Q&A FAA Special Review Team Report - Zodiac 601XL/650 - Zenith Aircraft Builders and Flyers2024-03-29T08:47:23Zhttps://zenith.aero/forum/topics/qa-faa-special-review-team?commentId=2606393%3AComment%3A49606&x=1&feed=yes&xn_auth=noI GUESS I AM ABOUT 80% FINISH…tag:zenith.aero,2010-03-09:2606393:Comment:496062010-03-09T01:03:58.565Zcharles leonardhttps://zenith.aero/profile/charlesleonard
I GUESS I AM ABOUT 80% FINISHED WITH THE MODIFICATIONS ON MY 601. AS SOON AS IT IS FINISHED, I AM GOING TO TAKE IT BACK UP AND ENJOY WHAT I BELIEVE IS A GREAT AIRPLANE.<br />
WHILE I BELIEVE THIS FORUM IS GREAT FOR LETTING OFF STEAM, I HAVE NEVER HEARD SUCH BULL FROM PEOPLE WHO KNOW NOTHING ABOUT AIRCRAFT DESIGN. IF YOU DO NOT TRUST ZENITH OR YOUR AIRCRAFT, JUNK IT AND FIND A NEW HOBBY.
I GUESS I AM ABOUT 80% FINISHED WITH THE MODIFICATIONS ON MY 601. AS SOON AS IT IS FINISHED, I AM GOING TO TAKE IT BACK UP AND ENJOY WHAT I BELIEVE IS A GREAT AIRPLANE.<br />
WHILE I BELIEVE THIS FORUM IS GREAT FOR LETTING OFF STEAM, I HAVE NEVER HEARD SUCH BULL FROM PEOPLE WHO KNOW NOTHING ABOUT AIRCRAFT DESIGN. IF YOU DO NOT TRUST ZENITH OR YOUR AIRCRAFT, JUNK IT AND FIND A NEW HOBBY. Paul, I understand you concer…tag:zenith.aero,2010-03-08:2606393:Comment:495932010-03-08T23:41:40.537ZKen Pavlouhttps://zenith.aero/profile/KenPavlou
Paul, I understand you concerns and desire to put all this behind us once and for all. But dude, give it a rest. Your condescending beratement of Mathieu is getting tiresome. Mathieu never insinuated that he makes engineering decisions nor does he pretend to be an engineer.<br />
<br />
The FAA in essence agrees that the structural modifications address the issues surrounding thr 601. It is now a matter of CYA. I don't believe the FAA, NTSB, or any government agency is going to proclaim the that the 601 is…
Paul, I understand you concerns and desire to put all this behind us once and for all. But dude, give it a rest. Your condescending beratement of Mathieu is getting tiresome. Mathieu never insinuated that he makes engineering decisions nor does he pretend to be an engineer.<br />
<br />
The FAA in essence agrees that the structural modifications address the issues surrounding thr 601. It is now a matter of CYA. I don't believe the FAA, NTSB, or any government agency is going to proclaim the that the 601 is 100% safe and structually sound no matter what Zenith does or how many tests and engineering reviews are performed. The most we can expect from the FAA is a statement to the effect that the 601 meets ASTM standards. Standards which they themselves feel are inadequate in certain respects to begin with.<br />
<br />
Ultimately it boils down to personal decision and comfort level. We review the available information and make an educated decision to build, buy or fly a 601. Hi Doug,
Perhaps I am all we…tag:zenith.aero,2010-03-08:2606393:Comment:495912010-03-08T23:33:53.226ZPaul Mulwitzhttps://zenith.aero/profile/PaulMulwitz
Hi Doug,<br />
<br />
Perhaps I am all wet here. However, it seems to me Mathieu is trying to compare numbers like "missed total load by 5%" and "Improved by 15%" as being proper to directly compare. He tried to make the same argument weeks ago before getting the latest letter from the FAA guys and it didn't satisfy them then. I don't see how it will satisfy them now.<br />
<br />
It seems to me like comparing apples and oranges. Of course, I am not a qualified aeronautical engineer. That means I am not qualified to…
Hi Doug,<br />
<br />
Perhaps I am all wet here. However, it seems to me Mathieu is trying to compare numbers like "missed total load by 5%" and "Improved by 15%" as being proper to directly compare. He tried to make the same argument weeks ago before getting the latest letter from the FAA guys and it didn't satisfy them then. I don't see how it will satisfy them now.<br />
<br />
It seems to me like comparing apples and oranges. Of course, I am not a qualified aeronautical engineer. That means I am not qualified to make such comparisons. My point is that Mathieu isn't either.<br />
<br />
This whole process could fall apart if communications with the FAA are not handled properly.<br />
<br />
I just don't understand why Zenith/Zenair/Amd engineers are not involved in this whole communication process. Are there any engineers left at these companies?<br />
<br />
Best regards,<br />
<br />
Paul Hi Mathieu,
The way I read t…tag:zenith.aero,2010-03-08:2606393:Comment:495702010-03-08T21:38:22.576ZPaul Mulwitzhttps://zenith.aero/profile/PaulMulwitz
Hi Mathieu,<br />
<br />
The way I read the current letter, the FAA is asking that the analysis be done now rather than accepting the previous analysis you seem to think solves the problem.<br />
<br />
The letter clearly states flight testing is sufficient for meeting the FAA requirement for flutter analysis, but I think you need to think about this a little. If you can find a "Noted Expert" on flutter who will perform the flight test without any ground testing then that might be a good choice. However, I doubt any…
Hi Mathieu,<br />
<br />
The way I read the current letter, the FAA is asking that the analysis be done now rather than accepting the previous analysis you seem to think solves the problem.<br />
<br />
The letter clearly states flight testing is sufficient for meeting the FAA requirement for flutter analysis, but I think you need to think about this a little. If you can find a "Noted Expert" on flutter who will perform the flight test without any ground testing then that might be a good choice. However, I doubt any such expert would be willing to do that. Also, you might expect there is at least a small possibility of loss of the aircraft when high speed flutter flight testing is performed. This is one of the expected outcomes of such a test on any airframe. I guess you need to compare the cost of the ground testing against the possible loss of the aircraft before making a final decision on this point.<br />
<br />
As others have said, I suggest you get an engineer to discuss the requirements with the FAA. You are just not qualified to make engineering decisions. You have said many times you are not an engineer, but you are in a position to hire one. Indeed, I thought you already have several engineers working for you. I think we all would gain if you got someone who speaks "Engineer" to discuss this with the FAA folks.<br />
<br />
I really don't understand why you continue to pretend to be an engineer. These issues need to be resolved with the FAA and your saying you think their requirements are already met does nothing to actually make them go away.<br />
<br />
I know you feel you are in charge of this whole mess, and indeed you are. I fear if you don't meet the FAA's stated requirements they will, once again, ground all the Zodiacs.<br />
<br />
Paul<br />
Currently installing upgrade. To all,
So here we start agai…tag:zenith.aero,2010-03-08:2606393:Comment:495652010-03-08T20:53:17.196ZMatt Heintzhttps://zenith.aero/profile/Mat
To all,<br />
So here we start again after a relaxing week in this Q&A. Please see the FAA response letter attached here.<br />
So I think that the FAA letter does clarify the type of tests and reports they would like us to do.<br />
<br />
"...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".<br />
<br />
Chris Heintz already completed the load calculations showing that…
To all,<br />
So here we start again after a relaxing week in this Q&A. Please see the FAA response letter attached here.<br />
So I think that the FAA letter does clarify the type of tests and reports they would like us to do.<br />
<br />
"...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".<br />
<br />
Chris Heintz already completed the load calculations showing that with the latest upgrade kit, the structural areas of concern exceeds the 5%.<br />
<br />
Chris's report states:<br />
The 1.25" aluminum plate at the root increases the strength in that area by 16.5%,<br />
The AN5 bolts were replaced by NAS increasing the bolt strength and stiffness by some 25%.<br />
More reinforcements as per drawing 6-ZU-2 were also incorporated.<br />
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%).<br />
<br />
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.<br />
<br />
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.<br />
<br />
Flutter.<br />
The FAA clarification letter states:<br />
Regarding flutter: Based on the service history of the aircraft, the original aircraft design<br />
did not meet paragraph 4.6 Vibrations, which states:<br />
4.6 Vibrations—Flight testing shall not reveal, by pilot observation, heavy<br />
buffeting (except as associated with a stall), excessive airframe or control<br />
vibrations, flutter (with proper attempts to induce it), or control divergence, at<br />
any speed from VSO to VDF.<br />
<br />
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<br />
vibrations, flutter (with proper attempts to induce it), or control divergence, at any speed from VSO to VDF.<br />
<br />
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<br />
vibrations, flutter (with proper attempts to induce it), or control divergence, at any speed from VSO to VDF, when built and rigged properly.<br />
<br />
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".<br />
<br />
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?<br />
<br />
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 My TD 601XL has centering spr…tag:zenith.aero,2010-03-07:2606393:Comment:493582010-03-07T07:09:37.559ZAndy Elliotthttps://zenith.aero/profile/AndyElliott
My TD 601XL has centering springs to keep the pedals from flopping around. They are not sufficient to apply any significant tension to the cables, maybe 3#. Yes, it takes a <u>lot</u> of rudder after takeoff to keep the ball centered, and any time I'm in a high-power climb attitude. The aircraft trim, in general, is <u>very</u> sensitive to power and attitude changes. Welcome to the world of light aircraft!<br />
<br />
I use large trim tabs on the rudder to center the ball for cruise conditions.<br />
<br />
There is…
My TD 601XL has centering springs to keep the pedals from flopping around. They are not sufficient to apply any significant tension to the cables, maybe 3#. Yes, it takes a <u>lot</u> of rudder after takeoff to keep the ball centered, and any time I'm in a high-power climb attitude. The aircraft trim, in general, is <u>very</u> sensitive to power and attitude changes. Welcome to the world of light aircraft!<br />
<br />
I use large trim tabs on the rudder to center the ball for cruise conditions.<br />
<br />
There is one other TD 601XL and he also has springs, and trim tabs. Am I correct is assuming that…tag:zenith.aero,2010-03-07:2606393:Comment:493532010-03-07T04:51:57.918ZBob Pustellhttps://zenith.aero/profile/BobPustell
Am I correct is assuming that the taildragger version does not have a rudder cable tension setting? Unless you build in some sort of left and right pedal interconnection bellcrank (which is not in the plans), the two cables are not connected to each other in any way, typical of most taildraggers. My Stinson (and many other taildraggers) just has springs to hold the pedals forward against the cables, so the only cable tension is the tension of the springs. I intend to put springs on my 601XL…
Am I correct is assuming that the taildragger version does not have a rudder cable tension setting? Unless you build in some sort of left and right pedal interconnection bellcrank (which is not in the plans), the two cables are not connected to each other in any way, typical of most taildraggers. My Stinson (and many other taildraggers) just has springs to hold the pedals forward against the cables, so the only cable tension is the tension of the springs. I intend to put springs on my 601XL pedals, even though there are none in the plans (that I have seen yet, at least, have not looked in great detail because I am not that far into the build). Just a thought on the hard ru…tag:zenith.aero,2010-03-07:2606393:Comment:493452010-03-07T03:06:31.489ZDoug Duggerhttps://zenith.aero/profile/DougDugger
Just a thought on the hard rudder movement after take off. Go back and look at your rudder cable tension with the nose wheel off the ground. You may have way to much tension on the cables if you adjusted them with out raising the wheel off the ground, it slides forward when leaving the runway to settle in the cradle. As I said just a thought.
Just a thought on the hard rudder movement after take off. Go back and look at your rudder cable tension with the nose wheel off the ground. You may have way to much tension on the cables if you adjusted them with out raising the wheel off the ground, it slides forward when leaving the runway to settle in the cradle. As I said just a thought. Thanks fellas, Keep up the go…tag:zenith.aero,2010-03-05:2606393:Comment:492202010-03-05T03:03:30.442ZDave Millerhttps://zenith.aero/profile/DaveMiller12
Thanks fellas, Keep up the good work.<br />
Dave
Thanks fellas, Keep up the good work.<br />
Dave Dave,
It is my understanding…tag:zenith.aero,2010-03-02:2606393:Comment:489512010-03-02T15:31:17.893ZMatt Heintzhttps://zenith.aero/profile/Mat
Dave,<br />
It is my understanding that we have not had problems with the fuel tanks or fittings or lines. So if nothing is leaking, I would not change things.<br />
<br />
Here is Rogers answer from Zenith.<br />
The fuel tanks and fuel lines were in great shape, but I replaced the fuel lines and cleaned the finger screen in the tank.<br />
<br />
On another note, I got a comment from a customer who is flying again after the upgrade.<br />
"...after take off one has to press on the rudder petals quite hard to center the ball..."<br />
<br />
My…
Dave,<br />
It is my understanding that we have not had problems with the fuel tanks or fittings or lines. So if nothing is leaking, I would not change things.<br />
<br />
Here is Rogers answer from Zenith.<br />
The fuel tanks and fuel lines were in great shape, but I replaced the fuel lines and cleaned the finger screen in the tank.<br />
<br />
On another note, I got a comment from a customer who is flying again after the upgrade.<br />
"...after take off one has to press on the rudder petals quite hard to center the ball..."<br />
<br />
My answer to him was:<br />
<br />
Take a look at the 55 page pre-flight check list, Nose wheel area.<br />
<br />
Line 107. "Inspect nose gear self centering at full deflection left and<br />
right. Nose wheel must snap back to center by itself."<br />
<br />
Also see line 190.<br />
<br />
<a href="http://zenithair.com/zodiac/xl/data/601XL-PRE-FLIGHT-INSPECTION-Feb-2010.pdf" target="_blank">http://zenithair.com/zodiac/xl/data/601XL-PRE-FLIGHT-INSPECTION-Feb-2010.pdf</a><br />
<br />
Also, if the rudder self centers, one can use the rudder as a trim tab. Adjust the cable lengths at the rudder so that the rudder is not centered on the ground (1 to 2 deg to the left or right depending on the rotation of the engine). When flying, the offset rudder will make the aircraft fly straight. This technique was used on the CH2000 very successfully (and approved by the authorities). You may have to adjust and fly the aircraft a few times before getting it just right. Adjustment should be made for cruise and not take-off, as engine torque in cruise is more but for a short period of time.<br />
<br />
So ideally, when in cruse, the ball is centered. Kick the rudder peddle and the aircraft should quickly center itself.<br />
<br />
Note that before anyone flies again, please go over the updated 55 page pre-flight inspection list. Ideally, you go over the list with someone else.