bent prop H

[arruntus]

Sorry @DronAirPro , bad luck ?

I have a doubt, didn't you lose sight of the drone at any time? Can we rule out that it was a bird?

I can confirm that an unbalanced propeller can produce large vibrations. What I find strange is that it is able to break the carbon fiber tube. It's true that the anchors used by Yuneec, with through hole, are not the most recommended (in my opinion). Anyway it seems that what breaks is the engine bracket that is made of plastic, right?

 

[DoomMeister]

@DronAirPro,

What would help immensely in evaluating this flight is to have all of the telemetry files from it. So the Remote, RemoteGPS, Sensor, and Telemetry. This allows us to see the inputs of the ST-16 and how it responds to those inputs. This would help determine what caused the sudden pitch movements seen just before the fall. Extract them from the ST-16 and zip them and post the zip file here using the Attach files button.

Being able to bend the prop back close to being straight without breaking is a major surprise to me. This is indicative of using the wrong type of plastic in the manufacturing process, or improper drying of the plastic before the injection molding. Especially that close to the root of the airfoil.

Also it is a pleasure to welcome you back. I am much newer to the forum than you, but I really love this hobby/profession and try to help as much as I can.

 

[Eagle's Eye Video]

As harsh as my post might have seemed, I also want to welcome back @DronAirPro ... we all want to be able to learn the root causes of crashes like this. Direct analysis of the telemetry is the most effective route to that end. Fortunately, we have some experts in that area on the board. ?

 

[AH-1G]

@DronAirPro
Do the other non OEM blades bend as easy?

 

[DronAirPro]

@arruntus
Yes I can affirm I didn't loose sight of the drone at any moment. Otherwise I wouldn't wonder about what Happened.
As I said, I made mistakes and certainly will make some again but not this time.
That's why I am really searching about what could happen.
I think it wasn't a bird, though I can't affirm this 100% but only 99.99%.
I agree that it seems strange to me as well that it could break the arm but, for now, it is the only reason I can figure out.
Unfotunately, I can't say and don't know what was breaking first, engine bracket, arm...

 

[DronAirPro]

@AH-1G about the other non-original blades I can't say.
But it is of course a thing I should have think about.
I am goign to test these (as anyway, I will never use them) and then tell you what happens.

 

[arruntus]

A vibration if it enters into resonance, we can't even imagine how destructive it can be. What doesn't add up is that you were in stationary flight, so the increase in revolutions doesn't affect so much.

The characteristics of the propellers, almost all manufacturers go in the same direction, hardness but with a little flexibility. That means that it is easier to split, has exceeded the limit of hardness, that doubles in half. Another of the propellers has been split in the central base, that is normal. Splitting in half is normal. That you are missing more or less big pieces is normal. I have never seen a bent propeller, or plastic composite or carbon fiber that are 99%. Wooden propellers are rare in drones.

 

[DronAirPro]

@Eagle's Eye Video and @DoomMeister
Of course, you're right.
Here are the telemetry logs.
Ihad to zip them in an archive as the site told me that the type of file (separately) wasn't recognize.
Thanks in advance for you feedback.

 

[DronAirPro]

@arruntus This is a point that I believed in, vibrations and if entering into resonance, in this case, not many materials could resist.
Even if I am not sure about it, this was my first theory and, in my opinion, could probably be the right one
Of course, I am still open to others explanations.

 

[DronAirPro]

Here are some picture of another no-original blade, coming from the same package than the one I used.
Hand bend an hand straightened.
Exactly the same behavior than the one That was in use during the crash.
I could bend it and straighten it without breaking it.
If it can help for the diagnosis...

 

[arruntus]

Well, I think you've got the cumpables. The propellers. I think that behavior is not normal, and if for whatever reason, material fatigue, has bent in mid-flight, that most likely has caused vibrations so large that has unbalanced the drone in such a way that has made a cascade effect and has broken more than one and therefore irremediably the controller has not been able to regain control.

Unfortunately, it is an expensive lesson for you, and a great warning for everyone.

I always use carbon fiber propellers except in the Yuneec. I've even tried propellers that are, let's say from an untested manufacturer, and in the balancing process leave areas with little resin and with use affects the first layer of the carbon fiber, and discard them immediately when I detect it. It is not worth the risk.

 

[PatR]

Normally, plastic deformation occurs after a sustained force is applied to a material. Not the case here. Most props use materials designed to accept elastic deformation, allowing them to flex slightly under load and return to their original shape after the load is removed.

What is evident is the prop manufacturer used improper materials which permits the blades to deflect under load and experience severe deformation under normal flight loads. The material used exceeded its stress limit and achieved permanent deformity with the bend it now possesses. In all probability the prop hit nothing and failed under normal flight loading.

Any prop that can be bent as you did by hand and forced back into shape is not one to fly with. Works fine for a propeller beanie cap or a whirlybird hand toy but not for anything with significant thrust loads.

You might consider telling everyone the brand and seller so they can avoid buying props that will end up costing them an aircraft.

 

[DoomMeister]

@DronAirPro

Thank you for uploading the telemetry. I am using @h-elsner 's Q500log2kml v4.1 to analyze your telemetry from flight 00071.

The total time was 8:24 minutes with the battery at 16.4V at the start and 14.0V at the end of the telemetry from the aircraft (it was at 8 meters traveling at 22m/s so had probably impacted).

The flight was quite normal for most of the flight although the battery seemed to sag quite quickly after takeoff. I concentrated on the last 37 seconds of the flight as that is when things started going wrong.

The first Low Battery alarm (error_flags = 1) came at 14:44:37 and lasted about 0.5 seconds and probably did not trigger the ST-16. You started getting a consistent Low Battery alarm at 14:44:46 while you were still in Angle mode of flight. Eight seconds later at 14:44:54 you switched to Home mode (RTH - f_modes 13 coming, and 14 landing). That is seen in the telemetry with the aircraft yaw changing.

At no time during this 37 second time period did you make any inputs on the sticks, so the reactions of the aircraft were not caused by pilot inputs. 5.5 seconds after RTH was initiated a strong pitch forward for about 3 seconds then back for another 3 seconds was seen in the telemetry. Immediately following this pitching at 14:45:06 the aircraft started spinning left and wobbling violently with battery voltage dropping to 14.0V sending a Low Battery 2 alarm (error_flags = 2) with Motor 2 stopping 3 seconds later at 14:45:09.

So the actual cause of the instability is inconclusive from a telemetry standpoint other than the likely possibility of the battery no longer capable of sustaining flight.

I still think there is a high probability of a midair collision with something that triggered the pitch change at 14:44:59.5 or as you say the prop could have bent in flight.

One thing is for certain, and that is that the third party props are of an inferior quality as they should not be as pliable as they are. It is very apparent that third party props need better evaluation before being used.


Flight path from kml file shown in Google Earth Pro


altitude in meters, tas in meters/second, and motor_status 255=all good 253=motor 2 off


error_flags 1=low battery1 at 14.3V, 2=low battery2 at <=14.1V, f_mode 3=Angle w/GPS, 13=RTH coming, 14=RTH landing


AC pitch,roll,and yaw telemetry


ST-16 pitch, roll, and yaw stick inputs (2048 = neutral position)

 

[DronAirPro]

Thanks to all for your pertinent comments and help!

About the props, I know, this was a very big mistake I did. Once again I thought they were original ones but stupidly didn't check it properly! My fault!
Of course, a prop that can be bent then straighten without breaking like we can see on the pics are really very bad ones.
I'll try to look for the invoice in order to find out where I did buy them.

@DoomMeister thank you for the very accurate telemetry analysis.
I use as well Q500log2kml V 4.1 under Linux to analyze the telemetry but couldn't manage to read all the data, some freeze the software, maybe the Linux version, I don't know.
Anyway, I am a tech junkie as well, but very faraway to have your level of expertise in this domain.

I thought that the battery alarm was short about 1/2s and that 14V (eg 3.5V per cell) wasn't a so big deal (for the crash process) but I noticed as well that the battery drained quite fast at the beginning of the flight.
Just one point to take in account is that I eared clearly a noise like something flapping fast and then saw the arm break, I think this couldn't be induced by a battery failure even if the power factor is, of course, to take in account.
I believe, maybe am I wrong, that the motor stopped when the arm broke still attached by the wires but with proper connection lost.

So I tend to think that, the battery wasn't that good for sure and that more than likely the prop bent in flight which could explain the variation of the pitch, the bent prop, the broken arm and the noise I eared

I didn't see anything colliding with the drone but this as well doesn't mean it didn't happen.

Of course all the theories and analysis here are very pertinent and are possible!
So, once again, many thanks to all the experts here who took the time to work on this and to give me their feedback.

I am curious about knowing if this kind of incident happened to others and what was the reason of it, if they could find it.

I wish all of you good and safe flights!

 

[PatR]

A blade bending in flight as the one you have would cause extreme vibration and could cause a boom to break. Had the blade bent in flight, in all probability the bend under load would have been more severe than is depicted in the picture. The effect would be more severe than actually losing the blade in flight.

For general PSA purposes, a severely imbalanced prop or a prop that tosses a blade in flight can induce enough vibration to rip an engine mount completely off an airplane, for both full scale and RC. The standard emergency procedure for dealing with a broken propeller blade is to shut down the engine as quickly as possible before the engine departs the aircraft to prevent a severe change in center of gravity due to the separated engine. The shift to an aft CG can render an aircraft uncontrollable.

This is why I suspect the prop was the cause of one boom failure. In all probability the remaining booms would not have been as severely impacted.

 

[DoomMeister]

Anyway, I am a tech junkie as well, but very faraway to have your level of expertise in this domain.

I am learning with every telemetry file I look at and still have much to learn. I am very sure you are being modest about your own abilities.

Would love to see video from the POI you shot in this flight with the rising pull up at the end. Hope you are able to return to flying again soon.

The wobble present in the telemetry would have made for some very strange noises as the H was on its way down. Hope I never experience that with my own.

 

[DoomMeister]

I just read a message I got from Steve Carr in response to the numbering of the H480 motors. He sent this graphic:



If you compare this to the photos of the aircraft taken at the crash site, you will find that Motor 2 that shut down near the end, is the one where the arm broke next to the body and left the wiring hanging.

This clears things in my mind a little more. DronAirPro did not see anything strike the aircraft, but heard an awful sound saw the aircraft become unstable and an arm break off then finish plummeting to the ground.

Referencing the 4th photo in post #20 of this thread the motor that had the severely bent prop was number 4 (right rear) and probably caused the first severe pitch movement after the RTH was initiated. The FC tried to compensate but the severe oscillations in flight attitude were too much and the arm for Motor 2 snapped. Now with only four functional motors there was no way to recover.

 

[PatR]

That makes things even more interesting.

 

[Steve Carr]

I am curious about knowing if this kind of incident happened to others and what was the reason of it, if they could find it.

This is the first time I can recall a motor arm breaking in flight without an observed cause such as a tree branch, over head wire or a bird. I also have never seen a prop bend in flight without a similar trauma.

Can you inspect the broken motor arm more closely and perhaps post some pics?

I do have a motor pod separated after contact with a tree branch. The glue failed and the rivet sheered off. At first it wasn't apparent but closer inspection revealed the problem. It's possible this happened to your H from a previous incident but was not "hidden" damage.

 

[DronAirPro]

@Steve Carr I inspected the motor and arms.
This is what I could notice and some pics as well.

- Motor (4) with bent prop:

The arm is still attached but its fixation is distorted and I can't lock it.
Motor is Out of order, hard to turn it and not able to unlock the prop.

- Motor (2) arm broken at its base:

The arm is broken 1 or 2mm inside the arm attach.

- Another global view of the drone. The cat is a bonus...


- Arm (1) is OK (as far as I can say) and motor as well.
- Arm (3) is OK but not totally sure about the motor. Should be OK but I have to check it more accurately.
- Arm (5 & 6) broken at their attach point on the drone, a bit like the N° 4 and not sure about the motor like N° 3.