Finding "Neutral" Position on Piper Elevator/Trim Tab

[[email protected]]

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

[[email protected]]

Just put tape on the surface next to the pointer, make several
landings, takoffs and mark each one on the tape. That will get you
closer then any other way. After all, you only use the setting during
the preflight to get you close on the trim setting. Once airborne you
will adjust it for various conditions like fuel on board, passenger
seating, flap setting, ect... Then get a label maker reproduce one and
stick on the mark you made...
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

[Roy Smith]

In article om>,
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

Two suggestions:

1) Find some other Cherokee with a friendly owner on the ramp and ask to
see his decal. Note the approximate position of the neutral point and use
that. It'll be close enough.

2) Go to the tail of the plane with the yoke free to move. Move the
horizontal stabilizer (stabilator?) until the trim tab moves to the fully
faired position (i.e. in line with the rest of the stabilizer. If the trim
is set to neutral, the main body of the stabilizer should now be parallel
with the sheet-metal joint in the fuselage skin. It'll be obvious what I'm
talking about when you go look at it. Tweak the trim wheel until it all
lines up right. Mark that position.

I am sure the official Piper Maintenance Manual has a procedure which does
indeed require protractors, string, and an advanced degree in Euclidean
geometry. Maybe even an A&P certificate, too.

[Michelle P]

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
>
Your best bet it to talk to your A&P and get the rigging procedures for
the trim. That way it will be right. Setting it by flying will result in
incorrect markings.
Michelle P (A&P)

[[email protected]]

I did. He was the one who told me about the protractors and string!
(Although the higher math degree was my add.) He said they don't even
bother setting it to neutral but rather try hard to rely on the old
sticker and position of the tab. Unfortunately, its too late for that
since the wheel was already moved by a co-owner.

--Jeff

Michelle P wrote:
> Your best bet it to talk to your A&P and get the rigging procedures for
> the trim. That way it will be right. Setting it by flying will result in
> incorrect markings.
> Michelle P (A&P)

[[email protected]]

Michelle P wrote:
> >
> Your best bet it to talk to your A&P and get the rigging procedures for
> the trim. That way it will be right. Setting it by flying will result in
> incorrect markings.
> Michelle P (A&P)

I know that there is a trim rigging procedure, but is there one for
matching a particular trim setting to a particular position in the
little window? Given the loose tolerances of the plastic trim wheel
cover, I've always thought is was an approximation. I've flown a lot
of Cherokees and one thing I've noticed is that the trim settings don't
always match up from plane to plane. One of the questions I'll always
ask the owner or instructor is where they normally set the trim for
takeoff.

John Galban=====>N4BQ (PA28-180)

[Ray Andraka]

wrote:
> Michelle P wrote:
>
>>Your best bet it to talk to your A&P and get the rigging procedures for
>>the trim. That way it will be right. Setting it by flying will result in
>>incorrect markings.
>>Michelle P (A&P)
>
>
> I know that there is a trim rigging procedure, but is there one for
> matching a particular trim setting to a particular position in the
> little window? Given the loose tolerances of the plastic trim wheel
> cover, I've always thought is was an approximation. I've flown a lot
> of Cherokees and one thing I've noticed is that the trim settings don't
> always match up from plane to plane. One of the questions I'll always
> ask the owner or instructor is where they normally set the trim for
> takeoff.
>
> John Galban=====>N4BQ (PA28-180)
>

Not only that, but that little wire pointer gets bent very easily when
the cover is off for an inspection. Mine is different after every
annual. You can get pretty close counting the number of turns on the
trim wheel from stop to stop, then counting up half way to get it in the
middle of the range.

[Jay Masino]

The sticker for my overhead trim indicator fell off at one time, and I
just glued it back in it's "approximate" position. I think you're
probably over thinking this. Benford2's idea was probably as good as
anyone's. I'd start with the center most position (half way between all
the way forward and all the way back), and then do 5 or 6 take offs and
landings and find what feels right. Then mark accordingly. I somehow
doubt that Piper was that precise when they were applying the decals in
the factory (especially since you can easily bend the little pointer).

--- Jay


wrote:
> I did. He was the one who told me about the protractors and string!
> (Although the higher math degree was my add.) He said they don't even
> bother setting it to neutral but rather try hard to rely on the old
> sticker and position of the tab. Unfortunately, its too late for that
> since the wheel was already moved by a co-owner.
>

--

Jay Masino "Home is where My critters are"
http://www.JayMasino.com
http://www.OceanCityAirport.com
http://www.oc-Adolfos.com

[Mike Spera]

> 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.

And an answer like that would turn me off totally to that shop. True, it
is not 1/2 way between the stops, but it also IS a simple procedure.
Given the slop in the plastic cover and the variability of the pointer's
position (when bent), why obsess? Fly it in still air and trim it off
level. Mark that position and you are done. There is no need to go
through complex and expensive procedures. Yes, it will change a bit with
varying loads, power settings, altitude, and temperature. The neutral
position is only approximate. So, approximate it!

Good Luck,
Mike

[Travis Marlatte]

> wrote in message
ps.com...
> Just put tape on the surface next to the pointer, make several
> landings, takoffs and mark each one on the tape. That will get you
> closer then any other way. After all, you only use the setting during
> the preflight to get you close on the trim setting. Once airborne you

I would think that you would at least want to know what the factory marking
indicated. Mine has a green band and the POH says that it MUST be in that
range for takeoff. The neutral position of the elevator is somewhere in that
range but it's not in the middle. If that's the case for the OP, wouldn't
you want to mark the practical limits? Weight and CG is going to alter the
"neutral" feeling position on takeoff and landing. I would use markable tape
and mark it under several different flight regimes.

I haven't flown a lot of different types but I have seen some that have just
the neutral position indicated. I don't remember if the SOP was to set it at
neutral no matter what.

I know that solo, I want it to be near the forward end of the range of my
green band. Fully loaded, I put it a little beyond the forward end of the
range. Keeping it in the range and trimming a lot just after rotation just
seems stupid to me. A little nose heavy is a good thing in my plane. When
the engine quits, it pitches up significantly.

-------------------------------
Travis
Lake N3094P
PWK

[John[_9_]]

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'