wrote:
I have a '79 Piper Warrior with a floor-mounted flap lever/trim wheel
and cover. The trim wheel has a metal needle pointing to a sticker on
the cover to show "neutral". The only reason this matters is that
setting the trim wheel/tab to neutral is part of the pre-flight
checklist.

The plastic cover was old and cracked so I replaced it, carefully
noting where neutral was and (my mistake) re-used the old label.
Whatever glue was left on the sticker after 25 years quickly faded and
the sticker is now gone. I can replace it with a new one from a label
maker, but I can only estimate where neutral is. My local FBO/shop
says finding neutral is not simply the 1/2 point between full up and
full down. You need protractors, string, and an advanced degree in
Euclidean geometry.

I'm not worried that the plane will violently pitch up or nose down on
take-off, but it would be nice to set it properly. Any guidance on how
to find the neutral position?

Thanks!!

--Jeff

Finding neutral is not that hard. There should be two screws under the
pilot's window, a straight edge is used to span these screws and that
is the neutral point of the airframe. Some Cherokee models use the
cockpit seat rails for this reference, see your manual. With a
reference line established an adjustable or digital protractor is used
to set zero. The book wants a a jig built to span the leading to
trailing edge of the stabilator. Instead I take the upper tailcone off
and set the protractor on top of the exposed upper spar cap. With the
protractor reading zero based on the level line the stabilator is now
at zero or neutral. Adjust the tab to fair with the fixed trailing edge
of the stab and you have trim tab neutral.

However what I see more in Cherokees than any other discrepancy is the
stabilator and trim tab travels are misrigged. The most common mistake
is to set the travels equidistant from the neutral point. This is
wrong. The tab and the stabilator have more travel in one direction,
about 12 degrees or so and less in the other about 2 or 3 degrees. If
the stabilator has more up travel then the tab has more down travel and
vice versa. I have seen the tab and stabilator rigged exactly opposite
in terms of travel with each having the wrong settings for up and down
travel. I don't have a manual handy or I would be more exact.

I usually use a china marker to make marks on the leading edge of the
stab and the side of the empennage so I can reset the stab neutral if
it gets bumped. Now you can use the digital protractor to record the
travel of the stabilator. Once those are set and the stab is set in
neutral you continue to use the digital protractor to set the tab
travel. Now though, you reset the protractor to neutral on the
stabilator and then set it directly on the tab and record the travels.

No string. No Euclidean geometry. Just a straight edge and a
protractor and the right page from the right manual for your aircraft.

John Dupre'