Logo 550SX 2017 - Head Failure

I've been flying my Logo 550SX 2017 for about 6 months, however, this morning while making a typical flight, the bolt holding the main blade grip to the spindle shaft snapped. The blade grips exploded away from the head and the heli crashed to the ground. Not Cool..

Attached is a picture of the snapped bolt in the spindle shaft.

Any ideas why this happened?

Thanks in advance for your opinions.
B

Hi Brian,

sorry to hear.

There are a couple of possible reasons: the bold could have been tightened too much or too little, the bolt could have come loose but not enough so you didn't not notice, since it was still within the tension of the dampening, the bolt could have had a nick in it, acting as a predetermined breaking point, it could have been weakened by an earlier mishap, blades touching the ground, tip-over, crash.

In general, the load limit for the bolts is a multiple of the loads which the bolt has to sustain, within the recommended rpm.
But what I can not tell is, if you would do the infamous overspeeds maneuvers frequently, how that stress would affect the longevity of the bolts, over time.

Kind regards

Eddi

Born to fly ...
forced to work.

I received parts today to repair the exploded head..

Not knowing the Spindle Shaft included End Screws, I purchased them as well.. As listed in the manual, these screws are M4x12 Cap Screws.

While opening the packages, I noticed the End Screws & Washers included with the new Spindle Shaft are shorter than the M4x12 I purchased separately. See Picture. The included screws measure about 9.5mm long..

3 Questions

1. Which screws should I use. The M4x12 seem to just bottom out when placed into the spindle shaft..
2. What size screw was included in the kit?
3. Could this have had anything to do with the screw snapping in the air?

Thanks

Hi,

I have to ask about the length of the screws, what is right.

The screws belonging to the shaft, as per the parts list, are M4x10.
The spare part listed is indeed M4x12.
M4x12 should just fit, with the washer in place, and it should cause no issues.

What screws did you have in your original shaft?

Kind regards

Eddi

Born to fly ...
forced to work.

I have no idea what was originally issued with the kit? That was one of my original questions..

And, I still have no idea which length screw is appropriate.

I'm new to this hobby, and maybe this isn't a big deal, but the last time I flew the heli it blew up in the air due to a cracked screw.. Now, I see there are consistencies in the parts list regarding what screw to use..

My confidence level is very low with my new Logo 550SX..

Hi again,

in the kit, there should have been M4x10 (as provided with the spare spindle shaft), so all well here.
M4x12 should also fit (just so), and it would not make a difference, even if it would bottom out in the thread of the shaft.
A bug in the manual, most probably.

A coarse calculation for the 550 SX:
The M4 / 12.9 screw should sustain approx. 950 kg tensile load, while the blades create a load of approx. 210 kg @ 2,300 1/min head speed.

I hope my just acquired math is right, I will stand corrected of course if I'm wrong, here, it's not my line of expertise but I was curious.

Kind regards

Eddi

Born to fly ...
forced to work.

I got her all put back together.. And, I think it's important to put this here, the issue was 100% my fault. The Logo 550SX was my first real heli build and lets just say that I should pay closer attention to the instructions and include every washer & spacer exactly where the instructions tell you..

The good news is.. she flew better than ever this morning.. So all is well that ends well..

Thank you for your time, patience and assistance!
B