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Loose RV-7A Elevator Counterweight

N743RV

Active Member
I recently noticed that both of my elevator counter weights are slightly loose. I hopefully have embedded a photo showing their arrangement below. It was built and installed according the plans. I was an early 7a builder and the design change soon after I started. The bolt you see in the photo has a locknut on the the other side that can't be reached without removing the elevator tip fairing, so there is no way to tighten the assembly with a fairing removal...which I really don't want to do.

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Has anyone addressed this issue? Any ideas on how I can bond the periphery of the lead weight to the aluminum with the limited access you see. I want something that will bond well and add little weight.

Bob Cowan
N743RV
RV7a, 300+ hours
 
Wow! While I don't have a fix for you, I certainly wouldn't fly it until that's addressed! If that weight came out a bit further I think it would ruin your day.:(
 
spouting off here just what comes to mind.........can you drill a hole in the fairing just large enough to get a long socket extension in there to capture the nut? You would have to feel around, and you would have a hole in your fairing, but you wouldn't have to remove the fairing.
 
Can you just drill two holes in the fairing large enough to get a socket onto the nuts? Of course, you'd have to patch the fairing afterwards, but it only has to be a cosmetic patch.
 
if you're not too OCD, you could buy speed tape to cover the holes while you fly and think about how you want to patch/cover the holes in case you need to get back in there again.
 
Maybe make a hole in the bottom of the fairing right below the nuts and use an offset wrench? Less noticeable when touched up. :)
 
Had same problem on my 9A after a few years.

Drilled a small hole maybe 1/2" in the bottom of the fairing for a box ended wrench. One hole between the two bolts. Had to take the nut off and add washers then retighten. Duct tape holds nut in wrench wasn't that hard to do. Still have not repainted fairing but it doesn't show. Close to 1000 hrs later no problem.
 
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I would try to use a battery drill with a socket on the bolt end. The friction on the nut on the back side may be enough to tighten it. Turn the torque adjustment on the drill way down to prevent snapping the bolt if this works to well. Worth a try before you start to cut into the fairing.

RV-10 started 11/2015 going great.
 
How does it happen?

Assuming the bolts were tight, is it loosening of the bolt(relative rotation) or simple material creep? I'dvote creep, which means it's something we've all got to check periodically, as the failure mode is fugly.
 
It is definitely a creep problem with the lead...it's a low melting metal and has a relatively high creep rate at ambient temperatures. I didn't mention it but there is a mating lead weight on the fairing side..that's why a nut plate wasn't specified...not a great design. Too bad that I was a real rookie when I built the empenage or I might have come up with a fix at the time.

Still hoping to hear some suggestions for bonding the weight to the rest of the assembly.

By the way, the weight is only slightly loose and is in no danger of causing an interference problem with the stabilizer. But I do worry about vibration causing it to continue to creep and making the assembly even looser.

Bob Cowan
N743RV
 
It is definitely a creep problem with the lead...it's a low melting metal and has a relatively high creep rate at ambient temperatures. I didn't mention it but there is a mating lead weight on the fairing side..that's why a nut plate wasn't specified...not a great design. Too bad that I was a real rookie when I built the empenage or I might have come up with a fix at the time.

Still hoping to hear some suggestions for bonding the weight to the rest of the assembly.

By the way, the weight is only slightly loose and is in no danger of causing an interference problem with the stabilizer. But I do worry about vibration causing it to continue to creep and making the assembly even looser.

Bob Cowan
N743RV

I think the concern, with even a little looseness, is flutter. I have the same design and had those thoughts of not liking a fastener holding lead in a moving part (as I followed the instructions).

To the present - - Now. as an experienced builder, what would you do to "fix" it? ProSeal the back? Hysol? Bond a stainless backer and make a steel hat shaped retainer for proper bolt tension? Recast with a brass matrix? Removable tip and just retighten it on annual?
 
Whoah, whoah, whoah...

I had the same problem.

The bolt didn't loosen up, the nut simply bottomed out on the bolt threads.

You need to install a washer on the nut side.

It is an elevator trim cap. Drill it off, put on the washer and re-rivet it back on!

Paint the heads of the rivets as necessary.

Is this a show plane or a go plane?

:confused: CJ
 
My build photos do show a washer under the nut as called out for in the plans. Also, the assembly was very tight initially and has only loosened over time. But maybe removing the tip fairing may be required.

Bob Cowan
N743RV
 
Whoah, whoah, whoah...

I had the same problem.

The bolt didn't loosen up, the nut simply bottomed out on the bolt threads.

You need to install a washer on the nut side.

It is an elevator trim cap. Drill it off, put on the washer and re-rivet it back on!

Paint the heads of the rivets as necessary.

Is this a show plane or a go plane?

:confused: CJ

+1 - fix it the correct way. Repainting rivets. Question remains: Is this a show plane or a go plane?
 
I use proseal to bond the weights to the structure when I install them (in addition to the bolts),
 
As a new builder (still building the empennage), I had similar concern about the rudder counterbalance weight. After riveting on the top rib above it, i thought "how will i ever know if this thing comes loose?".

Is this a concern for any of you experienced folks, or should be not worry about it?
 
Problem solved

Was able to get back to my elevator counter weight issue after some outpatient back surgery. The solution we used was to fabricate two aluminum plates containing two nut plates, one for each side. Then we cut two holes in the leading edge of the tip fairing to be able to reach in an remove the two lock nuts. The plate was then inserted, and with some finesse, the bolts were screwed into the nut plates. The job was finished by glassing in a small piece of fiberglass layup and a quick spray with paint. I can now re-tighten the assembly when needed without surgery.

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Note that much of the work was done by my "fiberglass friend", Steve Robinson
 
Looks like you came up with a good fix. Nice work.

When I get back home I am going to make sure my weights are solid. Maybe even epoxy all around it so it stays. 2nd maybe would be to drill a hole in the top and bottom into the lead, countersink the hole, and epoxy a screw into the lead. You would see the screw on the top and bottom, but if it was countersunk, it would not be noticeable.
 
Wrench in the bottom

The least intrusive is the hole in the bottom between the two bolts. Tighten then get some Click Bond adhesive and apply around the weight. It won't come loose again!!!!
 
I had the same issue

On the first annual inspection of my 6A. The IA noticed that the counter weights were loose. I had to remove the elevator for another issue (can't remember why). While I had it off I simply secured the weight with epoxy. I could have done the same thing with the elevator on. The IA was happy with the he solution and the weights are securely fastened. I still check occasionally. BTW I also did the other side the same way. No problems
 
That looks like a good solution. I also like how the tips are fitted with clear visible lines instead of glassed-in as so many builders do.
 
Preload Bolt with Belleville Disc Springs

This looks like it might be a good place to install a stack of belleville disc springs (washers) to maintain tension on the bolt as the Pb cold flows.

Not sure of the bolt OD but there are several options here:

http://www.mcmaster.com/#belleville-disc-springs/=12b7zny


I know the old school structural dynamics engineer I used to work with loved them in this kind of application. Helps keep joints tight in dynamic environments.
 
Hmmm - to revive the thread. I am finalizing my elevators for balance and revisited the torque on the #10 bolts.

Some numbers - some one check me - #10 washer area = .117 in^2 Lead yield stress 1700 psi. 1700*0.117 = 199 lbf

25 in-lb torque on a #10 gives 660 lbf per online calculator.

Limit for lead = 199/660 * 25 = 7.5 in-lb yield point :eek:

While it may be creeping, there is no way it can be attached with standard torque. For reference, I just tested a #6 screw in an aluminum rivnut, the screw stripped the threads at 20 in-lb, but the rivnut did not rotate. It was the locking tang style.

You may be thinking, why not a larger washer ? The countersink in the 614 counterweight will allow a .6" diameter steel washer. The area is 2.148X larger so the torque can increase to 16 in-lb - again, we can not use standard torque.

If there is room a spacer and larger steel washer would work, if it is on the 6-7 elevator, there is no clearance, so pro-seal/epoxy is the option.
 
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