1969 Piper Cherokee stabilator movement

[jmarine225]

As I’m continuing my quest as a new aircraft owner and utilizing this forum for various questions, I had one in regards to the stabilator on the Cherokee. During a preflight it appears the stabilator is free to move up and down no issues. When moving it up at a certain point, it seems it sticks for a second then extends up to the max. Upon manipulating the flight co trolls inside, pulling back and forth on the controls is free and clear. But, when continuously pulling back to near max position, it seems the controls rise upward until max position. This max position would pretty much only be used during power off stalls or something similar. Anyone know the theory behind this?

 

[GeorgeC]

There's a u-joint:

 

[jmarine225]

There's a u-joint:
View attachment 82595

So that doesn’t help me too much. Is it supposed to go up when it’s fully back?

 

[RyanB]

The Archer I fly does that. Pull aft yoke and it extends straight out. Pull aft a bit harder and it sorta tilts upward when fully aft.

 

[jmarine225]

The Archer I fly does that. Pull aft yoke and it extends straight out. Pull aft a bit harder and it sorta tilts upward when fully aft.

Interesting. Any idea why it does that

 

[RyanB]

Interesting. Any idea why it does that

I don't have a clue. To be honest, I've never really thought much about it.

 

[jmarine225]

Lol. Maybe I should do the same but being a new owner I have questions about everything

 

[GeorgeC]

Interesting. Any idea why it does that

The top of the column moves along an arc, not a line. At the end of its travel, the u-joint dips down a little and the yoke shaft tilts up a little.

 

[Gary]

As I’m continuing my quest as a new aircraft owner and utilizing this forum for various questions, I had one in regards to the stabilator on the Cherokee. During a preflight it appears the stabilator is free to move up and down no issues. When moving it up at a certain point, it seems it sticks for a second then extends up to the max.

Hmmm... when standing outside the plane and manually moving the stabilator, I do not believe there should be any "hitch" in the movement. mine runs smoothly up and down, no stick. Perhaps something is binding and you only feel it when moving the stabilator.

Upon manipulating the flight co trolls inside, pulling back and forth on the controls is free and clear. But, when continuously pulling back to near max position, it seems the controls rise upward until max position. This max position would pretty much only be used during power off stalls or something similar. Anyone know the theory behind this?

It's a matter of geometry. GeorgeC posted the diagram. As you pull the yoke back, the base of the "T" control arm moves forward. Due to the geometry, the actual yoke moves upward a bit. The u-joints located at the end of the yoke arm minimize this somewhat, but at the end of travel the whole yoke needs to move slightly upward. Mine does that as well.

 

[RyanB]

Hmm cool... learn something new everyday.

 

[jmarine225]

Hmmm... when standing outside the plane and manually moving the stabilator, I do not believe there should be any "hitch" in the movement. mine runs smoothly up and down, no stick. Perhaps something is binding and you only feel it when moving the stabilator.



It's a matter of geometry. GeorgeC posted the diagram. As you pull the yoke back, the base of the "T" control arm moves forward. Due to the geometry, the actual yoke moves upward a bit. The u-joints located at the end of the yoke arm minimize this somewhat, but at the end of travel the whole yoke needs to move slightly upward. Mine does that as well.

It seems when it begins that upward movement, the stabilator binds a bit and isn’t totally free. After freeing it moves smooth again. But it’s so far aft, the plane would never be flown in that configuration.

 

[Bill]

The Archer I fly does that. Pull aft yoke and it extends straight out. Pull aft a bit harder and it sorta tilts upward when fully aft.

The Archer III I used to fly exhibited the same when pulling the yoke full aft. I never thought anything about it as it seem to me to be operating as designed.

 

[Gary]

It seems when it begins that upward movement, the stabilator binds a bit and isn’t totally free. After freeing it moves smooth again. But it’s so far aft, the plane would never be flown in that configuration.

True (perhaps) unless this is just the beginning of a problem and it starts binding at a wider range of movement.

 

[murphey]

Every cherokee and archer I've flown (6) have the same upward pull at the end of the travels. As Gary pointed out, it's geometry on a very simple control design.

 

[Skip Miller]

Interesting. Any idea why it does that

Sorry for a no-answer answer, but they all do that. -Skip

 

[jmarine225]

Every cherokee and archer I've flown (6) have the same upward pull at the end of the travels. As Gary pointed out, it's geometry on a very simple control design.

Geometry. Never was very good at that.

 

[N1120A]

That upward pull has existed on all the Cherokees I've flown too, and seems to be geometry related. Pretty much only pull back that far when you're doing a soft field takeoff.

 

[lancie00]

All the PA28's I flown do that.

 

[Tantalum]

Any idea why it does that

There's a u-joint:

It's because of what George said.. if you follow the geometry of how the whole mechanism moves it's only logical that at full back the yoke will move up in your hand as the shaft that goes through the panel angles down to follow the radius of the u joint

I kind of like it.. at full up crank it makes me feel like the plane is giving me just that little bit of extra oomph

 

[455 Bravo Uniform]

It’s so it clears a beer gut at full aft stroke.

 

[dtuuri]

You need to clean the heck out of both sides then spray some Pledge on the shafts until they go in and out as slick as a peeled onion.

 

[Dan Thomas]

You need to clean the heck out of both sides then spray some Pledge on the shafts until they go in and out as slick as a peeled onion.

Pledge is a wax that eventually just gums things up. Dry silicone spray lube works way better and doesn't gum anything up. Very slippery stuff. It's amazing how often I've made elevator movement almost frictionless just doing that.

 

[murphey]

Pledge is a wax that eventually just gums things up. Dry silicone spray lube works way better and doesn't gum anything up. Very slippery stuff. It's amazing how often I've made elevator movement almost frictionless just doing that.

I use bike silicone on the yoke. Great stuff. And on the rails of the seats, too.

 

[AKBill]

I use bike silicone on the yoke.

Never heard of bike silicone. Is it a dry lubricant?

 

[jmarine225]

I use bike silicone on the yoke. Great stuff. And on the rails of the seats, too.

I actually have some bike silicone but it’s a liquid in a bottle. For my bike it says use only one drop

 

[jmarine225]

It’s so it clears a beer gut at full aft stroke.

Someone may have actually had that in mind. Suits it perfectly.

 

[GRG55]

So that doesn’t help me too much. Is it supposed to go up when it’s fully back?

Yes. All the Cherokees do that. The top of the vertical "control stick" portion of the mechanism (see the diagram in post #2) travels in an arc (in the vertical plane, parallel to the longitudinal axis), not in a linear back and forth path. That means the horizontal control yoke shafts must change angle - they cannot slide straight in and out from the panel (and hence the U-joints @GeorgeC noted).

It seems when it begins that upward movement, the stabilator binds a bit and isn’t totally free. After freeing it moves smooth again. But it’s so far aft, the plane would never be flown in that configuration.

It's unlikely the stabilator is binding. It's usually the control yoke shaft passing through the bushing on the panel that is the source of that. It can bind a bit with the noticeable change in angle of the shaft in the last part of the full aft movement (the shaft is no longer concentric with the bushing). Easy to overcome when pulling on the yoke to full travel. Harder to overcome when trying to force the yoke to full aft by rotating the stabilator around its pivot.

 

[jmarine225]

Yes. All the Cherokees do that.



It's unlikely the stabilator is binding. It's usually the control yoke shaft passing through the bushing on the panel that is the source of that. It can bind a bit with the noticeable change in angle of the shaft in the last part of the full aft movement. Easy to overcome when pulling on the yoke to full travel. Harder to overcome when trying to force the yoke to full aft by rotating the stabilizer around its pivot.

Nailed. That’s what I was trying to explain but as long as it’s all good.

 

[Huckster79]

Lol. Maybe I should do the same but being a new owner I have questions about everything

i completely understand that! I asked all sorts of stuff right at first that made ppl pucker and say “geez never even thought about that” still go through phases of it... its part of our maturing process of being new owners

 

[Dan Thomas]

I actually have some bike silicone but it’s a liquid in a bottle. For my bike it says use only one drop

"Dry" silicone spray lube sprays on wet, then dries.

 

[murphey]

Next annual, check the Ujoints. After 50+ years, they can get sloppy (worn). Not really dangerous but doesn’t hurt to replace them before it becomes dangerous.

 

[Huckster79]

Next annual, check the Ujoints. After 50+ years, they can get sloppy (worn). Not really dangerous but doesn’t hurt to replace them before it becomes dangerous.

On my to do list for next year’s annual... those and the bearing where it slides through the panel... possibly rechrome the shafts too.. same thinking, do it before its dangerous...