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Great Circles


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ckurz7000
ckurz7000
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Tim makes a good point about how old-RL routes are going to fare in a potentially new GC world. Well, this is a transitory problem which goes away over time and not a principal conceptual problem. Each new route (planned as GC-route) would need to know that it is a GC route. When re-using an old RL-route, SD would know that there could be potential problems and can warn the pilot to check the route. It would then be converted to a new GC-route.

I don't see‌ a problem there because the validity of a route  can c‌hange because of many other reasons as well. Changing airspace can necessitate a change in routing, which is a far more likely scenario than a route changing from being RL to GC and consequently infringing on some airspace. If that should be the case, SD will have a warning issued under the warnings tab. From the perspective of the user nothing has changed: the old route infringes upon some hitherto unproblematic airspace which now has become problematic -- either by a change in airspace of the one-time coversion of the RL-route to a GC-route.

-- Chris.‌‌

ckurz7000
ckurz7000
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peter@luthaus.de - 1/18/2018 1:30:10 PM

Besides being correct with most of your statements, I just can't see the terms heading and course mixed, so sorry I have to correct.
‌So point 1:
"A RL is a constant course between....." not heading. As you write yourself, the heading changes with wind and (academically for us) variation.
And point 2:
"... has to fly a constantly changing course" not heading (the heading is of couse likely to change too). Or as Garmin calls it DTK (desired track).
So  the PLOG has anyway the problem of a changing heading an building an average, because the wind can change. And it is a common practice to use the averages in flight logs.
‌‌

Thanks for the corrections. I, too, hate sloppy use of concepts and words. I tried to go back and correct my post but couldn't find how....

-- Chris.‌‌

Tim Dawson
Tim Dawson
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SemperFi, I don't really understand what relevance your last post has to what I posted. We have an excellent connection to our users and are well aware of how they're using our product. Some "straight" bits of airspace edge are rhumb lines and some are great circles, and our aeronautical database can cope with either.

Chris, I don't see there being a "new GC world". For most of our VFR customers, most of the time, RL is the best choice. You produce a PLOG, have one heading to fly, and that's it. If we were ever to default to GC, we lose the simple "one heading to fly" for a leg, and that simplicity is something that people are looking for.

jfw
jfw
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‌Just wondering, any reason why not implement option 1 of ckurz7000 proposal posted on 1/18/2018 12:00:02 PM ?
http://forums.skydemon.aero/FindPost25185.aspx
‌Would this not make everybody happy ?

Edited 1/24/2018 3:51:34 PM by jfw
ckurz7000
ckurz7000
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Tim Dawson - 1/24/2018 3:03:45 PM
SemperFi, I don't really understand what relevance your last post has to what I posted. We have an excellent connection to our users and are well aware of how they're using our product. Some "straight" bits of airspace edge are rhumb lines and some are great circles, and our aeronautical database can cope with either.

Chris, I don't see there being a "new GC world". For most of our VFR customers, most of the time, RL is the best choice. You produce a PLOG, have one heading to fly, and that's it. If we were ever to default to GC, we lose the simple "one heading to fly" for a leg, and that simplicity is something that people are looking for.


Tim, you would still have that simplicity for 99% of the users as the difference between initial and final heading would in most cases be negligible. Furthermore, few people navigate by looking at the heading given in the PLOG and attempt to steer it. They simply follow the line on the map. And winds are always different than forecast, so headings will be different anyway.

Threrefore I believe that your concern isn't really a big issue at all. And since that seems to be the only thing holding back GC navigation, I don't see the big problem.

-- Chris.‌‌

efrenken
efrenken
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Just noticed, SD simulator navigates GC.

Flying a north-south route simulated aircraft follows exactly the magenta line (RL), west-east route it always deviates from the magenta line, hence my assumption.

Eric
Cat Burton
Cat Burton
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Can I add one more vote for GC?

It would mean the track line and xte would match a paper plan.

As for the plog, take a leaf out of the likes of British Airways Cirrus plogs.

Initial true track and mean magnetic heading.

The heading will never vary by more than a few degrees. At 60°N, the Conversion Angle ½chlong sin lat for a 2° chlong, 60 Miles departure, roughly (chlong cos lat) is only .866° and none of us can fly that accurately. But the xte in the centre of that same leg is a more significant ½ mile.

Cat Burton
ATPL, ex BA, 30,000 hours and now FI and selling as many subs to Sky Demon as I can 😉

Cat Burton
SFI
Aeros Cardiff
Edited 3/22/2018 5:17:33 PM by Cat
Stratajet
S
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So, it came... and then it went... 

I was delighted at the beginning of the week to read that GC functionality had been added to IoS testflight. With a mission planned for yesterday I decided to test it out.

By the time yesterday came however, it had been removed with a simple note saying "nobody seemed to care". Well, I definitely care!

I am a huge fan of SkyDemon. I love the way I can do flight planning on my PC and then have it on my iPad when I fly. I was chatting to a friend who also flies long distances and uses the leading competitor ipad software. When I asked why he didn't use SkyDemon is simply said "It doesn't do Great Circle". It's a known thing for those of us who fly any large distance.

I also remember flying up in Northern Greenland with SD and going way out of my way by following the track - before I realised I was following a RL.

If the functionality has been written to make it work then please can we turn it back on? Even if it's a hidden option somewhere it would be so helpful. It may make 1% difference to distance but when it's costing me £16 / minute to fly (PA31-350 - if you simply have to burn cash, accept no substitutes) over a year it will pay for many, many beers.



rg
rg
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I liked it on the route page as in the beta but would be just as happy as a user level setting in planning options.
Tim Dawson
Tim Dawson
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I wish those people who were delighted with the temporary ability to switch to great circles had actually told us so, or given us some feedback, or indeed acknowledged the feature in any way. As it was, the only feedback we got was negative, from those who considered that it added unnecessary complexity to a product that people value for its UI simplicity.

It can only ever be a route-level option in SkyDemon, not a general one, because in the latter case all the routes ever planned and saved by people in the past would suddenly become great circles upon loading, therefore changing their course over the ground.

GO

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