Helicopter repairs

Parts arrived Wednesday! Very fast shipping: I ordered on Sunday, shipped out from Hong Kong on Monday (well, still Sunday by GMT+8:00 "Pacific" time), got delivered to my house on Wednesday. And all that for $25. So why does it cost $30 to get something overnighted from Oakland? The mysteries of international shipping...

Anyways, hit up hardware stores looking for a 5.5mm nut driver and got laughed out. Finally ordered it from McMaster. Since the nut is recessed deep inside the blade clamp, you need a nut driver with a small OD. 53965A17 is the smallest McMaster has (OD .318" = 8.0 mm), followed by 6919A13 (OD .343" = 8.7 mm), which just barely fits in the blade clamp. The power driver (8534A52) is way too big, and I didn't try out the hollow-shaft nutdriver (7299A19).

That arrived Thursday. The actual repair was very simple; took about 10 minutes. You can see the damaged shafts below: flybar (top) and feathering shaft (bottom).

For size reference, that's an M3 thread on the feathering shaft. The rubber mounting rings on the feathering shaft are damaged, too, but I don't have a replacement so I just stuck it back in. After repair I had to adjust some linkage lengths (just needed 2 turns) to get the two new blades to rotate in the same plane.

Today I flew; everything is fine. I got some sustained hovers and decent landings, which is pretty exciting. Need to do something about the yaw controller at takeoff: the integrator builds up angle error while it's on the ground, so when it lifts off there's a huge rudder command which causes the helicopter to whip around until it's in what it thinks to be zero angle error. Pretty disconcerting.

The goal, though, is not for me to get better at flying, but to improve the control system. So I put in some frequency sweeps (telemetry is working better now), which again was a really bad idea in my small parking lot surrounded by trees and fences. Caught a fence with a blade tip and was down for the count.

Damage report: blade tip smashed up a bit; not too bad. Swashplate popped out of the anti-rotation bracket; that was an easy fix. Flybar might be bent; hard to tell, so I won't reject the null hypothesis of "not bent". The two halves of the helicopter chassis split at the main shaft top bearing; this also happened last time and I think the threads in the plastic are stripped now. Maybe okay to ignore; otherwise will need a longer screw to go through the stripped half and into a nut.

Tried replacing the damaged blade with the un-damaged blade from the previous crash, but the blades are sold in balanced sets and mix-and-match don't work so well. So I kept the damaged blade. Needed to re-adjust linkage lengths to get the blades rotating in the same plane, and added some aluminum foil tape to the damaged blade in an amateur attempt at blade balancing.

Flew again this afternoon. Blades aren't as well balanced as they were pre-crash, but that doesn't seem to affect things too much at flight conditions (though we do see much more wobble while the rotor is spinning up or down). More flying (this time in a larger space) tomorrow.