Part 23: Installing the "Upgrade Package" to our Zodiac CH 601 XL: Re-Installing the Center Spar in the Fuselage

Continuing on where we last finished, now we re-install the "upgraded" wing center spar section into the fuselage and position additional fuselage doublers:

First we installed the beefed-up Front Wing Uprights (6-ZU-2-6). This replaces the original Wing Uprights (6B13-1) with the heavy duty .125-inch Front Wing Uprights. We are forced to drill a new row of holes parallel to the original row for the new Uprights (to accomodate both the wider upgraded center spar and the thicker Uprights). Below: the clecoed pilot holes for the new Uprights:

The Front Wing Upright (6-ZU-2-6) positioned in front of the center spar (view of the right side from inside):

Then we position and drill the outside Upright Doubler (6-ZU-3-5) on each side of the fuselage. The flat .032-inch plate overlaps on the outside of the fuselage side skins and covers the holes of the original Wing Uprights.

After back-drilling it, we cleco the outside Upright Doubler (6-ZU-3-5) in place:

In our demonstrator Zodiac CH 601 XL, we also replaced the center console between the seats and the right side seat bottom, due to "wear and tear" on the factory demonstrator plane...

Now we installed the Side Doublers (6-ZU-3-2), .063-inch plates positioned on the insides of the fuselage assembly sides behing the main spar. The view below is the Side Doubler on the left side, viewed from under the seat:

View from the outside where the Side Doubler is positioned:

Here is the "Z-angle" diagonal stiffener, after being positioned and drilled (on both sides of the fuselage) in front of the main spar:

With the center spar section still clecoed in place in the fuselage, we position and drill the Bottom Skin Doubler (6-ZU-2-9) along the bottom of the fuselage. Like the Upright Doubler, this is to cover the original holes drilled throught the floor skins for the center wing spar section:

Steve clecoes the Bottom Skin Doubler in place as Roger back-drills the existing rear center spar holes into the doubler.

We drilled a new rivet line along the forward edge of the Bottom Skin Doubler, and then backdrill the forward center spar holes into the doubler.

We then removed the center spar section to finish drilling and riveting the Top Doubler - we did this now only after we were able to verify the parts and fit:

...and we rivet it together:

Here's the first of two video clips:

After having riveting the Top Doubler and re-installed the spar center section, we positioned and drilled the bottom skin doubler (6-ZU-2-9) on the bottom of the fuselage, and then deburred and readied all the parts for riveting back together:

December 14 Update:
This past weekend Roger Dubbert from the Zenith factory attended Gus Warren's Zodiac CH 601 XL "Upgrade Workshop" in Edgewater, Florida. Below, Gus drills out rivets of the center spar section:

Roger was happy to meet with builders in Florida and for the opportunity of going over the upgrade package kit:

Gus Warren is an A&P mechanic and flight instructor, and he has extensive experience building and maintaining Zeniths. Gus is making his services available to builders who need help with the Upgrade Package installation. Contact Gus directly at 386-316-6324 or 505-363-9221.

We're pleased to have started shipping out Upgrade Package kits this week!

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Comment by John D Hirn on December 15, 2009 at 9:02am
Thanks to Roger,Gus and all the guys who attended the workshop at Fly with Gus in Edgewater Florida this past weekend. All of the practice work was performed carefully and professionally. We will finish it up this week because of the great head start you gave us. It was a great weekend and I enjoyed meeting all of you.
Jack Hirn
Comment by Larry on December 15, 2009 at 6:14am
Sebastien, I am still building the fuselage and I was wondering if I have not drilled the holes for the uprights yet, is the doubler still needed on the side of the fuselage. Looking at the thickness, I would think so, but I wanted to make sure. Also, is the doubler needed for the front bottom pan, if the holes are not yet drilled for the center spar.


Comment by Scott Thatcher on December 14, 2009 at 8:38am
Roger suggested that we place a support under the tail in order to avoid any wrinkling of the skin once the center spar and upright were removed. And it was necessary since we could see that any pressure on the tail at that point without the support would allow the skin to wrinkle and you are bound to have visitors while doing the upgrade who are not aware of the fragile nature of monocoque structures. This suggestion was made during the 2-day training session at Gus Warrens hangar in Edgewater, FL.
Comment by Scott Thatcher on December 12, 2009 at 9:08pm
Roger. Thanks for being there at the Edgewater, FL Upgrade training class held at Gus Warren's hangar ( The information supplied by you and Gus really helped tremendously. I had never even handled a bucking bar before but now I know a 3X from a 2X, a number 6 rivet from a 5, how to remove rivets like a pro and even how to buck them perfectly (from my vantage point). Also thanks to Jack for donating a 601XL for wing removal and training purposes. This was a great 2 day training program and it went really well.
Comment by Stephen Mineart on December 12, 2009 at 8:29am
What hardware if any is included in the Upgrade Kit? If we can be procuring hardware needed, are the 12/02 plan drafts the final word on what is needed? Do you supply the Avex rivets?
Comment by Richard Simmons on December 11, 2009 at 8:24pm
All that is left to see is the Aileron control tube supports/reinforcements.
Looks good I think! I am happy to see the improvements.
I dont look forward to the extra work but I am looking forward to see the light
at the end of the tunnel.

Hopefully, our planes will prove to be all we expected!

I can't wait!

Comment by Dan Dempsey on December 11, 2009 at 7:29pm
Excuse a dumb question. Is there a reason the doublers can't be on the inside of the skin?
Comment by Phill Barnes on December 11, 2009 at 6:08pm
Thanks Sebastien
These videos have cleared up a lot of niggling little questions that I had.


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