Critical Failure of T*Motor Props during shoot

[Phil DeVore]

Interesting thread. I fly the I2 and have only used the stock props. About a month ago I found a hair line crack in one of the props. The I2 has not had any accidents, props haven't hit anything that I'm aware of there were no leading edge nicks or damage.
The I2 has a little over 140 hours on it and these were the original props. I replaced all four props and also carry an extra set.
I have been around aviation most of my life, I'm almost 70 and I learned long ago pre-fligh inspections are critically important. As already stated, almost anything can fail, and some with no warning or signs of potential failure.
I was to ferry an brand new Cessna many years ago. I was about to rotate when the continental engine decided to come apart. That was a brand new engine but Cessna didn't discontinue using the continental engine, they realize that sh.... happens and that is just life.
The T props may be well tested and good props, but once you have been bitten, it's pretty hard to trust the old dog.

I’ve been flying my I2 with the Tmotor CF winglet style folding props that I purchased from Florida Drone Supply for about 150 hours and have had no problems with this setup. The best thing about them is the ease of getting the bird up in the air without having to fool around with putting the stock props on and off every time I wanna fly. The time saved for me is well worth it and I also believe that they help with many other factors. Including prop noise, air vortex and I also believe that they actually give me a little longer flight time. I have timed them against the stock props and I got approximately a minute or two longer flights. Well that’s my opinion on the subject of the propeller situation.

 

[The Editor]

I agree with you that people are making this issue way too complicated. It’s simply a matter of feel when you’re tightening the props. Kinda like when you’re replacing your tire after having had a flat. Just don’t strip the lugs when you’re tightening them down. Same idea here too.

Bad analogy - you should never tighten a wheel nut by feel. They should/must always be torqued to the manufacturers specification (and then re-checked after 50 miles or so).
Props are fine to be done by feel though.

 

[FlyaDrone]

One consideration for all of us using foldable props that are securely attached to the I2. Inspection of the blade undersides is problematic. I carry and often use a magnifying glass to help identify any micro cracks or fractures which might be difficult to detect without magnification.

 

[Phil DeVore]

One consideration for all of us using foldable props that are securely attached to the I2. Inspection of the blade undersides is problematic. I carry and often use a magnifying glass to help identify any micro cracks or fractures which might be difficult to detect without magnification.

Same here.

 

[dioriosigns]

Firstly let me state my positive experience with the T*Motor Folding Props for Inspre 2. I’ve used the folding T*Motor props actively since their release. I’ve appreciated the speed at which I can deploy the inspire from the LowePro drone guard pack and traveled from Tulum to Iceland and beyond using this combination. I also want to acknowledge Florida drone supply as a responsive retailer and active partner in this space.

In Brooklyn last weekend was flying the X7 for a shoot at a densely populated large scale venue at night (with applicable night waiver). Our 5th flight, around midnight, launched from a protected elevated platform. Immediately after launch a loud crack was heard and from about 6 feet above launch elevation the inspire went spiraling into the ground breaking the rear leg motor mount housing and all remaining props and the Imaging system on the Inspire 2.

Upon inspection one of the props cracked and sheared off from its pivot. The ejected half was not recovered. I constantly check the torque on both the prop bolts and the motor bolts and they were all appropriately torqued. There were no prior collisions or damage to the props, the full set was under 2 months old.

As it stands I appreciate the performance and convenience of the T*motor props and was looking forward to active use during Burning Man this year. However, I wanted to communicate my experience as a data point and a warning that as far as I can tell, the t-motor props under normal use have the potential for catastrophic failure.

I'm open to input and would like to hear if this is an isolated incident or if there are other similar issues. Am I wrong to no longer trust this product?

Video of the shoot at:
Mayan Warrior (@_mayanwarrior_) • Instagram photos and videos[/Q same here. went back to DJI props

 

[r62ewa]

I lost my I2 using T-motors this week. From the factory the blades are very tight and hard to open, so from reading here it is recommended to loosen the bolt a little to make the blades a little easier.

I guess I loosened mine a little too much as during the end of my flight I was returning to land and one of the blades came off at about 100ft elevation. The I2 with X4S came down and landed in about 3 feet of salt water. A total loss and write off.

I am going to be sticking with the stock set up from here on out, even with the red prop rattle. An expensive $5400 crash. I have a full brand new set of T-motors I had as backups that will never get used.

 

[MrTVR]

I lost my I2 using T-motors this week. From the factory the blades are very tight and hard to open, so from reading here it is recommended to loosen the bolt a little to make the blades a little easier.

I guess I loosened mine a little too much as during the end of my flight I was returning to land and one of the blades came off at about 100ft elevation. The I2 with X4S came down and landed in about 3 feet of salt water. A total loss and write off.

I am going to be sticking with the stock set up from here on out, even with the red prop rattle. An expensive $5400 crash. I have a full brand new set of T-motors I had as backups that will never get used.

Did you recover the blade that detached and were you able to identify the reason it came off?

Was it just that the screw fell out or was it due to some form of failure of the blade itself?

 

[r62ewa]

Did you recover the blade that detached and were you able to identify the reason it came off?

Was it just that the screw fell out or was it due to some form of failure of the blade itself?

I did recover everything and it was the screw had worked out. Kind of hard to understand why as the screw was still down through the top of the blade mount but out of the hole at the bottom of the mount where the threads are. Given how wide the end of the blade is where the hole is for the screw, I thought the screw would have had to come out completely for the blade to let go, not have the screw still in the top hole and just not in the threaded lower part.

 

[MrTVR]

I did recover everything and it was the screw had worked out. Kind of hard to understand why as the screw was still down through the top of the blade mount but out of the hole at the bottom of the mount where the threads are. Given how wide the end of the blade is where the hole is for the screw, I thought the screw would have had to come out completely for the blade to let go, not have the screw still in the top hole and just not in the threaded lower part.

I guess that once the screw has come out of the lower thread then the blade will effectively spring open the mount due to the upwards forces on the blade.

 

[r62ewa]

I guess that once the screw has come out of the lower thread then the blade will effectively spring open the mount due to the upwards forces on the blade.

Hard to figure looking at it later, but as you say I'm sure there must be great force and stress on the blade when it's rotating with the craft in the air.

Thought it must have been a bird strike first, which would have made the crash a little easier to take.

 

[mmarian]

I guess that once the screw has come out of the lower thread then the blade will effectively spring open the mount due to the upwards forces on the blade.

That does sound like a plausible assumption to me. I do not have those props but isn't there a locknut on the bottom and if not why not?
Edit.
Just looked at the design and there isn't one!!! That alone would make me not wanting them, full stop! To me this is a critical design flaw.

 

[r62ewa]

It was a very unfortunate incident and not having any experience with these props previously, to subjectively have to loosen the screw a bit I'm sure can lead to issues for others as well that also may make them too loose. I also then wondered about the continued folding and unfolding of the props and wondered if that caused loosening as well.

 

[cougar]

That does sound like a plausible assumption to me. I do not have those props but isn't there a locknut on the bottom and if not why not?
Edit.
Just looked at the design and there isn't one!!! That alone would make me not wanting them, full stop! To me this is a critical design flaw.

Not correct, there is a self-locking nut. Must have been backed out of the screw to far out of the locking part of the nut.

 

[mmarian]

Not correct, there is a self-locking nut. Must have been backed out of the screw to far out of the locking part of the nut.

That is good to learn. So, the locknut is hidden in a recess in the bottom plate, right? Then the only possibility is that the screw is simply not long enough to prevent what you have alleged has happened from happening.

 

[cougar]

That is good to learn. So, the locknut is hidden in a recess in the bottom plate, right? Then the only possibility is that the screw is simply not long enough to prevent what you have alleged has happened from happening.

You are correct in that the locking nut is in the bottom plate. The screw does go threw the locking nut, I think the poster simply backed out the screw too much, hence out of the locking part of the nut.

When we are talking about backing the screw out we are only talking very little, less the 1/10th of a turn. Hence why I have been talking about torque values.

 

[r62ewa]

I just inspected the prop that had failed. The nut is recessed in the bottom but it is not a locking nut of any kind, it is a standard type nut.

Also, I just put the screw in to where it would normally sit, it took me 8 full turns, yes 8, to get the screw to disengage from the nut. When I loosened the screw I was very nervous of it being too loose and only slackened it enough to get the blade moving a little easier, it was by no means close to one full turn, let alone 8!

 

[mmarian]

You are correct in that the locking nut is in the bottom plate. The screw does go threw the locking nut, I think the poster simply backed out the screw too much, hence out of the locking part of the nut.

When we are talking about backing the screw out we are only talking very little, less the 1/10th of a turn. Hence why I have been talking about torque values.

Only playing a devil's advocate here but if he did that wouldn't he has noticed that one half prop was loose, very loose and the screw was dangling up and down?? If the screw goes right through a locknut, it needs to be unscrewed at least 2mm to get out of the nylon locking part. This seems like highly unlikely scenario to me and one which could hardly go unnoticed.

 

[r62ewa]

Only playing a devil's advocate here but if he did that wouldn't he has noticed that one half prop was loose, very loose and the screw was dangling up and down?? If the screw goes right through a locknut, it needs to be unscrewed at least 2mm to get out of the nylon locking part. This seems like highly unlikely scenario to me and one which could hardly go unnoticed.

And as I just posted, there is no nylon on the screw that I could see. Maybe it's sandwiched on the top of the nut where it cannot be seen, I don't know? But I cannot see any.

 

[mmarian]

I just inspected the prop that had failed. The nut is recessed in the bottom but it is not a locking nut of any kind, it is a standard type nut.

Also, I just put the screw in to where it would normally sit, it took me 8 full turns, yes 8, to get the screw to disengage from the nut. When I loosened the screw I was very nervous of it being too loose and only slackened it enough to get the blade moving a little easier, it was by no means close to one full turn, let alone 8!

This is starting to get interesting. Firstly, confirmation of not locknut in the bottom plate is alarming finding. And the fact that the screw requires 8 turnes to get out from the nut indicates that something else might have caused the prop to fly away.

 

[cougar]

Only playing a devil's advocate here but if he did that wouldn't he has noticed that one half prop was loose, very loose and the screw was dangling up and down?? If the screw goes right through a locknut, it needs to be unscrewed at least 2mm to get out of the nylon locking part. This seems like highly unlikely scenario to me and one which could hardly go unnoticed.

Well I do have a set and they are fine.
The props actually comes pre-tourqued to 50 cN.m from the factory. (checked mine and they all where identical).
So here is what I did: backed out the screws 1/2 a turn and retightened to 25 cN.m and they are now fine without any vibrations and still stays fully extended when motors are stopped.

AND there is a locking nut.