Horizontal Stab side play

[kiwicubber]

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

[bob turner]

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.

[RAC cubs]

put safety wire to take up play.

[mike mcs repair]

put safety wire to take up play.

thats what I do as a well....

prefer none(cut all the excess fabric and soft paint off end before drilling holes..)

[mike mcs repair]

...you can probably get away with rotating it and re-drilling.

no....

[RAC cubs]

I learned the hard way about not cleaning the paint off the brass ends.

[cubdriver2]

put safety wire to take up play.

I like thin copper winding wire, it's softer and packs in tighter.

Glenn

[bob turner]

We used the safety wire trick once. Remember, it slightly changes some angles. I prefer to get them right.

[skywagon8a]

Hi,
does continued operation affect the stay wires were they connect to the horizontal stab?

cheers Bill

There are supposed to be bushings where the wires attach to the stabilizer which serve as bearings which takes care of this relative motion.

[behindpropellers]

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

[bob turner]

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.

[mike mcs repair]

biting my tongue.. which I am NOT good at doing!!

frick*nG I*&%s

[cub12]

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 ?

[hoangkiena912014]

upppppppppppp cho cả nhà chưa coi

[MoJo]

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.

[Steve Pierce]

Safety wire works on the front and rear tubes the same.

[MZ18]

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?

[Steve Pierce]

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.

[BC12D-4-85]

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

Gary

[MZ18]

Thanks Steve, pretty straight forward it looks.

[Steve Pierce]

It is. It gets complicated if you let it go and the vibration starts taking out other things back there.

[12Geezer2]

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.

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---

[skywagon8a]

...Was told the tube had been rotated and re-drilled which in my simple mind would weaken an important part.

Did it break through the holes? Or somewhere else? If it was somewhere else, the double drilling wasn't the cause.

[wireweinie]

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---

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

Web

[WhiskeyMike]

no....

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.

[WhiskeyMike]

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.

what Steve said...Yes!

[12Geezer2]

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

[cubdriver2]

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

[Fortysix12]

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.

[ag-pilot]

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

[skywagon8a]

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.

It might be advisable to make the spacers out of a sacrificial materiel rather than wearing down the wrong parts. Bronze?

[Fortysix12]

Good Point.

[Steve Pierce]

The issue is the paint and fabric left on the ends of the stabs when covered and painted. I have had to change the liner tubes on an airplane I rebuilt because the paint and fabric wears away in short order and then you get the play. Have seen it on new Cub Crafters stuff quite a bit. I take a flat file and clean the ends of the stabs where they but up to the carry through tubes, install the tail brace wires and have someone help hold the stabs tightly together when drilling the liner tubes. Have not had the slop issue down the road when I did this. Have also not had any issues with the safety wire. I have three different sizes and one usually fits well and takes out the slop. Worn elevator bushings aren't usually to tough but worn jackscrew ears and yoke are a pita and expensive and that is the end result if left to unfixed.

[12Geezer2]

ag-pilot----Thank you for the post----geezer Dan

[behindpropellers]

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.

Steve,

I have a ton of respect for you. I would be very concerned with the safety wire filling the gap. My primary concern is the vibration which leads to radial erosion of the liner tube, thus creating a point of failure. To be honest, I don't think a bit of play is bad in this location based on how the jackscrew moves coupled with the non-precision alignment of the parts associated with it.

Tim

[mam90]

Been using safety wire since 1978. Haven’t seen a problem.

[Steve Pierce]

Steve,

I have a ton of respect for you. I would be very concerned with the safety wire filling the gap. My primary concern is the vibration which leads to radial erosion of the liner tube, thus creating a point of failure. To be honest, I don't think a bit of play is bad in this location based on how the jackscrew moves coupled with the non-precision alignment of the parts associated with it.

Tim

I haven't seen any issue but put a lot of thought into what you have pointed out. I don't think the safety wire really gets tight around the liner tube. The tube is 4130 Type N which is then hard chromed and centerless ground. Do you think the safety wire is harder that the tube? Also do you think the wire would wear vs the back and forth of the horizontal stab and the carry-through tube. I have done this on a lot of airplanes over a lot of years and if it is an issue I need to correct them.

[dirthog4]

Safety wire works so do shims. But if you take it apart to put shims in might as well put new tube in. Or it's just a jury rig.

[Fortysix12]

So got out the parts manual both old and new(198. Both Figures, 42 show a part number attached here. It seems when I was assembling my airplane the tube was machined from heavier gauge material as specified and the bronze bushing omitted. What do the experts say on this, notice the specifications of the bronze bushing A3310071.pdf NL 14177-000.pdfNL 86062-80 .pdfFig 42 Parts Cat.pdf

[BC12D-4-85]

Here's lots of choices in safety wire - hard to soft> https://www.mcmaster.com/safety-wire/

Gary