Ridge thermals severely interfere with wind over terrain

[Rotareneg]

When trying to set up a ridge task I discovered that if I added very weak thermals to give the appearance of orographic clouds above the ridges without otherwise adding much lift, they instead almost completely killed the wind along the ridge, significantly reducing lift in the process.

To quickly demonstrate this, attached are three flight plans for comparison: One with thermals and wind, one with no thermals and wind, and finally thermals with no wind.

[MarkRebuck]

This!

I've been trying to fly some pure-ridge tasks from C1/C2 in C3, primarily tasks along the ridges in the Northeast USA, and finding them more or less impossible. Killing all thermal activity suddenly reactivates the ridge lift, but that makes it hard to fly tasks that require a mix of ridge running and thermalling. The tasks provided by @Rotareneg demonstrate the effect very well. no_thermals_wind works as expected (strong lift as the wind blows up the slope), thermals_no_wind works as expected (thermals on top need to be fed from somewhere, light updraft from below on the south face makes perfect sense), but thermals_wind feels really odd. Much weaker than just no_thermals_wind. That can't be right, can it?

Related question: Is there a "ridge helpers" equivalent to "thermal helpers"? I would love to be able to see EXACTLY what C3 is doing on ridges. It would be hugely instructional for pilots to be able to see the "river of air" as it flows over/around obstacles like ridges.

Thanks for all that the Condor team has done... this sim has given countless hours of enjoyment over the years!

[k6chris]

Agree. You can notice this in the "ridge" lesson .FPL which is unrealistic vs RL and way too hard compared to the Condor 2 version.

[wickid]

Thermals influence the wind field in Condor3. They have in and outflow modeled. So yes, they interfere with ridge lift.

[Rotareneg]

The air in the thermal is moving upward and downwind along the face of the ridge in the same direction as the bulk airmass flowing up over the ridge from the wind. If anything, it should increase the wind and lift, not decrease it.

[Tom]

Forgive me if I get this wrong but with outflow (sinking air as far as I recall the modelling) modelled in C3 that will reduce the lift. As far as thermals drifting down wind of the ridge then why would that happen if for example was hitting the ridge at a 90 degree angle then the thermal would be blown over the ridge downwind. If it was blowing at less than 90 degrees to the ridge then the thermals would move along the ridge depending on the wind speed and thermal strength. Again there would be outflow (sinking air) from the thermal along the ridge.

[havet865]

Thermals influence the wind field in Condor3. They have in and outflow modeled. So yes, they interfere with ridge lift.

I think that we need to understand that C3 is closer to real life than C2, and we should act accordingly

On C2, we used to set 12-15km/h of wind maximum, because that would give you plenty of energy on the ridges already.
In real life, you would not get such strong ridge lift with 15km/h... so maybe try with 25 km/h on Condor 3, and you will find that it's much better

Update 22/01: forgot to state that breezes are indeed missing, but I don't think that it is what you are talking about here.

[Vertigo]

I may be grossly oversimplifying or misunderstanding here, but I do think something isnt quite right.

Assume you fly very close to (and not above) a long tall 45 degree slope and the HAWK vario tells you there is 15KmH wind blowing perpendicular to the slope; that has to mean the air you are flying through is moving at 15 KmH either horizontally (with an additional vertical component since the wind cant go through the mountain), or thats the speed along the slope angle, not sure which of those the hawk calculates, I assume it only shows the horizontal speed component?

Simple triangulation would suggest the vertical component of this wind is either 10.6KmH, or more likely, 15KmH depending on if the hawk calculates only the horizontal wind component or not. That means 2.9 or 4m/s netto lift. Thats definitely not what I see in condor. And especially not at steeper slopes. This is just a snapshot as illustration, this was with zero turbulence, no thermals 8am:



With 25kmH set wind (actual measured wind varying mostly between 10 and 20KmH), the most I saw was a brief 2.3m/s netto, but 1.5 being more typical. As you climb above the ridge, the wind gets stronger, and so does the lift, but I have never, even briefly/randomly seen netto lift thats more than about half of what I would expect from triangulating the wind and its more often just a tiny fraction of that:

[wickid]

HAWK only shows the horizontal component of the wind.

In you first screenshot: The netto shows the vertical component (8 kph). horizontal component is 15 kph So in your screenshot total wind would be 17 kph.

Last screenshot: Vertical component is 9 kph, horizontal is 35. So total wind is 36 kph.

Remember that the closer you are to terrain, the more surface friction you have. So the wind will be weaker at the surface. You can see this as well when taking off. Did you have 25 kph set in the first example? That means a loss of 32%. I looked it up. The surface friction factor is between 0.06 (open water) and 0.6 (urban area, stable conditions). Unstable air above land has about 0.27. So it is not too far off what I would expect.

The second example, where you are higher above the ridge means you are out of the wind gradient at the surface making the wind stronger and thus also increasing the lift.

I fly with a HAWK vario IRL. Photo attached below. Wind 195/37, my track is 100. So almost 90 degrees. I'm only getting 2.9 m/s netto. Which almost matches your bottom screenshot. So yes, it works correctly in Condor3. Condor2 was WAY to overpowered on ridgelift.

[wickid]

And just to make sure... i set similar conditions to the photo I posted above. Same plane. No thermal activity:

Absolutely no issues with ridgelift... It is there and about as strong as I would expect. FPL attached.

[Vertigo]

HAWK only shows the horizontal component of the wind.

In you first screenshot: The netto shows the vertical component (8 kph). horizontal component is 15 kph So in your screenshot total wind would be 17 kph.

It also implies the wind was blowing at a 28 degree upward angle. Sure looks steeper to me. And that was about the highest (steepest) I saw.

Last screenshot: Vertical component is 9 kph, horizontal is 35. So total wind is 36 kph.

Thats an angle of just 14 degree! Now to be fair, that wasnt a representative screenshot, more of a wind surge, but it still barely affected lift.

Remember that the closer you are to terrain, the more surface friction you have. So the wind will be weaker at the surface.

Sure, but the hawk measures the air movement where you are flying.

I fly with a HAWK vario IRL. Photo attached below. Wind 195/37, my track is 100. So almost 90 degrees. I'm only getting 2.9 m/s netto. Which almost matches your bottom screenshot.

you are far above (and not even above) a shallow and low ridge. I certainly would never assume the wind there still even remotely follows the exact ridge angle. If my math isnt off, the wind there was at a 15.7° upwards angle, if anything, that is steeper than I would have guessed. Now look at my screenshots again.

[wickid]

And just to be doubly sure... I downloaded the porta westfalica 2 scenery and set the wind up to be the same. And put the glider in roughly the same position on the ridge:

Almost a match as well... The ridge in Condor is a bit flatter than in RL due to the lower resolution of the terrain data. But I can perfectly soar the ridge with similar speeds as in RL.

[Vertigo]

Strong wind on shallow ridges, I agree that looks plausible. Light winds on steep/high ridges, I struggle much more to make sense of those numbers.

[wickid]

Sure, but the hawk measures the air movement where you are flying.

Yep... 15 kph horizontal component and 8 kph vertical component. Suggesting a total wind of 17 kph. Which is perfectly reasonable when 25 kph is set and you factor in surface friction and blocking effect of the mountain. We did flow simulations when we were developing this. Wind strength is far from as strong as the free flow when you are so close to a mountain and below the tops. It really is correct. I'll sent you an email.

[Vertigo]

Thanks, Ill check the email later, but Im not questioning the wind speed dropping off. Its just the relation between horizontal and vertical speed (or angle) which are measured by the hawk for the air you are flying through. Using your screenshot:


I get a guestimated 31 degree. If you plug the horizontal wind speed component in a triangle calculator, I get 4.8 m/s netto vertical component. Thats not miles off from what you see, but its still a fair bit more than what you get, and Im guessing that screenshot wasnt the worst moment.

With steeper ridges, I should make better tests, but using my first screenshot:

I get 34 degree. Yes with wiggle room. But for 34 degree, 16KmH wind, you would have a 3m/s vertical component. Even if you draw a 30 degree line, its still 2.5m/s which I never saw. I got 1.5-2.3.

Anyway, I just want to make sure we agree on the methodology. If so, Ill try make some better tests