Warning: hidden point of failure on props found

[erkme73]

Not quite 2 hours after being delivered from FedEx, I had my first crash. I was flying indoors, and was attempting a manual landing. It went down about 12" from touchdown and then stopped. I had a brain-fahrt and seeing how steady it was, I did a CSC to shut it off. Wrong move... It shot about 3' across the room and into the wall. Scuff marks, but no knicks, dents, or cracks anywhere the props - or so I thought.

I inspected all four props (while attached) and determined it was no big deal. I took to the air again - both inside and out - and it flew like a dream.

As I was putting it away, I just happened to remove one of the props. I was just playing around with it, and wasn't really doing it for inspection purposes. When the blade off, I noticed only two of the three stanchions/legs were still there. The third had snapped off, and was still inside the receiving mount on the motor bell. I was able to get the broken piece out without much effort.



I quickly checked the remaining props, and found no other broken parts.

I don't know how critical it is to have three functioning points of locking for each prop, but suspect it's probably not a good thing to fly on only two. The scary part is, there were no outward indications - both from a visual inspection, or flight performance aspect - that would indicate a failure had occurred.

So, bone-headed move caused the crash, yes. But lesson learned is to regularly inspect those locking pegs on each prop.

 

[Anthony Viscomi]

I surely would rather break a $4.50 easily replaceable prop, then the motor mount it attaches to.

 

[erkme73]

I don't have ANY problem with it breaking. It's clearly designed to be the weakest link. My only point in this exercise of self-deprecation is to make others aware of possible hidden damage that may go undetected if not regularly inspected. I'd hate for the last two to give way while in the air.

 

[The Editor]

And that's why part of my pre and post checklist is a prop inspection.
To be honest after any sort of prop collision you should think about swapping them out.
I've seen videos/photos on here with people flying their Mavics with Nick's and chunks out of their props - why? They are the only thing keeping you in the air and damaged props will be unbalanced and cause vibration on the motor mounts and airframe.
I fly commercially so my checklists are quite exhaustive but yes, props should always be checked before every flight and regular checks of the airframe should also be carried out for stress cracks etc.

 

[erkme73]

Inspection which includes removal of the props. That's key. I never removed the props off of my Phantoms for inspection, as all part were readily visible. Not so with these.

 

[DodgeP]

How is the point of failure hidden though? You crashed and didn't do a proper post crash inspection. Lesson learned and thanks for sharing.

 

[kmaluo]

Yeah don't CSC shutoff unless it's an emergency in air. It takes a second or so to execute, but in the meantime your Mavic was trying to go backwards, to the side, turn, and down all at the same time. My friend flew my Phantom once and and forgot that the startup sequence was not the landing sequence. It exhibited the same behavior as yours.

 

[erkme73]

Yeah don't CSC shutoff unless it's an emergency in air. It takes a second or so to execute, but in the meantime your Mavic was trying to go backwards, to the side, turn, and down all at the same time. My friend flew my Phantom once and and forgot that the startup sequence was not the landing sequence. It exhibited the same behavior as yours.

It's like that moment where your brain realizes the keys are still in the car, but your hand is starting to close the door... You know it's wrong, but the signal doesn't get to the hand fast enough. I saw it sitting there so still, that for a split second it appeared it was on the ground. So the CSC was a legitimate attempt to turn off the props. Except, it wasn't on the ground. Laps in judgement, awareness, and attention. What got me was holding the left stick down until it stopped moving gave the appearance it had landed. I just wasn't used to that level of precision and prefect stillness.

As for the prop inspection, I didn't know how the tabs were constructed or that they were a weak link. Now that I do, I'm sharing that with others so they know not to fall for the same assumptions I did.

 

[kmaluo]

It's like that moment where your brain realizes the keys are still in the car, but your hand is starting to close the door... You know it's wrong, but the signal doesn't get to the hand fast enough. I saw it sitting there so still, that for a split second it appeared it was on the ground. So the CSC was a legitimate attempt to turn off the props. Except, it wasn't on the ground. Laps in judgement, awareness, and attention. What got me was holding the left stick down until it stopped moving gave the appearance it had landed. I just wasn't used to that level of precision and prefect stillness.

As for the prop inspection, I didn't know how the tabs were constructed or that they were a weak link. Now that I do, I'm sharing that with others so they know not to fall for the same assumptions I did.

Too funny that the Mavic is too stable. Love it! Good thread to remind everyone that you should thoroughly inspect you aircraft after any incident before you fly again.

 

[Kilrah]

For me a prop that hits something is a prop that goes in the trash, regardless of visible damage. Who knows what weaknesses have been created.

 

[AlexSP]

Thanks for sharing, yes I agree these aircrafts demand attention and regular inspection of all parts (those into R/C hobby know that very well and naturally develop the habit LOL).

But the title of the thread is a bit misleading: there´s no hidden point of failure, and it´s not exactly a point of failure as this would mean a design or construction flaw, which is not the case at least not IMO.

 

[Vicrimo]

I agree. If a prop is been in any collision I would replace it.


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[niclariv]

According to the mavic manual you can't do a CSC in midair unless the mavic detects some kind of error - to prevent accidental CSC's. Maybe in this case it thought it might be on the ground because it was flying so low? Anyone tested attempting CSC in the air to make sure it works as advertised and won't do it?


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[erkme73]

Thanks for sharing, yes I agree these aircrafts demand attention and regular inspection of all parts (those into R/C hobby know that very well and naturally develop the habit LOL).

But the title of the thread is a bit misleading: there´s no hidden point of failure, and it´s not exactly a point of failure as this would mean a design or construction flaw, which is not the case at least not IMO.

That's a good point. I can't edit the thread title any more, maybe the mods can?

 

[Kilrah]

You can set whether you want it to be always available or only in case of error.

Oh, and you're asking someone to crash their bird on purpose right there...

 

[The Editor]

According to the mavic manual you can't do a CSC in midair unless the mavic detects some kind of error - to prevent accidental CSC's. Maybe in this case it thought it might be on the ground because it was flying so low? Anyone tested attempting CSC in the air to make sure it works as advertised and won't do it?


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This can be changed via a setting in the app.
I always like the ability to kill the motors mid air if necessary in case of emergencies (aircraft flying directly at someone etc)

 

[niclariv]

Thanks!


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[kmaluo]

This can be changed via a setting in the app.
I always like the ability to kill the motors mid air if necessary in case of emergencies (aircraft flying directly at someone etc)

Or as a last option for an eminent collision with an airplane.

 

[The Editor]

Or as a last option for an eminent collision with an airplane.

Yup - or helicopter/air ambulance etc which are often at 200 feet.
I've never had to use it thankfully, but I want it there in case I need it (bit like ABS on a car).

 

[Mike_in_Letcombe]

Who on earth would do a CSC in mid air? On purpose? 'Oh look, my quadcopters flying, I wonder what will happen if I stop the engines?.......boo hooo hoooo, I damaged it.....'


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