Hatz Biplane Association

After carefully considering the options available for 1/4 x 28 threads I decided to go with a 5/16 x 18 coupler. I spent some time looking at the eyebolts for a 1/4 x 28 thread and they all seemed to have a hole that is too small to get most well frayed tie down ropes through. I also wasn't happy with how small the assembly looked with a 1/4 x 28 eyebolt. The engineering might be good with the 1/4 x 28 but for me it also needs to look strong enough, 1/4 x 28 did not pass that test.

Thanks Ed. I didn't order from Grainger. I'll look at 6/16 X 18.

I got a pair of 5/16 x 18 couplers from my local Lowes. Looking at Scotts picture it looks like he used something bigger than 1/4 x 28 also.

Just saw on his site it's 5/16….btw….8 pieces have a slot for a lug. It seems like the slotted piece mounts on the side of the spar facing inward (facing the opposite spar). Is that correct? Wondering if I should just slot all or determine ahead of time which ones to make a slot. Also wondering how to cut the slot; guess the scroll saw.

I was confused by the slot at first. It faces inside the wing and supports a tube with flattened ends that goes from front spar to rear spar. The problem that I had was not which piece to slot but which side to weld the lug on. I had the slots water jet cut and I made the lugs by hand, the lug is thicker material than the plate. If I was making the slot by hand I might drill two holes and try and connect them with a cutoff wheel then a flat file.

Thanks Ed. I just found a scroll saw blade that cuts the steel; should work even better with cutting fluid. I'll drill a small starter hole and feed the blade through.

Bought these at Lowe's…

Regarding the RSTW3 doubler, the plans indicate the doubler is welded on the outside of RSTW3, yet the doubler seems made to fit under the spar or on the inside of RSTW3. The note about not welding the top makes sense if it were to fit under the spar. I'm not sure why it's welded to the outside and why the top is not welded. Thoughts?

I had the same question. The best I could figure is that a weld typically has a small undercut at the edge of the puddle. This may create a stress area since it would run across the part. I was concerned that the area between the plates is bare metal and moisture can migrate down through the seam. When I powder coated the part I coated that section twice and it seemed to seal well. I have heard that they make weldable primer but I have never seen it.

Not having the Classic plans, I'm going to take a stab in the dark here.
If RSTW3 doubler is on the bracket that bolts to the wing spar and then the flying/landing wire lugs fit, I'm in the right spot; otherwise, I'll go back to sleep.
On my LB-1 I put them on the outside. The doubler strengthens the area around the bolt hole so it really doesn't matter which side you place it other than if you put it under the spar it reduces the length of the lug bushing.
As far as welding the top, I was taught not to weld across something like the bracket. The stress is in line with the lenghtwise dimension and if you weld across the bracket you effectively place a weak spot at that point.

Jeff Moore