The flying monkeys got me...

Helis and fixed wing

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Monday, May 5, 2014

EXI 450 Rebuild, Billionth Time


The other day I was flying the EXI450 Sport, trying to isolate some severe vibrations that were causing a tail wag, making the gyro gain very impossible to nail down, while also trying to figure out what rates and expo I like, when the tail belt snapped and she instantly pretzeled four feet off the ground onto the pavement. It was one big ball. One main blade sailed over my head (a good 15 feet), and the tail boom snapped off from the torque. The gyro took a blade hit as it flew off its perch and has a nice dent in the case, and the tail blades became shrapnel. The solid steel main rotor shaft bent at 45 degrees, and even the solid block aluminum rotor head got a 2-3 degree tilt in it (can't see it, but when I replaced the shaft there was a significant wobble in the rotor head not present with shaft alone). The tail shaft also got tweaked. Needless to say, the fly bar was a swirly. None of the servos failed, however, all passing inspection and motion testing. There is a tremendous amoun of energy in these helis, and it all instantly traded places.

I was annoyed and damned if once again I didn't fail to take a pic.

Ordered a new tail boom (of course I have hundreds in storage...) and a new Align Sport rotor head block. I didn't expect them so soon but they arrived today! I took apart the entire swash cage and rebuilt it with the new rotor head, cleaning and lubing up everything that moved. New flybar installed, a few mm shorter than the ruined one. While I was waiting for these parts I replaced the main shaft, the stripped main gear. I had also rebuilt the tail assembly. I didn't realize I had built it backwards, even after I installed the tail boom and it had to go in upside down (I even cut a new detente groove in the forward end). I have used Tarot booms which required an upside down installation on an Align machine, and I thought maybe the original tail housing on the frame was a Tarot, so didn't think too much of it. Today after I had reinstalled the tail housing, boom and tail rotor assembly, I realized I forgot to put the control rod guides and the servo clamps on the boom first ... (I was way distracted with an upcoming business trip). I took everything apart again, slid the tail boom pieces on there and rebuilt it. When I went to put the tail guard/vert stabilizer on, I realized I had assembled the tail assembly backwards! That's why the slot was on the wrong side and I installed the boom upside down, dammit. So I had to dis-assemble the tail assembly and re-assmble it properly, pulling it off the boom and drilling the rear pin detente hole on the "wrong" side, and reassembling it. In the end I basically installed the tail boom upside down and had to McGyver the forward and aft tail boom detentea. What a frickin' waste of time, but I didn't want to waste the tail boom. This is so not like me...

It all works fine. Without blades there is very litte fine vibration. I re-installed the tail servo and control rod, but haven't set them in place. I'll do that when I come back. Installed the brace supports and called it a night.

Took this photo during a break, before putting the tail boom braces back on. Next time, balance the new main blades and install them, and the tail blades, set up the tail and fix the tail servo in place, then see if all this cleaning and replacing fixed the vibration issues! This heli has been rebuilt so many times....


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