Empennage Hingeline Issues

[Toobuilder]

Flew to Vegas this weekend and in the course of doing my preflight for the return leg I gave the elevator a shake out near the tip. On the left side I detected a subtle amount of vertical motion relative to the stab rear spar. So I look down at the hinge and sure enough, the outboard rod end/hinge (lollipop) has a slight rocking motion relative to it?s attach point in the elevator spar. The jam nut looks snug, but it is in fact finger tight. OK, so a quick turn with a wrench gets me home, but closer inspection is on the near term agenda. I removed both elevators for a thorough inspection, lube and re rigging of the whole system and found some surprising things:

1. All lollipops were under torqued (not loose, but barely snug)

2. All the bearings (balls) were gummed up and essentially frozen

3. The ?hinge bolts? were snug enough not to turn by hand, but were not tight enough to clamp the ball securely. As a consequence, the elevator was pivoting about the bolt rather than the bearing and slightly elongated some of the mounting holes and was sawing through the bolt itself.

4. The lollipops were misrigged and placed a significant preload on the system. The center lollipop bolt was removed first (after significant effort) and ?popped? when the bolt finally came out. An inspection mirror showed it to be at least a half hole off.

5. When the center bearing (at the tailcone) bolt was removed, a large gap opened up between the elevator torque tube and the bearing. There was a spacer, but not the correct thickness. With both elevators hung and relaxed, the gap was .035 on one side and .100 on the other.

So long story even longer, everything is lubed, tight and working correctly. With this new experience I figured I?d go check out the relatively young RV-7 on the field for the same problems. Sure enough, not only was one of his jam nuts finger tight on one side, the other side showed the jam nuts completely GONE! The airplane had been flying for hundreds of hours with the elevator hanging on only by a couple of #40 rivets on the nutplates. Additionally, the hinge bolts were secured with castellated nuts and cotter pins (not a bad thing, but overkill), but were loose and free to rotate by hand. Again, not allowing the bearing to do its job. Worst of all was the center (tailcone) bearing ? at least a .250 inch gap between the bearing and torque tube on both sides, NO spacer at all, and a loose, castellated bolt/nut fastener. To say that bolt was worn would be an understatement!

So in summary, I?d be willing to write off the experience on my airplane as an isolated incident, but when another RV shows up with similar problems, I figured I should put the word out. There has to be more in the community. Some of this is craftsmanship, but some may be related to wear in service.
So the takeaways from this should be:

1. Check those jam nuts on preflight.

2. Ensure all connections with a bearing are in fact USING the bearing (clamp those balls tight!)

3. Don?t introduce preload in the system ? all hinge bolts should slide in easily. If you have to "pull something in", you're likely doing it wrong.

4. The center bearing/torque tube gap seems to be a huge variable between airplanes and even side to side on the same airplane ? measure each gap and install the appropriate spacer.

As an aside, I also took a close look at the tailwheel and noticed the axle was loose enough to spin a little by hand. Inspecting the wheel itself showed no center spacer between the bearings meaning you can?t tighten the nut without preloading the bearings. So I knocked the bearings out and machined a center spacer in my lathe. Now I can smoke the axle nut down as much as I like and the bearings will never see a preload. The wheel rolls much freer now and the axle can?t spin. Does the stock Vans tailwheel have a center spacer or was mine lost along the way?

[fl-mike]

I also found some loose jam nuts on my rod-end bearings after a 100 hours or so. Re-torqued and put some Lock-Tite on them since there is no locking feature on the jam nuts. No problems so far, but I check them every pre-flight now.

Your other issues seem to be a common problem. Takes a lot of time and patience to get the elevator bearings properly lined up, shimmed, etc. Seems many builders succumb to "good-enough" after a few trial fits.

[Mike S]

Michael, good report.

Pretty sure you saved the 7 pilot from a future bad day.

When I was re-assembling the tail on my plane after being painted, this is one area I paid particular attention to-----most of the balls in the rod ends were still moving in the correct rotation mode, but were pretty stiff in rocking motion, I freed them up and lubed them well. Also, the number of washers needed at the center bearing was different after being reinstalled-----and there was no paint build up in the area to account for it, just happened.

[BobTurner]

I believe our resident DAR, Mel, has previously commented that he frequently finds problems in this area.

Mel?

[David Paule]

I hadn't noticed that in the manual - anyone know this?

I suppose I ought to reread Chapter 5.

Thanks!

Dave

[Mel]

Originally Posted by BobTurner

I believe our resident DAR, Mel, has previously commented that he frequently finds problems in this area.
Mel?

Over the last 14 years, I would say that I could count on my fingers the number of aircraft I've inspected that didn't have at least 1 jam nut loose.

[Toobuilder]

Originally Posted by David Paule

I hadn't noticed that in the manual - anyone know this?

I suppose I ought to reread Chapter 5.

Thanks!

Dave

Standard torque for a steel shear nut with UNF threads should do you just fine.

[Toobuilder]

Originally Posted by Mike S

...Pretty sure you saved the 7 pilot from a future bad day...

Indeed. Though the rod end is captive, and the likelihood of the nutplate rivets breaking off and allowing the nutplate to back off on the inside is minimal, a flexible hingeline is just BEGGING for a flutter event.

This hinge design is borne from the need to make a wide variety of customer assembled airplanes work. It's adjustable and inexpensive so it serves Van well - I understand why Van went this way. But it is very inelegant from a functional perspective (both heavy AND weak), and clearly shows how susceptible it is to installation error and the rigors of continued use.

Not throwing stones at Van here... just making an educated observation.

[fixnflyguy]

I have orange torque seal on all of mine, which isnt 100% foolproof, but makes the walk around preflight alot easier to spot problems. I have it on every bolt that is visible inside and out.