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Horizontal Stab side play

kiwicubber

kiwicubber

PATRON
Te Kowhai, New Zealand
Hi,

how much side play are we allowed on the horizontal stab leading edge? (Through the trim jack area).
what do we do if there is too much?
does continued operation affect the stay wires were they connect to the horizontal stab?

cheers Bill
 
We try for zero. If your carry through tube has only been drilled once, you can probably get away with rotating it and re-drilling.
 
We used the safety wire trick once. Remember, it slightly changes some angles. I prefer to get them right.
 
kiwicubber said:
Hi,
does continued operation affect the stay wires were they connect to the horizontal stab?

cheers Bill
Click to expand...

There are supposed to be bushings where the wires attach to the stabilizer which serve as bearings which takes care of this relative motion.
 
This is an interesting subject that comes up from time to time.

I always shake my head when people are worried about a bit of play in the cross tube. I have a ton of respect for Mike S. but when I read his fix for it, it made me cringe.

The tube that runs between the stabs is pretty important. If it breaks....your dead. Honestly, I think you need a bit of play in it. Why? The hinge point is welded and the jackscrew tower is welded. Nothing is perfectly square so there needs to be just a bit of play. The play isn't hurting anything.

Wrapping anything around that tube to reduce the play will end up eroding the tube way due to vibration in one spot. Everything in a plane vibrates.....

Tim
 
A bit of play? Sure, maybe a couple thousandths of an inch. I have seen them with a quarter inch of play - airplanes that came out of famous Cub rebuilding facilities. As long as that tube can rotate, it has enough play. Opinion.
 
let it out Mike it's not healthy to keep your feeling bottled up! but how about copper wire as it's softer instead of safety wire ?
 
What about the aft tube? I just noticed on a friends cub that there is a tiny bit of play that if you grab the tip of the horizontal stab and lift, the whole tail assembly rotates a bit due to about a millimeter of gap.
 
My horizontal stab has a bit of side play but never thought much of it until reading this thread. How exactly are you wrapping and securing the safety wire to ensure it stays in place?
 
It is in one of the PA18 inspection videos I put on YouTube but basically find the right size safety wire that fits the gap, twist it where it is in the gap, put a courtesy curl on the twisted end and tuck it underneath where it is not seen and someone won't get snagged on it. I just happened to have a PA12 in here that I did it to. Here is a frontal picture.
PXL_20210228_175513120.jpg
 

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Having that gap makes it convenient to oil the cross tube there, run the trim up and down plus sideways some, then resafety.

Gary
 
It is. It gets complicated if you let it go and the vibration starts taking out other things back there.
 
bob turner said:
We try for zero. If your carry through tube has only been drilled once, you can probably get away with rotating it and re-drilling.
Click to expand...

Just a couple weeks ago I looked at a bent project for a friend. A 180 H.P.---18A used for glider towing. Was told the horizontal tube failed during a towing take off. Did not see the parts as FAA had taken them for study. Fortunately the loss of control was still at ground level, so not terrible. Glider managed release and get past the Cub O.K. Was told the tube had been rotated and re-drilled which in my simple mind would weaken an important part. Just my 2 cents. Y'all fly safe ! geezer Dan ---- would have been much different outcome at altitude---:cry:
 
12Geezer2 said:
Just a couple weeks ago I looked at a bent project for a friend. A 180 H.P.---18A used for glider towing. Was told the horizontal tube failed during a towing take off. Did not see the parts as FAA had taken them for study. Fortunately the loss of control was still at ground level, so not terrible. Glider managed release and get past the Cub O.K. Was told the tube had been rotated and re-drilled which in my simple mind would weaken an important part. Just my 2 cents. Y'all fly safe ! geezer Dan ---- would have been much different outcome at altitude---:cry:
Click to expand...

I'm curious about the re drilling, too. Will you have access to the tube or does the faa have pics?

Web
 
mike mcs repair said:
no....
Click to expand...

What he said....Abolutely no!

People have had a very bad habit of not replacing these tubes at recover or worm gear replacement. A banner plane had a stab tube break and the stab went up against the tail wire. As the pilot recalled, he flew about one mile before his leg collapsed trying to hold in enough rudder. Then he landed on the beach. Drilling an extra hole is just plain asking it to break, shimming with a safety wire is good preventive maintenance.
 
Last edited:
Steve Pierce said:
It is in one of the PA18 inspection videos I put on YouTube but basically find the right size safety wire that fits the gap, twist it where it is in the gap, put a courtesy curl on the twisted end and tuck it underneath where it is not seen and someone won't get snagged on it. I just happened to have a PA12 in here that I did it to. Here is a frontal picture.
View attachment 54417
Click to expand...

what Steve said...Yes!
 
Skywagon and wire guy----As I mentioned I did NOT see the parts----only going from what I was told by one of the glider guys----tube had been re-drilled and tube failed---at the drill holes----I don't know, but it dang sure failed and put the pilot in a heck of a situation.---Have a nephew who is an FAA guy---maybe he can give me details---???? geezer Dan
 
I still like the thin copper winding wire out of a small electric motor, about the thickness of thread. If you start with a 6' length and lay the center of the wire on the tube and wrap in both CW and CC direction at the same time crossing them each time they meet. Copper is soft and will not erode the tube from vibration.This trick was shown to me by an old time Cub guy 20+ years ago and kept my 11 stabilizer snug for another 1500 hrs

Glenn
 
I made nice .115 bushing shim spacers,. Measure with a caliper and have them machined out of chrome moly. Keep your same holes. A little more work but its nice when completed. 1600 hours later I'm ready to make some thicker ones.
 
I have pictures of a 180 hp cub that cracked between duel holes on the right horizontal liner tube.Pulling a glider on takeoff the tube let go and the horizontal went wild putting him back into the grass nose down and ended up on its back. Glider pilot released and landed beyond the wreck. Totaled the cub but didn’t hurt the pilot very bad.. I would never reuse a liner tube unless you mark it and use the exact same holes. On 180 hp Cubs I’d replace it every time I had it off.
dave
 
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