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Old January 23rd 14, 12:42 AM posted to rec.aviation.soaring
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Default Is the 200ft below Min Finish Height Rule Working?

On Wednesday, January 22, 2014 9:37:24 AM UTC-8, Bravo Zulu wrote:

John - Interlinear comments. My personal views - not in any official capacity.

In response to 9B:

The original post that started this discussion provided some data indicating that the current rule is not working as well as hoped in certain situations, and made some suggestions that might improve it.

As to the hard deck idea, I do not understand how that will affect a pilot who is faced with a deteriorating final glide that places him near the land-out penalty altitude just outside the finish circle. He will have been above any proposed hard deck all the way. A pilot who is watching the final glide knows early on that he might not make the MFH and is looking for lift all the way. The crunch comes in the last mile or so when he has not found it and is now looking to avoid a big penalty, as described (with concrete examples) in the original post.


The finish is a new use of the hard deck concept and makes a slightly different set of tradeoffs from the current rule. I'll try to articulate some preliminary thoughts on it, but it probably bears some detailed analysis.

First - in contrast to the current rule a hard deck would define the bottom of the finish cylinder in reference to the ground instead of 200' below MFH. Below the bottom of the cylinder means you didn't finish the task and you get distance points. For a 1000' MFH and a 500' hard deck this means the graduated "penalty zone" would be 500' instead of 200'. Points per foot of penalty TBD - choices are either to make it linear to 400 points (=landout) or something more like the current gradual penalty for 200, depending on whether having the penalty discontinuous at the bottom of the cylinder creates an incentive for risky behavior. I believe the second feature of the hard deck - a larger radius than the finish cylinder - decreases potential adverse incentives resulting from a discontinuous penalty at the bottom of the cylinder. More on that later.

Second - the hard deck as described here would extend out presumably 4-5 miles at an altitude below which a safe approach to an orderly landing starting at finish cylinder radius is not possible - This is consistent with the requirements of 10.9.4.1. In my thinking this hard deck height has been 400' to cover a variety of airport and finish cylinder configurations. Here it's been discussed at 500'. If finish cylinders were always 1 mile centered on an airport maybe you could MAYBE imagine 300' but I don't know who out there would make a serious argument that they could make a finish, fly to some sort of abbreviated pattern IP and make an orderly landing from 300' AGL..

Aside: Remember that GP-style starts will be allowed this year so you also have to think about being able to do this with a class of gliders finishing within a smaller time window than before. If we could be certain that every airport had a 1000' wide runway this would be less of a problem, but congestion is an issue at many sites. Somebody has to think about all this stuff...

I think the way a 4 mile (from the finish cylinder edge) hard deck might help is that it makes it a lot less likely that someone is going to come at a steep penalty zone all at once from the side. The so-called "penalty cliff" that started this thread has effectively been moved out to a point where most pilots will overfly the edge by 1000-1500', depending on MFH. If you were actually at 400', 4 miles out you would not be on final glide, you'd be on task (barely) and you be doing what pilots do when they are at 400' AGL on task, picking a field and (maybe) hoping for a climb.

So I think it's pretty clear that anyone coming at the hard deck would be coming at it from above, probably at best L/D because their glide computer has been telling them for some time that they are going to be WELL below MFH at the finish so they are stretching the glide. Once they are over the hard deck but not on a glidepath to get to the bottom of the finish cylinder, the correct and natural thing to do is head for the finish at best L/D and hope for lift. There's no energy to do a zoomie at the edge of the finish cylinder because you are trying to glide to it over a flat hard deck at best L/D. Pulling up to hit the bottom of the cylinder also means you already went below the hard deck and your day is done so that would be dumb. Would someone go halfway into the hard deck and then turn around so they could look for lift at below 400' outside of 4 miles? That would be stupid too as you probably close off more options than you open up by heading away from the finish. Would you bleed off airspeed trying to get a little more glide to reach the finish - maybe, but it would be counter-productive to go to the back side of the polar. So, maybe people would do stupid random stuff, but not for any rational reason that I can find.


The original post suggested increasing the penalty zone from 200’ to 500’, thereby reducing the per foot penalty and providing more incentive to continue to a safe landing. In light of the excellent explanation from 9B about the RC’s deliberations leading to the current rule, I would appreciate his opinion as to how increasing the penalty zone from 200’ to 500’ (with a commensurate increase in the MFH) would effect the pilot’s decision in the case of a degrading final glide where the pilot can still make the field safety but is facing a land-out finish penalty. It would seem to me that decreasing the penalty for a low (but safely above the bottom of the PZ) entry would increase the motivation to continue to a safe landing rather than stopping to thermal at an unsafe altitude. Imagine a pilot facing a small penalty for a busted glide vs the same pilot facing a huge penalty; which has the stronger motivation to continue to a safe landing rather than attempting a 'hail Mary' play?


The good thing about the hard deck idea is it takes the edge off the bottom of the finish cylinder by making it impossible to climb up or zoom up to a finish in order to avoid the landout penalty. That's good to the extent you believe the steeper the penalty the more unpredictable the behavior to avoid it. The other think it does is pin the hard deck/landout height to the ground rather than the top of the finish cylinder. This means that the higher you make MFH the more buffer you have between MFH and the hard deck. Without the zoomie/low thermalling potential at the bottom of the cylinder you can be more comfortable with a gradual penalty from MFH to the bottom of the finish cylinder. (BTW I agree with UH this is probably a rare event, but something you'd prefer not to encourage).

The fly in the ointment is that some sites really like the 700' or 500' finish (I think for ridge missions), so you need to be careful about setting MFH too low, but with a 400' hard deck a 700' MFH has 300' of gradual penalty zone and a 1000' MFH has 600' of gradual penalty zone. A 500' MFH (drum roll for the math) has only 100' of gradual penalty, but I only hear a few voices who think that's a preferred target height for finishing a fleet of gliders and you still have 100' of buffer. Again with GP-style racing an option, we should be a little careful about how much congestion we can handle.


I still suggest that we increase the width of the penalty zone as above for the 2014 season. This would be a trivial change to implement, and has the virtue that its effects can be easily measured and compared to prior-year data.


Actually I think there is scoring software programming for some of this and we are past the comment deadline for 2014 rules so this may have to go on the agenda for 2015 if there is broad support to consider it. This thread was initially promising, but I have also heard some voices against it so it remains to be seen what will happen. The process requires a pilot survey of any significant changes, rather than a r.a.s. discussion. I think that's prudent due process.

9B