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Author Topic: help determining if my rubber is good or bad?  (Read 1434 times)
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MikeM
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« on: July 23, 2013, 10:37:17 PM »

OK, i'm the greenhorne here, and although i do know how to build hot gas jobs, i know nothing about the quality of rubber other than that i want to buy Super Sport for my competition P30, Mulvihill birds.

thinking i might have gotten a good deal, i bought a pound of 1/8 Tan rubber from someone for 20 bucks.....says it came from FAI supply.

if i take a strand and stretch it pretty good it does break, and gives the fingers a good snappin' too  Wink

i'm sure there has to be a better way to evaluate the rubber, so please give me some input.

thx
mike
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Bredehoft
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« Reply #1 on: July 23, 2013, 11:07:06 PM »

Hi Mike,

I guess the first thing people might ask is "what is the date on the box?"  FAI Rubber is the most popular (and maybe the best) rubber you can get. 

Maybe I should back up.  FAI currently sells "Super Sport" and "Sport", with the Super Sport being the higher quality.  Several years ago, they sold "Tan II", and before that "Tan".  That should take you back about as far as your rubber likely to go.  Of course, it is all called Tan because of the color.  This varies from a light tan to a very pale yellow.

Any rubber, even rubber that is approaching 10 or 15 years old, should be elastic, without nicks on the edges, if it has been kept cool and dry.  Usually, this is simply like you might find in a basement.  All of the rubber described should stretch a great amount - like 5 to 10 times its unstretched length before breaking.  If it stretches, but does not return to its original shape, then that is the first sign that it is no longer any good.

I think the current rule of thumb is that you can get about 100 turns per inch of a 1/8" loop before it breaks.  That is, if you make a 10" loop, lube it with some silicon lube (special rubber lubes, Dow 33 grease, even ArmorAll car interior spray) wind it, you should get roughly 1000 turns in that loop before it breaks.

That should help. 

--george

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Tapio Linkosalo
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« Reply #2 on: July 24, 2013, 12:44:23 AM »

If you can take a strand in your fingers and stretch it until it breaks, either you have strong fingers or the rubber has come brittle.

Anyway, I test my F1B motors, made of 26 to 28 strands of 1/8" rubber, by pulling them of force of 38 to 42 kiloponds. That is 85 lb or more. The excact force depends on how much the rubber stretches, aiming for consistent strain (there are other discussions on this forum about rubber testing procedures). That intends to be 90% of the breaking strain. 85 lb on 26 strands equals 3.2 pounds per strand, so I'd estimate that your rubber should tolerate at least 3,5, rather 4 lb strain per strand without breaking. If it breaks more easily it has become brittle and is of little use, as the motors would also break unexpectedly and at low torque.

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MikeM
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« Reply #3 on: July 24, 2013, 08:15:52 AM »

thx for the replies.
this gives me some perspective on what i am doing.

George, you called it on the labeling..............box says "tan 1/8".......no date though.

http://images.rcuniverse.com/forum/upfiles/325061/Us53232.jpg

http://images.rcuniverse.com/forum/upfiles/325061/Sx60495.jpg
help determining if my rubber is good or bad?
help determining if my rubber is good or bad?
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Dimeflyer
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« Reply #4 on: July 24, 2013, 09:19:50 AM »

Mike
try making a loop about a foot long and put it on a winder , then see how many turns it takes to reach the breaking point -if it seems to be a fair amount of turns or tourq it should be ok to move to a full motor the size you plan to use in your models but remember to use a blast tube in the use of it in a plane !
 You should store the rubber in a cool place out of Sunlite to slow any degradeing during storeage .
I lube mine and put it in plastic bags with the lube applyed to help it stay usable if it will be there for a long time .
 so far it has worked well for me !
George
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Maxout
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« Reply #5 on: July 24, 2013, 11:18:57 AM »

George, you called it on the labeling..............box says "tan 1/8".......no date though.

Well at least from the photo, even at full size, it looks to be in good shape. I'm still curious that you could break it by hand, though. Either you're really strong (and have more guts to punish rubber than me), or something's awry. I can say that the stuff looks too dark to be Supersport. I've got some 3/02 that is that color, and it's really, really good rubber.

Anyway, I'd suggest starting with a winding test as others mentioned. Good 1/8 Tan II takes around 125 turns/in (in two strand format), and Tan Supersport should take 100-110 turns/inch (at a disturbingly high torque).

You'll also want to get some torque/turns data, but that might be hard to do without a calibrated torquemeter. You could put a spring scale on it and do a stretch test; there's some good data out there for that.
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Dave Andreski
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« Reply #6 on: July 24, 2013, 11:47:47 AM »

Mike,
Check for color variation along the rubber's length. Is the color uniformally TAN or are there lighter, white-ish areas?
If so, this may mean that the rubber has been exposed to light because the box was open for extended periods of time.

Pound a couple of nails into a board about 10" apart, cut a piece of rubber about 22-23" long, make a motor by tying a knot of your choice, stretch the rubber to 3-4 times it's length and by whatever means possible, put about 6-7 hundred turns in it.
Secure the motor on the nails and leave it for about an hour or so. NO lube here. If when removing the motor from the nails the rubber seems 'sticky', sticks to itself etc. the rubber is no good.

Dave
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Bredehoft
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« Reply #7 on: July 24, 2013, 12:40:38 PM »

I'd say that is original TAN, not Tan II, nor any of the current varieties - so it's pretty old.  It could still be good, though.  Note Dave's test.  Also, if it just came apart under less-than-incredible effort by pulling, I would say it's bad.

--george
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MikeM
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« Reply #8 on: July 24, 2013, 09:04:53 PM »

thx guys,

i will try some tests this weekend as you outlined.
i'm not too worried if i have to junk the stuff...........i bought it from a seller who sold me a Morrill sidewinder w/counter that he listed as "used" for 6o bucks. to my delight it was not used at all, but brand new. his description of the rubber was worthy enough for me to blow 20 bucks ( 4 glow plugs in AMA gas Grin) so i figured what the heck.
the first 2 or 3 feet were somewhat easy to break, but i had to really yank on it...........hence the snap pooee......ouch!...
for some reason, we gas fliers don't trust rubber that hold our wings on when stretched to a certain limit that reveals weakness.

when Volare has some fresh stuff in stock i'll just buy a pound or two and not have to worry about it.

the rubber flying bug has really bitten hard and i'm on a roll.

got all the rubber kits down to get going on......

thermals,
mike
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lincoln
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« Reply #9 on: July 24, 2013, 09:22:35 PM »

Even if it's not super duper contest rubber it may be useful for learning purposes. If it's good, I bet if you make a #64 sized loop out of it, it will outstretch by a factor of maybe 2 or more any #64 rubber band you've played with before. I vaguely recall an expectation that Tan II could be stretched 7 times its length before breaking, but I am not sure of the exact number. Keep in mind that if you stretch it near the limit a few times, it may become weaker.
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Tapio Linkosalo
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« Reply #10 on: July 25, 2013, 02:45:05 AM »

The stamp on the box says "TAN", which means that the rubber is quite old, TAN wa replaced by TAN II somewhere in the early 90's... TAN is also a bit different in characteristics than Super Sport: is has more pronounced peak in force/torque, and then lower cruise. So be prepared, that you may need to adjust the model trims when changing from this batch to the newer ones.

Modern rubber stretches to about 10 times unstretched length before it breaks.

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Hepcat
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« Reply #11 on: July 25, 2013, 07:29:57 PM »

I just saw Tapio's reply #10 as I started to write this and I agree with him.  I am also suggesting that a quick and easy check is to make a loop of rubber a few inches long, put one end of the loop over a reliable anchor, pull the other end of the loop and if the rubber is any good it should stretch about 9 or 10 times its original length.  Please be cautious and don't underestimate the energy which can be stored in stretched or wound rubber.  Keep your fingers out of the way.  Perhaps pull with a length of cord or similar. 

John
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gossie
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« Reply #12 on: July 25, 2013, 08:10:53 PM »

Sure sounds like some old Tan, but so what?Huh??   Ideal for trimming, but use a blast tube every time when it lets go.
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MAN
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« Reply #13 on: October 15, 2013, 11:51:13 AM »

Just to know:
Anyone is remember EXACTLY the years that FAI TAN was produced and sold?
Or when exactly starts FAI TAN II?
Tnx!
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Aryan
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« Reply #14 on: October 12, 2017, 04:26:58 AM »

On purchase websites 1/8" or 1/16" dimensions are given for FAI rubber band . Are these width or thickness? kindly confirm urgently
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Re: help determining if my rubber is good or bad?
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billdennis747
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« Reply #15 on: October 12, 2017, 05:10:07 AM »

width
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vintagemike
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« Reply #16 on: October 12, 2017, 01:33:20 PM »

Reply to #13
I remember when I came back into Aeromodelling in 1986 I used to purchase rubber (the old grey stuff) by the yard from my local model shop, didn't know any better then. (OK OK whoever said he doesn't know much more now is probably right!!) I decided that I would be better buying a whole box, ordered it and took delivery of it a few weeks later, just as Tan was announced!! this would be 1987 at a guess. I seem to remember Ken Cooper winning 8oz Wakefield at Middle Wallop using "the new "Pink" rubber" in either 1993 or 1994. Anybody be more accurate than that?
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