Replies to This Discussion

Permalink Reply by Mark Ertz on November 16, 2009 at 9:09pm

After reading all the statements from Zenith, FAA & the LAA, I am wondering if all the mods are necessary for Zodiac home builders or if the mods really address the problem head on? For example, I always thought the rear spar was lightly constucted and that makes sense to beef it up. The bell crank support makes sense w/ increased cable tension. But I am not so sure that the main spar center section has ever been a point of weakness. As for the counter balance, CBs put the ailerons into level position by design if you lose roll control, they generally are not known to address flutter.
Back to the rear spar bolt plate, why not make it one through-piece from one side to other side? Run the through-plate out the rear spar farther out with two bolts above the flaps past it's current position. The current design upgrade looks like a thick patches. Do away with the rivets and bolt the rear of the wing to the heavier through plate and bolt it to the body of the a/c. As for the main spar, why not run two through-plates that extends out of the center section 16 inches out into the wing on the inner portion of the "I Bar spar"? That is to say let the main wing spar bolt within the body of the a/c and let the body of the a/c bolt into the spar farther out into the wing. This would be a two piece fix for the spar bolt areas of the a/c, not several patches.
If flutter is the cause of failure, then stiffen the lower skin so it does not tranlate to the main spar. Use a thicker skin on the bottom or utilize cross-members to stop the flutter from crossing the wing. A patch on a wing is good, but a stronger wing over all is better. Replacing the flat bottom skin with a thicker skin would stiffen the whole wing. Remember the skin is big part of the uni-body construction or monocoque design of the a/c.
What I learned as a pilot about accidents is true in this matter. Most accidents are a series of mistakes. In XL case, How one built the a/c is just one element. How one maintains the a/c is another element. And last but not least, how one flys the a/c is another element in this case to be addressed. Too many XL pilots view their a/c as little WWII fighters but in reality it is more of a light weight Cherokee. The 6+/6- advertizing was a little misleading (drop this from the ads because most pilots misunderstand it). I have watched & heard too many pilots on you tube video flying their XLs beyond the flight envelope. Tail slams on T/O, loops, rolls & spins, and several hard landings. These are the builders and flyers that get killed. So, rebuilding the a/c must be followed up with retrainning pilots about the safe flight envelope.
As for AMD, well, factory built and certified are not necessarily better. After all, I know exactly who built my every inch of my a/c. I know how every rivet went into my wings. I did not hire the labor out and did not build for a pay check or to meet a due date. I know exactly who maintains my a/c and how. Quality control begins and ends w/ me, the builder.
I will upgrade my a/c w/ caution and fly my a/c w/ caution,too. The Zenith Zodiac 601XL is a good design & CH is a good designer, So all builders and pilots should get onboard and help get our a/c back into the air.

Permalink Reply by Basil Buwalda on November 16, 2009 at 11:58pm

I am hesitant in asking this question but here goes.

Good points raised above, but which manuevers do you guys believe can be safely done (with proper training) in the XL after it has been upgraded.

Spins in my mind remain a No-No but would simply manuevers such as Wing overs, Stall turns, Aileron Rolls, Steep turns and maybe, just maybe loops be okay?

The g- loadings on the aircraft did influence my purchase decision (Not complaining, just saying), and I would not mind if the aircraft retained some of its fun flying aspects as well.

From what Mathieu has indicated the structure will be much stronger than any of the authorities require which does make the aircraft +6/-6 aircraft does it not?

I must be honest that I do not wish to become a statistic, hence the question.

Permalink Reply by Matt Heintz on November 17, 2009 at 10:33am

Basil,
To be safe and clear, same manurers as a standard Cherokee 140 or C-172. Anything more than that is starting to be considered limited acrobatics and this aircraft was not designed for that. Yes, the "g" loads could be misleading but I think that the drawings are clear about +6 Ultimate. So +4 Normal is the max allowed.

Permalink Reply by Matt Heintz on November 17, 2009 at 10:15am

Mark,
Long questions but good points especially: " too many XL pilots view their a/c as little WWII fighters but in reality it is more of a light weight Cherokee" and "I have watched & heard too many pilots on you tube video flying their XLs beyond the flight envelope. Tail slams on T/O, loops, rolls & spins, and several hard landings. These are the builders and flyers that get killed"
These two issues are big problems that been trying to address through the Chris Heintz letters over the last year. A major concern of ours is that once some owners complete the upgrade, they will do even more stupid things.

The main reason for beefing up the rear spar at the root is the concern that a large person could possibly damage that area getting in and out of the aircraft. Also, if the flaps are not properly rigged, they could vibrate and stress that area. The German flutter expert is concerned about loose flaps in the up position.

Yes, we could change skins etc. but where do we stop? We know that with very loose control cables, there is a higher chance of getting flutter and we do know that with tight control cables, there is zero chance of flutter. So part of the upgrade is to make sure that control cables stay tight. Beefing up the bellcrank area is one of these things and we will be adding a second aileron stop in the fuselage at the torque tube. People getting in and out of the aircraft and holding on the stick as support can stress out the aileron stops and bellcrank area. Also, with the aircraft parked outside, the wind can do significant damage to the aileron bellcrank area if the controls are not locked. See http://www.newplane.com/Service_Letters_Bulletines/NOTICE%20January... (on the AMD site).
From the last photos on the above link, imagine what would have happened to the aircraft in flight if the owner had not done a good pre-flight inspection!! What you do not see in the photo is that the aileron bellcrank area is also damaged. Loose control cables, weakened rear spar and bellcrank area all because the controls were not locked when parked.

We are beefing up the main root bolt area as to make sure that this is not a weak point in the system. Yes, we do exceed the ultimate load tests with only a few upgrades but with all the accidents, we feel that its important to exceed the high stress/load areas by a significant margin. We are still finalizing this area of the upgrade.

Permalink Reply by Mark Ertz on November 17, 2009 at 12:07pm

MH, Thank you for your timely response. Total agreement. Keep up the good work. Mark @ KBRL

Permalink Reply by Matt Heintz on November 17, 2009 at 11:22am

Interesting point. Rotax may have the same requirements but I am not sure about that. We have dealt with vapor lock by installing large diameter fuel lines and by putting fire protective sleeves firewall forward.
I do not have any info on return fuel lines. Maybe others here have some good experience with this.

Permalink Reply by Gabriel Kremer on November 17, 2009 at 1:42pm

Jake,
I would look into getting some fuel tank sealer from aircraft spruce. Commonly referred to as pro-seal. You will have to look at like an RV or other aircraft design that uses a return system several are out there. ECI kit engines have some info on this but you will more or less the way I see it and theres many ways of doing it you will probably have to make a panel with the return in it and seal it to the tank or if you can drill a hold with a fitting and get it tight and sealed so it won't leak more power to you. I would suggest as few holes in the tank as possible. Hopefully this might give you an idea. Feel free to look me up in the builders list and give me a call I can supply some info for you if you like.

Permalink Reply by Phil Hale on November 24, 2009 at 1:34am

Jake
I have installed a return line in for the Rotax 912ULS which was recommended. The process I went through was to Machine up the Part E-400-000 outlet from drawing 6-K-1 an then drill a hole in the take using the same measurements from the Fuel Tank ends drawing but at the top to the tank end. Then had a LAME wled the outlets in to the tanks. Had the tanks pressure tested to ensure integrity. I have then purchased from Andair their duplex fuel value, to replace the fuel valve supplied. This has proven to be the best solution and is easy to implement if the tanks are out of the wing during the upgrade.

Mathieu might want to comment on this.
Cheers
Phil

Permalink Reply by Stephen R. Smith on November 17, 2009 at 11:04am

Mathieu,

I keep the cables to spec in my plane. The only play I have in my ailerons is in the bell-crank bushing. This play shows up in the ailerons. How much is too much? Should the bell crank bushing be replaced with a real purpose-built bearing such as those found in other airplanes? The cost is low the weight is minimal. Now would be the time. Speaking for myself I would like to see this as part of the kit but I gladly defer to more qualified minds.

Thank you in advance for your time and thoughts, Steve

Permalink Reply by Matt Heintz on November 17, 2009 at 6:01pm

Steve,
Its hard to set limits on how much movement is allowed in assemblies such as the aileron bellcrank area. With the existing bushing set-up, it is possible to get a relatively tight system, especially with tight control cables. If in doubt, replace the steel bushing and make sure its not too long. Since we did the GVT for flutter, there was no issues with the play in the bellcrank bushing. I believe that the tight control cables eliminates any play in the system.

Permalink Reply by Matt Heintz on November 18, 2009 at 8:28am

Yes, some owners have converted to the push/pull tubes for the ailerons. If you will do this, make sure that your tubes will not buckle. Half way down the wing, you can rivet spacers on a rib so that the tubes cannot go up/down and sideways. However, you have to leave enough space so that the tubes do not touch the spacers at full reflection.

Permalink Reply by Jerold Ebke on November 17, 2009 at 9:01pm

Mathieu, Another follow up question about the wing locker lid on the 650 for those of us completed with that task. In my opinion, it seems to be a matter of esthetics, which as you read this, you will see, follows closely on the heals of safety for me. Tim Juhl was clear that a gap will exist between the hinge pin and the rear edge of the nose skin where the aft top skin will be missing and leave the new angle visible, due to moving the hinge aft to the edge of the new wider angle. Are you suggesting we cut the leading edge of the lid to it's new shorter length, redrill rivet line into the forward edge of the lid using holes already present in rear edge of hinge, lock the lid down with installed fasteners and drill forward holes through new angle from forward hinge holes already present and fill this entire area of missing rear skin in front of the hinge with putty or did I misunderstand? A second question with a possible second option. Imagine we were to turn hinge with pin up. We were to eliminate the small thin strip of rear skin in the rivet line area where the nose skin and rear skin overlap. We could take new hinges, slide the forward hinge side under the nose skin into the place previously occupied by thin area of rear skin ( by eyeball about twice as thick as the skin it is replacing ) and use the previous drilled holes in the nose skin to drill holes in the new angle and hinge at the same position as previous. This would allow present fasteners to orient the lid in the opening at its same position. Again, by the tape measure eyeball method, I think I have approximately 40 mm from the centerline of the forward hinge rivet line to the forward edge of the lid hinge rivet hole This would allow me a length front to back of the top edge of angle to be about 50 mm and still miss the rivet line holding the lid to the hinge and not interfere with the aft edge of the new angle. I realize there would be a discrepancy where the nose skin on the spar and the leading edge of the lid would both be approx. taller by about the thickness of a wing skin, but it seems this would be less of an esthetic issue than trying to fill gaps and cracks with filler in a flex prone area. Also, the hinge pin will be up and more visible, but an acceptable trade off. Would the dimensions of this angle fall into these parameters.? Would cutting away the thin 10 mm wide area of rear skin in the overlap area be a structural concerrn? Does this seem to have any merit from your side of things? Thank you so much for this Q-A series. It truely shows your concern and the length Zenith and the Heintz family is willing to go to help those of us who have chosen to commit our lives and resources to building a Zenith aircraft with the idea it is one of the premier homebuilts. Sincerely, Jerold Ebke

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