Hysol ??

[southwind32]

I'm replacing my front spar on my project. Taking the hysol off is time consuming, but making progress.
My question is, can you put a new mixture of hysol over old cured hysol? OR do I need to remove every little bit of the old hysol. I'm only concerned with hysol on wood. I'm able to remove 95% free the ribs from the spar, but if there's any left, do I need to go back remove any remaining on the wood, or will it bond ok?
Thanks
Brian

[Esser]

Hey Brian, I think you could be ok, my only concern would be did the heating of the hysol affect its integrity. I think false ribs would be ok but remove all hysol off the ribs

[efwd]

Hey Brian. You should make good time at cleaning off the Hysol from the ribs by using a sanding wheel on a dremel.

[Slyfox]

when I went from long wing to short I needed to remove some ribs and hysol. I found if I heated up the hysol it scrapped right off. I used my 1500watt gun. :D . Now I don't know if I just got lucky or it will work for you, it did for me.

[jiott]

I agree, if it was me I think I would try to sand off most of the old Hysol on the wood. However, I wouldn't stress too much about it because the bond of ribs to spar is not a critical structural joint. The ribs only serve to space the spars one from another and to provide an airfoil shape for the skin (fabric) to adhere to. The Hysol is only there to keep the ribs from sliding around and getting out of position. Your critical structure is the spars, diagonal cross braces, and the lift struts.

[jiott]

As was stated, the false ribs are a little different story because the Hysol is the only thing holding them in place, so I would be more concerned about a good Hysol to wood joint on them, even though they are not critical to flight. On the main ribs I would bet that if all the Hysol to wood joints were loose you would not notice a difference as long as the Hysol to spar joints were intact to keep the ribs in position.

[David47]

I have to respectfully disagree with the comment that the rib to spar joint is not structurally critical. A significant amount of the airload applied to the wing fabric is transferred to the ribs, which in turn transfers the load to the spars. In our particular rib to spar joint geometry, the ribs interlock with the spars which forms a large part of that load transfer, however the Hysol provides stabilisation of the joint (eg prevents rib rotation) and also provides additional load capability. So I would say that the rib/spar junction are important to the manner in which loads are shared between covers, ribs and spars.

[Slyfox]

I remember reading once that you don't need the glue. ha, yes that's what I read. that the glue is mainly to hold things together until you get the covering on. I don't know if I would feel comfortable with that or not, but that's what I read. I think it might have been the original designer of the kitfox. but I remember reading such a thing is all I can say.

[jrevens]

I have to respectfully disagree with the comment that the rib to spar joint is not structurally critical. A significant amount of the airload applied to the wing fabric is transferred to the ribs, which in turn transfers the load to the spars. In our particular rib to spar joint geometry, the ribs interlock with the spars which forms a large part of that load transfer, however the Hysol provides stabilisation of the joint (eg prevents rib rotation) and also provides additional load capability. So I would say that the rib/spar junction are important to the manner in which loads are shared between covers, ribs and spars.

I absolutely agree, David.

[Esser]

Just to clarify in my post, I thought you might be ok leaving hysol on the false ribs as they aren't structural but to remove it all from the ribs.

[Slyfox]

I have a problem with your statement. wood is wood. if I know glue it will soak into the rib. I don't see any reason to try and get this out. just remove what you can and when you put the new on, it will bond to the old. just move on, don't be a perfectionist. it might bite you. meaning, if you remove the surface of the rib to get the old hysol off, you will more then likely remove rib material. just leave it and install and recover with the hysol.

[jiott]

I figured my comments might stir up some interesting discussion. Just for the record, my statement about the glue joints not being a critical structural joint is not original with me; like Slyfox said I heard it somewhere else but can't remember where. Also I want to be clear that none of us including myself would even for a moment consider not gluing those joints. That said, I still believe the statement is true. Think about it; there are no lateral forces on the ribs, there are no twisting forces on the ribs because the spar/cross braces ladder structure is all locked in STRUCTURALLY by the aluminum parts and the steel lift struts, the ribs only have vertical forces applied by the lift on the attached fabric. These vertical forces are transferred to the spars at the points where the spars go thru the close fitting holes in the ribs. No glue is required to do this; it is just like a big bolt loaded in shear passing thru a plate (you don't glue in shear bolts). As I mentioned previously, the rib can do all of this as long as it is stable and doesn't move out of position or tip sideways. The fabric itself with the rib stitching will accomplish this, the glue is only a secondary backup. Again as I stated previously, as long as you have a good glue to spar joint on each side of the rib with a nice fillet up the side of the rib, the glue to wood joint could be totally disconnected and the ribs would still be held tightly in position and stable and transferring the lifting loads to the spars. If those holes thru the ribs for the spars were sloppy loose my argument would not be nearly as valid.

Believe me I am not trying to be a know-it-all or to call others out as being right or wrong, its just fun to think about these things and to try and evaluate what we have heard.

[Dave S]

An easy way to clean up the false ribs, because of their simple shape (once they are removed) , is to get access to a simple bench belt sander - a quick touch on each side will clean those up and the open drum end can be used to get the edges. It's so darn easy it's hard to keep oneself from doing it. There will be some varnishing when it is all bonded back in but that's easy too.

I ended up with a cheap 6" disk/belt sander combo which was one of the most useful tools I had for shaping and cleaning up numerous small wood and metal parts for our build.:)

[Dave S]

Please disregard my previous post - I believe I misunderstood the original question.:(