Free Flight: Indoor

Free Flight: Indoor

Bud Tenny Box 545 Richardson, TX 75080

BIG SHOW TIME AGAIN! The 1991 U.S. Indoor Championships will be held at Johnson City, Tennessee on June 6 through 9, 1991, sponsored again by the National Free Flight Society. No details are presently available, but you can get entry blanks any time they are available. Just send a business-sized SASE to Tony Italiano, 1655 Revere Rd., Brookfield, WI 53005.

To bag or not to bag

The January 1991 column raised a warning about certain plastic rubber storage bags. This topic has generated more comments than any other topic ever presented here. I have received questions, suggestions, reports of bad rubber and letters from one skeptic who personally has lost no rubber. Roy Stewart asked about the disposable plastic from rolls in the grocery store. Tom Matterfis suggested using aluminum foil bags held together with double-sided tape. A broad range of information came from Boyd Felstead, summarizing reports from several international fliers. Another suggested source is the pleated sandwich bag (very lightweight plastic) available at the grocery store.

From personal experience, I have found a couple of different types of plastic bags holding deteriorated rubber, including a sealable bag with a piece of, formerly, prime Pirelli which appeared to be burned crisp wherever it touched the plastic. I also found other bags with rubber which seemed to be OK.

The bottom line is this: unless you have a chemist buddy with access to a gas chromatograph, you can't be sure that your bags are safe. Although vinyl chloride has been strongly implicated as the causative agent, it should not be assumed that any other material that might be outgassing from plastic is harmless. (Jerry Bockius insists that the rare chemicals, disasterol and infernalon, may also be involved.) If what you are using seems to be safe, keep using it (as long as you are certain you can keep getting exactly the same material). As for myself, I've switched 100% to glassine envelopes and oven bags.

The major downer from all this is two-fold: it takes a lot of time to individually move motors and raw rubber strip to new, individually labeled containers, whatever is used. Also, glassine envelopes are really intended to store thin stacks of stamps rather than a glob of rubber strip. Consequently, they store less gracefully and tend to spill the motors out unless carefully handled. The answer to keeping the envelopes closed appears to be solved by using pressure-sensitive (self-adhesive) paper label strips (I use Avery #S828 labels cut in half). If you keep lube off the label, it makes a reusable latch which works very well.

Flying Opportunities

The following listings are of all the contest dates presently on hand. CDs, please fill in for dates in June, 1991 and beyond.

• California: Los Angeles area. Monthly sessions at the 60-ft. downtown L.A. Armory on Stadium Way. Contact Ken Johnson, 16728 Bermuda, Granada Hills, CA 91344. Tel. (818) 368-0448.

• California: San Diego. Monthly sessions in Cat. I. Howard Haupt, 3860 Ecochee Ave., San Diego, CA 92117.

• Connecticut: Glastonbury: Indoor flying at Glastonbury has been cancelled until further notice.

• Connecticut: Norwich: Flying session Apr. 27, 1991. Jerry Bockius, 48 Division St., Norwich, CT 06360. Tel. (203) 887-5879.

• Florida: Miami. Dr. John Martin, 2180 Tigertail Ave., Miami, FL 33133. Tel. (305) 858-6363. Last MIAMA (No. 6) for this season — May 18-19, 1991 at McDill AFB.

• Idaho: Moscow has another Kibbie Dome session tentatively scheduled August 8 through 11, 1991. Andy Tagliafico, 650-B Taybin Rd. NW, Salem, OR 97304. Tel. (503) 371-0492.

• Illinois: Chicago area year-round weekly sessions in a 25-ft. gym at College of DuPage in Glen Ellyn, IL. Currently held on Wednesday evenings. Don Lindley, 420 Tupelo, Naperville, IL 60540. Tel. (708) 355-9674.

• Kansas: Topeka Class AAA Cat. II, Kansas Indoor State Championship, Whiting Field House, Topeka, KS, April 20, 1991. Jack Koehler, 3425 SW Arrowhead Rd., Topeka, KS 66614-3485. Tel. (913) 272-8439.

• Kentucky: Louisville. Due to site renovations, access is currently intermittent. Contact Burr Stanton, 9210 Darley Dr., Louisville, KY 40241. Tel. (502) 425-1915 periodically for information.

• Tennessee: Johnson City 1991 USIC, June 6-9, 1991. Tony Italiano, 1655 Revere Rd., Brookfield, WI 53005.

• Washington State: Seattle Area Cat. II Indoor meet at Naval Armory, April 27, 1991. Ed Lamb, 15911 SE 42nd Pl., Bellevue, WA 98006. Tel. (206) 747-7806.

TAN LOADING

I have heard it said that to wind Tan rubber too hard kills it, or that each motor is only good for four flights. Don't you believe it! Once or twice I have apparently overstressed Tan, only to find that it had apparently recovered by the next day. I'm not sure if I really overstressed the rubber or simply lost track of what I was doing; all I know is that a motor I thought was dead came to life again.

It is possible to wind Tan inappropriately; it is also very easy to be fooled by the unusual torque curve. Here's the case history on one piece of Tan rubber (all torque values are launch torque): New at 23.3-in. loop x .096 oz.

1. Break-in wind: 1790 turns at 0.6 in. oz.; the motor elongated to 24 in. as a permanent change.
2. 2040 turns at 0.87 in. oz. (length = 24.7 in. after 1/2 hour rest).
3. 2135 turns at 0.91 in. oz. (length = 25 in. after 1 hour rest).
4. 2220 turns at 0.90 in. oz. (length not measured).
5. 2250 turns at 0.95 in. oz. (length not measured). Washed and re-lubed.
6. 2275 turns at 0.9 in. oz. (length not measured). Washed and re-lubed.
7. Broke during winding.

This motor was built up and pre-wound but not used until a month later. All the rest of the windups were done on the same day over a period of about 5½ hours. The windup which broke the motor was hurried and happened after landing in the dirt in Hangar 1 at Lakehurst. Although I washed and re-lubed the motor, it is possible that I had not removed some of the dirt and grit which had worked into the coil and weakened it.

My point is that this rubber was capable of giving very high airframe torque for many repeats; in fact it actually increased slightly in torque after the break-in wind. The only explanation I can think of is that the rubber "set" and redistributed stress, and that warming it allowed it to relax and recover some torque. I feel sure that the motor could have been wound and flown again if I had taken more time in winding and provided it was clean. Note also that the motor's energy storage capability continued to increase until the motor broke; no sign of the motor getting tired.

Winding Tan rubber

Some fliers have had problems adapting to Tan, but somehow I felt comfortable with it almost from the first. (Actually, I was sort of forced to learn it quickly; the condition of all my Pirelli was poor-to-unknown at the time, and there wasn't time to test rubber while flying.)

#### Basic Winding

I consider the use of a torquemeter to be imperative when using Tan; read on to learn why. First, for less than full-power applications, Tan is very much like Pirelli after you learn to make the appropriate adjustments in cross-section and length. The following discussion covers taking Tan absolutely all the way; you don't necessarily have to push rubber quite that hard in most cases.

Begin a windup with no more than 4x stretch, and wind slowly as you watch the torquemeter. The torque will rise steadily for a while, more slowly for about the same number of turns, then ever more rapidly. When the torque rise speeds up, wind for short periods of time, then momentarily reduce the stretch. If the indicated torque drops lower as the stretch reduces, and remains there as you come to the original stretch, you are approaching maximum stress for that amount of stretch. When the torque rises as you come back to the original stretch, reduce stretch by about 15% and resume winding slowly. Repeat the unstretch/stretch maneuver until you reach maximum stress for the distance between hooks on the model. Hold the turns with the motor at model hook length and massage all the large knots until they re-arrange into smaller knots. If the torque drops during manipulation of the knots, add turns to restore the torque level. Winding is complete at max stress when further manipulation does not reduce the torque. If this torque level won't cause the model to out-climb the ceiling, hook up and launch. If the torque is too high for the ceiling, reduce turns slowly until the torque is at the right level. Tan has a very steep curve in the last few turns, so it is almost impossible to transfer full torque to the model even if you need it. Beware! It has been my experience that you absolutely cannot rush the last 20% of turns.

Any rubber must be scrupulously clean for blast winding; especially so for Tan because the surface is so smooth. There must be sufficient lube on the rubber to prevent scuffing! The motor must not have any nicks or other mechanical damage; otherwise, stress can concentrate at the damage site and cause it to break. Try it if you must, since you sometimes can get by with it.

Short Motor Tests

One very effective indoor model test for straight flyers has been to fly with 1/2- or 3/4-length motors. The rest of the equation is that the short motor is supplemented with a weighted stick running between the rear hook and the motor. That is, for a half-length motor, the stick is half the length of a full motor and weighs half as much.

Why do they do that? The half-length rubber holds half as many turns, the model climbs half as long, and the total flight time will be close to half as long as a full flight. In a high ceiling, the model never gets high enough to get into trouble and you get more test flying in a given time period. If you are worried about how the model behaves with full torque, the short motor test will tell you quickly. Over years of testing, by many fliers, the results have been very accurate. The key to the accuracy is that the weighted stick makes the motor weigh the same as a full motor, so the model trim doesn't change due to a shift in center of gravity (CG). The only time the CG won't shift with changing motor weight is when the CG is centered between the motor hooks.

What if you need a quick test flight and don't have time to make the spacer bar? Here is a shortcut which will allow a full-power test of flight adjustments: use a shorter motor of the same rubber cross-section, and add ballast corresponding to the missing rubber weight. For example, in a real-life situation, the model CG is ½ in. ahead of the center of the motor; that is, a lighter motor will shift the CG back. A normal motor is 22 in. long; the test will be done with a 15-in. loop. The rubber to be used weighs 0.00189 oz./inch, so a 15-in. loop weighs 15 x 2 x 0.00189 = 0.0567 oz.

To balance the model for the 22-in. motor (0.08316 oz.), add 0.02646 oz. to the model ½ in. behind the CG. The trim won't change, but the torque burst response of the model will be accurate if you use the same launch torque. The other flight parameters will change somewhat because the test loop has a different amount of slack as it unwinds. The climb will last longer than with a proper spacer, and the cruise will be extended unless the model runs out of turns too soon. The ratio of launch turns to turns left probably will be very inaccurate.

Mini-Stick revisited

The August 1990 column reported on Tom Vallee's Mini-Stick concept, a living-room-class model he uses to introduce indoor flying to new recruits. This class seems to be catching on, with some of Tom's plans and plans for original versions appearing in several club newsletters. Burr Stanton's INMARC Newsletter even had a design with both conventional tractor and pusher canard versions.

The abbreviated rules are: Maximum wing: 7-in. span, 2.5-in. chord; maximum length: 10 in. with motor stick, 5-in. maximum [motor stick?]; stab area: 50% of wing area maximum. Monoplane only; covering can be anything except microfilm, and all-wood prop. Special rules for contests in Tom's living room: Fly by AMA rules except three ten-second steers are permitted, and all winding must be done in the kitchen.

The Rescue

The photo documents one of my more spectacular goofups. At the 1990 USIC I had a new Intermediate stick which was totally untested. In desperation I made some test flights in one of the small practice areas at the end of the bleachers. I did my best to avoid an air circulation intake which served a laboratory. Unfortunately, the model found the air intake anyway and ended up plastered against the grill. Roy Bourke recorded the successful rescue effort. An extensible service platform was available to boost me to the right level (about 18 ft. above the floor). Luckily, the air flow could be blocked well enough by sliding pieces of typing paper between the surfaces and the grill. This allowed me to unplug the tail boom and get the model down in two separate pieces with only minor damage to everything except my pride!

Unusual Motor Stick

The models flown by Rene Butty (Switzerland) at the 1990 World Champs have unusual construction for the motor sticks. Thin balsa is spiral-wrapped to create a torsionally rigid motor stick. Not visible in the photo are four pieces of boron which add compression strength and stiffness.

Stan Chilton's props

Stan Chilton's props always run smoothly. That's because he uses a pitch checking gauge which allows him to precisely set the blade angle and measure the pitch anywhere on the blade.

Transcribed from original scans by AI. Minor OCR errors may remain.