On Thursday, March 8, 2018 at 9:06:25 PM UTC-5, Andrzej Kobus wrote:
I just found out that due to a short runway at Seminole a decision was made to restrict the weight of each glider to 1150 lb. Supposedly the decision was made after consultation with pilots, not sure with whom. I would love to know who thought that it was a great idea. This leaves gliders with higher wing area (mostly self launchers) at disadvantage. E.g. ASH-31 Mi would have to fly with lower wing loading by 1.1 lb/sq foot comparing to ASG-29. It puzzles me greatly who made this decision and why. A much more reasonable solution would have been to limit the wing loading for each glider. That is how it is done in a Grand Prix event. In my opinion it is the only fair way to limit weight at such a low, for 18 m class, weight range. I don't think an organizer should be able to limit weight effectively creating a different class. I decided to withdraw from the competition. It is one more reason contest participation is dropping.

There are two reasons for this approach:

1) Takeoff distance is driven primarily by takeoff weight and only secondarily by wing loading. A full aerodynamic factor analysis of takeoff performance was done to confirm this fact. A wing loading limit would have allowed gliders with larger wing area to take off at a heavier weight than smaller wing area gliders, compromising the takeoff safety goal.

2) FAI and Grand Prix rules are different. Grand Prix attempts to handicap gliders, FAA decidedly does not. Some glider designs are optimized for running at high wing loading and give up some climbing ability and others are the opposite. Pilots choose to fly different gliders in part because they are making choices for one design strategy over others. FAI rules specifically allow for different wing loading design strategies. The maximum wing loading of the various 18M gliders in this contest range from 10.4 lbs to 12.3 lbs. Setting a wing loading limit would have eliminated these design differences on the run while forcing smaller wing area designs to fly with a climb tradeoff. A wing loading limit would advantage large wing area gliders and disadvantage low wing area gliders as compared to flying within the normal limits of the 18M FAI class.

The minimum intervention in the relative competitiveness of gliders to achieve the takeoff distance goal for this airport is therefore takeoff weight. The approach you suggest would have conferred an advantage to the specific glider you are flying that is not part of the philosophy or rules of the FAI 18M class.

Hope that helps.

Andy Blackburn
9B
For the Rules Committee