Talon Universal joint failure

[Orv Neisingh]

Yesterday I was providing a client with refresher training in his 2010 Talon. As we were flying we suddenly lost yaw control and immediately lowered the collective to reduce torque and set it down safely. The helicopter has 350 hours on it with the VPS engine so the tail rotor shaft and Universal joints also have 350 hours on them.

On inspection we found that the front universal joint

had broken due to lack of grease. There was a ring of fresh grease around the inside of the tail boom that was not present before the flight. The grease was retained inside of the orange silicone sleeve but was not in the universal joint at all which was running dry as you can see from the photo. The center pivot of the U joint is frozen solid and will not move. We are making this a 250 hour replacement item as there is no way to inspect the internal lubrication of these joints.

[Tim Morris]

You seem to have all the fun.  Were you flying forward or in a hover?  What airspeed and how much yaw was observed?  Curious if the vertical fin provided enough force to keep the aircraft relatively straight during the event.

[Orv Neisingh]

Tim, fortunately we were at a 3 foot hover moving forward at a walking pace. The yaw was immediate and the ship rotated about 60 degrees before ground contact.

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This is the part number for the universal joint. Thanks to Geno. They are sending them next day and we should have them by noon today.

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The rear U joint has plenty of grease. We had to cut the silicone boot to inspect it. Both are being replaced. I have no idea how the front one dried out when the boot still had grease that splattered in a ring inside of the tailboom.

[Graeme Smith]

Maybe the wrong type of coupling, and it looks like it has rusted and it needs grease all the time,  I think the wrong application for a tail rotor shaft particularly if you have to remove the boot to inspect, how many of us would do that regularly?
It also looks like the curved washer that the bolt tightens against has been working, ie maybe loose?

[Graeme Smith]

This is what I am using ... flex couplings, no grease, fully visible, supported at each end.

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I am aligning the entire drive line with a laser that I have centralised in the gearbox part that locates in the boom cone, that laser then allows me to adjust each bulkhead plate to be square to the line and then the flex coupling centrality aligned with the laser as well, the photo shows the spacer with a small hole in it with the laser showing red the bearing plate can be moved within the bulkhead plate to achieve alignment, then the attach 3/16" holes can be drilled. To align the bulkhead plate to the RW boom bulkheads I use a simple right-angle jig that uses the laser line to manage the squareness of the bulkhead to the alignment of the laser

[Homer Bell]

This is WAKEUP call to the guys that say” I’d never fly that thing with all those belts driving the tail! They think drive shafts are going to fix everything. The belts on the RW will out live driveshafts and be much lighter, cheaper, easier to inspect, than all their high dollar fixes that can come up with. Only ignorant people down play our belts system with the new aramid fiber belts. People are changing them way too often. However like everything else, they need to be installed properly and they need to have the proper marking on them to make sure they are not the fiberglass ones that stretch a lot to start with. You can run those , but, they will stretch a lot the first few hours, and will not last the way the good ones do. These would be the ones to change out regularly.
Like getting the proper tool for the job, this is get the proper “part” not some other part that looks the same. A perfect example of this would be the improper oil pressure sensor on one of Joe’s engines that restricted oil flow and caused the engine to fail.

[Homer Bell]

Also, this is one of the differences between a homebuilt and a certified machine. Lots of testing before it get to the field. The JetX has had its problems over the years since it came out. Wrong gear in the Rotax gearbox, bad gear in the main tranny, that’s just two of the major things that I know of, oh and the drive shaft issue at the tail end of that shaft. Wringing out all the issues with some new design can take years before most of them can be found. That one reason I discourage big changes to the RW until it’s been tested for many hours. Yet we still have people who think they have a better idea and start changing all kinds of stuff. Some may be better, all changes should be tested thoroughly before offering it to all the other builders.

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I’ve seen some of these great changes nearly kill a couple here in Ohio several years ago. She broke her back and he has an ankle break I think still bothers him today. She lost their first child and had a broken back they misdiagnosed for days and was in a lot of pain.
It was a great idea to have an adjustable horiz stab, but didn’t incorporate all the necessary things to keep it from killing you in the event something failed. And it nearly did kill somebody.

[Graeme Smith]

Good point Homer, we will have 4 RWs being tested with the shaft drive I have come up with, my desire is always to improve the RW.
Although I must highlight that my reason for doing this is the continued tail rotor belt breakages, worldwide, causing an accident, I know the belt drive has been used for a long time, I also know there has been a lot of failures and yes some can be blamed on lack of maintenance but maybe twisting Vee belts as an idea, is not the best choice