Final glide

Tango Eight wrote on 9/23/2019 7:01 PM:
No one arrival height covers all situations.

T8
Of course not but it is still personal a personal preference, no need to be opiniated, there is always more than one way to skin a cat.
Try it the other way, you'll see.

After 40 years of using a 1000' arrival height as my "aim point", I probably
shouldn't be changing it now :^)

But, I have always added a few hundred (or more) feet if I thought there were
going to be difficulties at the landing area, or (rarely) subtracted a few hundred
when close to a landing place that had no problems, and the extra search time
might find me thermal.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

At 03:27 24 September 2019, Eric Greenwell wrote:
Tango Eight wrote on 9/23/2019 7:01 PM:
No one arrival height covers all situations.

T8
Of course not but it is still personal a personal
preference, no need to
be opiniated, there is always more than one way to skin
a cat.
Try it the other way, you'll see.

After 40 years of using a 1000' arrival height as my
"aim point", I
probably
shouldn't be changing it now :^)

But, I have always added a few hundred (or more) feet
if I thought there
were
going to be difficulties at the landing area, or (rarely)
subtracted a few
hundred
when close to a landing place that had no problems,
and the extra search
time
might find me thermal.

--
Eric Greenwell - Washington State, USA (change
".netto" to ".us" to email
me)
- "A Guide to Self-Launching Sailplane Operation"

https://sites.google.com/site/motorgliders/publications
/download-the-guide-1

Probably shouldn't comment but anyway..

Setting a fixed margin and then doing airborne sums
based on the current situation and that (remembered)
margin, is more difficult for me than just setting Zero
and seeing what AH is predicted on screen.

When I look at others' LXXXX devices I often find they
have 628feet (aka 200m), which suggests they may not
know what margin is set and indeed may never have
looked at the page.

Zander ZS-1 had the answer - AH welded at zero.
wysiwyg.

Steve has mentioned the key here. If you are about to head home, and find yourself saying somthing like the following, "I am 1000 over, my 1000ft reserve" then your reserve is doing you a disservice. It is somewhat of catch 22. You need to be aware of your reserve in case things go south and you fall below it, but the purpose is to keep you from needing to think about it (always have 1000 ft in reserve).

The biggest problem is when things go south. If you are close in, you fall below 0, now you need to subtract from your reserve to figure out your true arrival height. If you use somthing other than 1000 ft it gets harder. So right when you most need clear information you are doing mental math. Bad timing to insert a math problem before you need to make a critical decision. Some (in the admiralty), if not most, know how I know this.

It has been described as setting your watch ahead so you are not late.

I too had flown with a reserve for years, and was worried about switching, but just a few flights and you adjust. And a few more and you realy start to appreciate the fact that you are, for the first time, realy getting the number you want out of your flight computer.

How high will I be when I get there...

RR
Commodore

On Tuesday, September 24, 2019 at 12:32:32 PM UTC+1, RR wrote:
Steve has mentioned the key here. If you are about to head home, and find yourself saying somthing like the following, "I am 1000 over, my 1000ft reserve" then your reserve is doing you a disservice. It is somewhat of catch 22. You need to be aware of your reserve in case things go south and you fall below it, but the purpose is to keep you from needing to think about it (always have 1000 ft in reserve).

The biggest problem is when things go south. If you are close in, you fall below 0, now you need to subtract from your reserve to figure out your true arrival height. If you use somthing other than 1000 ft it gets harder. So right when you most need clear information you are doing mental math. Bad timing to insert a math problem before you need to make a critical decision. Some (in the admiralty), if not most, know how I know this.

It has been described as setting your watch ahead so you are not late.

I too had flown with a reserve for years, and was worried about switching, but just a few flights and you adjust. And a few more and you realy start to appreciate the fact that you are, for the first time, realy getting the number you want out of your flight computer.

How high will I be when I get there...

RR
Commodore

I think there is merit in having a small reserve of, say, 200 feet to allow for pressure altitude changes during flight, obstructions on the approach etc but to regard that as if it were a zero arrival altitude.

The biggest downside I find of a large reserve height isn't the mental arithmetic. With LXNav or Naviter glide computers it is to remember that it is added to the FAI or record "task arrival height" (1000m below start height). One day I struggled for a climb to make task arrival only to find I was getting there 1000 feet higher than necessary and way above ground.

I use an arrival height reserve. When flying to a destination airfield I readily and easily make mental adjustments up and down from it depending on conditions and distance to go. For me the benefit of setting the arrival height reserve is that if I see a green blob on my moving map when I am away from base I know that I have a fighting chance of reaching an alternate airfield. If you use a zero reserve then a green blob on the moving map is meaningless and you have to read the arrival height beside it.

By the way, at startup (after the gps has acquired) I check to see that the arrival height at the airfield I am sitting on is approximately minus my arrival height reserve. If the OP does this it might help him diagnose his problem. OP, please do report back to us on any further findings.

I am not convinced by the argument for a 200 foot reserve to allow for pressure changes or obstructions. That almost implies that you would be ready to arrive at an arrival height of 200 foot. If you have zero set but plan to arrive at 800 foot then you will be able to cope with pressure changes or obstructions. If you plan to arrive well below circuit height I hope you are using visual judgement before you get too low.

I am interested by the point about the reserve being added to your finish height where your finish height is different from your arrival height at an airfield. How does this work? I don't have 'Finish is 1,000m below start set' as it doesn't normally affect me - if I start above 1,000 m on a flight for which the scoring will be affected that is another adjustment which I make mentally. In the UK the rule does not affect competition scoring but does affect our BGA Ladder. I have never flown with a finish other than at an airfield - is there a way to set the minimum height at a finish ring?

On Tuesday, September 24, 2019 at 7:29:21 AM UTC-7, waremark wrote:
I use an arrival height reserve. When flying to a destination airfield I readily and easily make mental adjustments up and down from it depending on conditions and distance to go. For me the benefit of setting the arrival height reserve is that if I see a green blob on my moving map when I am away from base I know that I have a fighting chance of reaching an alternate airfield. If you use a zero reserve then a green blob on the moving map is meaningless and you have to read the arrival height beside it.

By the way, at startup (after the gps has acquired) I check to see that the arrival height at the airfield I am sitting on is approximately minus my arrival height reserve. If the OP does this it might help him diagnose his problem. OP, please do report back to us on any further findings.

Ditto..

On Tuesday, September 24, 2019 at 10:29:21 AM UTC-4, waremark wrote:
OP, please do report back to us on any further findings.

As mentioned before, CNv uses TE altitude for final glide purposes. The normal circumstance with correct setup and database is that it will show about -200 feet arrival with the glider at rest, on the ground, very close to the selected waypoint. So in the OP's case, with 1000' reserve altitude, it should indicate about -1200.

T8

I do agree about the desire to have a "reserve" for graphical purposes. I believe clear nav can show the landing amobia both with and without reserve.. I wish the Lx would do this as well. I could cheat this in XCSoar with a terrain clearance. So the marginally reachable did not appear to be reachable with a 1000ft terrain clearance. But the best solution is a reserve that is only applied to the map view. This becomes a quick visual filter, only show me landing spots where I have the altitude for a decent approach. For me, the advantage of having an accurate arrival height is better than the inconvenience of checking if a candidate field has the margin I want. You only really get that after you have pick to go there anyway.

Rick

On Tuesday, September 24, 2019 at 11:41:33 AM UTC-4, RR wrote:
I do agree about the desire to have a "reserve" for graphical purposes. I believe clear nav can show the landing amobia both with and without reserve. I wish the Lx would do this as well. I could cheat this in XCSoar with a terrain clearance. So the marginally reachable did not appear to be reachable with a 1000ft terrain clearance. But the best solution is a reserve that is only applied to the map view. This becomes a quick visual filter, only show me landing spots where I have the altitude for a decent approach. For me, the advantage of having an accurate arrival height is better than the inconvenience of checking if a candidate field has the margin I want.. You only really get that after you have pick to go there anyway.

Rick

In Tophat the moving map shows the arrival altitude next to each landable waypoint that is within glide range. I use that instead of the color to identify the ones within range. (No colors on the Nook anyway :-)
And since, like Evan, I set the reserve altitude to zero, I do see some arrival altitudes on the map that are really too low to be safe, e.g., 300 feet. That's still good for planning, though, since it tells me that if I were to get a little higher, or closer, that landing spot will become a safer bet.