Rubber breakage point? Or was it dud?

[paul]

Hi Guys.
Before applying tissue I thought I would test the rubber.
With disastrous results.
Twists... 50 - 100 - 150 -200 - 250 then it broke

Is there a way to test the strength of the rubber?

[WIDDOG]

Uploaded with ImageShack.us

Hi Paul,

There are so many things wrong with the rubber band that comes with the kit it’s very difficult to know where to start. I recommend this book highly. It has a very good chapter on rubber alone. BTW Guillow’s website sells this book.

[Phugoid]

There is a simple answer to this: don't use the rubber in the kits - it is useless! Buy some tan rubber from A2Z or one of he other decent suppliers you can find. The tan rubber will be able to store many times more energy than the blue bands supplied in the kits.

The other thing is to make sure tht you put some lube on the rubber, at the most basic level castor oil works well.

Andrew

Ps be careful winding the rubber up on an uncovered fuselage, the tissue does form an important structural element and the fuselage is weak without it.....,

[Wildpig]

Hi Guys.

Is there a way to test the strength of the rubber?

You just did. Seriously. A lot of modelers will buy a batch of rubber, take a section of it, make a two strand motor and wind it until it breaks. Sometimes the strength is measured with a torque meter or just the number of winds.

Somewhere on the internet I got a chart of max. turns for Tan II rubber. As an example from the chart:

2 strand rubber motor----106 turns per inch of motor length---- 3 .oz .in torque

[Mitch]

Ditto... on that is how you test the rubber... you can also use armor-all as a lube. I have used the grey rubber in the kits and get about a dozen successful flights before the rubber looks VERY worn out.

I can also break the good tan rubber...

...so dont feel bad about breaking rubber... 250 winds sounds like alot to me for that blue rubber.

I think you should start to feel it get hard to wind before it snaps. Mitch
PS this tan rubber was wound and ready to fly and then all of a sudden "PUGGAGHH" (I am trying to write a word of the sound it made )

[Bill Gaylord]

Mitch if you cut the broken ends off, the rubber band looks like a nice tight grape bunch. There's at least 2 or 3 winds in there.

I would assume most folks do this, but it's probably a good idea to give the entire length a light pull check, looking for any nicks that would cause a failure. I'm not a rubber flyer, but at one time I flew a number of planes with rubber band wing attachment, and learned to test the bands, and replace often also. A few rubber band failure stories I remember are: I had a GWS Beaver slowly lose the ability to climb, while gradually landing whether you wanted to, or not. It was due to the rubber bands stretching and giving out, causing a ridiculous incidence angle. Fortunately only minor damage. Another time was when an AR234 suspended by strings from the ceiling was not there anymore, when I entered the build room. It was on the floor, due to wing attachment rubber bands failing. Fortunately a cabinet just inches below broke it's fall, again with minimal damage as it only had another few feet for the whole mess to tumble to the floor.

[paul]

Thanks for your advice/tips
Bought Rubber Powered Model Airplanes by Don Ross for $5.99. Postage $11.75 to the UK. Ouch
Will make good reading while I'm at work.
Scrolling through the forum I found this www.ffscale.co.uk which will also help a great deal for a newbie

[Steve Blanchard]

Paul,

Mike Stuart's site is a great resource for information and helpful tips about freeflight scale airplanes. Go to his links page and be sure to visit some of those sites as well. Small Flying Arts is also a great site as well as Hip Pocket Aeronautics. DC Maxecuters has a great site with great pics. Be sure to visit the Flying Aces Club site. All of these resources will get you flying in no time. I've always said, as great as this site may be, there is a whole host of information out there for people in this hobby on other sites as well. There are definitely more experienced people outside of this web site when it comes to flying these little gems. There are some great guys here but being that it's dedicated to Guillow's kits it limits the builder/flyer to their line only. You'd be surprised to see what flies on rubber power if you look hard enough.

Steve

[WIDDOG]

Hi Paul,
I noticed from the picture that you are experimenting with the kit 508 Stuka. I would recommend 1/8” inch FIA Tan Super Sport Rubber at two loops or 4 strands. Also I would recommend “Braiding” the rubber and using Glycerin and soap as a lube. BTW I buy my Glycerin, from the drug store, in the laxative department. I buy it in the form of suppositories and melt them down in the microwave oven, for about one minute or less. Than mix in the soap, when it cools it thickens up to like a grease consistency.

[Steve Blanchard]

Or you could save yourself all of that trouble and start out just getting armor all or son of a gun and spray it into a zip lock bag with the rubber and use use that as lube. Also, it is neater than glycerin and soap when it unwinds in the model. Glycerin and soap has a tendency to splash all over in the fuselage while the rubber unwinds. If you really want a proven lubricant, Dow 33 is by far the best one to use.I agree with Widdog that you should use tan super sport and braid or back wind. To braid a single strand you twist one end of the rubber before you tie it together into a loop. This way it will bunch up along the entire length as it unwinds and distribute the weight evenly keeping the CG correct for glide. I would recommend that you get rubber with half the cross section and and create 2 loops and back wind (1/8" rubber get 1/16" and make two loops). What you would do is take one loop and put it on the hook of the winder and hold the other over your thumb or wrist. Wind the one on the hook for about 20 winds and then put the other loop on the hook. Backwind the two together and stretch and rub them together down their length to kind of combine them into a braid of sorts. What I like to do next is wind the rubber up for about 50% of max winds then attach the prop, put it into the model and hold the model while it unwinds. You will see the rubber all braided up when it is finished unwinding.

Hope this is helpful,

Steve

[WIDDOG]

Hi Paul,
I looked through that webpage you suggested and noticed they where using longer rubber motors than I use, maybe 1.50 times the hook to peg length or longer. Anyway I tried a longer motor in my EXP 500 Series kit. It did work better. I “Walk Back” my recommendation about 1/8 inch rubber. Thanks much for the tip.

[ekram]

The other thing is to make sure tht you put some lube on the rubber, at the most basic level castor oil works well.

Andrew

.....,

Sorry to drag up an old post but I was searching for information on rubber lubricants and this one came up. Don Ross says never to use Castor oil to lubricate rubber because of some sort of protein in it that causes rubber deterioration.