My questions or comments are in Blue and Nick Heintz in Black
I wrote:
I had a slight problem with the predrilled horizontal stab skins and the location of the end ribs. I think that the location of the end ribs may need to be a little more specific than what is in the Photo assembly guide.
From STABILIZER SKELETON 6-T-1C - Page 8 of 10 Spars fit inside the End Ribs 6T1-1
Any way there are 3 problems.
1. Holes are close to the bend radius. Concerns: fatigue. If they are in the bend radius then the rivet will not set and may cause a stress concentration. It is still on the flat so I am going to leave it as is.
What is the length of your stabilizer, Ref bottom diagram on drawing 6-T-2, length = 2205 from outside to outside end ribs.
2. I nicked some of the rivets on the forward upper doubler. Concern: failed rivets. I will drill out or add new rivets to either side.
Replacing the damaged rivets is the best thing.
3. No edge distance on some of the ribs. I will add another rivet just aft of the one with the edge problems on the ribs.
It is acceptable to add an extra rivets (with good edge distance) on each side of the rivets with questionable edge distance.
Nick Heintz
Zenith Aircraft Company
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I guess I wasn't clear enough with my description. The problem is not with the outboard placement of the end ribs but the fore and aft placement. The span wise dimension is very close to 2205 and this is not the problem. It is the in the fore and aft direction. The photo assembly guide has it located by lining up the aft edge of the top flange with the aft edge of the rib. “ALIGNMENT: The aft edge of the top flange is flush with the aft edge of the rib."
I think that this is adds too much variability. The better solution would be to locate the end ribs in the fore and aft direction by a dimension between the forward spar and the forward tip of the end rib. The problem I had was that the rivet line that was predrilled in the skin was further forward than desired on the upper flange of the forward spar. It would have worked much better to have my end ribs about 2 to 4 mm further aft. Then the rivet line on the predrilled skins would have ended up in the middle of the flange. Your predrilled skins make this distance critical.
The other problems are fixed. This one looks acceptable but the rivet line is very close to the bend radius rather than in the middle of the flange.
When positioning the skin on the skeleton, did you first check alignment of the leading edge of the skin with the front of the end ribs 6T1-1? Ref page 7 of 12 section 6-T-2A of the photo assembly guide:
www.zenithair.com\zodiac\xl\data\6-t-2a-stabilizer.pdf
I agree, it would be helpful if page 7 had additional notes to check the alignment of the pre-drilled holes in the skin over the spars, top and bottom surface.
I did check the center of the skin but I am not as confident that I had a good center. The other problem with this check is that the position of the skin is really determined by the holes predrilled in the skin for the pass through of the front spar attachment. At this point I probably should have drilled out the end ribs and relocated them. I still think that the better solution would be to give a dimension from the front spar to the forward part of the end rib. I think mine is fine now but maybe some others will benefit from this.
Thanks for the feedback, we will take a closer look at how best to install the end ribs for best alignment of the pre-drilled holes in the stabilizer skin with the skeleton.
Nick Heintz
Zenith Aircraft Company