Is bulkhead tabbing now redundant?

That will weaken the structure though. If the worry is crushing of the core, just upgrade the core to one that has better compression resistance.

 

That is an appalling structural joint for a hull-WTB. No load paths or continuity of structure at all. Highly UN-recommended.

 

Yeah, I'd expect to be shot building a sandwich like that. Dove-tailed bulkheads !

 

That would mean: Reindeer skin planks on a willow-twig framing.

I somehow cannot agree here.

 

I'm affraid here I will have to side with the 'old time methods' crowd. Sandwich constructed boats have been built like this for years,.... and it works.

 

clearly the hull to bulkhead joint needs to be different if your core was balsa and can carry more than then if the core was foam
I'd say boats get built to lowest common denominator hence many over built and as weight not an issue it works as we all know

 

Then don't look up because it is common in airplanes.

If you look at the load paths, and that is what matters, all skins are in contact (or close enough). The core is pushed back a bit on all parts and the pocket is filled with an aerospace adhesive and the joint assembled. The adhesive easily handles the load transfer from skin to skin since it is a stable joint and the discontinuity is very short. Except for the outside skin all skins are encapsulated both sides in adhesive. The outer skin has a large bond area the thickness of the core and length of the pocket. Each section between pockets just has a fillet as Groper has described. The key is the pockets are not too large and not too far apart so the weakly bonded areas between pockets are just secondary support for stabilization.

Tunnels, what you are asking is basic engineering. The outer shell is the furthest away from the neutral axis and hence most efficient for carrying loads. The inner skin is for stabilizing the core against buckling failure. The core is an efficient way of making a skin. Simple.

It's just a fact of life that everything isn't built like a boat.

 

I believe you and the fact that it works proves that if it was done correctly you could save weight in the structure. I think that is what Groper is after.

 

Interesting Link

Very interesting Link....with discussions of bonding, etc.
http://www.boatdesign.net/forums/fiberglass-composite-boat-building/infusion-plan-43380-30.html#post633658

May take awhile to get thru that discussion

 

Seems to me you have cut through half of the inside skin at the bulkhead, and lost a lot of strength in the sandwich panel as a result, I would not dream of doing it !

 

Beat me if I am wrong: Water pressure is from the outside. So inside skin is under tension, not? I would also expect the neutral axis of the sandwich WITHIN the sandwich - more or less close to its centre.
Further, panel curvature is ignored here.
With a hull working in waves, there will be altering loads - including torsion. And with a mast aloft, some other forces are induced as well.

 

You are not wrong just looking at it differently.

I was referring to the neutral axis of the whole structure. The most efficient use of weight is on the outer skin.

As Brian pointed out, bonding to the inner skin has worked for years. I'm sure boat builders learned through trial and error what was needed to make a stable inner skin so the foam would never see any loads it couldn't handle. Of course that is overkill but necessary if you choose that method of construction. I'm sure the comfort of that beefy inner skin is why some are appalled at the thought of cutting though the skin.

Anyway I was just throwing out some methods used in composite structures. The one I pointed out is definitely not the best possible but unless you want to spend a lot more money and time it is a simple method that properly done will be stronger and lighter than bonding to only the inner skin.

 

Er um..are you suggesting that the skin the fuselage the wings, the major structural components are made this way!!

Pure poppycock…but if that is what you believe, hey ho. Seems many on this thread have their minds made up what is or is not structural design based upon thoughts and conjecture and won’t be swayed; like a religion.

 

This looks like it's suited to joinery/furniture. Jeff.

 

No it is not. Attached typical tabbing of rib to skin of sandwich laminate.

The illustration you have posted is for joinery of furnitures as Waikikin has noted. Not for critical stress joints.