bent prop H

[Sarah]

I presented my apologies in FB, not to you, but to the group because by answering to your aggressive and not constructive comments I (and you = We) polluted the discussion.
As you can see, I think I haven't been upset by any comments (but some of yours) here.
I said many times thanks to all people who helped me if not to you (until your very last post, which was interesting, I appreciate).
I prefer to think about ideas flowing-in as they come, before wring them... As they come.

So, let's stay on the behavior of your last post and let's enjoy nice discussion.

Any other un-kindness to expell ? are you done with your ego, can we move forward ?

 

[DronAirPro]

Any other un-kindness to expell ? are you done with your ego, can we move forward ?

To expell ??? Or maybe to expect ?
As I said but it seems unfortunately you still don't want to read : "So, let's stay on the behavior of your last post and let's enjoy nice discussion."
Isn't this clear enough for you ?
OK so I leave you the last word about this as your ego is sooo big that you always want to be last one speaking.
I offered you to stay on a nice behavior, like in one of your last comment I appreciated and thanked you but...
So, I will just ignore you from now on.
Have a very nice day and keep on moving forward.

 

[AH-1G]

@DronAirPro I maybe missed something, did you write that you changed the motors ? If so why ? and during the remplacent can screws have caused some harm to arms like if not finely placed or if too tight or remplaced by inadapted screws ? Did you hear this typical tearing sound while remplacing ? have you remplaced motors due to a crash ? changed arms previously ?
[/QUOTE]
I've replaced motors, six to be exact, (replaced, not "remplaced). you can't hear the tearing when screwing to tight. If you over screw it will be just loose from that point on.

 

[Sarah]

No, I didn't changed any motors or arms, had no crash and what annoys me is that I didn't ear any scratching sound when trying (slightly) to twist the arms.
Indeed, you are right, it could have been a good reason for the broken arm.
I had, as I said before 2 or 3 "not so good landing" when I began with the H, like many of us I think, in high grass or brambles but I checked everything after, it was long ago and the H did many hours of flight since then.
So, could it be fibers tears, crushes or punctures, whatever, that happened at this moment which caused the problem much later ?
I honestly don't know if it could or couldn't happen.
If you have information about this point, I'll be more than happy to learn about this.

Thanks for your comment

Well I've presented a web site analysing how carbon fiber breaks, have you seen the video on it ? According to your archery souvenirs, and web site suggested, carbon fiber may have weaknesses that reveal later on when stressed. As you know already a accident happens when small incidents happen in conjuction.

Do you have a suggestion to the chain of incidents, that caused the crash ?

 

[Sarah]

I've replaced motors, six to be exact, (replaced, not "remplaced). you can't hear the tearing when screwing to tight. If you over screw it will be just loose from that point on.

Why that change of motors ?

 

[AH-1G]

After 75 hours of flying I noticed one of the motors making an unusual noise. So decided to replace all.

 

[FlushVision]

@PatR Wow ! Thank you for these information about the batteries.
I knew it was mandatory not to discharge them at low voltage per cell but discharged my H batteries several times down to 14V even once or twice to 13.9V.
So I believe I have to be cautious now, as my batteries are more than likely not so reliable after this, even if they charge fully and don't inflate or heat.
This is very interesting and I will keep in mind this 14.4V limit for the Typhoon H.

Those of us that are 'in the know' and want to be able to get a good number of charge cycles out of our H batteries and avoid premature battery failures are usually on the ground with the aircraft switched off by 14.5v...some look to be on the ground by 14.7v but I think that is being a little too cautious in my humble opinion. For me, 14.6v or 14.5 is the target. 14.6v on the ground after a 'normal' flight will give between 11 and 14 minutes in the air depending on the air temperature and how strong the wind is. 14.5v on the ground will give anything up to 16 minutes (if you are lucky) in the air, again depending on the weather. The best air time I've ever managed was 19 minutes but that was taking the power down to first warning at 14.3v. A few people have bettered this but I see that as unusual.

The most important thing, though, is never to see the first warning come up on the ST16.

 

[DronAirPro]

@FlushVision Even not wait for the first warning ?

 

[arruntus]

The fact that the controller cuts the electricity of the motors, has the battery the voltage that it has, neither I understand it nor I will understand it. It has neither feet nor head, it is the most absurd thing that can be done, you only have to compare the value of a whole drone that can be in the air with the value of a battery. If having to throw the battery because you go down with less than 3V per cell is to save the drone, what does the flight controller cut off my power?

For me it doesn't make sense, maybe I miss something, someone comes up with a reason to cut?

 

[PatR]

About hairline cracks it seems not to happen on carbon fiber

"When carbon breaks it does so with a tear, crush or puncture. Carbon does not develop small cracks which could fail later like a steel or alloy frame might, by nature of it being a composite material. "
[/URL]

As I don’t ride bicycles I can’t relate to their stress testing and inspection methods but as one that has inspected and repaired many cracked UAV and model airplane fuselages and wings I know with absolute certainty carbon fiber skins and shells can and do crack. Hairline cracks are also known to propagate at locations holes have been drilled in carbon tubes that are subjected to high frequency bending loads, especially holes where the wrong type of bit or tool was used to create the hole. Although many times stronger than steel or aluminum and considerably more tolerant of bending loads carbon fiber can and does crack under various conditions, and when bending limits are exceeded can fail quite dramatically. Watching and hearing carbon fiber propellers and wings explode during stress testing is quite startling.

As one that has been present during both destructive and non destructive carbon airframe stress testing for certification purposes I know that carbon fiber can develop cracks from both bending and impact loading.

Because of that I have serious doubts about the observations made in the UK carbon fiber article, along with the qualifications and intent of the author.

 

[Sarah]

As I don’t ride bicycles I can’t relate to their stress testing and inspection methods but as one that has inspected and repaired many cracked UAV and and model airplane fuselages and wings I know with absolute certainty carbon fiber skins and shells can and do crack.

As one that has been present during both destructive and non destructive carbon airframe stress testing for certification purposes I know that carbon fiber can develop cracks from both bending and impact loading.

Because of that I have serious doubts about the observations made in the UK carbon fiber article, along with the qualifications and intent of the author.

It is just a matter of wording, carbon fibers do break and show weaknesses as well, but not like hairline cracks on metal. Carbon fibers may tear, crush or puncture, according to what web sites shows. In your examples you talk about stress when bent and on impacts, they either crushed or teared. Did the carbon fibers show hairline cracks ?

Here are some samples that look like hairline "cracks", but they are just paint "cracks" and some other real "cracks". May you confirm of course from your experience, that carbon fiber makes a noise like a scratching when handled. (While metal or plastics, make no noise before breaking)

So that's the point of the author of web site quoted above.... carbon fiber behaves differently.

 

[Sarah]

Hairline cracks are also known to propagate at locations holes have been drilled in carbon tubes that are subjected to high frequency bending loads, especially holes where the wrong type of bit or tool was used to create the hole.

That's the other part of your post, which could lead to a clue on what happened, why the drone fell from sky. ... Could it be possible on this scenario that when changing motors or arms, small weaknesses appeared, say around the screw ? And with high frequency bending loads it broke ?
Dronairpro reports to have changed motors but not arms, and that arms made no scratching noise at all when manipulated.

 

[Sarah]

If that's possible we may have a scenario.

• Repair and motor change was not done optimally.
• Motor support broke due to weaknesses in carbon fiber, prop made a flapping noise. (45:00 to 45:06)
• Prop bent when hitting a second arm which might have broken as well. ( or when hitting ground)
• With two motors not giving lift anymore, and maybe due to a weak battery drone fell

 

[PatR]

Sarah,

Because people read something on the web in no way substantiates what was written. Having worked directly with composite materials for over 30 years, be it fiberglass, carbon fiber, silks, kevlar, and combinations of kevlar/carbon fiber. I make my statements from first hand experience. The subjects that generated the experience encompass boats, surfboards, and aircraft of various types, with the greatest emphasis in aircraft, many of them constructed to military/aerospace quality levels.

So I’ll simply say I think you are very gullible or don’t know what you’re talking about because you have no personal experience with the subject matter. Bear in mind I’m not trying to sell bicycles.

 

[FlushVision]

@FlushVision Even not wait for the first warning ?

Nope. If you've seen the first warning you have flown your battery too low for your battery's overall health.

 

[Sarah]

Sarah,

Because people read something on the web in no way substantiates what was written. Having worked directly with composite materials for over 30 years, be it fiberglass, carbon fiber, silks, kevlar, and combinations of kevlar/carbon fiber. I make my statements from first hand experience. The subjects that generated the experience encompass boats, surfboards, and aircraft of various types, with the greatest emphasis in aircraft, many of them constructed to military/aerospace quality levels.

So I’ll simply say I think you are very gullible or don’t know what you’re talking about because you have no personal experience with the subject matter. Bear in mind I’m not trying to sell bicycles.

Your experience does not answer any question concerning the crash, but very interesting...

 

[DoomMeister]

Thread is closed to further posts. The Telemetry shows possible causes for the crash, but nothing conclusive except for low battery voltage, shutdown of Motor 2, and wild flight fluctuations for the last 6 seconds. Anything beyond those facts is speculation and each can be content with their own version and move on without throwing barbs at one another.

I edited this post deleting my comment about what this thread was turning into. I am sure Steve C. will still agree with its replacement and this is a much nicer version.

From Steve C....I'll second that. This is a technical forum. We don't have time for members slamming each other.