Rubber

Rubber

Postby jander14indoor on Thu Aug 06, 2009 6:24 pm

Since we have a dedicated board for WS now, I thought it might help to organize by kicking off topics around the typical WS questions. Content of string to be driven by subject line (I hope).
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Re: Rubber

Postby blue cobra on Wed Aug 26, 2009 7:19 pm

Tan Super Sport seems to be agreed upon as some of the best rubber. However, if I am correct about this, it has a limited number of sizes. Are its advantages great enough to outweigh the difficulties of adjusting prop pitch?

How can you make something that allows you to wind by yourself/off plane?

What are the best lubricants, and is it best to lube before or after check-in?
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Re: Rubber

Postby andrewwski on Wed Aug 26, 2009 9:47 pm

blue cobra wrote:Tan Super Sport seems to be agreed upon as some of the best rubber. However, if I am correct about this, it has a limited number of sizes. Are its advantages great enough to outweigh the difficulties of adjusting prop pitch?


I believe so. However, even if you were to use another rubber than Tan Super Sport, would you be able to get it in different sizes?

There used to be some place that sold custom stripped Tan Super Sport (was it Dave Zeigler's site?). I can't find it anymore, but I got some from there once and it was good. Some people discussed the variations in ordering custom stripped rubber vs. stripping your own, but I found it to be close enough.

FAI Model Supply sells 3/32," which is about .093," and also worked pretty well for me. They still have .083" listed on their site for Science Olympiad, in my experiences I found it was a tad short on torque, but if I had more time to trim the plane and prop it may have worked. It's going to all depend on your plane.

How can you make something that allows you to wind by yourself/off plane?


I believe last year's thread had a detailed explanation in it somewhere if you can find it.

What are the best lubricants, and is it best to lube before or after check-in?


I find the best lubricant to be Armor All. You don't want to use anything oil-based, as it will break down the rubber. A few years ago I got a bottle of rubber lubricant that I believe FAI Model Supply sold and I didn't care for it too much. It was too viscous and extremely messy. Didn't give me any more winds than Armor All did.

Generally, you'll want to lubricate after check in. Therefore, the mass of the lubricant is not included in the mass of the motor when you check in. However, it may also be best to not use a new motor for competition, but rather one that you have broken in once or twice, thus, you may have used lube to break it in.
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Re: Rubber

Postby blue cobra on Thu Aug 27, 2009 11:40 am

Last season I used rubber from:

https://www.a2zcorp.us/store/

which comes in numerous sizes. However I ended up using .090" so 3/32 would probably work fine. Also that lube was extremely messy, I'll have to try Armor All.
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Re: Rubber

Postby jander14indoor on Sat Aug 29, 2009 6:57 am

blue cobra wrote:<snip>
How can you make something that allows you to wind by yourself/off plane?
<snip>

See the following two discussions from last years list about winding off the plane.
viewtopic.php?f=16&t=48&p=46368&hilit=winding#p46368
viewtopic.php?f=16&t=48&p=21033&hilit=winding#p21033

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Re: Rubber

Postby blue cobra on Sat Aug 29, 2009 11:21 am

Thanks. As you could imagine, it takes a while to find what you're looking for when searching through the WS forum for words like winding and rubber ;)
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Re: Rubber

Postby jander14indoor on Sun Nov 22, 2009 7:29 pm

Overtime there have been various stories some teams having access to magic, or super rubber. This note is to explain and dispel this myth. Also to let you know there is good news on the rubber front.

History:
Note, contest rubber has never been normal office rubber bands. Don't be tempted to grab any old rubber for Wright Stuff. Contest rubber is specially selected/formulated to store the most energy without breaking. Its actually a very severe and specialized use of rubber. But, its always been a VERY small part of the rubber market, so subject to the vagaries of forces outside rubber free flight. For years the best stuff was made by Pirelli, but not for free flight. When technology changed Pirelli dropped that product.
A dedicated free flighter worked with a rubber manufacturer to formulate rubber just for free flight. Thus was born TAN rubber. Over time the formula changed and improved and eventually became TAN II. It actually was a side product of the golf ball market from when the cores were a long string of rubber wound into a ball.
TAN II was the desirable rubber for many years, but tended to be widely variable. Some batches had distinctly more energy storage and durability than others. You had to know which batch to buy if you wanted to compete in the top ranks of indoor free flight, those planes that weighed 1-2 grams and flew 30 minutes. Thus the idea of magic or suber rubber. The range from worst to best was on the order of 20%. IF you know what you are doing, that's up to a 30 seconds under the current rules. Note, that assumes you are flying in the three minute range. If you are only flying one minute, that's a 10 second advantage.
This became even more important when a key ingredient in the rubber became unavailable due to changes in the larger market (solid core golf balls). No more TAN II.
With the demise of TAN II, TAN Sport was introduced. It was more consistent than TAN II, but only about as good as the lower batches of TAN II. Thus a loss of around 10 % or 15-20 seconds for the best flyers under current rules.
John Clapp, the current maker of contest rubber not being satisfied with that, introduced TAN Super Sport. Slightly more expensive, more consistant than TAN II, better than TAN Sport, about as good as the upper middle batches of TAN II. Down to about a 5-10 % loss or 10-15 seconds vs the old best batches of TAN II. Oh, and those batches are getting rare and near the end of their useful life (rubber ages, normally to its improvement initially, but eventually degrading to useless).

Well, here's the good news. John has not rested. The latest batches of TAN Super Sport are to a new formula and are testing out about as good as the good to best batches of the old TAN II. The loss (if any) is well within the normal variability of even good flyers. So, if you are using freshly purchased Tan Super Sport you have rubber as good as the old "MAGIC" rubber. And without having to know a generous free flighter, or spend a fortune on the internet.

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Re: Rubber

Postby calgoddard on Mon Nov 23, 2009 2:01 pm

Jeff:

Last year our team won WS using TAN II with a no-touch flight of 3:04 in a 25 foot ceiling.

Leading up to the competition the students flight-tested many different batches of Tan Super Sport (TSS). The best Tan II they had access to produced fifteen (15) seconds more flight time than the best TSS. The noticeable difference was the more sustained cruise yielded by the TAN II.

We have ordered the current TSS and will be interested to see how it measures up.

The legendary batch of TAN II (the vintage is well known to the experts) is not available anywhere, according to our information. I heard a local flyer has 15 lbs of it and won't part with any.

As you know, there are so many other factors that need to be optimized before the type of rubber will make the winning difference, but between the very top WS teams, it can decide the winner.

95% of WS teams should concentrate on those other factors.
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Re: Rubber

Postby jander14indoor on Mon Nov 23, 2009 6:26 pm

calgoddard wrote:<SNIP>95% of WS teams should concentrate on those other factors.


Absolutely agree, don't sweat rubber except to use contest rubber until you are flying well north of two minutes.

The nice thing though is very good rubber is again becoming available.

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Re: Rubber

Postby smartkid222 on Mon Nov 23, 2009 9:16 pm

Thank you for posting that Jeff it was very informative.
What do you consider "latest batches"?

*edit* According to the graph by June 2008 rubber had not gotten any better.
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Re: Rubber

Postby jander14indoor on Tue Nov 24, 2009 2:23 pm

After as much looking as I have time for I couldn't find the original disussion where the details were covered. On the comments I could find, Jan 09 and Jun 09 were mentioned as particularly good batches of TAN Super Sport. The discussion I remember said to expect continued better performance due to recent formulation changes, but I haven't refound that string. Arrrggghhhh.

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Re: Rubber

Postby calgoddard on Tue Nov 24, 2009 4:35 pm

June 2009 and September 2009 batches of TSS were sold out when I checked last week.
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Re: Rubber

Postby blue cobra on Thu Jan 28, 2010 9:00 pm

I'd like to use a torque meter, and the best plans I saw seem to be these. So, if I am correct, a torque meter can really just be a length of steel music wire fixed at one end with a hook at the other so you can twist it. If this is the case, the real challenge in building a torque meter is making the standard to which you will measure the movement of the needle. I assume this calculator is meant to assist in this. (Click the link then: Utilities>Torque Meter Calculator...). So...

What range of torque would our motors need?

How do you use that calculator?

Could I use my .020 music wire?

Could you put on enough torque to make the music wire permanently twisted, so that the needle does not return to its original location?
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Re: Rubber

Postby jander14indoor on Fri Jan 29, 2010 11:50 am

Yep, torque meters are as simple as that. Several plans available, which is best depends on tools available to you and your skill set. I don't mind soldering, so I used a different design, but that will work.

I find 2 in-oz for the full 360 range of the dial to be good for SO. Smaller motors tend to break around 1-1.2 in-oz, larger around 1.8 in-oz. For a good plane, launch torque will probably be in the 0.4 to 0.8 in-oz range, depending on ceiling height.

A 0.020 diameter for the torque sensing element of the design (the free straight length between the anchor and the pointer). That calculator can be used to iterate the length to a desired range. I set the units at 2, diameter at 0.020, and varied the length till 2 in-oz was as close to 360 degrees as I could get it. Around 9.3 inches.

Note, there are a lot of assumptions under that tool, if you want to understand it better, go to the referenced site for more details. Example, it assumes a steel wire for the stiffness coefficient. It assumes that you pick a wire size and max torque that does not permanently deform the metal (exceed its elastic limit) at 360 degrees twist. (0.020 in diameter wire for a 2 in-oz full scale range is OK)

Be warned though, I've found that torque meter hooks made from wire as fine as 0.020 tend to bend/open with use, sometimes releasing a tightly wound motor at a very inconvenient time. Two possible solutions I can think of. One, double the hook part back on itself to the pointer and bind it togehter with fine copper at the pointer. The other is to solder a thicker piece (say 0.032) onto the sensing element at the end, making the hook from the thicker wire. That's what I did. Make sure the free length of the sensing element is the desired amount between the anchor and where you solder it as that 0.032 wire won't twist at all compared to the sensing element.

Comment on calibration. You can find procedures on the web, I think one is described on the Free Flight Fantasies site. But frankly I'm not sure I'd bother other than as a demonstration of procedure to the students. I've found the calculated scale accurate enough, and careful building has allowed my meters to be comparable to each other within usable accuracies. You don't need much beyond two to maybe three digits of precision for these things to be invaluable. Of course calibration DOES let you compare to others. Which is a key element in science.

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Re: Rubber

Postby blue cobra on Fri Jan 29, 2010 2:10 pm

Thanks, I think I'm understanding what you're saying. If the distance from the right angle at the end to the needle is 9-11/32 (9.34375) with .020 music wire every 90 degrees would be approximately 0.5 in/oz of torque. So, I could draw a circle, mark every 10 degrees or so, and attach it behind the pointer to have a scale close enough for my purposes. Then I could make my hook/pointer like below and solder along the grey line.

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