Q&A - Zodiac 601XL -650 for the latest upgrade drawings of November 24 2009

This Q&A is for the upgrade kit of the Zodiac 601XL & 650 based on drawings of Nov. 24, 2009 and AMD Safety Alert of November 7. 2009

New drawings:
Nov. 24, 2009: We've updated the draft Drawings 6-ZU-1, 6-ZU-2, 6-ZU-3 and 6-ZU-4, and LAA Aileron Balance.

For very detailed questions (or if you must complain or vent), email me at newplane@gmail.com

Please post all your questions on the last page.

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Replies to This Discussion

Solid rivets are preferred as they fill the inside of the hole. This removes some of the stresses made by the hole area. Also, if installed properly, solid rivets will never move in the hole and there are no nuts that could get loose if not properly installed. No torque values to worry about etc.

With bolts and if installed correctly are extremely effective. When torqued correctly, they squeeze the material together which helps spread the loads past the hole. When using the bolts, it is important that the bolt fit tightly in the hole. Use the torque value as specified in AC 43-13.

Do I need any supports under the fuse when I remove the center section? It looks like just the main gear and nose wheel are OK from your photos.


Peter. Wonthaggi Australia
Yes, the fuselage is stiff enough without the center spar.
I have started a separate discussion directed specifically toward concerned builder/owners of 601XL aircraft already certified in the Experimental-Amateur Built category. This discussion is not about how to implement the published modifications, but about other alternatives. This discussion does not apply to S-LSA or E-LSA aircraft, and is probably irrelevant to not-yet-certified E-AB aircraft, unless the FAA changes its directions to the DAR community. This discussion is called What about already-flying E-AB 601XL's?

I would like to invite builders/flyers of already-certified 601XL's to visit that discussion group, read and comment about the open letter I have uploaded there (and also made available on-line at http://members.cox.net/n601ge/mods/ .

Andy Elliott, N601GE, 601XL/TD, Corvair
1 year and 145 flying hours so far.
Hi Andy,

I read your post and and it was well done. I understand the frustration that you and the other finished builders must be going through opening up a perfectly good airplane and making modificatons. My fuselage and wings were finished and I was planning on painting this winter,.I already have the bottom of the plane painted.

On the other hand, Zenith is offering me a way to strengthen my plane by 20% for a cost of around $350 in parts, and what I figure will be around 100 hours of labor! After watching the videos, I agree with the changes made and even though I am not an engineer, I can see where the changes will make a much stronger airplane for just a few extra pounds.

To me, it's a no brainer! I'm making, and I am welcoming the changes, my plane will be worth more in resale, and I can take up passengers with an added confidence. The icing on the cake, so far the Company has bent over backwards to help us. This never happened with the last 2 homebuilts I was involved with.

I don't want to change anyones minds, I just want to give you my opinion and post what I am doing. Would I fly in an unchanged 601 XL, YES.

One quick word to my friends who have a 601 XL LSA. From what I have seen in these posts, I have seen FBO's advertise that they can do the change for $2500 - $4500 + parts. As time goes by, other FBO's and A&P's will step up and offer their services. These changes are not that hard. This is less money than what some builders have in their glass instruments! If these accidents never happened, and Zenith stepped up and said we can make the plane stronger by 20% for $2500 to $4500, would you make the changes? I would.

If anyone in Wisconsin is making the change, call me at 920-237-1450. We can share the shipping costs and the experience. I am opening up my wings this afternoon.

Joe in Oshkosh
Hi Mathieu
I have a few questions,

1 Which rivet hammer should be use for the solid rivets a 3X or a 4X ?

2 What nuts and bolts are not included that we will need to purchase separately?

3 Is using a drive pin to mark the holes for the wing mounting bolts through the .125" wing root spar doubler the most accurate way to locate the holes or should we use a 5/16" bolt drilled out to say 5/32" on a lathe and insert it into the holes and drill through it get dead center, or is there a better way?

Thankyou in advance for your ongoing support.

Phill Barnes
A 2X or 3X rivet hammer is fine. There is a good chart at:

Zenith is trying to include all the hardware in the $352.00 upgrade kit. This will include the new NAS bolts with shear of 160,000 to 180,000 PSI. Tougher bolts are required since we are adding extra material at the spar caps.

For those of you who are not purchasing the upgrade kit, a good source for hardware is:

Yes, using a drive pin works great if you have on. I believe that Zenith used this. The other option is to use an old AN 5/16" as you mentioned.
Hi Mathieu,

I am concerned about the discontinuity at the 1680mm location between the existing spar angle and the new extrusion angle. Do you see any reason not to continue the new 6-ZU-1-1 extrusion outboard to just short of RR #8? (Other than having to R&R more solid rivets.)

Thanks to you and the other folks at Zenair for all of your efforts. I'm sure all of this work will result in a superior aircraft that will be safer for first time builders like me, and hopefully that will translate into improved sales for Zenair!

We exceeded the ultimate load test by quite a bit with the existing 6-ZU-1-1. The main purpose of 6-ZU-1-1 is for potential bending of the spar caps (bending forward or rear) and not for shear. Bending loads further out on the wing are very small and existing caps are more than enough.

So if you want to continue with 6-ZU-1-1 out to RR#8, that is fine but you are just adding weight.
I was originally concerned about this also, so I thought I would share a bending stress model of the spar I made a few weeks ago. This is for an UNMODIFIED spar. It only considers the spar and not the skins, but does account for the rivet holes. I used the loading figures and load placement provided by the document that zenith posted that documents the load test performed. I believe this model is fairly accurate, because the deflection caculations were close to the ones Zenith measured durring their load test. I guess I should have paid more attention statics and dynamic classes in college. Assumming this graph is correct the only part of the spar that would be overloaded is the first few inches of the root.

One other thing of interest. I found out by increasing the load out on the tip of the spar by only small amounts would very quickly overload the root area, so be careful with sudden full aerilon movements.
So my understanding is that you completed the attached stress report on the original UNMODIFIED wing. Based on that, I hope that you are satisfied with the upgrade as we are adding 0.125 to the caps.

Regarding the ailerons, Chris has said many times now that abrupt manoeuvres above the manoeuvring speed is not permitted. However, with the upgrade, we are significantly stiffening and reinforcing the rear spar, skins etc.

Also, note that the Static load test that Zenith posted is for the ASTM SLSA category which is tougher than FAR 23 for light aircraft. Most engineers agree that the original spar section at the root just passes when calculated to FAR 23. When performing the static load tests to Ultimate according to the SLSA rule (not FAR 23), what is required is that the airframe does not break for 3 seconds (at ultimate). We accomplished this and than added a lot more weight. After the test, we added another 0.093 to the root area. 0.032 to 0.125 (part number 6-ZU-1-2), and also added a lot of extra things to the airframe. Again, these things were added after passing the load test past ultimate.

The fore/aft bending loads at 1680mm are what I am concerned about; from the static testing it appears the new design has the wing sheer loads well under control. My thought is to get the end of the new 6-ZU-1-1 angle outboard of the aileron pushrod hole that is in the rear spar, in order to strengthen that section of the wing assembly. It's probably a belt and suspenders approach, but it is about 1 lb per wing and a few more solid rivets so why not as long as there are no objections. Thanks much.



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