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Old March 9th 18, 10:50 PM posted to rec.aviation.soaring
Andrzej Kobus
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Default 18m Nationals weight restriction at Seminole

On Friday, March 9, 2018 at 3:27:50 PM UTC-5, Andy Blackburn wrote:
On Friday, March 9, 2018 at 11:35:06 AM UTC-5, Andrzej Kobus wrote:
On Friday, March 9, 2018 at 11:05:04 AM UTC-5, Andy Blackburn wrote:
"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"

Andy, I can't believe what you wrote, did you read it before you sent it? Did you write it in the name of the Rules committee or is it your own opinion?

What advantage would I get, if I fly at the same wing loading as an ASG-29?
You must be kidding the 18M class weight restriction is 1320 lb. By limiting the weight you are handicapping me more than you are handicapping an ASG-29. On the east coast the optimum wing loading is around 10 lb/sq foot. You let the ASG-29 fly with that wing loading while handicapping me to 9 lb/sq foot. If not for the restriction I would be able to fly at the optimal wing loading. How is that fair? It seems to me the competition should never have been allowed to be held at an airport that can not handle the requirements of the 18 m class. Hopefully this is the last time Seminole is awarded a FAI class competition.


Hi Andrzej,

Thanks for your thoughts.

This was exhaustively analyzed and debated over a period of weeks, not a knee-jerk decision. I did supporting analysis, but the waiver request was from the contest organizers and approved by the SSA Board. Feel free to blame me as I support the approach taken and I meant exactly what I said above.

There were three approachers considered:

1) Fixed wing loading
2) Fixed MTOW
3) Fixed % reduction in MTOW from max certified

The criteria were basically twofold:
1) Address as directly as possible the concerns related to takeoff distance over an obstacle
2) Minimize any alteration to the existing relative performance differences across glider types - that is, minimize handicapping by glider type.

The maximum certified wing loading of gliders flying in 18M Class under the rules a

HpH 304S - 10.4 lbs/sf
ASH-31Mi - 10.8 lbs/sf
JS1C-18 - 11.0 lbs/sf
Ventus 3 - 11.3 lbs/sf
ASG-29 - 12.3 lbs/sf
JS3 - 12.4 lbs/sf (none signed up as of this writing)

Without any weight restrictions, the ASH-31 and JS1 would fly at close to 1.5 lbs lower maximum loading that the ASG-29 and JS3 and about half a pound lighter than the Ventus 3. A percent weight limit preserves the proportionate max wing loading differences but reduces the absolute differences by the amount of the % reduction. Setting a weight limit closes that gap to closer to 1 lb/sf and a wing loading limit totally eliminates it - effectively handicapping the higher wing loading gliders. To answer your specific question, handicapping most of the gliders other than yours gives you a benefit that you wouldn't otherwise have. I can see why you would prefer this as it would help you compete under strong conditions in particular.

However, there is nothing in the letter or the spirit of the rules governing 18M class (unlike Sports Class or SGP racing) that says we should handicap the performance of gliders - quite the opposite. People in non-handicapped classes purchase gliders for the specific design and performance tradeoffs of that design and have a right to expect that those choices wouldn't be deliberately diluted through changes in the rules. Motor gliders present some unique challenges because the designs represent an inherent tradeoff in wing loading range to accommodate a motor. That's the choice you make when you buy a motorglider - there are some benefits and some tradeoffs.

The other point is a wing loading limit doesn't purely address the takeoff distance challenge. It allows gliders with more wing area to fly at a higher MTOW, making them less safe in terms of takeoff distance due to higher rolling friction on soft ground, slower acceleration under the same thrust, etc. I can take you through the calculations if you like. Restricting takeoff weight is the clearly preferred safety option - it most directly addresses the takeoff distance challenge and does a decent job not changing the competitive capability differences across gliders (actually a % MTOW reduction does slightly better, but does less well on simply addressing the takeoff distance requirement).

I can see why you would have preferred a wing loading limit as it would have benefitted you by reducing the wing loading gap you'd otherwise have faced versus other gliders, but it's not the job of the Rules Committee (or the organizers or the SSA Board) to change that differential for you - particularly if it does a less good job at addressing the primary safety objective.

These issues are not simple to address as there are many moving parts. We attempt to maintain a safe and fair competitive environment consistent with the letter and spirit of the rules, but clearly different alternatives to addressing specific challenges will affect different gliders and pilots differently. Our attempt here is to minimize the changes in the competitive differences between gliders. I'm very comfortable this does the best job of all the alternatives, none of which is 100% perfect. The perfect solution is a longer runway, but that wasn't a realistic alternative.

Andy


Andy, your reasoning is completely flawed because on the east coast no one flies with wing loading of 12. You so called solution allows some glider to fly at optimum wing loading for the east coast while handicapping higher wing area gliders. I hope you can understand that. If the contest was held in Uvalde your reasoning would have been justified but not at the location the contest is going to be held. I hope you can admit this.

The other point is a wing loading limit doesn't purely address the takeoff distance challenge. It allows gliders with more wing area to fly at a higher MTOW, making them less safe in terms of takeoff distance due to higher rolling friction on soft ground, slower acceleration under the same thrust, etc. I can take you through the calculations if you like.


Again, you could take the weight 1150 divide by the highest wing area glider and establish weight for each of the 4 or 5 types that would never exceed 1150.

I can see why you would have preferred a wing loading limit as it would have benefitted you by reducing the wing loading gap you'd otherwise have faced versus other gliders


Wrong again! I was not disadvantaged on the east coast because I could not use a higher wing loading on the east coast anyway. Once again no one flies on the east coast with wing loading of 12. Your west coast 18,000 cloud bases experience with wide thermals does not translate well to making rules on the east coast.