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HomeMy Site✈️Aircraft🚁HelicopterHelicopter Main Discussion › Main blade failure
04-06-2013 07:33 PM  6 years ago
dkshema

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Cedar Rapids, IA

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Though I do not believe this to be the reason for failure.
What you believe does not necessarily match reality.

The other picture of a failed blade is that of an Align wood blade, not a carbon fiber or fiberglass blade. The blade did fail at the root, and it did rip out a path through the wood.

The shims do little, if anything to prevent the failure you saw. At 3800 RPM, there is quite a bit of centrifugal force keeping the blades rigid in the grips. Due to the fact that this is a helicopter, the blades flap UP and DOWN repetitively as they go round and round. They also lead and lag as the head rotates.

Vertical load on the blades? At the attach point? I suspect were you to actually do the math, you'll find a huge radial load along the blade axis, as well as a bending moment as the blade flaps up/down.

If you tightened the grips down to prevent the blades from flopping around on the ground, more than likely you ended up crushing the blades.

In any event, believe what you will, rationalize however you must, but in the end, you got what you paid for.
-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
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04-06-2013 08:07 PM  6 years ago
nickt919

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New Orleans, Louisiana

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Hi Rotormaster

Thankfully that slung blade didn't spear you in the eye with the jagged end. Think about that for a few minutes....a blade in the eye and having an emergency room doctor pull it out. It would have slowed the rebuild by a few days.

Get a few sets of Edge B-surface, cosflaw, or something similar. They're cheap enough and way more safe than $3 HK blades.

I think when most read about things like this they go hard on the poster to make a point then hopefully get some thinking and changes going. None of us want to read about catastrophic injuries from model RC helis. These models are dangerous enough even when you use quality gear.
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04-06-2013 08:49 PM  6 years ago
ICUR1-2

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Ottawa, Ontario

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remember murphie's law
in all probability it will be the spectator that gets hit
spending time, paying attention
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04-06-2013 09:28 PM  6 years ago
Richardmid1

rrProfessor

Leeds, England

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I think you'll find even the top CARBON blade manufacturers don't recommend 3800 rpm on their 325mm blades!60% of the time, it works every time!
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04-06-2013 09:42 PM  6 years ago
MartyH

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USA

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Rotormaster,

Don't put words in my mouth. I never said shims were irrelevant. I said in regards to analyzing the blade failure, you were turning FIBERGLASS from HOBBY KING and 3800rpm. That's where your problem lies, not in the shims. Of course they are important but there was plenty already wrong with this situation.

You're preaching to me about the importance of shims? You're the one that had catastrophic blade failure and did not have the blades properly shimmed to begin with.
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04-06-2013 09:51 PM  6 years ago
3dgimble

rrKey Veteran

Rochester

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Buy 3G Align blades, you wont regret it. $18, they are actually tough as well.
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04-06-2013 10:01 PM  6 years ago
KC

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WA

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Rotormaster, the force on a blade grip between two different rpms is difference of squares:

3800rpm^2 / 3000rpm^2 = 1.60

that means 3800rpm is 60% more force than the 3000rpm recommended limit of most 450s.

Then yeah theres all those vectors and crap for the other axes too. It should be clear though that 60% over one of the redlines is a bad thing...

HK blades are fine for low rpm, but they really are the undersized spare tires of the blade world. 2000rpm with that blade would be pushing luck
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04-06-2013 11:05 PM  6 years ago
rstacy

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Rochester, NY

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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.
You didn't get all of my point.
I don't want to see you get hurt either.
Keep flying that blade at your level of flying and someone is going to need medical attention.
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04-07-2013 03:22 AM  6 years ago
DarkSide41

rrVeteran

Sylacauga Alabama USA

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I think it is time you start using the $6 HK blades ." The biggest threat to our freedom is not from foreign terrorist , but domestic morons"
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04-07-2013 03:49 AM  6 years ago
AWittleWabbit

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O.C., CA

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Even if you were to work out all the stresses of the blades and what they could handle, you're eating into the margin built into the blades*
Coupled with production tolerances (do they have any?) you're bound to have more failures as you push them harder.

*Not convinced they even thought of that. Probably sized the root just to fit the grip without any consideration for the stresses involved.
Heli-itis sufferer.
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04-08-2013 04:56 AM  6 years ago
icanfly

rrElite Veteran

ontario

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They failed because you were running 3800 (why?) headspeed, the blades will flex less along the span during pitch changes, or a hard landing. All the flexing gets focused to where the blades broke.

If you look at the bolt on the clamp you'll notice very little aluminum beyond it toward the blade tip. This is a bit of a poor design flaw because the clamp will not support the blade while it twists and flexes in pitch, the clamps are too skinny at the bolt.

Your running airplane prop speeds on a mechanism designed for hover will shorten the life of all parts involved in the rotor assembly.

$3 hk blades aren't designed for more than 2200rpm as the standard rpm on a 3600kv/11.1v 450 t-rex equipped heli.

No one is saying you are crazy to be pushing your luck with anything cheepo when running 3800rpm, but help yourself to 2 changes, a higher quality blade, and blade clamps that have a broad area around the bolt.

The blades reached their maximum limit of pull exerted at those speeds. A tiny structural flaw can be terminal under stress, load, flex, and twist, failure may not happen immediately but might creep up to complete disaster. Essentially they tore off like toilet paper from a roll.

Make a vid of your heli running 3800 rpm, we'd like to see it, sure it wasn't 2800? No matter, you have to use a blade with better engineering inside. I have those hk blades and they are full of resin (at the root) with only an outer skin of 4oz cloth and a strand of cf tow from root to tip, over a foam core.

A pro would NEVER use those at 3800rpm, for reasons you have shown.
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04-08-2013 06:12 AM  6 years ago
GetToDaChopper

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Las Vegas , NV

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You should have known all these comments were coming your way when you made this thread, or did you ?    ▲
  ▲ ▲
▲ ▲ ▲ One of a Kind !!!
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04-08-2013 07:37 AM  6 years ago
Thatlumox

rrApprentice

NY

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I think you missed the part where I said I bought 20 pairs.
So I get to read 20 more threads just like this?
"I'm a dirt torpedo!"
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04-08-2013 04:21 PM  6 years ago
Ronald Thomas

rrMaster

Gainesville, Fl, USA

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You didn't get all of my point.
I don't want to see you get hurt either.
Keep flying that blade at your level of flying and someone is going to need medical attention.
I agree. It is just a matter of time to when the cheap stuff will cost you way more then they could have ever saved you. Be safe.
Team MikadoUSA 480XXTreme, 550SX, 600SX, 700XXTreme, 800XXTreme!!
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04-08-2013 04:44 PM  6 years ago
Rotormaster

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Australia

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After having read all your comments, and after having consulted with my own more sensible and mature side, I have decided to not continue to fly these blades. Of course, I was always well aware of the imminent danger of flying these blades in the given manner. I have admittedly come to be a little too comfortable with the 450, which, unlike the X5 does not provoke the same feeling in me of my life being in danger. The 450 may hardly be life threatening, but the event I witnessed could easily have cost one of my eyes, and I thank you all for reminding me that this is not a price I am willing to pay.

Of course, there is a slight sense of fraudulence in me stating risks that I am not willing to take... as I am not at this point prepared to avoid these risks all together by giving up the hobby. Whether we like it or not, the reality is that it's literally impossible to be involved in this hobby, with out at least some level of risk. Even an intermediate pilot doing some scale flying, or a beginner learning to hover... there is some level of risk involved. There is nothing to say I won’t suffer a stroke the next time I’m at the sticks....

The reason I am saying all this, I guess, is because it’s been some time since I’ve sat down and though, and I mean really though about the risk I put before myself with this hobby... all to fulfill some trivial sense of ‘fun.’ Some people get their kick out of scale flying, and when I stop and think about the way I enjoy the hobby and the direction I’m going with it... I wish I were one of them.

Even the most expensive equipment in the world can fail. This though scares me.
Perhaps not with my 450 (though it should), but when I am flying the X5 it certainly plays in the back of my mind. And to think that I am looking at 700s...
I’ve seen brand name blades fail.... and of course we’ve all read the stories about radio lock-outs leaving their pilots with no control, or the odd FBL unit who got upset at God knows what and commanded itself into the ground.

I’ve just made an order for $500 worth of parts, including some Align and RJX blades to try out. I did not necessarily feel like spending upwards of $40 per pair for 325 SABs or Edge, but I’m sure these cheap ones should be OK. Though, as dkshema likes to point out, what I believe does not necessarily match reality, so perhaps I will kick myself for my stupidity in not having gone with the name brand in the first place, no, DK?
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04-08-2013 05:15 PM  6 years ago
Rotormaster

rrVeteran

Australia

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just out of curiosity,whats the recommended max rpm of those blades?
Do you think that these blades come with a recommended RPM? I doubt HK even knows the answer to that.
also how many flights on THOSE blades?And whats the max flights you have gotten on any 1 set before having to replace them?
Good questions.

That was actually the very first flight on that particular set. I fly this heli with very little regard for crashes (like the sim), so on average, no set ever saw that much use. The highest count wouldn't have been much more than 20 flights.

I did always inspect them before going out, but obviously like I said, they were being crashed too quickly so none of them ever got to the stage where they needed replacement.
The shims do little, if anything to prevent the failure you saw. At 3800 RPM, there is quite a bit of centrifugal force keeping the blades rigid in the grips.
Are you saying that centrifugal force alone is enough to keep the blades parallel to the grips? Even if you believe that, surely you didn't really mean what you said about the shims having no physical effect... Which makes me wonder why you would bother to say such a thing at all.
Vertical load on the blades? At the attach point? I suspect were you to actually do the math, you'll find a huge radial load along the blade axis, as well as a bending moment as the blade flaps up/down.
With all due respect (which I do have for you), what on the bloody earth are you talking about?? Had I done the math for what???? How much flower to put in the cake? I genuinely have trouble understanding what (if anything) this entire paragraph has in relevance to the effect a loose fitting has on a poor quality blade.

Please expound what it is that you are on about.
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04-08-2013 08:38 PM  6 years ago
MartyH

rrProfessor

USA

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Did the blade separation scare you Rotormaster? I hate to think a crash can have you thinking about leaving the hobby. You're absolutly right about risk, even when it's benign like a light sport flying crashing and losing your setup time and a few dollars for some parts. I think you just went too far with cheap gear. Step up a little in quality and back down your setup and I bet you can still find fun at a reasonable risk.
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04-09-2013 04:07 PM  6 years ago
Rotormaster

rrVeteran

Australia

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Marty, when the incident occurred, I found it rather amusing, probably due to the surprise more than anything else. Also, I was actually having my fare share of fun with all that power just before the incident. Not to mention, usually if I crash after a good flight where I had been having fun, it doesn't dampen my mood, and most often walk up to the wreck with a smile on my face.

In retrospect, I'm not sure why the incident didn't scare me. It certainly should have. As soon as it happened, the first thing I though was 'another mechanical failure.' I have been rather disappointed with the quality of Align compared to my Gaui (issues with tolerances, play, etc). So when this happened, I though it was yet another spindle bolt failure (had this happen before)... It was only once I retrieved the heli that I realized I had snapped the blades.

icanfly, I have no videos of this heli flying in its current setup, and I won't ask anybody I care about to come and stand in front of this thing and do the honours. At least not until I sort out the issues with this 'DFC' head, anyway. I have one of those little keychain recorders that I used to strap to my cap to film... If I can find it by the time the new blades arrive, I'll take a video the next time I go out.
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04-14-2013 03:03 PM  6 years ago
Chance

rrNovice

Melbourne, Australia

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Tic tocs 2m from your face? Crazy man!
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04-14-2013 03:31 PM  6 years ago
nocontrol1

rrApprentice

Melbourne, FL, USA

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Tic tocs 2m from your face? Crazy man!
I was thinking the same thing. Blades, headspeed, proximity. I'm glad it had a good(no injuries)ending, usually three strikes and your out!

Rob D
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