On Sunday, December 4, we were flying south of Madras, Oregon, in the Crooked River National Grasslands. Among our goals for the day was to finally commission a new hexacopter. Its development has been stalked by every conceivable setback and delay, but we thought it was finally, at long last, ready to fly.
Initial flight testing seemed promising but then, in keeping with the theme of this build, disaster struck. It started gyrating wildly and tumbled out of the sky. With a crash inevitable, Techinstein cut the power to the motors to avoid any additional damage – and thereby revealed the cause of the failure.
Prior to impact, he could clearly see that a blade had separated from one of the six 10-inch Gaui 330x propellers that we were using. The location of the damaged propeller was consistent with the direction of the aircraft's uncontrolled descent.
Bad things happen, to be sure, but this incident fit a larger pattern of failures that we've been seeing with Gaui 330x props attached to powerful motors.
While documenting sprint boat racing in Tangent, Galaxian lost a blade off of an 8-inch Gaui prop. Fortunately, it was during a casual flight over the pits – not over the water during a race – and Techinstein was able to make a semi-controlled descent into the back of a cargo cart. Nice bit of piloting, that.
This phenomenon would also explain a crash we experienced at Red Rock Canyon, outside of Las Vegas, Nevada. Galaxian made and uncontrolled descent while hovering maybe 100 to 150 feet AGL. At the time, the cause of the crash was undetermined, but several people who witnessed it reported seeing something separate from the craft a split-second before it came down.
Physical evidence at the crash site did not preclude a propeller disintegrating in mid air, and we never managed to find one half of one 8-inch Gaui 330x prop.
No doubt you noticed that Little Bird hasn't shown up on the hit list, in spite of the fact that it also flies with 8-inch Gaui 330x props. A likely seeming explanation for this fact is that Little Bird's props are replaced rather more frequently than Galaxian – primarily because I bend or break them by less mysterious means. Furthermore, each of the failures involving Galaxian has occurred after an extended period of crash-free flying – meaning that there has been time for fatigue to take a toll on the props.
The crash of the hexacopter was more troubling, because the props were right out of the bag with less than an hour of flying time before one failed.
Based on this result, we're moving away from using Gaui 330x-s propellers on all of our birds. We're taking the 10-inch version out of service immediately and, to the extent that it is necessary to continue using the 8-inch variety, we are going to replace them at intervals, even if there is no visible wear or damage.
We haven't settled on a new manufacturer yet, and it will probably take a while to establish a track record before we can say anything at all about their durability over time.
And again, I want to emphasize that we have only ever had these problems using Gaui 330x-s propellers with motors that are much more powerful than the Scorpions that come with the stock Gaui 330x-s kit. Galaxian is swinging its props with Exceed RC Rocket Brushless 2215-1050KV motors, and both Little Bird and the new hexacopter have Cobra 2217/16 1180 KV motors.
These propellers have always performed flawlessly for us when used with standard Gaui hardware which, in Gaui's defense, was all that they were designed to do. Even as we've upgraded our birds, we haven't wanted to move away from Gaui 330x props because we really like them: they are light, well balanced and inexpensive. Bummer.