Focus on Competition

Focus on Competition

A Note From the Technical Director

Bob Underwood

The day dawns bright and clear. A gentle breeze wafts down the runway. More participants than anticipated grace the scene and everything is going just fine — since it's the first RC event at your new field you really are happy that it's working out so well. Then it happens. The dreaded word rings out loud and clear from the flight line: interference! Everyone watches helplessly as the model crashes far out in the field. When the pieces are returned to the pit area the post mortem begins.

Several persons are convinced it was pilot error. Another recalls this individual having problems with the same system "just last week." Still another, a long-time modeler, surveys the wreckage and pronounces the cause radio installation problems. The most chilling statement comes from the person who says that "a channel such and such always gets hit around this area." If no subsequent problems surface, the problem and all the related "reasons" will probably fade from everyone's memory bank within the week (except for the fated pilot, of course). But those of us who have been a CD for any period of time know that such incidents seem to come in bunches, like bananas. And therein we face a potential serious problem related not only to safety but to the establishment of rumors that can destroy the prospects of future events at that site or the reputation of your club. Thus the subject for this month.

To bring some of this problem into perspective, let me use personal experiences and a few reports from reliable individuals. First, consider several incidents that are easy to document.

A few years back, at the Mint Julep Scale contest, a scenario developed where known interference was produced. The two flight lines at the site were separated by some 200 feet. During one round, as I was about to taxi out for takeoff, the judges told me to hold because a model was in the middle of its takeoff run on the other line. The other line left the flight path as a model taking off was going about 20–30 feet off the end of my transmitter antenna. I could not turn my transmitter off since my model was on the runway with both engines at idle. As the other model flew by it suffered throttle and elevator bounces; while it didn't crash, an otherwise beautiful takeoff was spoiled. The two lines are now placed closer together at that event.

This year at Top Gun we saw evidence of a classic 2‑IM situation. On the practice day I was flying on channel 25 and another contestant was attempting to get airborne on channel 48. He was experiencing problems; when I landed and shut down my transmitter, his problems went away. The event information had made it very clear that all 50 channels would be used and that all equipment — transmitters and receivers — had to be narrowband. The channel 48 receiver he was using evidently was not narrowband and the 2‑IM problem was very clear.

Fortunately I was in the air first. Incidentally, since I was the only one flying on an odd channel I spent quite a bit of time checking with persons flying on adjacent channels (24 and 26) and on 48. In this case the difference resulted from the other plane being a practice model that was not actually part of the competition.

These two occurrences were rather simple to document. But more often than not they are not clear-cut at the time of the incident and "MRM" takes over. "MRM" stands for Modelers Rumor Mill. This communication system is the fastest form known to man. It is also much better at producing garbled output than the old party game Telephone. Sometimes these rumors are produced in spite of accurate information.

Several years ago, again at the Mint Julep event, I crashed a twin-engine model on takeoff. The wind had shifted across the runway and during the takeoff run the model turned toward the far edge. I lifted it off too soon and by sheer luck kept it airborne a couple hundred yards but never managed to recover. Finally the model rolled over and went in. My daughter, who was watching, remarked, "Dad, it flew farther than I thought it would." She doesn't fly or build and she knew I was in trouble and fighting a stall.

Following the incident people came up and asked if I had lost an engine or had radio problems. I replied to each person, "No, the pilot suffered dumb thumbs," and explained the problem. Two publication reports nevertheless listed the demise of the model as due to an engine failure and another claimed radio problems. I had talked to both reporters shortly after the crash; one of them had witnessed it. I suppose I should appreciate that reporters were attempting to save time and space in their stories rather than attempting to save my reputation — but at whose expense?

For over a decade I CD'ed events at Buder Park in St. Louis County. I flew there regularly, usually at least once a week. Since it was a public flying site many newcomers gravitated there for their first flights. As a result crashes involving big names on the contest circuit were often blamed on problems associated with newcomers. Buder came to enjoy the title of "Glitch Alley." It's true Buder, located in an area with higher RF levels, could produce minor bounces and throttle hits under certain conditions, such as when a scale model was tail-on to the antenna in the middle of a figure-eight. But between 1967 and when I moved in 1985 I cannot remember losing a model for an unexplained reason. None of those reasons ever added up to interference.

The following letter arrived while I was working on this column. It speaks volumes on the subject; I've edited it to remove names and specific areas.

• May 25, 1991 — Letter excerpt
• The past three months have seen the crash of seven models in the same general area just east of our flying site. A couple of the pilots concluded their crashes were due to outside interference and the rest of the pilots jumped on the bandwagon. Several of us "old heads" decided the recent phenomenon needed thorough investigation, just in case it was true.
• Our field is located 4.5 miles south of an Air Force base and 20 miles due east of a large metropolitan area. I had overheard remarks such as "The interference probably came from the base" because there have been a lot of radar tests there. Desert Shield/Storm began. Sometimes "probably" became "must have." I spent 21 years in the Air Force, the last five at that base, and I still know people who work there. I talked to personnel in Command and Control, Command Headquarters, and electronic maintenance shops. None had knowledge of anything nasty in electronic transmissions.
• When the military goes to high alert or war, communications go to "Situation Minimize." They reduce message traffic and any electronic transmissions to the absolute minimum to reduce the chance of interception. The Gulf conflict would have caused a drastic reduction in electronic transmissions from the base, not an increase.
• A local hobby shop owner bought a Radio Shack scanner in March that can be programmed to cover the 72 MHz band. He brought it to the field several times and found nothing on the RC frequencies except our own transmitters. He did detect weak noise on 72.240 and a couple of other 27 MHz frequencies. Because his scanner lacks a signal strength meter, he couldn't be sure. We requested the loan of the AMA scanner to further investigate.
• With the AMA scanner, the hobby shop owner and the chairman of the club frequency committee found nothing significant on the 72 MHz band. We found absolutely nothing that could be classified as significant outside interference.
• I was asked to take the AMA scanner to the field. I spent a total of 23 hours on several separate days and found absolutely nothing that could be classified as significant outside interference.

The point of these stories is simple: before blaming interference, do the homework. Check installations, check batteries, check antenna placements, and verify equipment is narrowband where required. Rumors and assumptions can do great harm to a flying site and to the reputations of pilots and clubs.

The letter continued with more detailed testing and interviews:

• Frequencies: The writer found what he believed were pagers on 72.240, 72.395, and 72.865 MHz with signal strength barely moving the needle. He also found several harmonic frequencies generated by transmitters that concerned him.
• Two transmitters on channels 16 and 38 generated a harmonic on channel 60 at about 7 to 7.5 dB.
• Transmitters on channels 14 and 38 generated a harmonic on channel 13 at about 7.5 to 8 dB.
• Transmitters on 16 and 14 generated a harmonic on channel 12 at about 8.5 to 9 dB.
• Several other combinations generated harmonics strong enough for the scanner to lock on, but all were so weak as to be unreadable on the strength meter.

Armed with this information, which reinforced his suspicion that the crashes were not caused by outside interference, he attempted to identify the real problems:

• First pilot: Started flying the previous year, barely capable of solo flight. He reported that on the fifth flight of the day all controls went to the limit and the plane crashed. He had checked the airborne battery pack with a small VOM (no-load) and it read 3.8 volts. Someone had told him 3.3 volts was sufficient. The investigator operates on the theory that 4.4 volts is a minimum and 4.6 volts a much safer cutoff point.
• Second pilot: Involved mostly because his 14-year-old son flies. The son was flying when the plane nosed over from level flight and crashed about 1,000 feet from the field in a low area 10–12 feet below the flying field. All servos were at a limit at the crash site; they had left the transmitter at the field, turned on, and as they came out of the low area and could see the field the servos re-centered. The father concluded that meant interference over the low area; the investigator believes the receiver simply regained line-of-sight to the transmitter and started working again.
• Third pilot: Flying a Quickee 500 with failsafe set for low throttle, slight up elevator and everything else neutral. Over the low area the radio went to failsafe for 2–4 seconds then returned to normal; the pilot recovered without crashing. He later concluded the problem was a loose connection in the airborne switch rather than external interference.
• Fourth pilot: Flying a small scratch-built .15 A/V Pylon Racer with a Cox .049 turning at about 24,000 RPM. Over the low area he lost aileron control but retained elevator and managed to settle the plane gently in a wheat field with no damage. He blamed interference; on close inspection at home he found a broken wire to the aileron servo.
• Other pilots: Could not give enough information to reach conclusions. They were convinced interference caused the crashes despite lacking logical reasons.

The investigator then flew four airplanes over the suspect area for several minutes each at various altitudes, speeds, and directions using channels 16, 38, 52, and 56 and experienced no problems.

This appears to be a careful, considered approach to information gathering. I have gone to rather great lengths to address this point. It's important.

Two recent phone calls reinforce this message. One came from a CD in Texas who experienced several so-called "interference" problems at the club's first Pattern contest. Since the frequencies involved were used regularly at the field with no previous problems, the CD was at a loss to explain the condition. He was rightly concerned that publicity from the incident could be detrimental to future events. It was suggested he use the AMA scanner to monitor the field and pass any information obtained to the contestants; a follow-up call to each affected pilot might also help determine if a cause surfaced when the individual returned home.

The second call came from the organizers of Top Gun. Apparently someone had suggested the site used was known to be more subject to interference and that the event was held there anyway. Do you really think the organizers of such a prestigious event would run that risk? When one individual suffered "interference" during the meet, one person told me he had witnessed the same thing happening to the affected party at several other events. Makes you wonder. I also had AMA equipment in use all four days of the event. Yes, we found some pager activity but it was no more powerful than far-away narrowband equipment.

In conclusion, it is my considered opinion that we do the hobby a disservice when we pass along information created from conjecture or rumor. Do your homework: check installations, battery voltages, antenna placements, and equipment narrowbanding before blaming external interference. Has your club suffered from this problem?

Until next month!

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Competition Regulations Supplement

From time to time new events appear on the international scene. Often these attract a significant following and are offered at AMA events. Since the FAI rules are no longer included in the AMA Competition Regulations and the FAI Sporting Code does not include provisional events, we will, from time to time, print items in Model Aviation.

PROVISIONAL FAI EVENT — F1L (Indoor EZB)

Indoor EZB model: establish provisional rules for this new event.

• L.1 Definition
• Monoplane aeromodel powered by one (1) extensible motor, in which lift is generated by aerodynamic forces on fixed surfaces.

• L.2 Characteristics
• Wingspan, maximum projected: 45.72 cm (18.0 in).
• Wing chord maximum: 7.62 cm (3.0 in).
• Stabilizer area maximum: 50% of wing.
• Structure: Only balsa wood and adhesives for the basic structure. Exemptions: prop shaft, rear hook, thrust bearing, surface holding fittings and reinforcements for their attachments. No external bracing allowed except balsa wood wing struts.
• Motor stick: must be a solid, single piece of balsa. Tail boom must also be solid and one piece but may be an extension of the motor stick. Balsa splices up to 1 cm may be used to repair breaks in the motor stick or boom.
• Propeller: must be all balsa except for ground-adjustable pitch fittings if used. No devices for changing geometry or torque during flight except normal structural flexing.
• Covering: any commercially available solid sheet material such as paper or plastic. Microfilm is not allowed.
• Weight: minimum weight without rubber motor is 1.2 grams.

• L.3 Number of Flights
• Each competitor is allowed six flights; the two best flights constitute the score.

• L.4 Definition of an Official Flight
• Only flights of 60 seconds or more are considered official. A flight may be terminated by physical means within the first 60 seconds. A flight less than 60 seconds is a delayed flight; one delayed flight is allowed for each of the six official flights; delayed flights are not accumulative.

• L.5 Number of Models
• No limit to the number of models a competitor may use at an indoor contest.

• L.6 Collision Rule
• In the event of a collision between two models in flight, each competitor must choose the time span between the collision and two minutes following the termination of his flight either to retain the flight time as official or to recommence the flight. The recommenced flight must be flown before the next official flight.

• L.7 Steering of Models
• a) Steering must only be used to avert collision with the structure of the building, its contents, or other models. Movements must be primarily in a horizontal plane. Note: If, in a timekeeper's opinion, a model's altitude change is approaching 0.5 m (or 1 m for each 25 m of altitude, whichever is larger), he will warn the competitor. Continued disregard of the timekeeper's warning will result in a terminated flight.
• b) A balloon with its line attached, or a rod 2 to 8 m in length, may be used to alter the course of the model or reposition it. No time limit or restriction on number of steering attempts, except all steering must be done from the front end of the model and never from behind.
• c) During steering the propeller may get caught by the line/balloon/rod and stop. As soon as the propeller stops, a third watch should be used (preferably a double-button watch) that records accumulated prop-stopped time. That time is deducted from the running total shown on the score sheets. If the steerer cannot control the model after steering, all three watches are to be stopped together and the total prop-stopped time deducted as detailed above.
• d) No ref light is allowed other than if fouled by another model during steering.
• e) The decision to steer is the competitor's responsibility. A physically handicapped competitor must arrange for a substitute with contest officials. In the case of poor sight, a medical doctor's affidavit certifying corrected vision to 20/40 for the better eye must be submitted to permit a substitute steerer.
• f) The timekeeper must observe steering equipment use and warn the competitor if other models may be endangered. If other models are fouled by the steerer, the fouled competitor has the choice of a substitute flight, which, if taken, is his score for the round. The fouled competitor must exercise this choice within five minutes after termination of his flight. If he chooses to restart, he must do so before his next official flight.

• L.8 Timing of Flights
• Flights must be timed by timekeepers with stopwatches or timing devices recording to at least 1/10 of a second. From General Section para. 2.9, only 2.9.1, 2.9.2, and 2.9.6 apply to this event. Timing commences when the model is released. Timing terminates when:
• a) the model comes to rest on the floor;
• b) it hits the building;
• c) the model comes into contact with any part of the building or its contents other than the floor and translational movement ceases.
• Note: In case (c) the timekeeper shall continue to time for 10 seconds after translational movement ceases. If the model remains in contact after 10 seconds, timing ceases and the 10 seconds are subtracted from the flight time. If the model releases itself in less than 10 seconds, timing continues normally.

• L.9 Number of Helpers
• The competitor is entitled to have one helper.

• L.10 Launching of Models
• a) Launching is by hand, the competitor standing on the ground.
• b) Winding of rubber motors may be done by either the competitor or his helper.

• L.11 Ceiling Height Categories
• The following ceiling height categories are recognized for contest and records:

1. Less than 8 meters.
2. Between 8 and 15 meters.
3. Between 15 and 30 meters.
4. Higher than 30 meters.

• The ceiling height is the vertical distance from the floor to the highest point at which a circle of 15 meters can be inscribed below the primary structure of the building.

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