Markerbeacon
Veteran
Location: Charles City, Iowa
| Any of you ever had one break in flight? Happened to me. Not my heli though. Was setting up an EVO 50 for a buddy. First flight. 2 foot hover. Felt good, nice and smooth, no vibes, typical EVO first flight right? I was on my way to setting it down to tweak the gyro sensitivity when all of a sudden it started banking to the right and climbing. Very aggressively! Went up about 20 ft. Came down on it's side, maybe a little inverted, can't remember, it all happened so fast. Never went into lock out. Held it's heading the whole time. Didn't have any control as far a pitch and cyclic. Was able to pull the power back and that was about it. Post-mortem revealed that the screw on the left aileron lever that attaches the push-rod from the lever to the swash broke. It broke at the head of the bolt. One would think that this would allow the left rear side of the swash to drop causing a left bank. But I have seen demonstrations where with the right amount of vibration you could cause a ring to rise vertically on a shaft. If this isn't what happened, then I'm at a total loss. Now, I know for fact that he had broken a couple of these bolts during assembly. Over torqued. I too think they're easy to over tighten. I personally use the JIS screwdrivers on these because the fit is excellent. However, it's the second largest screwdriver in the set that has the best fit, and has a fairly large handle for working with a tiny 2mm bolt. Hard to get a good feel for torque. Before this ship makes another trip to the friendly skies, I'm going to replace every one of those cheesy bolts with a socket head cap screw. The Hirobo bolts, p/n 2532-028, are kinda spendy at over a buck a bolt. I think Ricks sells a nice big bag of these for a reasonable price, and that's probably what I'll go with. Should be able to get a nice feel for torque with a hex driver on these.
I know that there have been posts on these bolts before, but they've been more about not using the right screwdriver and mucking up the heads of the bolts. Oh, in case you were wondering, about $175, give or take. Fortunately, the owner was very understanding. And, I'm very thankful no one else was near this thing went it happened. Could have been WAY worse!
We have 2 EVO 50's and an X-Spec under this roof that have the original bolts in them and have been operating that way for several years, very successfully. So I think it's just a matter of good judgement during assembly, not so much a fault with the design. But if I'm going to change them all on my friends machine (because I don't know which one is next in line to break), I think I'll put socket heads back in.
If you have other theories or suggestions on what might have happened, I'm certainly open to them. Don't want to leave anything overlooked (underlooked?)
-Mark
Charles City, Iowa? Wear the fox hat! |
