Spars Construction

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The spars are in my opinion the most important parts of the whole aircraft, as well as the ones requiring the most precision in manufacturing (0.5mm).  They hold everything together and they must wistand an important load (1200lbs*6g's=7200lbs).  I was quite anxious about starting to work on these parts.
 
Looks like the same routine
For all components, it always start the same way.... from an aluminum alloy sheet.  Out of that sheet, I cut the two outboard wing spars and, if I remember, the rear Z.  I used the remaining of the sheet to make other parts.
Making a precise cut
It is quite hard to make a precise cut.  One way that works quite well is with a straight edge and a knife.  However, with a little inattention, this method may allow for sliperage of the knife, resulting in an unfriendly mark in the metal.... something I did not want on a spar. 

As a result, I decided to use the straight edge to cut my worktable straight and then use the worktable as a guide to cut the sheet metal with a router.  This worked very well and my spar width varies very little over 8 feet.

The joy of amateur building...
While keeping part of an eye on the kids who are playing with their remote controlled cars, I was deburring and smoothening the lightening holes of my spar webs.  For details about drilling the holes, see the wing rib construction page.
Flanging the holes
The shape of the spar web after flanging the hole is not great... (banana).  I called Flypass about this and they said that it is normal  and installing the extrusion and L angles will solve this issue.
To cut the extrusions
I use a normal mitre box (with wood saw) to cut the extrusions.  It works well.
"Piloting" holes
I decided to use a multiple steps (a lot more than what is suggested in the manual) sequence.  My first step (after the extrusion is cut to 6.5 degree on one side and left a bit longer on the other end) is to pre-drill the extrusion as required with #40 drill bit.  Prior to drilling, I used a center punch to mark hole locations at every 40mm. 
Continue to pilot holes....
Once my angled extrusion (spar cap) is drilled, I drill the spar cap doublers with the same size of drill bit.  To ensure perfect alignment, I use short piece of L angle that is attached to the spar cap with a clamp.  I then push the spar cap doublers to squeeze it against the short L extrusion while I drill it.   As soon as I can, I install silver clecoes.

Once this is done, I then pre-drill the spar web using a similar technique (the L extrusion clamped to the spar cap).  However, I did it with a hand drill on the side of my work table (sorry, no picture).

No pilot anymore... the real thing
Once the spar cap is pre-drilled, the spar cap doubler is pre-drilled and the spar web is pre-drilled, I drill the whole "chibang" with a #20 drill bit.  Notice the clecoes... silver (3/32) on the right side of my drill and black (5/32) on the left. 

I did get a leaning experience when I did this on my first spar....  the stuff that gets into the drill bit needs to be removed!  At the beginning, I was happily drilling, not taking care of the aluminum staying in the bit from hole to hole.... well, after I noticed a resistance while taking the drill out of the hole, I decided to stop and look....  The holes were getting enlarged due to scrap aluminum in the bit that was grinding the hole bigger.... MAKE SURE THE DRILL BIT IS CLEAN ALL THE TIME!  As a result, I have 8 enlarged hole that will be redrilled with #12 bit for 3/16 rivets.

My first spar ready for rive^H^H^H^H deburring, sanding, polishing, cleaning and priming...
OK... I did not simply drilled the whole thing in one shot... however, the alignment of parts is simply perfect... the spar web is flush with the spar cap and with the spar cap doublers.

One I attained this step, I then marked the cut line on the spar caps at the outboard end, and I cut and grinded the caps to fit exactly with the web.

The technique for the center wing spar is very similar, but involves some additional steps due to the formed cap on top of the spar.

After deburring, smoothening, cleaning...
All parts are primed with Zinc Chromate replacement (I believe it is Zinc Oxide).  Note that the center spar is mostly primed. I primed only surfaces in contact (ok, the spray can primed a bit more than that) for the outboard wing spars.

If you are like me, this is one step that may really frustrate your wife!  I did this late in the evening.  The smell was so bad and it waked her up and she was really pissed at the project.  Not goooood....  I was then told that brush application of the primer would have been less offensive than the spary can.

Not alone on this project
My son really likes puzzles, Lego(tm) blocs and things like that... no wonder he always volunteer putting the parts back together..
Really proud of his accomplishment!
 
A critical step
I did not trust my ability to drill the spar attachment plates correctly.  So, my mentor graciously came home to help me (or, did I help him?) with this task.

Using trigonometry, we determined the position of the outboard wing relative with the edge of the table, 72" away from the junction of the spars.  It is quite simple...: y=72*sin(6.5)  and x=72*cos(6.5).  Everything was clamped in place prior to drilling the pilot holes (1/4"). Bolts were inserted before moving the assembly.

Mentor at work!
My drill press is in really bad shape after making all the lightening holes.  But being an expert, this guy can achieve good results with almost anything. I am still impressed when I think about how he corrected the shape of my 5/32" riveting head.
 

 

 

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