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Marc Zeitlin

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Marc Zeitlin last won the day on May 21

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About Marc Zeitlin

  • Birthday 08/06/1957

Flying Information

  • Flying Status
    Flying - 1966 hrs.
  • Registration Number
    N83MZ
  • Airport Base
    KTSP

Personal Information

  • Real Name (Public)
    Marc J. Zeitlin
  • Location (Public)
    Tehachapi, CA 93561
  • Occupation
    Principal - Burnside Aerospace
  • Bio
    www.mdzeitlin.com/Marc/bio.html

Project/Build Information

  • Plane Type
    Cozy Mark IV
  • Plane (Other/Details)
    COZY MKIV
  • Plans/Kit Number
    386

Contact Methods

  • City
    Tehachapi
  • State/Province
    CA
  • Country
    United States
  • Email (Visible)
    marc_zeitlin@alum.mit.edu
  • Phone Number
    978-502-5251
  • Website URL
    http://www.cozybuilders.org/

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  1. You need to remember that the aircraft is made of epoxy, which is essentially fuel. So if there's softening or melting aluminum inside the engine compartment, the airplane has long since become a smoldering heap of burned fiberglass and epoxy (and people - at least one) on the ground and the softening of the aluminum belcranks (or anything else aluminum, like the whole bloody engine, or oil lines, or fuel lines) is # 867 on the histogram of things with which to be concerned. The firewall belcranks are steel because they're weldments, and the rudder belcranks are aluminum because they're not.
  2. Interesting - you're right, in both the LE and COZY plans. So both Nat and Burt (both engineers) draw a part with a +/- 0.001" tolerance, and then say "nevermind - we don't actually give a crap what the fit is". Which is definitely the case - a sloppy fit is NOT a problem. But why have 0.001" tolerance on the part drawing. That's just bad engineering, and makes the part cost more than it needs to. All I was looking at was the drawing. Thanks for the pointer.
  3. That is slightly funny. So the specification for the ID of the LWA9 bushings is 0.500" +/- 0.001". I have no idea why that tight a tolerance was chosen. You stated that the tolerance was 0.015", which it is not. Now, the issue here is that AN-8 bolts have a maximum shank diameter of 0.499". The minimum ID of the bushing is stated to be 0.499". Anyone see a problem here? As a mechanical design engineer, knowing the design of the wing attach fittings and the way that the loads are transferred, as well as the tolerancing of the AN-8 bolts, I'd modify the design of the LWA9's to have an ID of 0.500 +0.003" / - 0.000". This way, ANY AN-8 bolt will fit, rather than just most of them. With respect to machine shops, I've had excellent service from online shops Xometry.com and Hubs.com. Easy online quoting, ordering and delivery - submit a 3D and 2D file and you're off and runnning. While I have designed and am selling (for a while anyway) electric nose gear components and other nose gear components that work with 3:23 Composites' nose gear forks, I do not have any/all Long-EZ COZY parts designed and in stock. Maybe eventually...
  4. What was the tolerance that you found them worn out of, and where did you find that specification?
  5. Nice saw. But Nichrome wire also works great, and usually can be had in thinner diameters for a smaller kerf than the SS. Of course, if you use oversize hot wire templates and then correct size templates for the final sand to shape of the cores, the kerf is immaterial.
  6. It is not possible to tell the quality of layups from pictures. It MAY be possible to tell if the layups are really lousy, but there's no way to tell wet, dry, or marginal layups from pics. I've seen pics that looked fantastic, and when I saw the plane in person the layups were marginal at best. Conversely, I've seen pics that made me very doubtful, but when I saw the plane in person everything was completely acceptable and decent quality. So, do not believe for a second that you can tell the quality of layups by some pics on Barnstormers. You're doing well if you can judge contouring by light reflections in pics, but that's about as far as it goes.
  7. The templates are not the same, because the spar cap trough depth is different, and the depth distribution is different, and the lift tab location is different. The airfoil shape is the same, but that's ALL that's the same.
  8. Generally, corrosion will occur on the top wing fitting before the bottom one, just because rain falls down from the sky, not up from the ground. So even if the cracking in the fill/paint is on the bottom, I'd want to examine all eight fitting areas (both wings, top and bottom, strake and wing). So here's what I would do as a first step: I would very carefully (and it might not be too hard, as the micro fill that most folks put over the AL plates doesn't stick particularly well, so it may just pop off with a bit of prying or gentle persuasion, being careful not to scratch the fittings) remove all the micro and fill on ALL of the aluminum wing attach plates. This will at least allow you to see the exposed portions to examine them. If there's corrosion there, you can guarantee that there's corrosion where you CAN'T see, but if there's no corrosion, that's not a guarantee of no corrosion anywhere, although it's a step in the right direction. See: For a previous discussion on this topic, and some images of what you should be able to see from the outside with all the fill removed. Then you can start evaluating what might or might not be going on.
  9. Since there is no way to know whether there is corrosion or not in places you cannot see, your claim that there "is no corrosion" is unverifiable. Here's a picture of a wing attach fitting with severe corrosion: I've drawn the red line where the aluminum disappears under either glass or filler on many VariEzes - in any case, the opposite side of this plate is in contact with the top of the spar cap and is not visible. In THIS case, one can see a tiny bit of corrosion peeking out from under the glass/filler, above the red line. However, had the corrosion started just a bit lower - maybe 1/4" below the red line, one would only see pristine Aluminum and would have no idea that very bad corrosion was there. Here's a side view of this piece, with extreme exfoliation corrosion visible: As you can see, a substantial amount of the Aluminum is gone, cracked, or in the process of disappearing. Obviously any bonding strength to the underlying spar cap is essentially nil, and the strength of the screws holding the plate to the spar cap is also severely degraded. Does your plane have this corrosion? Who knows? Without disassembling the fittings for examination, alodining/priming, and re-assembly, you'll never know. You seem to believe that an external visual inspection is adequate to determine the condition of the wing attach fittings - it is not, and RAF made very clear that it is not in its warning to VariEze owners. Delaminations occur between layers of composite plies. What you're referring to is knows as a "disbond", where the bond between two dissimilar materials has lost it's adhesion. This is a common error in descriptions of failures. And if you are correct that a disbond has occurred, this implies two things - first, that strength has been lost, and second, that a void is now extant into which moisture (rain, humidity - any water) can ingress and start a corrosion site. Do not minimize the issues here, or think that just because you cannot see an obvious corrosion issue that there cannot be one.
  10. Bolding mine. Kent, you know I respect your knowledge about these airplanes, and I know you're interested in safety. But two "probably"s and a "may not", while not technically wrong, is nowhere near enough to hang the safety of an airplane on. Your recommendations for a thorough CI are obviously warranted, as are the rest of your recommendations. But they don't go nearly far enough. Particularly with VEs and the wing fitting issue, it's critical to understand the provenance of the aircraft - where was it built? How was it stored? Where was it stored? How much did it fly? What protection was put on the metal parts? How much did it fly in rain/moisture? Was it ever tied down outside for any length of time? Who were the intermediate owners after the builder? How did THEY treat and store the aircraft? While San Diego is in SoCal, it's also right on the Pacific Coast; is humid, wet and foggy. The first picture certainly gives the impression that at least for the last 3 years, it's been stored outside. This would have been a huge "move on to the next airplane" warning sign for me. And if I'm scaring the new owner, well, good. "Probably" doesn't cut it...
  11. Eh. This is a questionable (at best) recommendation. First of all, the VariEze was specified as a +5G airplane (limit load - top of the V/N diagram) at 1050 lb. No one knows what safety factor Burt used to design it, so we have no idea what the ultimate design load was. 2X is relatively standard in the industry, but many suppose that Burt used 3X to account for builder/MFG variability. So we can GUESS that the ultimate load (where failure would occur) would be somewhere between 10G and 15G. However, numerous folks have performed load tests on various parts of VE and LE aircraft, and they've failed anywhere from 3.5G to 14G (the VE _I_ tested failed the main wing attach fittings at around 7.5G - 8G. All of these, of course, assume intact and non-corroded wing attach fittings. Of course, it's completely contraindicated to test any airplane to a load higher than the limit load, so your recommendation to test to 6G is a poor one - any load over the limit load, even if it does not cause failure, is allowed to cause damage. 5G (at 1050 lb.) would be the absolute maximum that anyone should test to in a static load test, unless the object is to determine the failure level. And then what does one learn if one gets to 5G? Only that if one gets to 5G (limit load) the plane doesn't break. What happens at 5.1G? No idea. What's the safety factor over 5G? No idea. So the only reason to test to 5G is if one DOES intent to limit (per the mandatory requirements of RAF for VariEze's, due to the corrosion issue) the plane to 2.5G @ 1050 lb. THEN, assuming one got to the original 5G limit load level, one would have a safety factor of 2X when limiting to 2.5G. Actually, this method does not get one to within a few percent, as the canard loading changes tremendously with not only CG position and GW, but also with IAS. The moment coefficient of the main wing is substantial, so as speed increases, the moment increases, and the load on the canard increases. So maximum canard loading would be at fwd CG, MGW, Vne at Sea Level. And can get to > 1/3 of the total lift. Canard load varies tremendously in different configurations. Now THIS may be a reasonable approach, if one was going to attempt the evaluate the structure by other than visual inspection (or static test). Back in the day, NDT was difficult and required a perfect sample of what was being x-rayed in order to be able to compare the subject to it, and then required a lot of interpretation. I'm not familiar with what's available today - it may very well be the case that a good analysis of the state of the wing attach fittings can be made without a perfect sample - only with the sample to be evaluated. If this is the case, then this type of evaluation could be extremely useful in understanding the state of the wing attach fittings. Now, I will say that even with perfect wing attach fittings, the VE _I_ tested failed at the aforementioned 7.5 - 8G level, due to the attach fittings failing the attach screws (they tore out of the lower composite spar caps). This is barely a safety factor of 1.5X (not the usual 2X - 3X for composite structures).
  12. I concur with 95% of what you wrote, but there's this, with respect to your note and Cameron's followup regarding glide, in THIS particular case. I have not seen the posting either of you are referencing - maybe it was on FB, because it doesn't seem to be on any of the mailing lists. But I have spoken directly to the pilot in this case and it's possible that I have information that might not have been publicly posted. I was not asked to keep this private. The engine failure occurred at 9500 ft., and the distance to the airport to which he attempted to glide was (IIRC) 17 NM Interestingly, these are exactly the numbers that _I_ experienced during my propeller loss - we were at 9500 ft., gliding to an airport at 500 ft. elevation that was 17 NM distant. We arrived at the airport 1000 ft. above pattern altitude - IOW, 2K ft. above the airport, with (obviously) more than enough energy to make the field. So when the pilot told me that he landed 100 ft. short of the threshold, I was very surprised, because there's no way he shouldn't have made it as long as the wind was not excessive (which it wasn't). After a bit of questioning, he told me that he, too, arrived at the airport very high - approximately the same 2K ft. AGL as I had and that the issue occurred because he misjudged the unpowered APPROACH. In this case, there was no issue with glide rings, L/D ratio estimations, or anything like that (although obviously all of those are important) - the issue was completely in the pattern approach positioning - over the airport at 2K ft. AGL, we should all be able to touch down on the runway. I was not in the plane - I don't know how that type of error was made - but I will say that although I attempt all of my landings in my plane with the power pulled to idle at mid-field, downwind and try to touch down within 500 ft. of the threshold, one of every 10 landings or so require a blip or two of power, if I've misjudged the wind or my IAS a bit. But when I do NOT have the knowledge that my engine is working, I do not rely on the ability to blip the throttle - I shoot for a landing brake down touchdown at 1000 ft. from the threshold with the LB down, and retract it if necessary to improve the glide. In any case, THIS particular accident was caused by a misjudged unpowered approach - NOT a distance glide issue.
  13. I'm not sure whether there was a question in there somewhere, but all I can say is that I would have recommended doing that prior to purchasing one. Get a copy of the the plans and the POH, as well as copies of ALL the Canard Pusher newsletters and the Central States Newsletter (Now the COBA magazine). Get the RAF documentation of the wing attach fitting corrosion issue and the recommended solution (I don't use the word "fix", since they didn't specify a "fix"). Then read the parts of all of all those documents that apply to VariEzes 3 - 4 times. Then read them again. Everything is available online. Then consider whether purchasing an unknown provenance VariEze was a reasonable thing to do and consider how you're going to ensure that it's a safe aircraft from the standpoint of wing attach fittings and engine. The engine is the easy part.
  14. A review of the POH and the documentation for the plane would have been one of the first items on my Pre-Buy checklist prior to purchasing an aircraft. But to each their own, I suppose. Planes are weighed with no fuel aboard. The VE POH sample W&B indicates an expected empty weight of 535 lb. No VE on the planet has ever weighed less than 600 lb., to my knowledge. The lightest one I've ever heard of is Joe Person's plane, at 610 lb. (Day VFR, no starter). Now, most of the VEs I inspect and work on weight between 680 lb. and 750 lb. A 750 lb. VE is a total pig. Anything over 700 lb. is pretty heavy. If you're near 650 lb., be VERY happy. With a POH MGW of 1050 lb. (1110 lb. under certain conditions) you can see that anything over a 700 lb. VE isn't going to be able to carry much more than the pilot and full fuel. Also be sure that you know whether you've got the long or short canard and which CG range that implies. To the extent possible (which isn't much, for such a safety critical component), inspect the wing attach fittings for corrosion. Ensure you're familiar with the wing attach fitting corrosion issues that are well known and documented on Variezes. Have (and review) all the CP's, mandatory changes, and wing fitting corrosion warning documentation. Be aware of the concomitant "G" loading restrictions. mandated by RAF, as indicated in the wing fitting corrosion documentation.
  15. Belcranks and pulleys take approximately zero maintenance. 15 seconds at the CI to make sure they're still attached, and never lubricated, since they have sealed bearings. The fact that people have installed these tubing guides does not imply that they were fixing a problem. Never seen them and can't imagine why they would be required.
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