Top Skin

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Top Skin


Dcp01249.jpg (91378 bytes) To position and measure the bulkheads
I've put an extrusion on top and positioned the three builkheads at 90 degrees with the extrusion.  Then, I measured the distance between the bulkheads so I can pre-drill the center holes on the rear top skin.

My middle bulkhead is installed a little bit forward (10 or 15mm)of the plans specified position.  This is because at the specified position, it was deforming the fuselage, pushing it on both sides.  I also installed a 0.064 shim to make that bulkhead a bit higher.  In fact, that shim is quite good as it attaches the bulkhead with the longeron with several more rivets (2 in bulkhead flange, 3 in longeron).

Dcp01254.jpg (87652 bytes) Da da dA da dA....You can keep your hat on....
I cut the skin a bit larger than needed and drilled the three center holes to match the predrilled bulkheads.  The difficulty is in holding everything square... for the drilling phase.
Dcp01263.jpg (95223 bytes) Talking about square
We can't see it, but the center bulkhead is fixed in position using straps of aluminum (1/2" wide) clamped to the bulkhead, fore and aft and on both sides.  This is a fair starting point.  The key is in fixing the skin so nothing moves... I used duct tape liberally and I also clamped the skin at the front end so the assembly does not move during the drilling phase.

To drill, I work from inside-out, as shown in the sequence manual. 

Dcp01267.jpg (81402 bytes) One side done
One side is pre-drilled.  I taped the other side in preparation for drilling.  Only after it is taped and clamped at the front-end, did I remove the clecoes on the left side.  (notice that this is actually my second attempt.... I did not do that step on my first attempt and trashed the skin as a result).

As I did for the left side, I drilled from inside-out by working under the skin.

Dcp01268.jpg (81625 bytes) Quite impressive!
for me, at least.  Both sides are drilled to final size, except for the front bulkhead which I leave with #40 clecoes.  I will have to drill the top middle skin with it later.  To ensure that nothing moves when I do that (the middle top skin), I installed a few (6) 3/32" flush solid rivets.
Dcp01270.jpg (97837 bytes) The right side
As you can see, my skin is cut quite a bit oversize.  This is something I learned very early in the project.  It is easier to cut oversize and trim later after it is all drilled.
Dcp01271.jpg (67766 bytes) Those B2 and B3... ouf!
To bend the B2 and B3 frames, I filled the 3/4" X 0.035" tubes with sand and plugged the tubes at both ends.  This way, we can work the tube without undue risk of kinking it.

I used a variety of form blocs I had depending on the bending radius I needed.  This nose rib bloc was used for the more severe curves.

The layout have been drawn on computer so I have the required smooth curve... but beware!  The plans are not pefect!  A lot of fitting and rework are required when installing the tubes on the plane.

Dcp01273.jpg (82470 bytes) B3 being positioned
I used the upper longeron forming template as a straight edge to position the B3 tube.  It is in perfect extension with the rear top skin.  However, I found it very difficult to have the contour follow the top rear skin all around... eventually, I just tried a skin on and declare myself satisfied.
Dcp01274.jpg (85715 bytes) B2 with B3 (why not U2?)
The B2 tube required even more work than B3...  I ended up installing the skin to the side, rear bulkhead and B3 and then fit B2 in there.  
Dcp01275.jpg (95932 bytes) Stop working the tubes and go for it!
I was starting to feel that these tubes will never be perfect so I decided to stop and just go ahead and drill.  Well, this was a good idea and I am very please with the fit.  

I did a couple of things different from the plans... the rivet pitch on the longeron, between B2 and B3 is 30 instead of the mandated 40mm.  This eliminates some bulking that so many people complain about.  I also kept a pitch 40 instead of 50mm on the B2 tube for the same reason.  Finally, I installed a top skin of 0.020" in thickness instead of the mandated 0.016". This also helps. (note that my rear skin is also 0.020" just because I ran out of 0.016") 

Dcp01276.jpg (77260 bytes) The corner gusset
This was fairly easy to install, but make sure you don't attempt to install it square with the baggage shelf corner stiffener.  The last rivet hole may be closer to the upper longeron than you wish.

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Michel Therrien, (c) 1999 - 2003.