6th December 2017

In the following matter I am currently in dispute with DJI the manufacturer of the Inspire 2  Drone helicopter. I informed DJI that there needs to be a safety  recall of the DJI Inspire 2 helicopter for public safety and legal  compliance reasons, but the company seems unwilling to take any  action.  In informing DJI and other users, the UK BMFA and the UK CAA of  this problem, I am discharging my responsibility under the UK BMFA and  CAA guidelines for ensuring safe operation of a model aircraft.  

The rotor blades and blade mounts on the Inspire 2  are an unsafe design.  Every DJI Inspire 2 supplied to date has the  same design defect.  Due to a loose fitting quick release mechanism, the  blades are improperly clamped to the motors, and there is up to 5 mm of  play at the blade tips.  With this amount of  free play in the blades, ensuing vibration will cause stress fracture  of the blades, and will also cause damage to the motors and motor  bearings.   

I am personally unwilling fly the Inspire 2  drone with the standard blades and quick release mounts because I do  not want to risk the safety of the general public through the high  likelihood of blade or motor failure, and nor do I want to cause damage  to the rest of the drone through the vibration caused by ill-fitting  blades.  Various 3rd party companies have recognised this problem.  For  example, these rotor blades and blade holders are available at a cost of  over 200 Euros.  https://www.heliengadin.com/coll ... -folding-propellers

By  fitting these properly designed rotor blades and blade mounts, I will  overcome the design fault in the DJI quick release blades and thereby  will satisfy the UK BMFA and CAA guidelines for ensuring safe operation  of a drone.  I urge other pilots of the Inspire 2  helicopter to take action to ensure safe flying by fitting properly  designed rotor blades, and not the ones as supplied as standard by DJI.

Thank you,
Robert Sherratt
CEng MIET

you do not want to - do not fly. who is forcing it? goodbye

Or just put shims on the original props.  Works great.  No play at all.

Shims? Did you apply cyno to the bottom of each prop, then file the cyno down to fit?  Like this ?  ...

What are these BMFA and CAA guidelines you refer to?

Hi, Robert, thanks for the feedback and suggestions to our products.
For the propellers issue, I have explained in many threads, I will explain again.

As the propeller and propeller mounting plate are plastic parts made through injection molding, there might be an engineering tolerance with them.
The shipped Inspire 2 aircraft have been tested and quality assessment has been conducted. The tolerances are within a standard range. This issue does not affect the normal use and flight safety.
Thank for the kind understanding.

Did you buy this from DJI direct or through a Dealer? The reason I ask this is that I received mine about a month ago and there are no issues with the props.

I really do not understand the unfriendly responses from other users.
Robert, as an attentive and caring pilot, simply wishes to publicly denounce what hundreds of dij Inspire owners have been complaining about since this drone entered the market.
Everyone is free to act as he/she thinks to solve the problem, either provisionally or definitively, but I do not think it is right to minimize the hazard, especially if you work professionally in various scenarios, where you could not just destroy your investment, but you could also create serious damages to things and / or to people.
I personally spent money for an alternative to the original plastic propellers, which would allow me to take off feeling more comfortable.
I am a professional atplh helicopter pilot with thousands of flying hours on multi-engine turbine helicopters, but every time I started up the dji inspire (at first the Inspire1 and then the Inspire2) my skin was getting stuck. Now, at least as far as propellers are concerned, I am quieter and I can concentrate on the work I am doing rather than thinking every moment about what could happen if the "bird" falls down. Therefore please, rather than criticize, appreciate the effort of one of us who diligently points out that it is not possible for such an expensive drone to have such frail and unsafe propellers.
It's like buying a Ferrari or a Lamborghini with the tires of a bicycle.
All the best..

Mark Guille Posted at 2017-12-6 18:14
What are these BMFA and CAA guidelines you refer to?

Mark,

In the UK the CAA's document CAP658 has the status of law.  The BMFA is deemed as a competent organization in the UK for purposes of training r/c pilots and ensuring public safety.  You can download a copy of CAP658 here:

http://publicapps.caa.co.uk/moda ... =detail&id=5631

The BMFA handbook cites CAP658 and on matters of safety of model aircraft the BMFA add further checks and requirements that also carry the force of law in the UK in the event that a member of the general public was injured.  You can download the BMFA handbook here:

http://handbook.bmfa.org/

The BMFA stress the importance of checking rotor blades before every flight, and such checks include checking for damage, balance, tracking and lack of vibration.

The DJI Inspire as supplied "out of the box" fails these tests for tracking and lack of vibration.  The blades do not track properly, there is extreme vibration and it is attributable to the loose rotor mount permitting up to 5mm free play at the rotor tips.

I read the reply from DJI Mindy stating "this issue does not affect the normal use and flight safety".  I disagree because the BMFA trains all r/c drone and helicopter pilots that loose fitting blades on a model helicopter will lead to structural failures in the blades and motor bearings, and it is a basic pre flight safety check that must always be done, to ensure there is no blade vibration and the blades track correctly.  I have reported this matter to the CAA in the UK, and have asked the BMFA in the UK to intervene and make a determination and ruling on this matter, since DJI dispute what I say.  Maybe I am wrong, we will see.

The fault is easy to fix by application of CA glue and filing the blades to fit as per the video above.  But that is not the point.  This procedure should be done by DJI when supplying a "ready to fly" drone.  

Rodger8 Posted at 2017-12-7 04:03
Did you buy this from DJI direct or through a Dealer? The reason I ask this is that I received mine about a month ago and there are no issues with the props.

Hi Rodger,

I bought from a dealer in the UK.  Maybe DJI have done something about this for the USA market, but if so, why DJI Mindy's reply below stating that "this issue does not affect the normal use and flight safety".

As DJI Mindy states, the plastic props are "parts made through injection molding, there might be an engineering tolerance with them".  In my case, every propeller has "engineering tolerance" so that the tips of the blades rock up and down by at least 5 mm.  In your case, it seems the "engineering tolerance" happened by chance to give a perfect tight fit.

DJI Mindy Posted at 2017-12-7 01:22
Hi, Robert, thanks for the feedback and suggestions to our products.
For the propellers issue, I have explained in many threads, I will explain again.

Hi DJI Mindy,

Thank you for your reply.  DJI has done a great design job on the other aspects of this helicopter.  But I strongly disagree with DJI concerning the issue of the loose fitting propellers.  You state that "this issue does not affect the normal use and flight safety".  This contradicts organisations such as the BMFA (British Model Flying Association) who train r/c helicopter and aeroplane pilots that this is a very dangerous situation.

For example, what happens if the propeller nut on an aeroplane propeller is loose?  It is just the same issue with the DJI quick release propellers when they are a loose fit.

Because of my public safety concerns,  and because of the disagreement from DJI, I have referred the matter to both the BMFA and to the CAA in the UK.  Can I assume that DJI will take action when either or both of these organisations also disagree with DJI in this matter?

Thank you also, for your kind understanding.

Cesare Lanza Posted at 2017-12-7 07:48
I really do not understand the unfriendly responses from other users.
Robert, as an attentive and caring pilot, simply wishes to publicly denounce what hundreds of dij Inspire owners have been complaining about since this drone entered the market.
Everyone is free to act as he/she thinks to solve the problem, either provisionally or definitively, but I do not think it is right to minimize the hazard, especially if you work professionally in various scenarios, where you could not just destroy your investment, but you could also create serious damages to things and / or to people.

@Cesare@ Thank you very much for your reply, at least there is one other pilot who agrees with me :-) ... I will sleep easier now!

I have also taken this matter up with DJI. It went on for months (see https://forum.dji.com/thread-100223-1-1.html).
It got me EIGHT sets of props - all with foam inserts and of them ill-fitting!
There are of course solutions, one that I devised myself, but sadly none from DJI.

Kind regards
Allan

allanart Posted at 2017-12-7 10:12
I have also taken this matter up with DJI. It went on for months (see https://forum.dji.com/thread-100223-1-1.html).
It got me EIGHT sets of props - all with foam inserts and of them ill-fitting!
There are of course solutions, one that I devised myself, but sadly none from DJI.

Allan, is that your video I linked to above?  In which case I thank you for making it.  I like the solution with cyno applied to the bottom edges of the blades and then filed to fit with no play, and it's what I am doing with the stock blades so I can keep them as spares.  I'm also ordering some after market folding props with CF blades.  

This design / safety issue, and DJI's response is a big enthusiasm dampner after spending over 6,000 Euros on a "top of the market" drone.

Allan, my apology to you.  I have now read your thread and the complete saga you've been through with DJI all this year.  Congratulations to you for sticking to your principals!!  My thread must feel like Groundhog day to you!  It is good to know that we and many other experienced pilots share the same opinion, that these loose fitting propellers are a real, genuine safety issue.  And in the UK this matter can be legally enforced by the BMFA and the CAA, so that is the route I have taken because I felt this action is the only thing that will get DJI'sattention.  I am very surprised to learn that DJI Engineers are issuing statements that "this is not a safety matter", when clearly in accordance with BMFA and CAA in the UK, any loose fitting propeller is absolutely and definitely a critical safety matter.  For commercial use of drones in the UK we now have to prepare an operations manual and undergo training in which it is again and again emphasised that propellers on drones must be correctly and tightly fitted.  The DJI I2 will definitely not "pass" the criteria for commercial use in the UK unless modifications like your shims or the CA glue layer or after market propellers are added.  Shame on you DJI!

Incidentally, although I'm working in Albania at the moment (hence my handle), I am a UK citizen.

"I am very surprised to learn that DJI Engineers are issuing statements that "this is not a safety matter", when clearly in accordance with BMFA and CAA in the UK, any loose fitting propeller is absolutely and definitely a critical safety matter. "
Well, DJI is a modern company. That means the engineers probably have to shut up and obey the managers. Like the programmers, the doctors... and anyone who actually happens to know something.

The CA glue solution only works for a bit of time as the slight movement within the mount grinds down the CA glue to dust and the same issue happens. The center hub to the props also has play so that wiggle is what wears the CA glue.  Im sure that anyone that rides in a helicopter or airplane would like their props tight and not to wobble?. LOL,  I place a piece packing tape cut to the same outline as the mount on the motor and this takes up the slack. If it fails under warranty DJi can replace the bird.

RobAlbania Posted at 2017-12-7 08:42
Hi Rodger,

I bought from a dealer in the UK.  Maybe DJI have done something about this for the USA market, but if so, why DJI Mindy's reply below stating that "this issue does not affect the normal use and flight safety".

In my case DJI corrected the issue. I have no prop rattle and a very acceptable amount of give which is necessary for longevity. The reason that I asked as to where you purchased your Inspire was with the thought that you received older inventory. I would contact DJI, I am sure they will take care of you.
r

RobAlbania Posted at 2017-12-7 13:28
Allan, is that your video I linked to above?  In which case I thank you for making it.  I like the solution with cyno applied to the bottom edges of the blades and then filed to fit with no play, and it's what I am doing with the stock blades so I can keep them as spares.  I'm also ordering some after market folding props with CF blades.  

This design / safety issue, and DJI's response is a big enthusiasm dampner after spending over 6,000 Euros on a "top of the market" drone.

No, my own solution was a set of precision cut vinyl shims. There is a photo of these posted somewhere within the (long) thread I referenced - and several more elsewhere on the internet. I supplied quite a few of these to others, but I am not keen to do so anymore.
Kind regards
Allan

I saw this repair video some time ago and it seemed very logical to me - enough so that I found an after-market solution for my I2 that I'm satisfied with for now.  

To say simply, "you do not want to - do not fly. who is forcing it." is not much of a solution for someone who has spent thousands of dollars on the product.  
My only comment is that a recall of the propellors/mounts would seem like the appropriate thing, if there was going to be a recall - not a recall of the whole aircraft. Of course, even that would have to involve a "fix" or, indeed, the whole aircraft would be worthless.

I don't mean to contradict the assertions of the original post, and i understand that being safe means not waiting for a problem when you can see a problem coming, but if there was actual stress-testing or even an actual event that demonstrated fractures I'd really be interested to see that.  Of all the posts I've read from this forum I do not remember a single mention of (or image of) a fractured prop that wasn't the result of an actual impact.  

It does make sense, though, that wear related to poor fitment would just get worse (probably at an increasing rate) with added use. I think that applies to any mechanical situation.

I worried more about possible unnecessary wear on bearings while the props were dancing around the shafts at 10,000 RPM - and what THAT could cause while flying.   I wasn't willing to risk it - especially since the approach to any sort of "breaking point" would not be something that I could easily assess for myself - but I would be held responsible.

Rodger8 Posted at 2017-12-8 09:01
In my case DJI corrected the issue. I have no prop rattle and a very acceptable amount of give which is necessary for longevity. The reason that I asked as to where you purchased your Inspire was with the thought that you received older inventory. I would contact DJI, I am sure they will take care of you.
r

Hi Rodger,

I'm glad that DJI corrected the issue for you.  Yes, I probably did receive older inventory.  In my case DJI have not corrected the issue ... see DJI Mindy's response in this thread, which is identical to the response I received from the DJI support department on Monday and Tuesday this week.   I received an email from DJI's support manager today (Friday), and I am responding to it, by providing a link to this thread.  Meanwhile, I have now modified all propellers with the "cyno" technique in the video posted above.  I am going filming this weekend.

DS924 Posted at 2017-12-8 10:03
I saw this repair video some time ago and it seemed very logical to me - enough so that I found an after-market solution for my I2 that I'm satisfied with for now.  

To say simply, "you do not want to - do not fly. who is forcing it." is not much of a solution for someone who has spent thousands of dollars on the product.  

@DS924@  I agree your comment about recall of propellers/mounts, thanks.

Re: you question about stress testing and fractures of propellers.  I understand from correspondence in the past with their safety officer, that the BMFA in the UK has a library of crash investigation reports where someone was injured after a mid-flight propeller or rotor failure.  In one case I read in the Uk press, someone died after a rotor blade came off in flight and hit the pilot, puncturing his chest and heart.  The "fault" was attributed to improperly fitted or balanced rotor blades.  The BMFA insist that before every flight, UK helicopter pilots shall ensure the rotor blades and control linkages and control surfaces are a tight fit with no significant free play / wear.  Also blades must be balanced, and rotor tips tracked so there is no vibration at the tips.

Now, in the case of the I2 with the "latest generation" props supplied to me this week, when the props spin up there is a 5 mm "fuzzy line" at the rotor tips that indicates a serious problem with either balancing, tracking or the mounting point.  The blade noise and rattling also indicates a serious problem.  This is not a figment of my imagination.  And this is something that DJI state "is not a problem" and "has been passed by their safety department".  Well, DJI's safety department must be high on poppy seeds.

I am not prepared to compromise on this issue, especially since my roles in the past in the UK have involved setting up and chairing a BMFA model helicopter club, and subsequently being the area safety officer.

I’ve also had exactly the same response from DJI Customer Support - they just aren’t interested. My bet is they’ll only react after an accident.

Having said all of this has there been a case where the aircraft has crashed due to blade failure/detachment in flight which could be attributed to stress/vibration? I’m guessing that some aircraft out there by now have many hours logged on original props without any modifications?

RobAlbania Posted at 2017-12-8 10:46
Hi Rodger,

I'm glad that DJI corrected the issue for you.  Yes, I probably did receive older inventory.  In my case DJI have not corrected the issue ... see DJI Mindy's response in this thread, which is identical to the response I received from the DJI support department on Monday and Tuesday this week.   I received an email from DJI's support manager today (Friday), and I am responding to it, by providing a link to this thread.  Meanwhile, I have now modified all propellers with the "cyno" technique in the video posted above.  I am going filming this weekend.

If you did the CA trick you should be all set then. Sorry about the grief but alls well that ends well. I have a very small amount of give on the white props but acceptable. The red props are very firm. Nothing of any concern. You have to have a bit of give here and there.

RobAlbania Posted at 2017-12-8 15:55
@DS924@  I agree your comment about recall of propellers/mounts, thanks.

Re: you question about stress testing and fractures of propellers.  I understand from correspondence in the past with their safety officer, that the BMFA in the UK has a library of crash investigation reports where someone was injured after a mid-flight propeller or rotor failure.  In one case I read in the Uk press, someone died after a rotor blade came off in flight and hit the pilot, puncturing his chest and heart.  The "fault" was attributed to improperly fitted or balanced rotor blades.  The BMFA insist that before every flight, UK helicopter pilots shall ensure the rotor blades and control linkages and control surfaces are a tight fit with no significant free play / wear.  Also blades must be balanced, and rotor tips tracked so there is no vibration at the tips.

There are SO MANY sUAVs out there and many of them are best thought of as toys, even though they have some video or still-photo capability.  It wouldn't surprise me to know that some of them are being employed beyond their safe capabilities because the technologies are filtering down to fairly low-end devices, i.e., less reliable, less capable, and undoubtedly less tested aircraft.

So, when you refer to reports that your read or otherwise heard about are you referring to reports specific to the DJI prop mounts or are you talking about problems identified in sUAVs, generally, that simply add to the concerns that some of us already have about these particular props/mounts?

Just curious...

DS924 Posted at 2017-12-9 06:59
There are SO MANY sUAVs out there and many of them are best thought of as toys, even though they have some video or still-photo capability.  It wouldn't surprise me to know that some of them are being employed beyond their safe capabilities because the technologies are filtering down to fairly low-end devices, i.e., less reliable, less capable, and undoubtedly less tested aircraft.

So, when you refer to reports that your read or otherwise heard about are you referring to reports specific to the DJI prop mounts or are you talking about problems identified in sUAVs, generally, that simply add to the concerns that some of us already have about these particular props/mounts?

None of the reports that I have read or otherwise heard about are specific to the DJI Inspire 2.  However the teaching and instruction from the BMFA about loose fitting propellers is very clear, and this is a key item we are required to check in our pre-flight check list.  It is a required part of the operation procedure manual for commercial use of drones.  I have solved this issue, no thanks to DJI.

RobAlbania Posted at 2017-12-10 08:58
None of the reports that I have read or otherwise heard about are specific to the DJI Inspire 2.  However the teaching and instruction from the BMFA about loose fitting propellers is very clear, and this is a key item we are required to check in our pre-flight check list.  It is a required part of the operation procedure manual for commercial use of drones.  I have solved this issue, no thanks to DJI.

Yeah, I solved it, too.

There maybe a connection between the loose prop vibration and the motor mount to arm glue failures.  I see glue failure reports during extreme high temperature and low temperature flights.  Could vibrations cause failure of poorly bonded surfaces by inducing shear forces in the joint at temperature extremes?  Or could thermal expansion and contraction be the cause of glue failures or a combination of both.  Being that the glue joint is hidden there is no way to test the integrity of the bonding by external visual inspection.

RobAlbania Posted at 2017-12-10 08:58
None of the reports that I have read or otherwise heard about are specific to the DJI Inspire 2.  However the teaching and instruction from the BMFA about loose fitting propellers is very clear, and this is a key item we are required to check in our pre-flight check list.  It is a required part of the operation procedure manual for commercial use of drones.  I have solved this issue, no thanks to DJI.

How did you solve it?

Altitude Drones Posted at 2017-12-19 23:54
How did you solve it?

I solved it using the "cyano" technique in the YouTube video I posted earlier in this thread.  

eggbeater Posted at 2017-12-19 17:07
There maybe a connection between the loose prop vibration and the motor mount to arm glue failures.  I see glue failure reports during extreme high temperature and low temperature flights.  Could vibrations cause failure of poorly bonded surfaces by inducing shear forces in the joint at temperature extremes?  Or could thermal expansion and contraction be the cause of glue failures or a combination of both.  Being that the glue joint is hidden there is no way to test the integrity of the bonding by external visual inspection.

Yes, I agree and so does one of the top trainers in the UK for commercial drone flight, who was a helicopter pilot in the UK army air corps.  He will not allow any drone to be flown under his instruction unless its rotor blades have no free play in the mounting point.  It seems "obvious" that there is a high risk of fracture or damage to any rotor craft when its rotor blades are loose in their mounting.  We are very surprised that DJI state otherwise.

RobAlbania Posted at 2017-12-20 05:53
I solved it using the "cyano" technique in the YouTube video I posted earlier in this thread.

Thanks.

I've done the same. Just make sure that you re-check often as the glue wears down with time and you'll need to re-apply to ensure a tight fit.

I ordered one of those prop balancers off eBay for the I2 blades after reading this.  Evidently you need to use it in conjunction with a red or white hub for the props as well.  I've also done the cyano glue to tighten up any looseness.  There is a video demonstrating the use of the balancer on Youtube with an Inspire 1 prop and it shows the imbalance of the factory props.

I can see where a bubble of the assembly glue in the tubes can fail if the assembler does it wrong from some glue videos on carbon fiber joints.  Maybe wouldn't hurt to examine the joints to see if there are any openings and maybe use a thin cyano glue to wick into the joint.  If one could see into the motor area of the tube and examine the joints inside there it might not hurt either.  I know from playing with epoxy type glues that the slow-setting ones often will provide a stronger joint as it etches a bit into the material for a stronger joint than the rapid drying ones that DJI might be using and if they are using the correct glue too.  The J.B. Weld Slow and their Quick dry come to mind.

DJI Mindy Posted at 2017-12-7 01:22
Hi, Robert, thanks for the feedback and suggestions to our products.
For the propellers issue, I have explained in many threads, I will explain again.

When the props are tight fitted I get 40% less noise of the Inspire 2, less vibration etc !!!!

Vincent

allanart Posted at 2017-12-8 09:25
No, my own solution was a set of precision cut vinyl shims. There is a photo of these posted somewhere within the (long) thread I referenced - and several more elsewhere on the internet. I supplied quite a few of these to others, but I am not keen to do so anymore.
Kind regards
Allan

Hi Allen

This is definitively reading about the same problem again!  I remember your post. I purchased my Inspire 2 from Best Buy because of their customer service.  My first Inspire 2 had some problems with alignment.... so I returned it and ordered another one that was perfect, except the loose props. DJI was very nice to me and sent replacement props and a couple of hubs. But they really were not much better than my originals.  I have several ill fitting sets of props from DJI over several months of requests. I even tired to replace the hubs.
So, the other point is with continued use, the material can start to wear causing the tolerance to become slightly more loose fitting.  I keep a close watch on the props, preflight checks that every pilot should perform. I have not noticed any vibration or stress on the arms at all.  Now our weather has become pretty bad in our area, so I am not flying much at all. I was thinking about your shim solution...
  
What is the possibilities of getting a set of shims from you?  I will send you a PM

All the best
Rich

Rodger8 Posted at 2017-12-8 09:01
In my case DJI corrected the issue. I have no prop rattle and a very acceptable amount of give which is necessary for longevity. The reason that I asked as to where you purchased your Inspire was with the thought that you received older inventory. I would contact DJI, I am sure they will take care of you.
r

Rodger
Some of us were not so lucky    but I am not complaining.

I am curious if you have props with the V2 stamped in them or V3?

For me, I saw no difference between the different prop versions that DJI sent me.  I mixed and matched to get the best fitting set on my Inspire for now.

Rich

My red ones were tight, just checked, but the white ones were now loose.  Had to resort to the CA Medium glue on them and now they are tight again.  I think the plastic just wears over time or it compresses and leads to the looseness matter.

One part that bothers me is the little black plastic finger that holds the prop down (Two of those that you twist to lock it on.). If that plastic finger develops a crack while locking, I can see a prop coming off in flight.

RichJ53 Posted at 2017-12-22 09:19
Rodger
Some of us were not so lucky    but I am not complaining.

I'll check for the version #. I thought they sent you new Hubs? On mine the red is very tight and the white has a very slight amount of give. I have no rattles or vibration. You got yours quite a while before I got mine.

I'm much more concerned about the quality of the assembly line I'v seen extreme differences on the amount of loctite particular around the motor screws.

Some of them where drown and others had almost none loctite.

Also the the motor brace that's glued to the carbon tube is an extreme likely spot where workers did a loser job on it.

Why would some one came up with this solution?



Here just a few other examples of this mess

$5000. And you still have to jury rig the props....Rediculous!