View Full Version : 180 horizontal stab is loose...
04-22-2006, 09:56 PM
I tried to figure out how to post this question on the Skywagon site to no avail, so here goes:
The '53 180 I am restoring (with my AI) has play in the horizontal stabilizer. After removing the fairings, it is obvious that the rear 2 lower hinge plates are moving (rocking) on the bottom surface of the horizontal stab when the tip of the stab is moved fore and aft by hand. There is also too much motion when the tips ar pushed up or down, though that has less travel.
There is only one HOLE drilled for 1 BOLT on each hinge plate to stab connection, though the Service Manual shows 4 holes/bolts for each hinge. In contrast, the front pair of trim jackscrews are relatively tight -very modest amount of movement up there.
Any ideas or proven methods to keep the 180 fully trimmable tail healthy?
Yes, the airplane is flat grounded until this is sorted out.
Hi Bob, can't help with your question but I did move the topic to the "other plane" forum on the site, just so ya know!
04-22-2006, 11:13 PM
04-23-2006, 02:37 AM
I can't help with your exact question, except to say that yesterday we put the stab and fin back on, and I can tell you where our looseness was.
But first, the castings on the lower aft of the stab have more than one screw holding them on ours - a J-model. I think it was four, and they were flat/phillips screws. Totally tight.
Our problem was the holes in the airframe, and those in the top part of the jackscrews. Turns out that the rear was trivial to fix, with the help of Tom up at Genuine Aircraft - 805 239 3169. NAS6204-9x came in the mail the day after I called, and with an adjustable reamer, they went in like they were designed that way. They are 17/64, or the grip is 1/64 over, and they are fully certified and traceable. The top of the jackscrew was also loose, and I made a new set of eccentric bushings about 7 thousandths oversize, then reamed the holes for a light push fit. The bushings are eccentric so you can line the holes up vertically on assy.
Do a couple of things to make assy easier - first, hook up the trim indicator wire before you even start. Then do the tops of the jack screws. Then the elevator control horn, and last the rear bolts. Torque them to Cessna specs - they are supposed to grip the steel parts of the bushings firmly.
When we started we had one inch travel at the stab tips - and decided that flutter might be a problem. After an instantaneous "down" cancelling a neat Mexico trip, and two weeks of machining and thinking, we have zero movement at the tips. Zero!
Dumb when I started, but now quite experienced! Do not hesitate - flutter can be a very disconcerting problem.
04-23-2006, 06:47 AM
I wonder if the Cessna Pilots Assoc in Santa Maria would have any info on your problem.
04-23-2006, 07:53 AM
Bob, I have a stab that is apart and needs rebuild. There are 3 flush machine screws for each of those hinge brackets---2 in the rear corners and one in the forward inside corner. That is the way just about every 180/185 I have ever seen is. Mine is a "54" with original stab and it is different--- 2 machine screws in the rear corners and 2 small universal head rivets in each forward corner of the brackets. Mine looks mickey mouse compared to the newer style. The newer 3 screw style has a triangular gusset on the inside that adds beef to the forward screw attach point.
04-23-2006, 08:08 PM
I'm with 180 marty on what he said.
Bob Turner, in your paragraph about making reassembly easier, you called something a 'trim indicator wire'. If it's the cable that gets bolted to the front spar of the stab, it's actually an elevator downspring cable. The trim indication is handled by a wire that rides in a groove in the trim wheel by the flap handle.
Also, most of the 180/185's that I see with a loose stabilizer have 1 of either of 2 issues. One issue is the bushings/bolts/brackets/holes on the rear hinge are worn. The other issue (more common, yet less well-known) is that the fuselage stiffener that the rear stab hinge bolts to has a sheared rivet at it's aft end. If you look at the stab hinge bolt, the next rivet aft is the one I'm talking about. It is uncommon for guys to catch this because the the rivet head and bucktail both will be retained in the sheetmetal after the rivet is sheared, so guys will miss it. However, if the head is smoking, and your stab is somewhat loose, and the bushings/bolts/holes,etc. are okay, then take a 3/16th" wide flat blade screwdriver and attempt to spread the sheetmetal where the rivet clamps it. You'll have to look at an airplane for this to all make sense, but believe me, this stuff happens. And you want to know about it before the stab goes back on the a/c, because the easiest way to buck the oversize rivet you're gonna put in that hole is to have the stab off.
Maybe I'll post a picture.
04-24-2006, 12:08 AM
I will look tomorrow. I was in that area very heavily, since the holes had been enlarged. One mechanic was telling me how easy it is to replace the entire structure back there. Hockey sticks and all . . .
The "wire" was indeed spring loaded, so it must have been the "downspring" you refer to! I just made sure it came through the pulleys exactly as it had when I took it apart.
See? Think you'd get this much this fast over on the 180 site?
04-25-2006, 01:02 AM
Okay, so I've got a couple of photos. Click each photo to get a large, high resolution view. If you want to learn how to put a picture in a post, click on these couple of links: http://www.supercub.org/phpbb2/viewtopic.php?t=6744 http://www.supercub.org/phpbb2/viewtopic.php?t=6873 and take the time to go through the motions. Then PM Cavy with a thank you.
The first photo below is the side view of the right-hand side of a 180 under the horizontal tail. The wire is pointing to the rivet that often fails. It is usually a #4 rivet, the one in the photo is a #5. The nut visible to the right of the pointer is the nut on the stab hinge bolt.
The next photo is an above view looking down between the hor. stab. trailing edge and the rear fuselage bulkhead down onto the rivet that shears. The lower right hand corner of the photo is occupied by the leading edge of the right hand elevator. The entire top half of the photo is occupied by the horizontal stab trailing edge. In the area just right of center in the middle of the frame is a dark slot. In it is the rivet bucktail, just barely visible.
If this begs more questions than it answers, I guess I'll get a few more photos.
These a/c break in lots of places that not everyone wants to look or wants to find them broke. DAVE
04-25-2006, 01:56 AM
I checked them. Solid as a rock. But I can see that there is stress in that area; I will include that in my preflights. Hard to really see on your photos, but really easy to check using your suggestions, even with stab installed. Haven't put the control surfaces on yet; busy making special tools to guide the AN4-11A's into those tight spaces.
My next area of inquiry is failure modes in the main gear attach areas. We have P-Ponk castings, and all is well except for the occasional clunk on an "assault" landing. I haven't been in there yet, so am starting with zero knowledge. I know that the P-Ponk is a major advantage over just a big bolt in tension (?).
04-25-2006, 05:01 AM
Thank you Bob Turner, Marty, Pa12 Pilot and Dave Calkins! Your responses are very much appreciated. We have our work now cut out for us to get this bird back in shape!
04-25-2006, 11:33 AM
Bob B., you're welcome.
Bob T., special tools are always nice if you enjoy fabricating them. However, I don't use any special tools at all. I am able to reach in there and put the bolt in the hole. What kind of tool do you have cooking?
Also, did you click on the photos to enlarge them?
04-25-2006, 03:09 PM
Three of us just finished with the tail. All rivets were tight, no smoke, no shear, no paint breaks. All bolts (3 in each hinge, and the 2 hinge bolts) could be taken up and were tightened. Now very tight tail. All of the slight remaining rocking is from flex in all the doublers and the horizontal tail underskin. No sheared doublers.
Thanks for the help.
04-25-2006, 06:28 PM
Bob, tell me about your tools. You got me interested.
If anyone is hanging Cessna flaps, I've got some nice alignment pins/locators and a couple of tricks to make flap roller installation easy.
04-25-2006, 07:56 PM
I made two bullets from 1/4" copper rod (was looking for brass) and drilled/tapped a transverse hole 2-56. They went right in to the holes, aligning everything perfectly. The tool to hold the AN4-11As is a piece of square brass rod 1/4" on a side, about a foot long. I drilled through one end with a 1/4" drill, and attached a piece of .016 brass to the side, so it wraps around the bolt that is nestled in the half-hole left after the drilling operation. The other end of the brass strip is formed into a finger-size loop. I'll let you know Thursday how it works - gotta be better than forceps or needle-nosers.
05-10-2006, 06:17 PM
Didn't work worth a darn. Here's what did work, beautifully! I got two strips of cold-rolled steel, 3/16x1/2x6". I milled square slots in one end of each piece to grip the AN4-11A bolt. I drilled and tapped for two 10-32 cap screws, one about 2" from the slot, the other at the far end, making a sort-of long machinists' clamp. I had to round off the end that holds the bolt, so it would easily slip in the tiny slot in the elevator/rudder. I rounded back over an inch of length. I also made new bullets, pressed or threaded into a similar piece of metal. One bullet was an old AN-4 threaded into a brass handle, with very little taper,and just long enough to act as a perfect alignment tool.
So now I could hold the bolt securely, maneuver it into position without dropping it, and tap it home if necessary. But with the short bullet aligning the holes, the bolt just slid into position. I still used the long bullets for getting preliminary alignment; the ends of those look a lot like a 30-30.
The other sneaky trick is using a set of ratcheting box wrenches. I gotta tell you when I took these surfaces apart, I was not at all sure I had the talent to put them back on the aircraft. Special tools made it trivial!
The entire project was very satisfying. It is nice to wiggle that stabilizer and not feel any play at all!
05-11-2006, 01:50 AM
Good for you, Bob!!
I have an alignment tool for installing rudder and elevator hinge bolts. It's a simple hook made of 1/4" round stock (a #4 bolt of suitable length) that's got a tight bend in it and is welded to a handle made from 1/2" square tube.
I get the control surface slipped over the hinge bearings, then use this tool to align the tabs and bearings, then install the bolts with a long-nose pliers.
"Gear wrenches" (ratcheting box-end wrenches) that have been ground to make 'em smaller do the nut tightening duties. I use missile nuts instead of nylock's becuase they're small and my little tiny gear wrench can get in there a bit easier.
Bob, thanks for the description.
05-11-2006, 09:30 AM
Thanks for the info guys. I'll keep my eye on it.
05-11-2006, 09:41 AM
N4653B, Check your PM.
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