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HomeAircraftHelicopterMain Discussion › Aluminium Blades - Why not?
11-04-2004 01:31 PM  13 years agoPost 41
zoom boy

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Alistair I can say they are ignorant because of what I know about it, and that the BMFA just copied CAP658 instead of looking into it (talking to a person who has studied aero engineering here) I am not saying I am right (there is no way to say that without actually testing it) but from the experience I do have I would say that the BMFA havnt looked into it at all and have just copied and pasted

Now on to some of the things that would happen

An extruded aluminium blade is going to bend and deform greatly on contact, it will not "go like a buzz saw", it will fold on the upper or lower surface and snap off very close to the root, or split along the trailing edge of the blade, letting the blade fold directly backwards, probably within the first hit relieving a lot of energy that way, and will do nowhere near as much damage as those SOLID metal paddles on the C30DX, now the BMFA didnt ban them did they (see what I mean about ignorant, they ban the one that would probably do the least damage out of the two - BMFA talking out of their collective arses)

I am not an expert on aluminium specifically itself, but I can tell you what will happen in an impact with a hollow structured blade compared to a solid CF blade (re-read the above)

Personally I think we really need someone to set up a test, building a frame to hold a side of beef and setting up a high speed impact of all the main types of blades with high speed cameras recording so we can see how long the impact lasts, if anyone has equipment that could be used to try a test then post the results, that would settle it

If given the choice between being hit by FG, CF, metal or wood it would be wood, the others are just going to cause a lot of damage, but I suspect not much different from each other

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11-04-2004 04:56 PM  13 years agoPost 42
ChristianM

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I see a lot of arguments along the lines of the full size uses AL so why not our model heli’s. Let me give you my perspective on this why we should not use AL blades.

The full size helis have a very regimented inspection and maintenance scheme that in particular look for cracks in all metal parts. It takes special equipment and knowledge to detect cracks unless they become so large that they can be visually observed. Also rotor blades on full size have a limited life before they are replaced. We all like to think that we take great care of our helis but using AL blades would certainly raise the bar significantly. Also more and more full size helis are using CF blades so why should we move backwards

The fatigue properties of AL is about three orders in magnitude worse than CF so any cracks in the root area of the blade could quickly propagate and send the blade flying. This would be compounded if the blades were used for heavy 3D flying where the blades would see a lot of heavy cyclic loading. Like Jerry mentioned, AL does not have a fatigue limit so it is a certainty that they would fail at some point in time. That would probably be many, many years if they are properly used and maintained but once they have been through a crash then all bets are off. I would be VERY concerned to be around a heli with AL blades that have been in even a “light” crash.

During a significant crash all blades will break regardless of material used. Aluminum has very little ductility (it can take very little permanent deformation before it breaks) so the blade would not loose much energy during the break and as such be free to travel at high velocities (ouch). CF blades will “crumple” and tear apart which consumes a lot of energy thus reducing the velocity of the “remains”. It is unclear to me what the weight of these blades are but I assume that they are heavier than the CF blades and that is also a big negative if someone should get hit (energy = ½ * mass * velocity * velocity). Regardless of blade type, if you are in the vicinity of a crash then duck .

I have never flown AL blades but I would expect that AL blades would fly differently compared to CF blades. CF has typically about 8 to 10 times more natural damping compared to AL which will effectively damp out vibrations in the blade. I am unsure how this will affect the flying characteristic of the blade but I would expect the AL blade to feel more “nervous” in the air.

My 2 cents

Christian

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11-04-2004 05:40 PM  13 years agoPost 43
Sticky

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Frederick MD

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I would like to see some lite weight blades either aluminium blades or some else. I hate trying to take weight out of my heli, then mounting a heavy set of blades on it to do autos once in a while.

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11-04-2004 06:27 PM  13 years agoPost 44
zoom boy

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beg to differ about the ductility of aluminium, with an extruded blade, like what we have been discussing, the crossection will be very thin, meaning that with blade would bend very easily under the loads of an impact,, which would make it fold and most likely snap off, which means its no longer attached to the rotor head getting power from the engine, whereas a splintered carbon blade may not be severed, meaning it could come around and hit you a second time

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11-04-2004 07:05 PM  13 years agoPost 45
zoom boy

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"Take a tail boom and whack it around a tree or post: and then get back to us"

Exactly, and the skin of these blades are probably not much thicker than the average tail boom, you hit something with them with the force you would have in a rotor system and you will fold it and snap it probably near the root, but it wont turn into small schards flying everywhere like bullets, it will do the funky chicken dance

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11-04-2004 07:38 PM  13 years agoPost 46
ChristianM

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Zoom boy: If you get hit by a heli blade under power then I agree with you a CF blade MAY come around for a second pass while the aluminum blade is more likely to break off. Heli’s hitting people is easily deadly regardless of blade type but is luckily a very rear event. I am more concerned about for example a crash, which is a much more frequent event, resulting in a blade flying off at high speed and hitting someone. Also there is in my opinion a significant increase in the likelihood that an aluminum blade will fatigue and come off in flight. The longer the blades stay attached to the heli the safer it is. Also, smaller lighter particles are much less dangerous than one large one and the smaller particles will also loose their velocity a lot quicker.

Stephen: You are correct in that there are differences between aluminum grades and that the aluminum blade would bend if you whack it around a tree. The CF blade would probably get some surface damage but would not be permanently bent. However, the remaining strength in the aluminum blade would probably not keep it attached to the rotor head.
The point I tried to make about the ductility is that the CF blades would require much more energy to break in two thus reducing the speed at which they fly away from the heli. As an example you see many bullet proof vest’s made out of composites (Kevlar primarily) since they absorb the energy from a bullet very well. There are also vest’s using steel plates but as far as I know not any using aluminum even though they would be significantly lighter. Steel have much higher ductility / ability to absorb impact energy than aluminum.

Free flying heli blades => not good

Christian

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11-04-2004 08:29 PM  13 years agoPost 47
zoom boy

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If hit by the rotors in the torso without much impact speed (ie not much more than 10 -15 mph) you would probably have a few broken ribs and a bit of bruising, any hit directly to the head would most certainly kill

much more than 10 -15 mph to the torso and I would say its too hard to tell

but not everyone is killed when hit by a helicopter, many injured but only some killed, and most of them usually involved a head injury

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11-04-2004 08:34 PM  13 years agoPost 48
Obsessive

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We've been over this time and time again. Aluminum does not have the physical properties to perform well, due to creep, softness, and other metallurgical and stiffness/strength issues.

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11-04-2004 08:36 PM  13 years agoPost 49
zoom boy

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yes we have been over it before, but we are on about what would happen in an impact with these sorts of blades and why they would be a bad/good idea

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11-04-2004 08:51 PM  13 years agoPost 50
ChristianM

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The biggest issue with aluminum blades is that there is a much higher likelihood that they will break in midair and send the blade flying like a knife. If this should occur while you’re hovering or doing some low 3D then I would certainly not want to be anywhere close by.

Christian

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11-04-2004 09:52 PM  13 years agoPost 51
Branzzz

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i read this up some time back and the reason was that metal blades tend to bend, instead of break off when there's an impact. carbone fibre and fibreglass blades simply shatter or crack, and they most likely won't survive coming around to hit you again. metal simply bends and not shatter like cf or fg, and that shattering effect takes up lots of the impact energy too. that was the official reason for metal blades being BANNED.

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11-04-2004 11:09 PM  13 years agoPost 52
Peter65

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Who here has flown these metal blades or tested them? Anyone?
If not than this whole thread is mostly speculation.

What was the first helis made from? Who made them?

Would you not expect the Germans to have fully tested these blades before putting them on the market?

What grade is the aluminium? A/C grade snaps after bending it does not accept being bent twice. Look at your telescopic antennea. It's tubular and if hit will bend very easily and you well not be able to bend it back without snapping it off

Before we condemn these blades I would like to see them tested first or atleast get some more info from M-Blades on what the process was they put them thru before marketing them.

I think they would be more rigid and there fore more responsive. Why not give them ago.

Laughing at yourself will lengthen your life. Laughing at me will shorten it...

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11-04-2004 11:32 PM  13 years agoPost 53
Alistair

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i think they use the blades for industrial uses... last i read... don't ask where i read it, 'cause i don't recall... it was some 6-8 months ago i read it...

squigle

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11-05-2004 08:36 AM  13 years agoPost 54
Pliczner

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Szczecin - Poland (middle europe)

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As I know German people and i know a lot of them (i speak german too) - they have tested them in many ways before putting on market. It is not a piece o junk. When they do something - then very good quality and always according to rules.


I can say you, that M-Blades are more responsive, flying with them was more fun. As I tried GF Blades just before using m-blades for the first time I can say also that glassfibre ones were more "lazy".

Autos were also nice....

Alistair
as industrial use of M-blades - it is possible - they produce whole range of blades from 240 mm - 1500mm and tailblades as well.

I don't know people using 1500mm long blades (over 3m rotor - thats gigantic) - so the may be used in some UAV's or for military uses.

You can bend them once, but it's all. After that you have to throw them away. And it is not solid aluminium block of airfoil shape. They are empty inside, they have 3 empty sections. This also means that this structure is much stronger than aluminium block in the same shape.

My blade weights about 114 gr. So as usual blades, but they are more tip heavy.

I was runnig them in hovering at 1450 rpm, and in flight (3d too) 1700-1800, and they performed very well.

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11-05-2004 08:44 AM  13 years agoPost 55
Alistair

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no where land

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lol.. i know they're not solid mate. they sound neat, just seem a bit dodgy that's all...

have you got any photos of them? i'd like to see them.

squigle

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11-05-2004 01:35 PM  13 years agoPost 56
Pliczner

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http://www.mhm-modellmotoren.de/m-blade.php - there are some pictures, but propably they can send you more if you ask them.

I can not do pictures right now - my camera is broken...

Two ultimate life rules: 1. Never say all you know.

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11-05-2004 09:16 PM  13 years agoPost 57
cmartin

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Kouts IN

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Blades
I would also like to see a test done on these blades to see exactly what happens in a crash. Also NRI I believe used Aluminum main and tail blades on their autocopter, or so it says on the 1st page of their website under specs. I think aluminum blades are pretty cool, if they do not have any really bad downsides, which remains to be seen. Pure assumptions so far.

Chad

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11-05-2004 09:21 PM  13 years agoPost 58
Alistair

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no where land

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I got a wicked idea!!! Since aluminum heads are probably not safe either (just like the blades) lets go to CF rotor heads!!
that is just stupid....

all full scale blades have a -life span-

squigle

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11-05-2004 09:58 PM  13 years agoPost 59
Alistair

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no where land

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i never said i'm afraid of them... being that they are alloy, they would not break up like composite ones would. not sure it i want that when i'm low and close to myself...

squigle

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11-05-2004 11:04 PM  13 years agoPost 60
zoom boy

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You shouldnt really be low and close to yourself, when flying IC I never land closer than 30ft from myself, and never fly past closer than that when below 10ft, its just asking for trouble

Alistair dont take this the wrong way but it does seem like you are "afraid" of them, there seems to be a lot of this on the subject of metal blades, which seems silly, until you know the facts how can you decide they are dangerous.

I would be willing to bet ppl said the same things about CF and FG blades when they came out, when everyone was used to using wood, now everyone is aware of how you should treat such blades and dont treat them with fear, once ppl learn how to look after the blades then there shouldnt be a problem

It seems that the ppl at the BMFA and the AMA havnt done anything to reasonably come to the conclusion that such blades are more dangerous, other than copying and pasteing what other organisations say, and even they say it in the form of a guide, they are NOT illegal contrary to the claims of some, all using them currently means is that you cant expect cover if something bad happens until the rules (NOT LAWS) are changed

It just seems like complete fear of the unknown

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HomeAircraftHelicopterMain Discussion › Aluminium Blades - Why not?
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