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HomeMy Site✈️Aircraft🚁HelicopterHelicopter Main Discussion › Main blade failure
04-06-2013 09:19 AM  6 years ago
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Rotormaster

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Australia

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Main blade failure
This occurred the last time I was out, last Saturday.

I had brought it in close and started doing left-in tail-down tic-tocs, and made them progressively faster (for reference, the 450 in question is spinning 3800), just a touch over 2m from my face. After about 3 seconds of tic-tocs I punched out toward my left, and just as I did this, the main blades parted. It was a rather comical sight as the heli catapulted about 5m spinning like crazy on the roll axis and the motor overreving before hitting TH, and eventually the ground.

The blades being used were $3 HK glasfibre blades. Though I do not believe this to be the reason for failure. I have been using these blades from before I could hover inverted, and I continued to use them as my skills slowly progressed. bit by bit, I flew them increasingly harder at increasingly higher head speeds, so these blades have been tested progressively (safely) and they have thus far proven themselves fit even for my current setup. I wasn't flying my hardest, and have put these blades under higher stress than what they were under when they failed... They have always held together.

What I do believe to have pushed them over the edge is user error. I failed to install shims when I knew that the blades were not tight in the grips... This prevents the even distribution of vertical load that the blades present upon the grips. As you can see in the photos, both blades snapped clean at the stress point.

I'm posting this as a precaution to those in the hobby who might be like me and get a little lazy at times. I seldom have time for this hobby and I find my self using this to justify my lack of care. I knew those blades needed shims, but I ignored it... Lesson learned.

Stay safe guys!


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04-06-2013 09:30 AM  6 years ago
DarkSide41

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I don't think l could ever trust glass fiber at those headspeeds. Carbon fiber sets are not much more from HK" The biggest threat to our freedom is not from foreign terrorist , but domestic morons"
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04-06-2013 10:03 AM  6 years ago
yammx

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Munich, Germany

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You are doing 3800rpm with glass fiber blades from HK, sorry you are crazy!
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04-06-2013 10:18 AM  6 years ago
Rotormaster

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And I don't blame you... Especially ones from HK!!

Trust me, if I had never used these before, and then Suddenly somebody told me to install these $3 GF blades from HK on my heli and smack them at 3800 RPM, I would probably laugh.

It's not about the price, though. When I was progressing from sport flying into 3D a while back, I bought like 20 sets of them. I slowly pushed them more and more as my skills progressed, sometimes expecting them to fail, but they just kept progressing with me... They always held together so I just kept using them.

Only other blades I have tried are the Aligns that came with my kit. Interestingly, the Align blades had noticeably more flex than the cheap GFs! either way, I could not notice any difference in the air, but that was a while ago so I can't really comment.
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04-06-2013 10:29 AM  6 years ago
Rotormaster

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This is what the heli looked like when I recovered it.

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04-06-2013 11:19 AM  6 years ago
yammx

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A long time ago, I had this issue and I was not even close to 2500rpm.

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04-06-2013 01:46 PM  6 years ago
wrongler

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Brewerton, New York

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Nope, Sorry, I would never trust those blades at that headspeed!Bill Whittaker
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04-06-2013 03:06 PM  6 years ago
MartyH

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USA

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You are way over analyzing the blade failure.

They're fiberglass,
They're HK
You're spinning them 3800rpm.

I don't think you need to be thinking about shims or anything beyond the obvious.
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04-06-2013 03:31 PM  6 years ago
Rotormaster

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Australia

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A long time ago, I had this issue and I was not even close to 2500rpm.

This is a typical example of what a blade looks like when it fails due to over-revving. The lateral force of the blade is such that it simply shreds itself around the centripetal force of the main blade holder bolt.

When you look at the photos I posted there is not a slight hint of the root trying to force itself around the anchor. The point of failure in my case shows that the cause was predominantly vertical force as opposed to lateral force.

Of course, both vertical and lateral forces are equally relevant in stressing the material to the point of failure- It likely wouldn't have failed if it were only the lateral load present, as in the same RPM running with zero pitch. Nor would it have been likely to fail if one were to simply apply the same vertical load on an idle blade.
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04-06-2013 03:33 PM  6 years ago
ICUR1-2

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Ottawa, Ontario

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yeah

you have something to be happy about

you have finaly progressed enough to cause the blades to snap

if you gave the same blades to tareq for example they would have failed in 30 seconds or less

just because you push something to it limit doesn't mean it's ok
obviously you went beyond the limit
spending time, paying attention
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04-06-2013 03:40 PM  6 years ago
Rotormaster

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Australia

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I don't think you need to be thinking about shims or anything beyond the obvious
That part I have to disagree with.

You do not want ANY blades flapping about inside the grips. Whether they are $3 blades from HK or Rail blades is entirely irrelevant to this.
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04-06-2013 03:56 PM  6 years ago
ICUR1-2

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Ottawa, Ontario

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Roto your blades broke at weakest point adding shims may help but you would still be maxing those blades

it would be easier to lower your HS
spending time, paying attention
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04-06-2013 04:00 PM  6 years ago
rstacy

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Rochester, NY

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You do not want ANY blades flapping about inside the grips. Whether they are $3 blades from HK or Rail blades is entirely irrelevant to this.
You can defend $3.00 blades all you want but what it comes down to is that's its just plain stupid to fly at your level of flying with $3.00 FG blades.

Helicopters are dangerous but you take it to a whole level of danger when you fly parts that are in no way up for the task.

Unfortunately this is a growing trend as helicopter flying becomes more main stream.

You are certainly free to fly whatever you want but can you do me a favor? If I am in the vicinity of your next flight, please warn me. The next person to get hurt might be me.
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04-06-2013 04:42 PM  6 years ago
stubbs

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Tuscon, AZ

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Jesus, dude... You're at the point of doing tic-tocs and still flying $3 crappy blades? Pro tip for ya: buy better blades. You're lucky to have gotten away with flying that crap for that long.
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04-06-2013 04:46 PM  6 years ago
Rotormaster

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Australia

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You can defend $3.00 blades all you want but what it comes down to is that's its just plain stupid to fly at your level of flying with $3.00 FG blades
I think you have misunderstood my "HK blades-Rail blades" comment. I was responding to the comment implying that shims are irrelevant, and I was simply pointing out that having the blades loose in the grips is not desirable, and is a disadvantage, whatever the blade may be.

I respect your freedom to opine of me as stupid, but the reason I defend these blades is because I believe from my experience that they are adequate.

I must say though, that my progression has been quite rapid, so I haven't necessarily been flying them like this for very long. But if I find myself experiencing more of these failures in the near future, do you really think that I will continue to defend some $3 blades?
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04-06-2013 04:49 PM  6 years ago
outhouse

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auburn ca

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cheap HK blades in the past had issues and guess where that issue was?

Right where yours failed.

You got lucky this time.
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04-06-2013 04:53 PM  6 years ago
Stephen Born

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USA

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The money you saved on the blades will be used to fix your helicopter.
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04-06-2013 05:00 PM  6 years ago
Rotormaster

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Australia

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By the way, rstacy, I fly alone and away from crowds. In the rare occasion that somebody turns up to watch, I inform them that they may want to stand next to or behind me... they usually get the point.
The money you saved on the blades will be used to fix your helicopter.
I think you missed the part where I said I bought 20 pairs.

The money saved could have bought a couple of spares for the 450, with a little left over for a nice 1000W power supply, which come to think of it, could do quite nicely right now. I wonder what I spent that money on.....

Either way it's not money that I'll need to get it back in the air. I have a box full of spares sitting here. It's been a week but I still don't feel like fixing it.
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04-06-2013 06:07 PM  6 years ago
HeliOCD

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San Diego, CA

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if I find myself experiencing more of these failures in the near future
So you are still going to use the 3.00 blades and put yourself in the path of another potential blade failure using them. You may want to go with better blades from this point forward.
Its all earth!
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04-06-2013 06:22 PM  6 years ago
fenderstrat

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Aston,Pa

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While the blades may hold up for a particular flight at those headspeeds,this is obviously the work of the cumulative forces.After many flights they are getting weak and then its just a matter of time.

just out of curiosity,whats the recommended max rpm of those blades?

also how many flights on THOSE blades?And whats the max flights you have gotten on any 1 set before having to replace them?
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