Dragon2115
Key Veteran
Location: New England
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| Well, Dragon2115, with a handle like that, that must be fire that you're breathing out of your mouth.
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Nah, not even close. But I do get intense when blatant disregard for safety is concerned.
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| If you're going to take a stand on a technical point, then back up your position with technical data and pertinent facts.
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Please refer to where I said;
I have made no claim to be a materials science expert. I have made no claim to be an AP mechanic. I have made no claim to be an aircraft designer. .
and...
All this when I am the one that chooses to err on the side of caution and safety while you are the one that wants to use a product that is banned by both the AMA and BMFA and possibly endanger everyone around you.
and...
It is up to YOU to prove that this product does not suffer from metal fatigue resulting in catastrophic failure and is safe to use.
Remember it is YOU that wants to deliberately violate the SAFETY code. Therefore the burden of proof is on YOU.
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| I'm not going to buy "this expert says" or " that expert says"unless those experts are talking exactly about the subject at hand.
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Question: "Phil, (Sr. Scientist w/ PhD in Materials Science) what would happen if I used aluminum instead of carbon fiber epoxy for the rotor blades on my model helicopter?"
Answer: "It wouldn't be a good idea unless you do regular inspection for fatigue. In a crash they would transfer a lot more energy into the rotor head probably breaking a lot more than usual as well."
I'd say that was "exactly about the subject at hand." wouldn't you?
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| Yes, aluminum will fatigue crack over time ... IF it is over stressed repeatedly.
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Oh thank god, we're making progress.
The way that line should read is; aluminum will fatigue crack over time if it is flexed repeatedly. If you are half the ME you claim to be and have one shred of integrity you have to admit that you know this to be true.
It is also evidenced by the fact that the orginal R-22's had all aluminum rotor blades. They were required to be inspected every so many hours and then replaced after so many hours total. Current blades are composite with an aluminum leading edge as a impact sheild for the underlying composite. They only have to be inspected every so many hours but there is no life cycle for them.
I know, an R22 doesn't have the same stress pattern and blade length as our models. But then, an R22 doesn't fly inverted or do tic-tocks, death sprials, and rippers while turning 1800+ rpm either. Now refer to point one of this post about it being your responsiblity to prove that this product doesn't suffer from the same weakness.
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| The mistake I see you making is that you assume that just because it is on a heli, it is therefore over stressed and will fail, period.
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Not true. I've owned an SE. Tons of gold anodized CNC aluminum all over the place and never worried about them failing at all. But the one place that wasn't aluminum was the highest stress place on the entire helicopter, the rotor blades.
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| That is a false assumption. It fails to take into account the design and application.
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Again, not true. It is perfectly valid because it is based on demonstrateable past history of this material used in very similar applications and a lack of evidence to the contrary. It does not question the design itself but specifically the material used in the design.
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| All things will fail if over stressed and as such, things in the real world are designed to not be overstressed in expected operation plus usually a safety factor.
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Steel bridges have to be inspected and maintained otherwise they would eventually fail right? Are they being overstressed during normal use? No they are not, the steel is moving as was intended. It is well known that metal when flexed, even within design specifications, will eventually wear out. It is also standard practice to inspect metal that is constantly being flexed in order to avoid failure. The reason this is so important is because it is well known that when metal fails it tends to fail suddenly and without warning.
And we also know of many real world engineering projects that have failed because of some oversight, or cost control measure that compromised the design. So lets keep that in mind too.
Btw, what's the street price they'd have to compete with if they want to sells these blades?
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| It is for precisely for this reason that FEA, your FMEA review and a few other analysis tools exists.
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Problem is, they don't do any good if they aren't used.
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| To prove a design with respect to the application. In the case of full size aircraft, the safety factor is 50% over the maximum design load.
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That's correct. And it's also mandated by law by the FAA too. It also requires rigorous testing to validate the design. Who decides what this mfgrs' safety margin is? Do you have any idea? What testing has been done on them? Simple flight testing and visual inspection or have they gone through more scientific testing that tests the sample to destruction to determine it's maximum ratings? Or are we relying on someones' calculations and hoping for the best?
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| So before you get back on your soap box, please back up your assertions with a FMEA review
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Ok
Probability of failure:
Low initially but increasing to definite as time progresses. Time constant is as yet unknown.
Severity of failure:
Mission critical component, catastrophic.
Risk to property:
Low when being used at reasonable safe distance.
Risk of injury or loss of life:
Moderate to high when pilot or spectator is in close proximity such as during take off, hover, landing, or during crash. Reducing as distance increases.
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| (is that not what you do for a living?)
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Nope, just one aspect of new product development, which is what I do for a living.
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| and save the evangelizing for your religious persuasions.
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Sorry, can't help you there. I'm not a religious person. |
