So, I finally figured out what caused my Furion to crash. After digging through all the bits and pieces that I picked up at the field after it went in, I found a swash linkage rod that was missing a plastic link on one end. Upon further review of the rubble, I also found a stray plastic link…hmmm. Could the two be related? You guessed it! Yes, they are related! 😀 When I tried to put the plastic link back onto the metal control rod, it slipped on. Not threaded on, not even pressed on…SLIPPED on. The plastic threads were absolutely obliterated.
So, how could this have happened? Well, remember that I bought this heli used and in quite a bit poorer condition than the ad had suggested. Not the seller’s fault, in my opinion…he probably just didn’t realize how bad the model was because he lacked experience or a good local support group at his field.
Nevertheless, one of the biggest issues that I had found upon inspecting the heli was that the swash links were so far off from level that the elevator servo link pitched the swash forward by about 10-15 degrees. So, of course I corrected that by lengthening the link to the point where the swash was level. Now, at the time of doing this, I didn’t notice anything amiss. The link FELT normal, the threads FELT normal, so why should I be worried?
Well, after an exhaustive one-month failure analysis (I’m really not joking, this is part of what I do for a living, by the way ;)), I have concluded that I SHOULD have been worried because the link must have been on the hairy-edge of acceptable thread depth. It may have even been cross-threaded a couple times by the previous owner. Whatever the situation was, all it took was my modification of the link, the load of an 8-pound heli in a hover, and a bit of vibration and it let go sending my in-the-midst-of-remaidening Furion 6 nose-first into the ground.
So, let’s do this real official-like:
Problem statement: Furion 6 crashed.
Direct cause: Plastic link thread failure.
Root cause: Poor workmanship during build/rebuild.
Corrective action: Replace failed plastic link.
Preventative action: Always check ALL link threads on used helis. Also, periodically check ALL link threads on your own helis, especially if it’s a nitro or gasser model.
The photo above is, of course, an example of the famous Ishikawa fishbone diagram, which I have employed to great benefit during this and many previous investigations, both on helis and rockets. When used correctly, this and other similar failure analysis tools can be used to solve all the problems we encounter in our hobby. Had I not followed through with the investigation and remained rigorous about proving or disproving my hypotheses, I may have concluded that the failure was due to a faulty servo or FBL unit, which would have been wrong and consequently cost me a whole lot more money than a single, plastic link.
Is this for everyone? No. It’s definitely for me though…like I said above, this is a huge part of what I do professionally and it’s just kinda how I think. 🙂 If you’re interested in learning how to become a Heli-Sherlock Holmes too, stay tuned…good things come to those who wait. 😉