Q&A FAA Special Review Team Report - Zodiac 601XL/650 - FAA clarification letter

This Q&A is about the FAA's clarification letter of March 8th, 2010.

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 or email me at newplane@gmail.com

Thank you for your continued support.
Mathieu Heintz
Zenair Ltd

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To all,
So here we start again after a relaxing week in this Q&A. Please see the FAA response letter attached here.
So I think that the FAA letter does clarify the type of tests and reports they would like us to do.

"...it is acceptable for AMD to use stress analysis to resolve the five percent difference between the maximum loads sustained in the company’s September 2009 static test and FAA estimates of the maximum loads".

Chris Heintz already completed the load calculations showing that with the latest upgrade kit, the structural areas of concern exceeds the 5%.

Chris's report states:
The 1.25" aluminum plate at the root increases the strength in that area by 16.5%,
The AN5 bolts were replaced by NAS increasing the bolt strength and stiffness by some 25%.
More reinforcements as per drawing 6-ZU-2 were also incorporated.
All these reinforcements increases the possible loads in bending from 2,084 to 2,500 kg m (+20%), in shear and torsion from 1,252 to 1,560 kg (25%), -300 to -375 kg m (25%).

It is my opinion that the airframe structure with the upgrade is more than what the FAA is looking for. I believe that any reputable aeronautical engineer will have a hard time proving that the Zodiac 601XL & 650 structure does not meet the LSA ASTM rule.

However, if a lot of existing owners are still not comfortable with this, I recommend that they hire a reputable aeronautical engineer to redo the complete stress analysis of the aircraft.

Flutter.
The FAA clarification letter states:
Regarding flutter: Based on the service history of the aircraft, the original aircraft design
did not meet paragraph 4.6 Vibrations, which states:
4.6 Vibrations—Flight testing shall not reveal, by pilot observation, heavy
buffeting (except as associated with a stall), excessive airframe or control
vibrations, flutter (with proper attempts to induce it), or control divergence, at
any speed from VSO to VDF.

If the FAA is talking about the AMD SLSA aircraft, I do not know of anyone stating that their aircraft had heavy buffeting (except as associated with a stall), excessive airframe or control
vibrations, flutter (with proper attempts to induce it), or control divergence, at any speed from VSO to VDF.

If we are talking about the Experimental aircraft, yes, we have had customers stating some of the above. However, all of them confirmed that their control cable tensions were not to spec or control stops were not installed etc. Bottom line is that I do not know of a single Experimental XL or 650 that has heavy buffeting (except as associated with a stall), excessive airframe or control
vibrations, flutter (with proper attempts to induce it), or control divergence, at any speed from VSO to VDF, when built and rigged properly.

The large FAA report does not state flutter as the cause of the accidents but they do recommend that "you go beyond the basic ASTM flutter requirements and perform a complete flutter investigation (GVT, flutter analysis, and flight test) accomplished by a noted flutter expert".

I agree that its maybe good idea to do some type of additional flutter testing as this issue will not go away until we do. If we do a GVT, flutter analysis, and flight test, the costs will exceed $50K. Can we pool that much or do we settle for a flight test only. Also, the German GVT and flutter analysis (one GVT and flutter analysis was done on the 601XL and another separate one for the 650). Both reports were done without the aileron balance weights and passed. So if we redo some of the tests, do we do them without the balance weights?

When responding to the FAA clarification letter, please remember that this is a very emotional issue, so lets respect each other when posting responses on this site. For those who want to release some steam, call me at 705-526-2871 or email me at newplane@gmail.com
I'm still trying to figure out why we had to rip open a perfectly good airplane. The upside is that it has been worth the extra 60+ days I spent improving my XL :-)

Jake
Stress analysis to resolve the five percent difference between the maximum loads sustained in the company’s
September 2009 static test and FAA estimates of the maximum loads.

Chris completed a 9 page report with graphs and charts detailing the extra load margins of the latest upgrade. So yes, Chris is proud to say that the stress analysis that the FAA is talking about is complete.

If someone is in doubt about this, hire an aeronautical engineer who can than go over all the data. The FAA will not state that the aircraft meets the requirements as this would put the liability on them. So again, if in doubt about the stress analysis or structure of the aircraft in general, please hire an aeronautical engineer to go over the data.
Jake,
Glad to hear that you are improving your XL. You are a logical person and from what I can gather, you do not let your emotions get the better of you.
Cheers to that.
Mat,

Thanks for posting this.

It seems like "a flight test only" would be the right thing to do.

..lance
Steve,
Sounds like you did an excellent job and good to hear that you are enjoying your great little aircraft. You are correct about the 0.125".
I know that you are respecting the aircraft limitations but for all you out there, the overall g loads of the aircraft has not increased with the upgrade.

Here is what is posted in the AMD POH:
LOAD FACTORS (LIMIT):
Flap up: + 4 g / -2 g
Flap extended: + 2 g / 0 g

PROHIBITED MANEUVERS:
Intentional spins prohibited.
Aerobatics prohibited.

WARNING
Exceeding the maximum load factors will lead to an
overstressing of the airplane.
Saturday three upgraded Zodiacs took to the skies. Alan flew his plane home to Shelton WA (645 miles).
I followed along as far as Grants Pass OR and then returned home (638 miles).
As I flew past Cloverdale, Doug came out to meet me.

http://www.zenith.aero/photo/albums/three-upgraded-zodiacs-go

Fantastic guys.
I was just wonder how this blog is considered "non-model specific;" why it, and the last couple of blogs, have not been in the Zodiac series section where more people would logically stumble across it? Thanks.
Ted,
This was considered but it was decided to post things here as to not give anyone the impression that we are hiding things. Now that we are getting into the details, it may be a good idea to move things over to the Zodiac builders section.
Mathieu, thanks.

Ted
Mathieu - Glad you did post it where everyone can see. I looking at airframes now for my next build and the 650 looks like it will be the one. I already scratch built a 701 and enjoy flying it. Thanks for the posting. - Chris Aysen / Louisiana.
Hi Steve: what is the glide ratio on 601XL Harold Gochenouer

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