February 10, 2011

Several small tabs need to be welded to the fuselage to attach the floors, door and window opening formers, windshield, etc. The tabs are made from 4130 steel plate that is .040" thick.  The size of tabs will depend on what attachment device you are going to use.  The smaller the better to save weight.  I will be using clip nuts and screws for removable items like the floors. Those are small, so I'll make the tabs 3/4" x 3/4".  If you plan to use nut plates, make your tabs 1" x 3/4". On some of the tabs you will be attaching items with stainless steel pull rivets so you can make those tabs smaller, 1/2" x 3/4".  

I measured and marked the sheet of steel and cut the tabs out using a bandsaw:

Here is a bunch of the tabs after cutting:

The goal is to position each tab so that it is at the correct height and angle for whatever is attaching to it.  So for the floors, I want the tabs positioned to be at the top of each longeron or diagonal tube and angled flat or parallel with the floorboard.  I found the fastest and easiest way to do this is to clamp the tab to a piece of angle iron and just lay the angle iron across the adjoining tubes as shown here:

I had this piece of galvanized angle laying around the shop and found it works fine.  Use caution with galvanized material as heating it up can cause it to put off dangerous fumes. Since I am only tack welding the corner of the tab, this worked fine.

As you can see above, the tab is held at the correct angle and location. Now when the floors are attached they will lay flat and the tabs will be correct.  After tack welding the corner, the angle is removed and the tab is finish welded. Here is a tab just tack welded:

Here are some tabs finish welded:

Generally speaking, you will need two tabs per diagonal tube and about 2 or 3 per bay along each longeron depending on the length of the bay.  Spacing should be 8" to 10" or so.

Here is a picture of the Station "A" to Station "B" section of one of the factory finished fuselages to give you an idea of the tab locations and spacing:

Next I'll continue on with tabs for the door opening formers, window opening formers,  windshield, skylights, etc.

The goal here is to get the tabs aligned to hold the door former at the correct angle to align with the former on the opposite side.  To do this, use a long straight edge and clamp it to the tube on the opposite  side as shown here:

The straight edge holds the tab at the correct angle and height. The straight edge I am using is simply a piece of shelving channel.

The tabs are spaced about 5" apart and tack welded in place, then final welded:

The aluminum former is the then drilled and clecoed to the tabs:

Now I'll go ahead and attach the tabs for the remaining door and window formers.  

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