Zenith Aircraft Builders and Flyers
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Redrive Belt Failure
I recently had a redrive belt failure in-flight in my 601HD. It is powered by a Subaru EA-81 with a Stratus redrive turning a Warp Drive 3-bladed prop. All the teeth sheared off the belt instantaneously, but luckily I had enough altitude to make an emergency landing in a frozen, snow covered corn field without any damage to myself or my airplane. I do believe that the Stratus redrive is a good, safe, solid design.
I was wondering if anyone else has had a belt failure similar to what I have experienced. In my particular case, the belt had 152 hours of service on it before failure. They should perform safely for about 300 hours. I believe that the root cause of my belt failure is the age of the belt. We bought the redrive back around 2003-2004 and this belt came with the redrive. Yes, it was a long build time, 13 years from plans. That means that the belt was at least 7 years old. In hindsight, I should have replaced it during our annual inspection, but it was not showing any sign of deterioration. Admittedly, I had not even thought about the belt having that many years on it at the time.
I believe that this engine/redrive combo has been used on more than just 601's. I would just like to know if this is an isolated occurrence, or something that has happened with some regularity.
Thanks for your input.
Replies to This Discussion
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Permalink Reply by Greg Browning on
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Dennis, Congradulations on a succesful off field landing! ! ! ! Many times the outcome is not so great. . . . I had a belt driven redrive on my rotax 503 and never had a problem. I did notice however that in the winter it usually drawed up a bit which increased the tension on the belt. The cold also made the belt less flexable and probably more prone to fatigue. Seeing how your emergency landing was in A "frozen" corn field this may have been a contibuting factor. Just my two cents. Greg
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Permalink Reply by Dennis Hutchinson on
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Greg,
Thanks for your compliments. Completing a successful off field landing is only the result of a lot of emergency procedure training and practice. I grew up as a high school kid flying sailplanes. I continued soaring for about 20 years, and part of flying sailplanes is always at least being aware of the terrain that you are flying over, and keeping potential landing sites in mind. That practice has been deeply ingrained in my flying psyche. Also, my normal practice for landing is to reduce power to idle abeam the numbers on downwind and complete the approach without adding power. So in many ways, it was a relatively normal landing, just not at an airport.
Dennis
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Permalink Reply by Paco Pineiro on
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Dennis:
As someone who has dealt with many cog-belt driven engines I can tell you that you should never assess those belts by their outward appearance. You must keep track of their age, the prevailing ambient conditions where they are used and, most importantly, the manufacturer's suggested replacement time. The outer cover of the teeth is generally composed of a weave, much like a radial tire, which is quite strong. The weakest point therefore tends to be inside at the base of the teeth, where you can't see it until it's too late. Good show on keeping a cool head when it counted!
Paco
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Paco,
You are correct about keeping track of the belt's age, something that I had not even thought about until after the fact. The particular belt that we had was a Jason HTD880-8M, which did not have a weave cover on the teeth, so the teeth were clearly visible. However, all the reinforcing fibers are in the outer belt, not across the plane at the base of the teeth with the outer belt, making it the "Achille's Tendon". I found a vendor that supplies an HTD belt manufactured in Germany by Opti-Belt, the Opti-Belt Omega HP. It is used extensively as the drive belt for kart racing in Europe, and is designed to take high loads with a lot of shock loading from instant acceleration and deceleration forces. In other words, the teeth are reinforced with aramid fibers. They are available though Polybelt at 1-800-859-7659 for around $60 plus shipping. From here on out, we are replacing the belt with every annual inspection, even if the amount of time is still under the 300 hour limit. Cheap life insurance.
Dennis
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Permalink Reply by Bob McDonald on
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I flew 380 hrs on my Rotax 503 Challenger, with a cog drive belt. The belt was rated at 100 hp for 200 hrs. Manufacturer (Quad City Challenger) recommended changing every 2 yrs or 100 hrs of service. The belt was made by GATES. The Rotax 503 2-stroke is 50hp. Belts are cheap, lives and aircraft are not. The failure was most likely related to age... 7 years. Now then how old is the bungee in your CH601HD???? Bungee has a color coded braid system and a replacement cycle of every 5 years. I got caught on that one and only by routine inspection did I catch the nose gear bungee getting ready to break and ruin my day. Always fly like your engine is going to quit...then when it does you already have a "plan B" and safe landing field picked out.... it just reduces the pucker factor when things do go "quiet". Well done on getting both you, and your aircraft safely back on mother earth.
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Bob,
Thank you for the head's up. I stopped by the hangar on the way home from work to take a gander at the nose gear bungee. I have the cowling off right now to replace the belt, do an oil change and sundry maintenance things, so the bungee is fairly visible. You are right, the bungee is exhibiting some fraying around the stop pin that passes behind the gear leg. I just ordered 5 new bungees, and will replace them all. Not particularly looking forward to replacing the main gear bungees, as they were difficult even without the wing skins riveted in place.
Thanks again,
Dennis
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Permalink Reply by Steven Ward on
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Dennis; awesome job on your engine out landing. Regarding your power off landings, I do the same thing on every landing I make also. How did you get your bird back to the airport?
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Steven,
My partner, dad, and a group of friends from MQJ came down to the landing site, about 7 miles south of the airport, helped me disassemble the bird and trailered it back to the hangar. It is sitting there waiting to be re-assembled as soon as it warms up a bit here. Also have some new redrive belts and bungees on order, will begin re-assembly as soon as they arrive. The wheel pants are in the paint shop getting a replacement coat of paint. The corn stubble in the field scraped it off of the lower front fairings on the landing rollout. The only damage was done by an overly enthuastic fireman who crunched my left tip trailing edge. He started heaving on the wing before I had a chance to explain where to safely push on the airframe. I am cutting out that section of skin and replacing it. Looking forward to getting back in the air.
Dennis
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Look on my pictures page, you can see how I lifted the aircraft to change out the main gear bungee. Its as pleasant a job as stuffing a Porqupine in a blender... but cheaper than fixing your aircraft when they fail. Check out my picture on how to replace the nose gear bungee. Good luck.
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Bob,
I remember thinking when we installed the main gear legs originally, without the top skin riveted in place, this is a difficult install. I had hoped at that point that I would never have to replace the bungees. Could you get the leg out of the wing without removing the crossbar that held the upper end of the bungees? I think it will be very difficult to remove the bolt through the crossbar while still in the wing. Any pointers?
Thanks,
Dennis
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Its a simple job, but a real pian clearence wise to do. Unbolt the plate on the top of gear assembly. Unbolt all the AN3 bolts holding the gear assembly in place and it slides out as a complete unit with the aircraft suspended in the air with the ATV style jack. Make some special tools or buy them from www.macsmachine.com
I bought them and followed the instructions on Mac's web site... about 4 hrs / side to remove and install.
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Permalink Reply by John Ellis on
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Bob,
I have a new belt that is about 5 years old. It has been stored indoors. Would you use it? Or do they degrade with shelf age like tires?
John
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