Author: Lee Estingoy
Edition: Model Aviation - 2009/11
Page Numbers: 127,128
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What is F3J and why does it matter?

Byline

Lee Estingoy [[email protected]]

Most of us are familiar with traditional Thermal Duration (TD) and many have heard of F3J soaring, but the subtle differences between the two contest formats are not widely understood. I didn’t fully grasp them either until I attended one of the premier U.S. F3J events, F3J in the Rockies, traveling from Kansas City, Kansas, to Denver, Colorado.

What does "F3J" mean?

"F3J" is the citation in the FAI rulebook that details the rules for this contest class.

Executive summary of F3J rules

  • Each pilot is given a flight window of 10 minutes.
  • Pilots launch simultaneously.
  • Each competitor earns one point for every second the glider is airborne during that window.
  • Time spent on the towline does not count toward points and is subtracted from the time score.
  • There is a precision landing component using a decremented measuring tape anchored at one end; that point is the target for maximum landing points.
  • The towline is monofilament and the distance to the turnaround is carefully measured to be identical for all competitors.
  • The tow is provided by human muscle power: two people pull the line on the launch command.
  • Scores from preliminary rounds determine which pilots make the flyoff to decide the winner.
  • The F3J World Championship is held every other year (next scheduled, as of this article, in Dole-Tavaux, France, July 29–August 8, 2010). The U.S. team selection was held September 5–7, 2009, in Denver.

Primary differences between F3J and U.S. TD contests

Simultaneous launches

  • In F3J, pilots launch simultaneously, typically coordinated by a public-address system that plays a prerecorded countdown and announcements. This exposes all pilots in a flight group to essentially identical weather conditions.
  • Some U.S. TD contests use a "man-on-man" (head-to-head) format that is similar, but many TD rounds cycle through pilots so not everyone is airborne at the same time.

Towline and launch method

  • F3J uses a springy monofilament towline pulled by two people; TD commonly uses an electric winch and braided nylon line.
  • The F3J human-pulled system can impart tremendous energy into the airframe in a very short time, adding significant difficulty. Teams are responsible for providing and staffing their tow crew.
  • There is a pulley system, so the actual pulling run is short but very powerful. Having reliable tow crew willing to spend long hours in the field is a practical challenge for F3J teams.

Strategy differences

  • In F3J the pilot may choose to take a shorter launch (less time on the line), leaving more of the 10-minute window for thermal time, which can improve the score since line time is subtracted. This introduces strategic risk/reward decisions during launch selection.
  • Top pilots in both formats usually target predetermined goal flight times, but the launch choice in F3J adds additional gambling.

Airframe and handling differences

  • F3J launches are brutal, so sturdy sailplanes are required. F3J landing scoring typically deducts 5 points per meter from the target spot.
  • TD contests often deduct 1 point per inch from the target spot, which incentivizes airframes with larger flaps and bigger elevator and rudder surfaces for more precise control.
  • V-tails are more common in F3J because they can produce a lighter airframe and some drag reduction.
  • F3J pilots commonly "land" by driving the model's nose into the ground, so F3J gliders tend to have pointy noses and fuselages reinforced to survive such impacts.
  • TD aircraft generally avoid nose-first impacts; some TD contests allow skegs or pointed teeth to reduce sliding on touchdown.

Why F3J matters

  • F3J is the format used widely outside the U.S.; it is to soaring what soccer is to (American) football. Because F3J is far more popular in Europe and many leading airframe manufacturers are European, F3J benefits from more rapid evolutionary cycles in model design, resulting in greater variety in airframes and airfoils.
  • Events like F3J in the Rockies run with tight schedules and flyoff systems that keep many competitors in contention through the final rounds, which makes the format engaging and efficient.

Related trends: F5J and electric soaring

  • Some U.S. soaring formats are shifting toward rules similar to F3J. One example is electric F5J (not an FAI classification but a growing rule set).
  • In F5J-style contests, pilots have a working time and motor run time is counted against the final score. This encourages minimizing motor use and rewarding thermal flying rather than simply climbing high and coast-gliding.

Sources

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