Re: COZY: O-320 / O-360 Long-EZ/COZY Engine Mount Cracks [2 Attachments]
Dear Tim,toggle quoted messageShow quoted text
We've been making mounts maybe 16 years? So far so good no cracks reported.
Not long after making our early LE mounts Ken Miller contacted us and recommended adding the two additional upper tubes, we adopted that right away. In Ken's experience the highly cantilevered LE mounts cracked most frequently at the top tube within the heat affected zones of the welds (within 1" of the weld) or on the top cross tube.
Most LE mounts out there are original Brock's or Weldtech (Weldtek?) typically smaller diameter tubes on the dynafocal ring and all wall thicknesses were 0.049" these mounts were mostly per plans for much smaller motors than are common today.
The example Marc shows is a typical crack and if it were under powder coat you would never be aware of it until the tube is fully broken. This is why we strongly recommend to prime lightly and use a rattle can of high gloss refrigerator white.. or shoot gloss white epoxy paint, just make it a light coating of glossy white paint. It is easier to clean, inspect, and detect.
From: Tim Andres tim2542@... [canard-aviators]
Sent: Wed, Feb 8, 2017 10:44 pm
Subject: Re: [c-a] Re: COZY: O-320 / O-360 Long-EZ/COZY Engine Mount Cracks [2 Attachments]
I have one of your mounts, standard 0-360, purchased maybe 8 years ago, inspected recently no evidence of cracks. Is this something you think ought to a preemptive repair or just watch? How many have you gals seen crack?
Thanks, Tim Andres
From: "CozyGirrrl@... [canard-aviators]" aviators@...>
To: marc_zeitlin@...; cozy_builders@...; canard-aviators@...
Sent: Wednesday, February 8, 2017 8:24 PM
Subject: [c-a] Re: COZY: O-320 / O-360 Long-EZ/COZY Engine Mount Cracks
Marc, untrue, probably since you emailed us about it I think over a year ago we have added this mod to Cozy Mk-IV dynafocal mounts. All LE & Cozy III dynafocal mounts have included this mod for years.
From: Marc J. Zeitlin <marc_zeitlin@...>
To: cozy_builders <cozy_builders@...>; Canard Aviators Mailing List aviators@...>
Sent: Thu, Feb 2, 2017 7:56 pm
Subject: COZY: O-320 / O-360 Long-EZ/COZY Engine Mount Cracks
While in the process of getting a customer's Long-EZ ready to sell, I performed the equivalent of a Pre-Buy examination. During this exam, I found a crack in the engine mount. The crack is located at the tip of the purple arrow in the picture below and wraps from the top of the horizontal tube all the way around to the bottom - about 180 degrees.
This is a relatively standard place for cracks to occur when using the original engine mount design (I had my O-360 engine mount on my COZY MKIV crack there at about 1100 flight hours as well), due to a design that was carries over from the original O-235 Long-EZ engine mount and never upgraded for heavier engines, with more vibration and G forces.
Any structural engineer (or anyone that understands structures, engineer or not) will be able to look at this and tell why they crack there - the top dynafocal mounts are cantilevered at the weld where they meet the two other tubes - the vertical one coming from the bottom, and the horizontal one coming from the top fuselage mounting points. The dynafocal mount wants to bend aftward and down with G forces and the weld zone takes all the bending stress. Very bad.
The fix, and it's been around for a zillion years, has been to install triangulation tubes in the location of the large red line - connect a point on the top cross tube, near the dynafocal mount, to the horizontal tube, close to the fuselage. This removes the bending loads at the weld and turns them into tension loads in the new tube. Voila' - problem solved. This is almost certainly what we will have to do with this aircraft - PITA to remove the engine/mount, fix it, and then re-install everything.
Here's a picture of the crack in an inspection mirror:
It's just a faint black horizontal line in the mirror, but it's there. I saw a small crack in the paint (which sometimes is just paint cracking), so I sanded off the paint and primer. The crack was hard to see until I blew out all the dust with compressed air, and then it was obvious that it was, in fact, a crack in the tube at the weld heat affected zone starting at the base of the weld.
Anyway, for those of you with larger engines on your Long-EZ's, or for those of you with COZY's, you should be inspecting this area of your engine mount very carefully at every CI, if not every time you remove the top cowl, especially if your aircraft has more than a few hundred hours on it. If you don't have reinforcements welded onto the original engine mount, you should think hard about installing them. I figure about 15 hours to remove an engine and mount, weld in the reinforcing tubes and reinstall everything. Not too much time, especially if you're not paying someone to do it.
The CG Products Long-EZ mounts have this reinforcement. However, their COZY O-360 mounts do not, and they should. I don't know about anyone else's engine mounts, if there even is anyone else selling mounts for these planes anymore.