Some are having an issue going past page 9 of this Q&A so I am starting a new discussion.

Please note that the upgrade package kit goes well beyond just meeting the FAA’s conservative
methods and no changes are being considered.

Like previous Q&A's, post all your questions / concerns at the bottom of the last page of this Q&A.  If I do not have the answer, I will consult with Chris Heintz and or other engineers.
If you have a very technical question or just want to vent, call me at 705-526-2871.
Thank you for your continued support.
Mathieu Heintz
Zenair Ltd

Views: 2461

Replies are closed for this discussion.

Replies to This Discussion

We all want to be safe climbing towers or flying aircraft.

Experts are telling us that the aircraft does not have a flutter problem, structural load tests are telling us that the aircraft exceeds FAR 23 and meets the LSA requirements and an FAA report supports our upgrade 100%. The FAA is so confident about the upgrade and documentation supplied to them that they are allowing you and everyone else to fly the aircraft as per the AMD safety directive (5.2 Summary of Recommendations #1). The Germans, Dutch and UK did independent analysis and are now allowing the aircraft to fly once the upgrade is done.

Yes, the report is very hard on the original design but we are trying to move past that. Just like your tower climbing, there have been tower failures in the past but you continue to climb them as you are confident that the government and manufactures fixed these problems.

Unfortunately, the FAA cannot certify LSA's and not authorized to approve an LSA aircraft or say that the Zodiac 601XL / 650 meets the requirements of the LSA rule. That type of statement is approving a product. Yes, this is very political in nature and we are stuck in the middle. However, the Germans do issue type certificates and the aircraft in Germany is certified. It is my understanding that the German authorities did not even want the added UK aileron mass balance weights as they were satisfied with the flutter report.

Talking about the Germans, when the Dutch grounded the aircraft, the Germans went over the Zodiac file. They confirmed that the tests done by CZAW were incorrect and demanded that we redo them with new safety margins in place, even though these new safety margins are not part of the German regulation. Zenair did the new test and the aircraft did pass, without any changes to the original design. This is not important to USA owners as the aircraft in Germany is in the ULM category at a gross weight of 460 kg. What is important is that the FAA makes reference to the CZAW tests but not to the new tests that passed for Germany. And yes, the FAA did have access to this data and had the opportunity to discuss things with the Germans. So we need to be careful on how we read the report as the report is politically correct for the FAA, but more on that later.

The FAA is constrained by law to treat S-LSA planes differently from E-AB. That means little to owners and passengers.

With all the questions surrounding safety of the XL design I feel it is imperative that any testing suggested by normal and proper engineering practice be accomplished before risking the life of a passenger in my plane. The fact that the FAA can't force that testing on me because my plane is E-AB doesn't change my opinion about the needed for proper verification one bit.

If the only problem getting the proper testing done is lack of funds, I feel we can fix that. Considering how many owners there are, I am hopeful the cost of testing could be spread out enough that it would be less expensive than the upgrade kit.

I am satisfied enough with the safety implied by the massive structural changes to install them and take my plane into phase I flight testing. Since we never found the cause for all the accidents I am not convinced the design is now safe, so I would like to see all the normal and proper testing done before I take my plane into Phase II.

In answer to your question...and some comments..

There's a lot of unrealistic things being discussed here.

Having upgraded one wing, and started on the centre section, I can see an amazing amount of strength added to areas I see as important, areas I see as 'a good opportunity to upgrade at this point' and other areas to appease cosmetics.

Looking at my upgraded airplane, I feel VERY confident with it.

I think if the FAA can firm up there 'estimates' and agree with Chris what they would be happy with 'unestimated', he should be able to provide calculations based on the final upgrade kit.
Those calculations - documented for us to see, plus the load test so far, I feel would be ample to put this situation to a close.

I have full confidence in my airplane with the comprehensive upgrades. So, yes, I'm thrilled that it is safe. If Chris can publish calculations that the FAA agree pass their 5% estimate, I'd be even more thrilled.

350+ hours on my XL
Paul and Doug,
Good points and well noted. I am looking forward to exactly what the FAA wants. Doug, the report is very contradicting in nature and the FAA needs to clarify things.

One issue that really upsets me is that the 5% the FAA is talking about is based on "estimates" only. So here we are all worked up about 5% which is based on "estimates".


“4.3 Stress Analysis. An in-depth stress analysis was not performed on the structure of the CH 601 XL. However conclusions regarding the stress characteristics of the design were gathered”


" airfoil that appeared to be similar to the one incorporated into the CH 601 XL wing."

So we are dealing with an improper FAA evaluation of the aircraft based on "estimates" and not an in-depth analysis that we were hoping to get.

So as you can tell we are all frustrated.
We are getting good input from only a few Zodiac owners / builders. Would be great to also hear from you.

I find Doug Norman’s position well reasoned and I agree with it – this is political and requires political thinking. Wanting to complain about the FAA is very understandable but not productive. Unfortunately more testing may be the remedy to this mess. I sense that it is also unpalatable for Zenith because of the additional cost of more testing. Conducting a successful test will benefit Zenith because it will restore confidence in the brand. A successful test will benefit builders and flyers because it will restore value in their aircraft.

In this industry we have seen countless small aircraft companies go under because they get into a scrap and don’t have the funds to power through. Seems to me we are, as Doug says, almost to the goal line. If it turns out more testing is needed and money is needed to get that done we need to address that straight on.

We are conditioned as consumers to hold manufacturers accountable. If you buy a defective item you return it and demand your money back. Thinking that way is understandable but simply will not work in this situation. Whether we like it or not, we builders are in a partnership with Zenith. If Zenith is unable to do what is necessary to protect our investments it only makes sense for the builder community to help out in some reasonable way. Perhaps Zenith can cover some portion of the cost to keep some skin in the game. Of course in a group this large there will be those who can’t or won’t contribute. There will be those who will let others carry the load while they benefit. We should not be surprised or disappointed by that.

If collecting a pool of funds in necessary to enable adequate testing I suggest that pool be segregated from Zenith so it can not be taken through lawsuits. A dollar goal should be set and progress toward that goal should be posted, similar to fund raisers for charity. Perhaps donor’s names could be posted, at the discretion of the donor of course.

Steps for us to take:

1) Get over the shock of more bad news and stop whining
2) Learn what the FAA wants
3) Estimate cost to comply
4) If necessary establish a fund and a public fund raising system
5) Get the job done and behind us
6) Fly your Zodiac with confidence and enjoy life.


I agree with every point you made.

I would like to volunteer my time and potentially some funding to support this notion. I don't know how to set up such a system, but I suspect some sort of corporation or other legal entity is called for. I would be glad to work with you and any other well-meaning builders to establish a formal Zodiac builders and owners association. This could have as one of its stated goals to raise and expend funds to insure the Zodiac design is as good as it should be.

I think, unlike previous efforts in this area, everything done by the new organization should be open and "Public". I would like to see a severe limit on "Proprietary" information. The purpose of this group should be to have widely distributed information. This supports the goal of improving the public image of the Zodiac and would help with individual owner property values as well as manufacturer's public image.

Of course this group should work in concert with Zenith/Zenair/AMD. Also, it should be working in concert with FAA and NTSB. Indeed, we should invite all of those organizations to join in our efforts and supply whatever goods and services they would like to help the process along.

I hope anyone wanting to work toward this goal would include me in the process. My personal email is

Camas, WA
Here are my suggestions:
1) Find an attorney/builder who is among the 601XL builder/pilot community. Ask them to establish a non-profit corporation whose sole purpose is to perform testing on the aircraft. Some sort of board of directors (BOD) would need to be established. The BOD should be comprised of at least a couple of engineers who could offer advice as to proper testing protocol. No ZAC (or affiliated company) employees or owners could be on the board.
2) Solicit contributions to this corporation. Maybe they could be charitable contributions, maybe not. Regardless, contributors and directors should be shielded from any liability resulting from the activities of the non-profit.
3) The BOD would ask ZAC to sell a kit to the non-profit at a much reduced (as much as possible) price. They would also ask them to assist in making the fund raising efforts of the non-profit known to the builder community.
4) Current builders/pilots would be asked to volunteer to build a 650 airframe for testing purposes. Maybe a concentrated effort could take place in conjunction with Sun-n-Fun or AirVenture (or both). The aircraft would be built to the most current ZAC specs incorporating all safety mods published by them and AMD.
5) Conduct GVT testing on the airframe by an independent enginer hired by the non-profit.
6) Conduct a static load test to destruction/deformation on that same airframe, again performed by an independent engineer hired by the corporation.
7) Make the results public (not just to those who contributed).
8) Destroy the aircraft and recycle the aluminum.
9) Distribute any leftover funds to EAA and disolve the non-profit.

I was one of the initial contributing members of ZBAG, and this is really sort of a continuation of our initial mission. Maybe we could leverage some of the existing interested ZBAG community to assist.

The primary issue here is one of credibility of the design. This would provide a mechanism to either prove or disprove numbers based on a very plausible scenario (a kit built by amatuers to the most recent factory specs). If the results prove to uphold the current design claims, it should go a long way to insuring that the design stays viable and that current aircraft built or modified to those specs have a decent resale value.

Based on Mathieu's comments, it is clear that ZAC et al does not have have the financial resources to accomplish this, so whining about that won't help.

Doug Sire
As a new man to the group i rarely post anything, but here it gos. My zodiac was all but done when this got started. It has been my first kitplane and i have to admit I was quite proud of the finished product. Then the upgrade came about and it was a real setback (heartbreak) having to tear apart what I just got finished. I now am getting very close again to finishing it. With 4 years of work and roughly 50,000$ spent i am ALL FOR chipping in for more testing if the FAA feels it needs to be done. Having never flown my creation yet its hard to have alot of confidence in it when you hear so much negative. I am very aware of the dangers amoung experimental aircraft but I would like to be confident in the design before I get into flight testing ECT. Just my 2 cents. Greg
Hi Guys,

I have completed the wing upgrades and this last weekend the center spar upgrade.

None of this has yet been re-installed into the aircraft as yet, however the increase in the strength as a result of the upgrade is very obvious once its has been done.

I know my statements carry no engineering proof, but for anyone who has done the upgrade the improvement is obvious, what was a flimsy center spar if now a solid structure.

Even though it would be nice to see the wing / center spar re-tested to identify what its new maximum load carrying ability is, at present I feel no hesitation with re-assembling my aircraft and resuming flight.

Like others am trying to get my head around the sequence of events ,please correct me if I am wrong.!
1.It is now very clear from the FAA report that the original WING design was not strong enough to hold the advertised 600KG MAUW at +6 -3 ULTIMATE loads ,period .
As most of Europe operate this aircraft with the SAME WING STRUCTURE at 450kg MAUW it is hardly surprising that the were happy with their load test results,BUT to these LOWER limits!.
2.Was the ORIGINAL STANDARD WING tested to these calculated 600kg loads PRIOR to fitment of the EXTRA MATERIAL listed on the last page of the Canadian load test report?
Once again correct me if I am wrong but the way I read this ,is that the STANDARD wing was showing severe signs of premature bucking some 20-30% below the required pre calculated ULTIMATE load for 600kg-The tested was halted at this point and the wing was modified to include the EXTRA MATERIAL found on the last page of the load test report. (THE SAME UPGRADE PARTS FOUND IN THE FIRST DRAFT DRAWINGS 8TH NOV 09- albeit with a 0.032"root doubler of the same profile as the 0.064" one in the drawings ).

This MODIFIED airframe was reloaded and this time the test was halted some 5% below the UTIMATE loads pre calculated by the FAA as once again it was failing ,although it was -ALMOST GOOD ENOUGH.

WING -You then redesigned the root doubler completely out of 0.125" plate now extending further into the wing ,you added 0.040" additional nose rib angles FULL DEPTH ,you added span wise L-angles to the wing skins .

CENTER SPAR SECTION -you added additional vertical spar uprights ,extended the legs on the top and bottom 0.063" angle doublers to allow them to be solid riveted to the 11/2"x1/4" SPAR CAP BARS thus creating a strong box section across the top ,and upgraded the wing attachment bolts to NAS grade.

You did not LOAD test these later developed upgrades as everyone had long gone and your test airframe was wreaked from the previous test .

For me ,these additional mods ,and everything else we now have in the LASTEST 25th Jan 2010 UPGRADE DRAWINGS more than makes up any 5% shortfall in comparison to your first MODIFIED VERSION .

Its such a pity you didnt add $150 to the price your upgrade kits ,a thousand sold would provide you with $150 000 -probably several times more than enough to cover the cost of a bare fuselage ,wing set ,and a few tons of shingle,I am sure you would get numerous qualified Engineering witnesses to attend for free.

This would have put this wrong saga to bed once and for all !.
Why dont you do this? -Re-test and PROVE you structure and put this story to an END .
In the long run it may also do your business some good.
All last 6 comments are good.
If you guys want more reassurance than what we presently have to offer, the first thing needed is a reputable aeronautical engineer to go over the FAA's and Chris Heintz's data. This engineer should have a good understanding of the LSA rule. ZBAG had used an engineer, who could do this for all or you.

There is no point doing anything else such as load testing until the engineer confirms that our test was short of the LSA rule.


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