Crowned (not bowed) ribs

[NorthernRV4]

Hi all

Just wondering if anyone has experienced crowned rib webs, no not bowed from forming. I have two ribs for my -4 empennage (HS-407/8, new from vans) that have a defined crown to the web and I can't seem to press it into shape. I even tried placing a flat block inside and driving another flat block on top and clamping but it just springs back. I fluted to remove a slight bow but the crown remains. Do I need to worry about this? The lighting in the photo makes it look more pronounced but it's probably about 1/16" gap at each edge.


HS-407/8 by jim_soutar, on Flickr

[CATPart]

You would do best to point that out to Vans and see what they have to say about it. If that is within their design tolerance then it should be good. If it is an out of tolerance part then they should give you new ones. It sure looks weird to me, and I would assume it is meant to be flat. Is that an elevator end peice? It probably is not an issue structurally, but if Vans is supplying parts that far out of tolerance then they should be made aware of it. It would make me suspicious if the part is 1/16 out of shape in any other dimensions.

[NorthernRV4]

Thanks, I'll call Vans. These are the mid span horizontal stab main rib and tip rib. I measured it and the main ribs have a 1/16" gap at each edge. The tip rib has a 1/32" gap at each edge. The root ribs are perfectly flat but they have flanged lightening holes and that would certainly make a more rigid web. The tip ribs seem flat too.

[fl-mike]

Some quality time with a soft faced dead-blow hammer or rubber mallet will fix that up. Just go slowly. You will have to re-square the flanges after and probably touch up the fluting. This is also a common issue with the newer tip ribs that go back to back. Otherwise the pre-punched skin holes don't line up with the holes in the rib flanges.

[DaAV8R]

Originally Posted by fl-mike

Some quality time with a soft faced dead-blow hammer or rubber mallet will fix that up. Just go slowly. You will have to re-square the flanges after and probably touch up the fluting. This is also a common issue with the newer tip ribs that go back to back. Otherwise the pre-punched skin holes don't line up with the holes in the rib flanges.

What Mike said. I had this problem on the -8 elevators. After much head scratching I finally got out a big hammer, beat them into submission and once again all was right with the world.

[NorthernRV4]

Ok, I'll try again with the wooden blocks and rubber mallet. I stopped when the web started to look uneven on the first one tried. These are actually undrilled and are for a -4 tail. I just thought it was a bit strange. Not unworkable but strange. I also considered adding 1" flanged lightening holes in an effort to straighten them.

[LifeofReiley]

might also try the block and turn your air way down then massage with a smooth flush set. Works...