Safety Comes First
5063 Benton Boulevard, Pace FL 32561
CHANGING OLD RUBBER BANDS?
In my May '96 column I wrote a piece titled "Wing Away" in which an aircraft transformed itself into an air-to-ground missile when the four-year-old (or older) rubber bands on the main wing suddenly lost their elasticity—ouch! The postmortem revealed slim pickings.
Having read the story and formulated a few thoughts of his own regarding "the life of a rubber band," longtime engineer and modeler Tom Cater of Grand Rapids, Michigan, thought the rest of us might benefit a little from some of his personal observations.
It has been my personal observation as an engineer and user of rubber bands in this hobby for more than 40 years that the life of a rubber band is determined foremost by the amount of sunlight that falls on it. I have observed rubber bands going from new to breakage after just hours of exposure to maximum sunlight.
I have always used my rubber bands until they are worn out, to the dismay of other fliers, and I have never lost a wing, even in flying conditions ranging from 90°F to -10°F. I determine when a rubber band is worn out by examination for cracks and deterioration. I try to replace only half the rubber bands when replacement is indicated. This way half of the rubber bands are new "untested" and the other half are used "previously proven flightworthy."
Here is my list of factors affecting rubber band life:
- Exposure to sunlight's ultraviolet light
- Composition of the rubber
- Storage conditions, both new and used
- Exposure to raw, unburned fuel
- Exposure to hot engine gases
Exposure to sunlight's ultraviolet light
In my experience this seems to be the most deteriorating factor for rubber bands. The amount of ultraviolet light that strikes the earth at any given time varies with the seasons and atmospheric conditions. Therefore the deterioration rate can be very different on two different days of the year. On clear summer days the deterioration rate is at its maximum, and often so is the length of time the airplane is at the field. This combines to compound the danger of broken rubber bands. On such days I often cover my airplane's rubber bands with a rag when it's not flying. Under these conditions deterioration is at its greatest—preflight inspection of the rubber bands is advisable.
Composition of the rubber
I have seen some rubber bands turn into a liquefied substance when exposed to certain plastics. Model fuel dissolves some rubber bands rather quickly. It is a wise move to buy your rubber bands at the hobby supplier and pay more for a product that is (hopefully) tested for our sport than to buy bargain rubber bands at the office supply store and test them on your airplane.
Storage conditions, both new and used
As with most chemically produced products, storage above room temperature will reduce shelf life. Storing new rubber bands in a light-tight and airtight container at room temperature will maximize their life; good new ones should last 10 years stored this way. Used rubber bands seem very adversely affected by burnt fuel residue (oil). I have found that blotting them with a rag is as good as anything. The ones I did this to in the fall and flew a few times in the winter were still flyable in the spring, but not for long in the spring sun. Never leave new rubber bands out in the sun at the field.
Exposure to raw, unburned fuel
Raw fuel with nitromethane is hard on rubber bands (as well as many aircraft finishes). Contact between the two should be avoided.
Exposure to hot engine gases
Hot engine-exhaust gases can heat rubber bands. As they become heated they lose their elasticity (become softer) until they become so hot that they melt. The engine's muffler exhaust should not flow over the rubber bands. Check before mounting the engine.
Cold
It has been my experience that rubber bands will work in much colder temperatures than the pilot will! In cold temperatures the rubber bands will become stiff, and it is advisable to put them on while they are warm to avoid unnecessary stress to both the rubber band and the aircraft.
Having read Tom's comments and compared them to my own experiences, I would have to agree—his observations are right on the mark, although I would like to add extra emphasis to obtaining quality rubber bands. The quality of rubber bands always seems to vary greatly, even with the ones we purchase from the hobby shop. Be sure to stretch a few before you buy. Check a random sample for cracks and yellowing before purchase, and make sure the store is aware of problems so that the next modeler won't end up with them. Again, as Tom mentioned, I'd only recommend that you purchase and use bands from a hobby shop.
Once the bands are in use on your airplane, my personal policy for changing them is this: "When in doubt—throw them out." Why? They're just too cheap to even worry about, and the results are potentially disastrous if you don't have the knowledge or desire to care for them like Tom does. If you stop to consider how much a rubber band costs compared to the cost of replacing an airplane, a reasonable person would have to agree that the risk of using them over and over again doesn't make good sense. A simple analogy involves comparing how much it costs to put gas in a car for a month to the cost of motor oil for the same period. Which fluid costs less to use per mile? The answer: oil. Which will damage the engine if it isn't maintained in a proper manner? The answer: oil. Which item—fuel or rubber bands—is less expensive per flight, but has the greatest potential for damage if it goes bad? (Remember, you can always glide the model down when the engine quits.) So, comparing the damage potential of rubber bands and motor oil, do you think it's wise to push the margins of safety for either? I don't! Avoid some grief and discard rubber bands at the end of the day.
Sticker Requirements
While reading through the AMA National Newsletter recently, I ran across a piece that should interest many of us since it relates to improved radio technologies. As written by Bob Underwood:
As of January 1995, the so-called "sticker requirement" was dropped from the AMA Safety Code. Since March 1, 1992, manufacturers have been required to meet narrow-band transmitter specifications. They were given until March 1, 1993 to clear their existing stock. Therefore, any transmitter produced after March 1, 1992 or purchased after March 1, 1993 may be considered narrow-band.
Contest directors may wish to consult pages 13–15 of the Membership Manual for guidance concerning transmitters and receivers. Rule 4.12 on page 13 recommends that Contest Directors or club officers require tests or implement special frequency control arrangements as may be necessary to reduce the probability of harmful interference among RC systems. Within the document you will find empirical tests for both transmitters and receivers. Additionally, AMA equipment is available through your AMA district Frequency Coordinator or Vice President that will aid in frequency management.
It should be noted that the primary problems inherent with the use of older, wide-band equipment center around the receivers. Since the FCC does not require type acceptance of receivers, and a complicated laboratory test is necessary to determine whether they meet narrow-band specifications, the only course left is date of manufacture, or the empirical test found on page 14 of the Membership Manual. A bill of sale indicating that the unit was purchased after March 1, 1993 may also be a helpful guide.
Finally, Contest Directors will find that a good portion of the equipment being used will still carry a gold RCMA sticker. Some AMA members are continuing to have their equipment tested by both manufacturers and independent sticker stations. The key for Contest Directors is, however, that the AMA Safety Code no longer contains a gold-sticker requirement. The next important date for consideration is March 1, 1998. At that time all older wide-band transmitters will become illegal by FCC regulation.
That's it for this month—thanks for the mail. I hope all of you have been having a great flying season! Isn't it time to start thinking about what Santa should bring for Christmas?
Transcribed from original scans by AI. Minor OCR errors may remain.
