Hatz Biplane Association

Regarding the roll wire attach point at the upper motor mount points on the firewall:

Is the back side of the roll wire attach tab welded to the top fuselage firewall crossmember? If so, then it seems this weld bead would interfere with a good fit and welding of the roll wire doubler on the back side of the aforementioned roll wire attach plate. Undoubtedly the doubler tab is welded on the back side to the fuselage cross member. Another option would be to weld the doubler tab to the back side of the front roll wire attach plate before welding that onto the motor mount pad,and then welding the doubler on the back side to the cross member. Although I think the first bead would again interfere with the fit along the fuselage cross member.

My thought would be the best way would be to weld the front plate of the roll wire attach only around the face of it at the motor mount plate made from .050 and not across the back to the fuselage cross member. Then weld the doubler plate across the back side to the cross member of the fuselage, and of course edge weld the roll wire attach plate and doubler around the perimeter. This seems like it would make sense, but I do not want to leave out an important weld bead on this assembly.

Then to complicate it, the inside doubler plate (.050) for the forward cabane attach comes into contact with the roll wire attach along the aforementioned back side of the doubler plate along the fuselage cross member. Should a single weld be attempted which attaches the edge of the cabane attach doubler, and the back side of the roll wire doubler, and the fuselage cross member, or is it advisable to weld the back side of the roll wire doubler with the cabane attach doubler absent, then install the cabane attach doubler and weld it to bead along the back side of the roll wire attach doubler, or I suppose the cabane attach doubler could be trimmed back so it is actually welded on a separate bead to the fuselage cross member directly.

OR...... Does it really even matter???

Hi Jackal,
I took a look at my fuse and it differs some from the plans. Richard Lauzon (Weld-Tech) used rectangular tubing in a lot of areas. He gusseted the corners of the frame at the firewall with it. The roll wire fitting is a single .125 piece edge welded to the doubler at the motor mount hole. The front cabane fitting is two parts as the plans show it. The inner piece butts the roll wire fitting. I tried taking a picture but being black, it does not show itself well.
Al

With disappointingly little input from the forum (Thank You Al) I proceeded with the welding of the fittings.

Either there are a lot of viewers who don't want to talk about this fitting, or their are 69 people still facing this fitting in their future. For the benefit of those in the latter group I offer my experience to add to the forum knowledge:

Because mine is different than Al's from Weld-Tech (Instead of a single .125 roll wire attach tab mine is composed of a .090 attach tab with an .090 doubler - per CB-1 plans in other words) I felt (I have no credentials) I should attach the separate back doubler to the fuselage cross member. Welding the doubler (now .180 thick to the cross member of .035 I think) concerned me. I did not think I could puddle the doubler, at least not without burning up the .035 tube. I did not attempt it with one torch (It could probably be done with TIG) but instead had a helper heat the fitting from the front side with a standard cutting tip (don't hit the juice!) concentrating in the vicinity opposite the weld bead. I then welded from the back side and connected the .090 doubler tab to the fuse cross member. This was very effective but still it was difficult not to burn through the .035 tube a bit, but that was easy to fill in with rod as I progressed. I used a #2 tip but looking back a #1 might have gotten the job done with less risk of burning the tubing. If I were doing it again I'd try that first. Do not use a #3!!

After welding the back side of the doubler I then put the cabane attach doubler in place (trimming it back to clear the bead just completed) and repeated the weld procedure again. This time it was a lot easier to get it done without burning through the .050 cabane doubler since it was backed by the .035 tube - but still a bit tricky.

If I were doing it again I would probably attach the .050 cabane doubler first. So long as you don't "wrap it too far around" the front of the fueselage crossmember and keep the bead from being excessively thick there appears to be room to then place the .090 roll wire tab (even with the 20 degree back angle) without interference. Then attaching the .090 roll wire doubler would require only a single pass (instead of 2 passes as I did it) and burn through would probably be eliminated since the single pass would be the .050 backed by the .035 tube and the two .090 cabane attach tabs would not also have a bead of weld added to the back side, making it even heavier metal.

NOTE: This method does not directly attach the roll wire attach doubler to the cross member (but rather only to the .050 cabane attach doubler) which might be a structural issue - I don't know about that. From simply a "weldability" perspective I think it would work better though.

Incidentally - each time I made a weld pass on the back side of the roll wire attach tab it "pulled" the roll wire attach tab back at a sharper angle (a couple degrees a pass) as the bead cools and shrinks. Its a minor amount, but knowing it would happen now, I'd start with the back angle maybe more like 17 degrees to arrive a the 20 degrees called for in the plans.

I hope this helps someone,

-Jackal