3-D and waiting.

On January 18th I posted my last blog update; both fuselage sides were tack welded. That was seven months ago now. I should update more regularly.

Okay, self-flagellation over, let's get to the content!

Once both fuselage sides were tack welded, I pulled all the jig blocks off the table, elected not to repaint again, and just laid out the stations for the top view of the fuselage. We lay out the top view because the top of the fuselage is flat which makes it a lot easier to jig things up if you lay out the fuselage upside-down. With the top view lofted out on the table I could start adding in jig blocks starting in the cockpit area where the sides are parallel. A stick and some clamps help hold the sides parallel for this photo op.

 Now may be a good time to mention, if I haven't already, that I am widening this fuselage from stock. The original Jr Ace (Model E) was 33-1/8" between tubing centerlines at the widest point. This makes for a pretty cramped space when two people are aboard. I have decided to widen mine out by 4-7/8" to give me an even 38" between tubing centerlines. This gives more space for modern sized bodies as well as widening the gear stance which will improve ground handling. I widened the firewall as well, adding the same 4-7/8" width to that station in order to give some more foot room and preserve the angle the longerons make between station 1 and station 2.

Once the sides are stood in place I can start cutting the cross-tubes for the cockpit section. These first tubes are all the same length and have 90° notches, so they're pretty simple to make. Don't forget to drill a small vent hole in the longeron where the cross tube intersects it. This will allow air to escape from the cross tube as you finish weld it instead of bubbling out through your weld puddle. It will also let us oil the inside of the tubing to prevent corrosion after all the welding is finished.

With the cross tubes made and jigged out the diagonals start going in, just like the sides but hovering in space this time. How do I manage that? Well, you might be able to see in the following picture (you can click them for full-size). I bought a couple sets of hardware-store turnbuckles and made up some diagonal wires which wrap the longeron and hook to some little plumber's strap tabs screwed to the table. With the turnbuckles in the wire I can adjust the diagonals to pull the sides together and hold them square to the table. The turnbuckles also allow me to back off the tension on the wire so I can more easily slide in the diagonal tubes.

Now with all the cross tubes, diagonals, wires, etc holding the cockpit box in shape I can start pulling the tail together then add the jig blocks to hold it there.

I worked back one station at a time, adding my temporary brace wires to hold everything square, add the cross tubes to make a box, cut the diagonal to hold it all square, add the top and bottom diagonals between the last station and the new one, tack weld all the new tubing in, then move on to the next station. There is a little back-and-forth than needs to happen here because if you weld things too early you might not be able to get the tubes in place for the next station. Forethought is paramount. On that note, I completely forgot to put the seatbelt attachment fittings onto the lower cross tube of station 3 before tacking it together. I had to go back, cut the tacks, slide the fittings on...

you did remember to drill those vent holes I mentioned earlier, right? 

... drill the vent holes, re-square that station, and tack it back together. Not a big deal, but annoying and preventable.

The tailpost caps off the aft end of the fuselage. The tailpost is a little tricky because it is supposed to stick up above the fuselage by 3/8". But if you recall, the fuselage is being jigged out on the table upside-down. That means I have to drill a hole through my tabletop to fit the tailpost in place. Not a big deal, but in retrospect it would have been easier to shim the whole fuselage up off the table. That way I wouldn't need to drill a hole, plus I would be less likely to burn my table while welding AND I could have wrapped my cross wires around the upper longerons instead of needing the plumbers-strap tabs screwed to the table. Well, maybe on the next airplane.

 There is a further finesse involved with the tailpost because the longeron centerlines line up with the outside diameter of the tailpost, meaning that the outside half of the longeron tubing has to be heated and tapered in to meet the tailpost. 

Once everything was all taken care of at the tail end I directed my attention forward from the cockpit box to the firewall, fitting cross tubes and diagonals as before. I did a once-over to make sure everything was thoroughly tack-welded and then I could break down the table, but we'll get to that later.

Total Time: 512.5hrs