PDA Thermal view

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Smithers-1968
Posts: 19
Joined: Fri Mar 06, 2020 3:46 pm

PDA Thermal view

Post by Smithers-1968 » Tue May 19, 2020 1:45 pm

Quick question on the PDA thermal/lift view.

Does this follow air mass or is it fixed to ground position?

i.e. if a thermal is sloping slightly downwind but I'm perfectly centred would the display show a single circle (so following air mass) or a series of loops moving downwind.

I think you can tell how poor my thermal centring is by the fact I'm even asking this.

janjansen
Posts: 1068
Joined: Wed Feb 24, 2016 9:26 pm

Re: PDA Thermal view

Post by janjansen » Tue May 19, 2020 2:05 pm

its relative to the ground, so a slanted thermal should result in overlapping loopy thingies.

Smithers-1968
Posts: 19
Joined: Fri Mar 06, 2020 3:46 pm

Re: PDA Thermal view

Post by Smithers-1968 » Tue May 19, 2020 2:45 pm

janjansen wrote:
Tue May 19, 2020 2:05 pm
its relative to the ground, so a slanted thermal should result in overlapping loopy thingies.
That's the technical term I was trying to remember!

At least now I know where I'm going wrong. Guess there's no way to change it? I know there are 3rd party apps but not so practical with VR

janjansen
Posts: 1068
Joined: Wed Feb 24, 2016 9:26 pm

Re: PDA Thermal view

Post by janjansen » Tue May 19, 2020 3:08 pm

You cant change it. But Im not sure why you would want that. I actually think its helpful to see the wind drift in the thermal helper. You should not use the helper to make your circles round, the plane will do that by itself with a constant bank angle. You need the helper to help gauge where the thermal center is relative to your turn.

Also note that not all thermals drift with the wind, some remain attached to their source and you need to constantly adjust upwind. If the thermal helper would assume the thermal drifts with the wind, it would become very hard to interpret. Similar story with wave.

But if you want to use another app like xsoar (not sure it does what you want, it has a weird thermal helper I struggle to understand, so I turned it off), you can, even in VR. If search this forum there are few threads and I recently saw a video showing how to use condor+xcsoar in VR.

Smithers-1968
Posts: 19
Joined: Fri Mar 06, 2020 3:46 pm

Re: PDA Thermal view

Post by Smithers-1968 » Tue May 19, 2020 3:23 pm

TBH I think I want it because I saw someone demonstrating an app, probably xsoar, which showed them tracing the same circle, which they explained was relative to air mass.

I didn't mean to imply I'd use it to make my circles round, just trying to explain what I'd expect to see. Hadn't thought about thermals not drifting with the wind though. If it was relative to air mass that'd cause the exact opposite problem.

As long as I understand what I'm looking at I'm happy, thanks.

janjansen
Posts: 1068
Joined: Wed Feb 24, 2016 9:26 pm

Re: PDA Thermal view

Post by janjansen » Tue May 19, 2020 3:45 pm

TBH I think I want it because I saw someone demonstrating an app, probably xsoar, which showed them tracing the same circle, which they explained was relative to air mass.
I just opened the xcsoar manual. It does indeed do something like you want:

Image

Ive never seen or used it, as I use xcsoar zoomed out to maintain an overview of the task or navigation.

The thermal assistant that pops up by default is this one:

Image

It only shows 1 turn and lets just say I dont find it very intuitive. IOW, I dont understand it :). im sure its great if you do understand it though :)

MrHerisson
Posts: 216
Joined: Sat Mar 30, 2019 9:11 pm

Re: PDA Thermal view

Post by MrHerisson » Tue May 19, 2020 4:11 pm

janjansen wrote:
Tue May 19, 2020 3:08 pm
...it has a weird thermal helper I struggle to understand,...
Basically the same as the inboard except:
it goes from brown to green instead of white to red
it drifts with the wind (so overlapping circles are expected.....only happend to me once or twice...made me so proud I almost took a screenshot... :lol: )
Depending on the settings, the way out of the therm (hdg to TP) is always up....nice


the next features do show what you already found,...not what you should do.

By this i mean, let'say you turn but miss the thermal center, XCSoar will show a thermal center at the average between best and worst lift in your turn....if you offset the turn and find the center of the lift, then XCSoar will shift the position of the thermal....thus it wont help you find the thermal center but if you found it and lost it you can find it back.....

So...

it has a dot thas shows the expected thermal center
it has an overlay that shows therm from upside (not that helpful)
it has a vertical cut of the therm (some therms are much wider passed a certain alt....this helps spot the alt below which you will struggle in a narrow lift.)

but once again, the best tool to center a therm is your ear

Hope it helps.
Image

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