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When 'Rounding' gone wrong

MekMouse

Active Member
So pretty sure I interpreted how to round the HS-905 nose ribs wrong. After rounding the entire front section held at 90 degrees to the wheel and cleaning up the resulting knife edge, I was left with this.


Given the location of these in the Horizontal stabilizer, should I order new and try again? Or would these be ok.
 

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There is insufficient edge distance for the nose rivets on most of those ribs, so I don't think it would be advisable to use them.
When doing the rounding, it is safer to do it manually with a file and fine sandpaper. This method is slower than the wheel, but gives much more control over the end result.
 
agreed

That's pretty much the direction I was figuring with these. especially after re-checking through section 5 and AC43.13.

It would be nice if Mothership could add a guiding image in section 5 for what they infer with such a vague instruction as "Radius the corners at the forward end of the nose rib flanges" for us visual based newbie builders.
Of course I did try to search the forums here for some insight, possibly I used the wrong search terms.
 
alternative rib rework

In answer to the question "would these be OK?".......no they would not. Way under the edge distance rule. Would not hold a rivet without tearing through.

One alternative to scraping/replacing the ribs: cut off the offending flange tab, fabricate new single tab flanges, fit and rivet them to the rib, back drill through the skin for the new tab. Once riveted together and drilled through the forward hole, then (and only then) round the corners.

There's a few re-flanged ribs and bulkheads in my build. Properly done, it works fine.
 
Edge distance?

Edge distance is certainly compromised in at least a couple of those holes.
It is one of those places where the skin really can't go anywhere, even if there wasn't a rivet at all. You might get away with a small doubler on that flange to capture the shop head. Secure the doubler with a single flush rivet to the flange
and set your rivet.The trouble is, that this very rivet in the most forward and tightest location is also the most difficult to set without buggering up the skin, not to mention properly placing your bucking bar without creating a dent.
In short, make sure you only have one thing to fix before you are done with that skin.
I am not telling you what you should do but it is what I would do in your position.
 
Neither the skin or rib going anywhere at those front rivets.
Yes it dosent meet spec but I’d ask the factory before junking it.
Maybe you get away with another rivet 2xD behind it.
Maybe it’s fine as is.
Maybe you have to re-do.
 
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I did the same to one of mine - factory advised replacement.

If you have a Dremel, I would highly advise the purchase of a Dremel 500 wheel. It's one of the more used tools in my "shop".
 
Verdict is back

I did the same to one of mine - factory advised replacement.

If you have a Dremel, I would highly advise the purchase of a Dremel 500 wheel. It's one of the more used tools in my "shop".

I will most certainly be adding one of those to my toolbox!

Got word back from mothership, all of my nose ribs are compromised and should be replaced.
New ones on order. With any luck I'll have them this weekend. Not a big bill, but it is annoying :(

I think after I properly radius the ribs, I'll post a fresh photo here for future builders to find and avoid my mistakes.
 
In my opinion - get rid of the Scotchbrite wheel(s).

By hand with a file, keeping an eye on what you're doing, you won't get into trouble. Best to get fine files.

Dave
 
Could you post a picture of the "before" part? Were these pre-punched, as well as the skins? I'm not a builder, so am not familiar with the "before" part, or the "rounding" one must perform. I cannot grasp how one could remove so much material to result in such a short edge distance. I would assume by these pics that 0.1" or more was removed from these parts. I am not trying to criticize anyone, I am simply confused.
 
Could you post a picture of the "before" part? Were these pre-punched, as well as the skins? I'm not a builder, so am not familiar with the "before" part, or the "rounding" one must perform. I cannot grasp how one could remove so much material to result in such a short edge distance. I would assume by these pics that 0.1" or more was removed from these parts. I am not trying to criticize anyone, I am simply confused.

Would be happy to post a before shot. I just need to the get the new ones first.
I'll post a before, sharpie lined 'don't violate this', and maybe an after shot.

Looking at the shipping info, they should be waiting for me when I get home from work Fri. :)
 
Radiusing nose ribs

OK, after all the helpful advice from this wonderful community I feel better with these results.
First pic is the as supplied HS905.

Next is the forward flange marked for a conservative safe edge distance. It also happens to be the same as a cleco body:).

Then after radiusing the corners and some minor deburring.

For now I'll strategically hold off on the rest in case our experienced members advise for less removal
 

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Great pics thanks! I totally see how they made it a bit confusing, and think you are on the right track now.
 
That step puzzled me for a long time. It would have been helpful to have diagrams from several angles to see what should be happening. I spent a few hours digging through blogs to find photos that showed how others had done it and I also think you're on the right track (or at least doing what I finally did.)

I'm well into the wings now and haven't found anything else nearly as difficult to follow as that one diagram.
 
Agreed and thanks guys.

My biggest mistake on these parts was presuming that the shaded removal area extended down through the entire part.

Now, on to more progress... and more second guessing the quality of my Vertical stab.
 
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