Rubber FAQ
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Frequently Asked Questions...
about High-Starts and Mandrel Dipped Latex Rubber Tubing

What is this "mandrel dipped rubber" I've been hearing about?
Mandrel dipped rubber tubing is 99% pure latex rubber tubing which is made in a way that optimizes its mechanical properties in lieu of ease of manufacture or chemical resistance. Due to the superior mechanical characteristics of mandrel formed rubber tubing it is best for high-starting your RC sailplane.

What other kinds of rubber tubing are there?
Many high-starts are usually sold with extruded latex rubber tubing, also known as "surgical" tubing. This tubing is often lower cost, with tighter dimensional tolerances, higher chemical resistance rubber that is optimized for the medical industry who is its largest consumer. While clear plastic Tygon tubing has replaced it for chemical resistance, surgical is still made for turnicuts, stethescopes, artificial heart pumps, dialysis machines, etc. The need here is for high chemical resitance, and moderately "rubbery". A maximum of 100% elongation is all that is required in these applications. Other compounds are formulated in with the latex to enhance these other properties while they increase durometer (rubber hardness) and reduce the stretchiness. The compound is forced as a powder through a heated press, which extrudes the finished tubing out like a ziti noodle maker. The dimensional tolerances are very accurate. High quality extruded rubber (99%+ latex) is available in the market, and some high-start makers do use this type. Its performance when new is comparable to mandrel dipped rubber, but it does not hold up under abrasion or UV nearly as well as dipped tubing. Extruded rubber of this high quality costs more than the best dipped latex tubing.

Another type of rubber tubing is silicone. It is usually clear or dark red in color, and used for fuel tubing. It is available at marine supply dealers like West Marine. It feels pretty stretchy to the touch, but stiffens quickly when stretched beyond 300% elongation. It is not suitable for launching sailplanes at all.

Another type of rubber sold as a sailplane launching engine is plain old bungee cord. This is usually made of synthetic silicone type rubber, or low quality extruded rubber strips (grey). These small 1mm x 1mm square bar strips are aligned in parallel, and wrapped in a nylon or polyester jacket. The jacket limits the ultimate stretch that the cord can achieve, acting as a over-stretch protector while also reducing UV and oxygen exposure. It needs this because the many strands within the bungee have much higher exposed surface area which means more of the rubber is exposed to oxygen. That is why bungee goes limp after a few years. The little strands become hardened and break easily. We all know that bungee is the world's second greatest invention (behind duct tape), but bungee cord is best used to hold your fuselage steady in the car trunk and not for launching sailplanes efficiently.

FIA tan rubber is available from SIG by the pound. It is thin slices cut from pure latex rubber sheet. It is the same material in dark tan rubber bands. Very tough and very stetchy. For launching small sailplanes like MHLG and free flyers it is great. Peck Polymers also sells this stuff.

How it is mandrel dipped rubber tubing made?
Mandrel formed latex tubing is manufactured by dipping a long steel rod (mandrel) repeatedly into a vat of liquid latex rubber, applying about 0.003" thickness of rubber to the outside of the tube with each dip. It is just like making homemade bayberry candles! A tall tank is used to hold the liquid rubber, and the mandrel must be raised between dips high enough to completely remove the tubing from the liquid. The rig can be as high as 120 feet just to make 50 foot lengths! The tubing is removed with great manual labor from the mandrel and boiled in a highly alkaline solution for several hours to cure.

Why is dipped rubber better than other kinds  of rubber for sailplane launching?
The dipping process produces concentric layers of rubber through the tubing wall thickness. You can actually see rings with your eye on a cleanly cut cross section of transluscent amber tubing. These layers cause the rubber's spring rate to stay relatively flat with respect to displacement, even at high elongations past 400%! Other latex rubber tubings, like surgical, are extruded from dry latex powder pushed through a extrusion machine under high heat and pressure. This method of manufacture is the norm for latex tubing nowadays because it is more easily controlled, holds much better dimensional tolerances, is less messy, requires less space on the factory floor, eliminates cosmetic defects common to dipped tubing, and requires much less manual labor. Extruded tubing can be of extremely high quality but because of its homogeneous, non-oriented internal structure it will never have the exceptional mechanical performance qualities of dipped latex rubber. Longer stretches at the same tension mean that our rubber will store significantly larger amount of potential energy without placing larger stresses on your airframe during launch - the efficiency of our rubber is higher. Also, dipped tubing is tougher. It resists tearing from dragging through tall rough grass much better than extruded tubing. Our tubing should lats you at least 5 years with normal care. Try our Rubber Milk protectant for even longer life.

What about splices? Do you still splice short lengths together to make high-start size tubing?
We now offer 100 foot continuous lengths of mandrel dipped tubing, something that has never been offered for sale before in our hobby. 2 Meter, 3 Meter and Unlimited size tubing are available in 100 foot continuous lengths. 1.5 Meter tubing is available in 50 foot continuous lengths. The Bungees are still only available in 25 foot lengths, which is suitable for their application. Bungee Binders can be used to make a reliable splice of any size tubing that we carry, if a longer length than available as continuous is required.

Everyone says their high-start rubber is the best, what makes you any different?
Over the past 3 years, hundreds of people have bought high-start rubber from Hollyday Designs, and not a single customer has complained about poor performance of our rubber. To the contrary, I have talked to many of our satisfied customers who were previously frustrated with other company's rubber tubing. They tell me that they finally found what they were looking for, and that they cannot believe that their could be such a difference in rubber tubing of the same dimensions. This rubber really is the best you can buy, anywhere. Don't ask the guy selling it, ask the guy who has bought and used it! There is no better rubber for high-starting sailplanes available anywhere - and we back it up with our 30 Day Money Back Guarantee!! No other rubber seller offers a 30 day money back guarantee so you can see for yourself how good our rubber is without risk. Hollyday Designs high-start rubber tubing is recommended frequently on the Radio Control Soaring Exchange email list. Try the searchable website.

While browsing another website selling high-starts and rubber tubing, it was suggested that I should ask you why you make your tubing black, and to ask you to prove that it resists UV radiation better than plain amber latex. Why do you make it black?
Adding carbon black to rubber compounds is a method proven to prevent premature aging of rubber which has been used in the tire industry for over 100 years! Coloring rubber with less than .5% carbon black has been proven to have no noticeable effect on elastomeric performance, and certainly not a 20% difference as claimed by our competitor. Our tubing manufacturer has proven this to our satisfaction by performing side by side tensilogic tests of pure amber and black colored rubber. There is no noticeable difference in performance within the stated margin of error of the tests. Even if there were a slight performance impact, such a minute performance loss would be more than made up by the superb mechanical advantages of dipped rubber tubing compared to the standard surgical extruded tubing sold by many of our our competitors. With the cost of a good piece of replacement rubber for your high-start costing $65 plus shipping, black coloring adds much needed protection to prevent failure of your rubber before its time. Read more about black rubber coloring, UV and Ozone.

Amber latex tubing is transluscent and UV rays can penetrate farther into the rubber and cause damage to the inner layers of the dipped tubing as well as the outermost layer. Black tubing is opaque and being opaque is what blocks the UV penetration, and is what prevents the additional sun damage, not the black color specifically. Since the base material latex is naturally light amber in color, no other colorant besides black will mix with it and produce an appealing color without being affected by the amber base color. Carbon black powder is cheap and very concentrated, so that little is needed to make the rubber very opaque. It is the cheapest way to color the rubber, and it looks pretty good. This is why rubber tires have been black for the last 100 years. Black colored rubber is the exact same cost to Hollyday Designs as amber rubber since our factory makes both as standard colors. If amber were better, we would offer it instead.

Another advantage is that black rubber is much easier to see in tall, dry grass, green grass, dark or light dirt, etc. It is more visible than natural amber, which blends in with dry grass.

While carbon black coloring may prevent the penetration of UV rays to the interior of the rubber, the exterior of any natural rubber material, no matter what color, is rapidly attacked by UV rays and Ozone gas. Use our Rubber Milk protectant frequently to protect your investment. Read more about rubber and vinyl deterioration caused by ultra violet rays and ozone. Freeze your rubber for long term storage to halt deterioration!

Are there any safety issues with high-starts?
High-starts are designed to store a tremendous amount of energy. Our Heavy Duty High Start Tubing, when stretched to 300% elongation as recommended for a normal launch, is storing ~7,000 foot pounds of potential energy! With enough leverage that would lift a VW a few inches off the ground! Now picture that VW landing on your foot, even from only a few inches altitude - OUCH! Our high-starts must be treated with great respect to avoid any possible injury or property damage.

In a normal launch, pull of the high-start is converted into forward airspeed, which is converted to lift by the wing's airfoil which resists the pull of the high-start and allowing this tremendous stored energy to be released slowly and in a very controlled manner. When a component in the high-start system or on the airplane fails, the energy is released much quicker. If your person or property is in the way when a high-start releases with no resistance, injury or damage could result.

Warning! High-starts are not toys. High-starts can be very dangerous if not used correctly. Please ask for help from an experienced sailplane pilot if you have any doubt about how to use your high-start safely.

Here are some safety tips:
Inspect the rubber thoroughly at least once a month throughout the flying season. If you see any cracks or signs of hardening, plan to replace your rubber asap. Until it is replaced, do not stretch past 250% elongation and be on guard for a possible break.
Ozone reacts with rubber in the presence of UV light to harden it. Ozone is in our air in small quanities, more in cities and higher altitudes. Protect your rubber from deterioration which could cause accidental breakage with Rubber Milk.
Make sure you use the right kind of stake to fasten your high-start to the ground. Use a twisting dog run corkscrew style for loose dark "garden" soil or sand. Use a long spike and a hammer for firm soil or rocky clay. Check your high-start fittings occasionally. Inspect all knots, swivels, connectors, parachutes, split rings, etc are in perfect order. These parts are cheap. Replacing worn parts will cost pennies and might save someone from getting a bad bruise or far worse.

I heard that exposure to natural latex rubber can be a health hazard. Is that true?
Some people have had allergic reactions after contact with latex rubber products. The phenonenon is most often associated with medical professionals' frequent use of surgical gloves. There have been no reported cases of allergic reactions to handling natural rubber tubing. Little research has gone into this illness since it is rare and easily cured by discontinuing contact with the allergen. There are two basic beliefs as to the cause of the allergic response.

The first belief is that some people are allergic to the proteins found in natural latex rubber products. Latex is the white milky liquid that is drained like maple sap from gum rubber trees in Central Asia. As with any plant material, there is always some small amount of protein present, and this is usually not harmful in its natural state. By the time the latex liquid is processed into a modern elastomer and formed into solid objects like tubing, there is little residue that can transfer to the skin upon normal contact.

The second major theory for the cause of the allergic reaction to latex products is that it is not the latex product at all, but the powder that is sprinkled on latex gloves to keep them dry and easy to stretch over a damp hand. Frequently, corn starch or talcum powder is used to dust surgical gloves. Both of these powders (especially talcum) are known to be skin irritants to some people. Since surgical gloves are usually manufactured in less than ideally controlled conditions, in hot and humid climates in Asia, a barrel of corn starch dry lubricant may be many years old and thoroughly rotten before it is used to dust rubber gloves. The proteins in the powder could become a very toxic skin irritant.

Without scientific research it is impossible to form any conclusion. Hollyday Designs rubber tubing contains extremely low amounts of latex protein, in fact, the manufacturer claims their rubber is more than 99.995% protein free, the lowest of any natural rubber tubing in the world! The tubing contains less than 50 micrograms/gram - 50 ug/g is the detection limit of ASTM D 5712-95 standard, so whatever amount is in the tubing is undetectable by standard testing methods. There is no dry lubricant used with our rubber tubing.

See more detailed information at the latex webpages of the Center for Disease Control.