/s/iyqod5cb5pmeom3/IMG_8615.JPG?dl=0
here is a shot of the amount of trim I need for landing
https://www.dropbox.com/s/dn8dgb5y836j3um/IMG_8611.JPG?dl=0
another photo with cover
https://www.dropbox.com/s/z8yrzf99baj1zeg/IMG_8612.JPG?dl=0
It sounds like you have a problem of moving your trim lever but the tab
is not following. Whatever system you use, eliminate all slop in the
system. You really don't want the tab moving either as the elevator
travels up or down. Only "anti-servo" tabs on the Piper stabilator does
that to induce feedback to the control yoke. Next time you're standing
behind a Piper move the stabilator up and down and check it out.
Larry Flesner
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