SB 00067 Complete, Some Notes

[Tacco]

1. I completed the mod solo with no problems. Just took time.
2. Be sure to tape the fuselage in the vicinity of the stabilator leading edge to avoid scratches.
3. I used two adjustable sawhorses and some closed cell flexible packing foam pieces to support the stabilator and to shim the stabilator to precisely align the mounting brackets and bearings.
4. A couple of sacrificial AN4 bolts with the threads removed and shaped into a bullet are helpful when reinstalling and to temporally mount the stabilator for balancing.
5. Remove the trim motor tray and apparatus. I just let mine hang on the cable off to the side. You might be able to work around it if left attached to the bulkhead, but why suffer the aggravation.
6. Upon initial removal, note the position of the PITA (MIL SPEC term) washers you used in original assembly. These are the glued washers, thick and thin, used to space the stabilator and ensure no end play. They will fall off! Fortunately, I also wrote a note in the plans as to which ones I used and where.
7. I didn’t weigh the kit before assembly. Should have in order to “ballpark” the amount of weight I’d eventually remove from the counterbalance weights. Account for the long bolts.
8. Balance the stabilator, it’s just not that hard and lets you precisely determine the amount of weight to remove from the weights. Follow the KIA. FOLLOW THE KIA.
9. Don’t forget to reinstall the trim tray and REST the actuator arm on the bolt per the KIA. It won't work if the arm is connected. The weight of the arm is not insignificant – 3 oz by my measurements.
10. I drilled three 3/8 holes in the lead counterbalance weight to achieve the reduction indicated by the procedure in the KIA. I drilled out the existing/unused bolt hole and one above and below that area. On the last one, I was carefully weighing the shavings until I achieved the desired reduction. The third hole did not extend all the way through before I got there.
11. One head scratcher. Checking the final balance, I found the stabilator to hold position as long as the trim arm rod end was perfectly positioned on top of the retaining bolt. Slightly off that position the stabilator would slowly settle forward or aft. In other words, the rod end would “push” the stabilator if off center. I reposition the rod end with the trim motor to confirm the stabilator balanced in any position as long as it was top dead center on the bolt.
12. Lastly, go slow and gentle when positioning the stabilator when reinstalling. Seemed easier than when I did it originally. Didn’t knock of any washers!
13. For those who think installing the mod with the stabilator attached in order to avoid the hassle and PITA washers, think again. It would take at least three trips into “the hole” and you’d need a helper to remove/reinstall the counterweight bar from the stabilator spar. For the really adventurous among you who might think you can perform the entire mod (fitting the braces and reducing the weights) from inside the tail cone, seek counseling. At the very least, file a flight plan so your loved ones know where to find you.

[Tony_T]

Nice PIREP Tacco! This will be helpful when we do 3 ships here. From your note number 12, it appears you did not do SL00068 to install the shims and not have to fight the washers? Any particular reason why not?

[Tacco]

Originally Posted by Tony_T

Nice PIREP Tacco! This will be helpful when we do 3 ships here. From your note number 12, it appears you did not do SL00068 to install the shims and not have to fight the washers? Any particular reason why not?

Hi Tony. I considered it. Given the number of times I'm going to remove the stabilator, it seemed like a lot of reconstruction for the convenience. So, I decided not to do it.

That said, there is one reason it might be a good thing to do. It's just my unexpert opinion but here goes. Using the current design (PITA washers), you are never going to get a flush installation, bearing to bracket. There will always be a gap of at least half the thickness of a 416L washer. When you torque down the AN4 pivot bolt, it's going to pinch the bracket. Just a seat-of-the-pants opinion, but that pre-load might lead to a crack later down the road. I'm assuming the new design results in a flush installation.

This area will get careful inspection during my condition inspections for that reason.

[seagull]

Tony, did you aim for neutral balance? I found that spec in the 12is KIA but not for the classic.

[Tacco]

Originally Posted by seagull

Tony, did you aim for neutral balance? I found that spec in the 12is KIA but not for the classic.

Yes, you neutrally balance. Use the 12i KIA page U-11 to do it.

[seagull]

I did mine today and Steve’s write up is spot on. I did a few things slightly different.

#3 my saw horses were not adjustable so I lifted the nose of the plane and it lowered the tail to the height of my saw horses. Same result.

#4 I used the old “short” counter weight bolts, AN3, easy in and out for temporary testing.

The weight of the kit minus the parts you remove, short AN3 bolts, nuts, washers, and rivet shafts was 66 grams.

I ordered the stabilizer hinge spacer kit but did not use it. I read that it solved the tedious spacer installation process. Instead I removed the stabilator the night before and re-glued the spacers in place using long set JB Weld. First clean the area with scotch bright, scuff the washers with 220 sandpaper, and clean the area with acetone, then glue, the washers will never move again.

I first weighed the servo pushrod by laying the clevis on a scale after the stabilator was removed. I added that weight plus the bolt, nut and washers, it was 87 grams. I created an 87 gram dummy weight using buck shot in a container and taped that in the same plane as the clevis hole. Next I hung the stabilator with counterweight from the ceiling using the hinge bolts. I used a fish scale to pull on the end of the counterweight to give an estimate of the amount I would need to remove. This technique worked well, I had to do an 8 gram adjustment on final install in the plane.

My weights were stock size, never trimmed, 2015 kit, painted tail surfaces. I removed ½” from the front of all 4 weights a total of 270 grams, the balance is perfect.

[rmac1376]

Any recommendations for an A&P in the Southern California area to accomplish the last 5 AD's RV-12is? Plane is at KSNA. Rod MacDonald rod@calventuremanagement.com

[bobg56]

I did mine today, I removed 7.8 oz for a perfect balance...I'm interested to see if there's any notice able difference in flight, especially auto pilot altitude control, I always had a bit of oscillation.

[rtlongdon]

Another data point (for whatever it's worth), I had to remove 28 grams at a point half way between the middle clamp bolt and the unused bolt hole at the end of the weights.

Measured downforce of the trim actuator arm = 88.6 grams.

Wing rack with a 2x10 clamped to the top and sticking out about 28" worked great to suspend the stabilator for balancing.

[bobg56]

Flew today and noticed that my auto pilot holds altitude much better than with an unbalanced stabilizer. I was happily surprised. Didn't notice any difference when hand flying.