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Broken Jackscrew

Todd long

Todd long

Registered User
Minneapolis
So not mine, but a friend had this happen today while out flying. Said he noticed a vibration then some flutter. No doubt, right? Lucky as hell I'd say. Anyone else had this happen? Pa-12
6866db73a3a2ac588badb69403b157ca.jpg



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From the picture it looks like the lower bushing and the yoke don't line up very well.
 
Appears that way. But that is just from the tension still on the trim pulley.


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i've only seen them bent from accident.....

maybe someone tried to straiten a bent one somewhere in it's past??
 
My banner cubs get new ones every 500-700hours depending on how big the signs are.alot of times you look back and horiziontal is moving a lot,a blurr.but never had one break.
 
Is there a possibility that the flutter occurred before the break? Maybe that is what broke it?

Web
 
There is vibration and there is actual aerodynamic flutter. If you can come home and suggest that it might have been flutter, it might not have been?

But then again.......I wouldn't want to try to duplicate it again to find out if it really was. I'd be happy to get home!
 
Yep, I had one break on me towing a 65' tall panel, big ass banner, had to fly wide open the first hour til i burned off some gas, over the jersey shore and it broke, trim was stuck til i landed but noprob flying. Pa-18
 
We have a local AD to inspect these for cracks every annual. They broke a few in the topdressing days I understand.

Andrew.
 
Broke recently, but didn’t know it at first because in the neutral trim position and just didn’t move the stab when turning the handle- fully separated when we took it out of the water and was bounced around by the float truck- new Dakota parts on the way.IMG_4605.JPG


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Well then..... mine broke this morning. I was out goofing off around the valley and it was a beautiful morning. When I got home I decided to make a "carrier" landing, by which I give it about 5 turns up and carry a little power. I can really drag it in that way. Also good for the tailwheel only exercise. Anyway, it didn't perform as expected and touched down in a perfect 3 point at normal speed. Kinda disappointing, but wasn't dwelling on it. As I was rolling out I returned the trim and casually glanced down at the indicator button, which was now all the way forward. My first thought was that the indicator wire had broken. When I got to the hangar, the leading edge of the H.stab was all the way up. At this point things are feeling a little Twighlight Zone-ish, until I pushed down on it and realized what had happened. I guess flight loads kept it in place (down) until after landing when the elevator bungee pulled it up. I don't understand how it broke yet. I keep the threads lubed and it cranks very easy and smooth. I had the screw and yoke replaced 7 years ago at rebuild and it doesn't get used much except when making the aforementioned carrier landings and at annual when it gets a full range. This is strictly a land based plane hangared in the northern Sacramento valley. No salt, modest humidity. It'll be interesting to inspect the break when I get it out. -- I'll probably just replace the screw since the yoke is fairly new and has little usage. Any suggestions to expedite the job are appreciated. Yes I am going to zip-tie the cable to the pulley in a couple places.
 
Think the Charlie Center tail brace would help prevent that? I'm building a 180 PA-18A and heard the 180 really shakes the horizontal. Don't need to add any more weight but I'd rather have something of value in the tail instead of lead.
 
PerryB said:
Well then..... mine broke this morning. I was out goofing off around the valley and it was a beautiful morning. When I got home I decided to make a "carrier" landing, by which I give it about 5 turns up and carry a little power. I can really drag it in that way. Also good for the tailwheel only exercise. Anyway, it didn't perform as expected and touched down in a perfect 3 point at normal speed. Kinda disappointing, but wasn't dwelling on it. As I was rolling out I returned the trim and casually glanced down at the indicator button, which was now all the way forward. My first thought was that the indicator wire had broken. When I got to the hangar, the leading edge of the H.stab was all the way up. At this point things are feeling a little Twighlight Zone-ish, until I pushed down on it and realized what had happened. I guess flight loads kept it in place (down) until after landing when the elevator bungee pulled it up. I don't understand how it broke yet. I keep the threads lubed and it cranks very easy and smooth. I had the screw and yoke replaced 7 years ago at rebuild and it doesn't get used much except when making the aforementioned carrier landings and at annual when it gets a full range. This is strictly a land based plane hangared in the northern Sacramento valley. No salt, modest humidity. It'll be interesting to inspect the break when I get it out. -- I'll probably just replace the screw since the yoke is fairly new and has little usage. Any suggestions to expedite the job are appreciated. Yes I am going to zip-tie the cable to the pulley in a couple places.
Click to expand...
Please post some pictures.
 
I'll do that Steve. It broke right at the bottom of the yoke, just like in post #12 above. I'll put up a good pic of the fracture once I get it out. It'll probably be a couple days before I get to it.
 
It broke at the bottom of the yoke while in a non-typical trim configuration? That may be worth investigating.
 
It broke in cruise trim. It happened apparently when I attempted to crank it up. I had no indication it broke, no "pop" through the crank, etc. Just the stab didn't move.
 
Personally I'm more focused on the flying wires. My tail is big, the plane is longer and heavier than normal, and it has considerably more the 180hp. The tail shakes and it looks to me like the flying wires take the worst of it. Especially the top wires and that transfers to the fin.
 
PerryB said:
I have a double wrap trim syatem. It doesn't slip. The screw is broken.
Click to expand...
I am referring to when it broke and you were trimming, figure the cable slipped and wasn't turning the jackscrew from the binding from the screw being broken.
 
Ah, sorry I misunderstood. Actually the bottom half of the screw still turns just fine, just freewheeling in place. Dammit anyway....
 
With all the stab rocking the vert fin action maybe its bending the screw? Full up trim at the wrong time would be Oops.

Gary
 
Also if you had repairs that might have made stabilizer jam against yoke or screw in up position. Also check under rear stab attach fitting for cracks.


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The one I know about is out of a certified cub, probably the original one 79 vintage, 150 hp most its life.
 
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