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Old Mar 01, 2012, 12:42 PM
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Airdog67's Avatar
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Why no medal/aluminum props

Just curious why there is no metal or aluminum props used in this hobby. I have only been flying for a year or so and here alot of people wanting the scale look. I wouldnt think that it would be because of weight as aluminum is relatively light. Any input. Thanks.
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Old Mar 01, 2012, 12:56 PM
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Victoria B.C. Canada
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I would have to think it is a safety thing. Who wants a knife blade spinnng at very high rpm. plastic and wood are bad enough but atleast they will/might break before doing crazy damage. possibly cost?
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Old Mar 01, 2012, 01:02 PM
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United States, TX, Houston
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Metal props are insanely dangerous. think of a knife spinning at 7,000 rpm, and it accedently hits your hand.
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Old Mar 01, 2012, 01:03 PM
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Yeah maybe, although I have seen a guy at our flying field lose part of his finger with a plastic prop.
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Old Mar 01, 2012, 01:05 PM
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Quote:
Originally Posted by srt8madness View Post
Metal props are insanely dangerous. think of a knife spinning at 7,000 rpm, and it accedently hits your hand.
If thats the case, then why do they make pointy metal spinners for planes that will do over a 100mph. If that were to hit somebody that could kill em.
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Old Mar 01, 2012, 01:13 PM
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Birmingham, Alabama
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1) extreme weight = lower performance & much rougher on bushings/bearings & shafts. many electrics would struggle to support them
2) extreme cost. props are CNC routed, milled & sanded. or injection molded
3) propellers are meant to be broken before anything else. doesn't matter if you're talking 150watt electrics or 150cc gas
4) extreme danger to use

RC Plane Accident - Why you shouldn't stay near the propeller ! (1 min 43 sec)


wood propellers are very blunt. plastic and composite propellers are not knives (tho the TRAILING edge of an APC is sharp, as are master airscrew & other plastic/composite/nylon propellers if you do not deburr the casting edge) and all propellers have an amount of give to them. metal does not.

take it from a glow flyer that's been scathed countless times by hand starting & tuning glow engines. metal props would be very, very bad.


there is not a TOTAL SCALE competition anywhere in the world that will detract points for using a wood or plastic / composite prop painted to simulate metal. at any level of competition... Makers like Zinger, APC, XOAR, Graupner, Master Airscrew make enough prop profiles to cover from the dawn of flight to modern age.
At scale events you are also allowed a static display propeller. (for example a nice milled metal propeller, or a multi-bladed propeller like 4 blade MAS prop to simulate a HS 4 blade for WWII birds.) But you do not FLY on them. You install a propeller for flying that suites the period & performance level required to fly. It is very common at scale events to see nice metal static props & multi-blade propellers. Then everyone swap to normal 2 blade props to fly on.

absolutely, positively no use for metal propellers in R/C or modeling use. ever
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Old Mar 01, 2012, 01:16 PM
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Birmingham, Alabama
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Quote:
Originally Posted by Airdog67 View Post
If thats the case, then why do they make pointy medal spinners for planes that will do over a 100mph. If that were to hit somebody that could kill em.
that's stupid
1) they look better
2) they're more durable & won't lead to a catastrophic event like slinging a prop off into spectators adjacent of the airframe
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Old Mar 01, 2012, 01:16 PM
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Hey now,
I've seen wood props shed a blade and hit somebody in the chest. It wasn't pretty. It wasn't a through and through but it stuck in far enough that it pierced a lung *after* cutting through a rib. A solid prop can be traveling at very close to the speed of sound. Plastic props being heavier can go even faster and carry more momentum. A through and through cut. Could easily kill you.
Even worse, a metal prop would be far more likely to shatter than just shed. Think about it, a handful of razor sharp shrapnel hitting you at near sonic. You prolly won't survive the bleed out till the ambulence gets there. Seriouly dead.
On top of all that everytime you start an infernal combustion engine you strike the prop with you hand or chicken stick. Each. Low or ground strike or? Adds to metal fatique. Leading to fracture and failure. Not *If* but *when*. So no mtela props. Turbines are even worse. At jet meets you see impellers explode all the time. Nasty!
Now if I want scale I'll spary the prop silver or maybe Presto-lite it and likely switch to a regular prop for the flight. You can't really tell once it starts spinning anyway.
RobII
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Old Mar 01, 2012, 01:36 PM
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Fort Wayne
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Pretty simple answer if you are a AMA Member. Directly from the AMA safety code.
I will not operate a model aircraft with metal-blade propellers
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Old Mar 01, 2012, 01:37 PM
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Staffs, UK
Joined Nov 2003
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In this country it's pretty simple. There are no metal props on models because they're not legal. Our equivalent of the FAA has said so.

At least some rules make perfect sense .

Steve
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Old Mar 01, 2012, 01:38 PM
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Having been around airplanes all my life (models, and the one's you strap on and go fly), the issue isn't that the aluminum prop would be more dangerous than a plastic (nylon, carbon, glass-filled, etc.) from a standpoint of sticking your hand in it. Other than the cost to manufacture (believe it, or not ali props were available in the 40's, and 50's.), the main issue is harmonics. An aluminum prop is a big tuning fork. At certain lengths, and rpm, the prop will reach resonance, and self-destruct. One doesn't have this issue with wood, or plastic.
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Old Mar 01, 2012, 01:58 PM
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United States, TX, Houston
Joined Nov 2011
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Quote:
Originally Posted by Airdog67 View Post
If thats the case, then why do they make pointy medal spinners for planes that will do over a 100mph. If that were to hit somebody that could kill em.
Because the spinner doesnt have a sharp blade. Its not protection from propstrikes from a flying airplane, its from when the plane is on the gound or being handled. If your finger touches the spinner it slides off, if it touches a metal blade it ceases to exist. pretty simple.
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Old Mar 01, 2012, 02:11 PM
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United States, CA, Oakland
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Hey now,
Also because of the round shape a metal spinner is far less prone to fatique.
I've never seen or heard of a metal spinner coming apart under power. But I've sen plenty of props let go.
RobII
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Old Mar 01, 2012, 02:18 PM
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dedStik's Avatar
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Joined Feb 2012
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Not just all the above reasons but do you really want the chance of metal shavings getting into your engine? This is also the same reason most electric motors have nylon flywheels or gears in their assembly housings, nylon tends to not muck up an electric motor like metal shavings would. This is why your garage door opener is probably 10 years old or older without having to replace the motor.
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Old Mar 01, 2012, 02:32 PM
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zeezee's Avatar
United States, LA, Angie
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Go to the electric warbirds forum and look at some of the giant foamie threads like the FMS 1700mm P-51. Shredded and "exploding" spinners and props are not too uncommon on these threads! Cheap unbalanced spinners. One reason I bought a Hanger9 balanced aluminum spinner for my H9 P-51.
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