Cracking of Bonnet Near Spring Hook

[aerobod - near CYYC]

As usual, always another issue to deal with. This time I have noticed cracking where the bottom flange ends on the bonnet due to the fatigue forces on the spring hook. Looks like I need to create a longer backing plate for the hook and put a couple of rivets further back on the bonnet through the extended backing plate, where the flange can add support:

[SamC]

I’ve noticed the same this winter although my crack runs perpendicular to yours along the fold line to the chassis panel.

I bonded a 90 degree doubler along the back, but seeing yours I suspect it’ll just run vertically now.

A doubler behind the hook that runs round the return looks to be the best plan then!

Edited April 10 by SamC

[aerobod - near CYYC]

5 minutes ago, SamC said:

I’ve noticed the same this winter although my crack runs perpendicular to yours along the fold line to the chassis panel.

I bonded a 90 degree doubler along the back, but seeing yours I suspect it’ll just run vertically now.

A doubler behind the hook that runs round the return looks to be the best plan then!

I'm planning to replace the steel backing plate behind the hook with a larger and longer aluminium one that is actually a bit thinner (1.6mm), a bit of epoxy on it, too. The issue of adding to the thickness behind the hook is that it is already kept from the proper position by the rivet body that contacts the Dzus fastener for the nosecone. The plate should increase the strength of the bonnet material where the plate is added by about 2.5 times what it is now.

[SamC]

Yep, I agree, just warning that it appears a crack can form both vertically and horizontally in that location, so worth heading the next failure point off at the pass. 

[SamC]

Example from a Facebook post (not mine). Mine has a small horizontal crack but no vertical.

[aerobod - near CYYC]

29 minutes ago, SamC said:

Yep, I agree, just warning that it appears a crack can form both vertically and horizontally in that location, so worth heading the next failure point off at the pass. 

I will bond my strengthening strip to the flange as well as the bonnet side to hopefully alleviate both vertical and horizontal cracking.

[aerobod - near CYYC]

Put a strengthening strip on the inside of the bonnet, across the crack area and laminated with epoxy:

The rivets on the inside have been compressed with Mole Grips to avoid interference as far as possible with the Dzus fitting for the nosecone

It doesn’t look too bad with the extra rivets:

[PROBE2]

Looks a good permanent fix aerobod, I have a similar vertical crack, preparing bonnet for paint and considering best solution. 

Has anyone welded from behind or is aluminium too thin? 
 

[Miker7]

It should never be too thin, it's just the welder & equipment aren't good enough 🤣

I can't remember if the bonnet is 1.2 or 1.5mm Ali. This is easily weldable by someone with ability (ie not me). Will ruin the paint - hopefully that's obvious.

If you need a short term fix that could turn long term there is the aluminum "braze" that you see sold in the shows. I'm not personally convinced as to it's structural strength.