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z06z33

Problem with visibility

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I’m having an issue where the visibility is to high regardless of the setting in the sim when it comes to low viz. At distances it works fine but not low vis tonight I was doing practice approaches to ILS minimums is 200agl 1/2mi when I broke out of the clouds I could see over 2 miles despite having the vis set to 1/2 so I tried putting it all the way to cat 3 and still the viz was over 2 mi. I’m running xp11.30rc2


David Womacks CFI,CFII,MEI

Copilot: Captain have you ever flown a 777 before?

Captain:Nope,but we got a strong tail wind and the bar in Hong Kong stays open till 5am, so lets kick the tires, light the fires and, get the hell outta here.

 

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40 minutes ago, z06z33 said:

I’m having an issue where the visibility is to high regardless of the setting in the sim when it comes to low viz. At distances it works fine but not low vis tonight I was doing practice approaches to ILS minimums is 200agl 1/2mi when I broke out of the clouds I could see over 2 miles despite having the vis set to 1/2 so I tried putting it all the way to cat 3 and still the viz was over 2 mi. I’m running xp11.30rc2

Two things coming into effect here:

X-Plane always sets a VISIBILITY - despite the slider saying RVR. There is a big discrepancy, especially at night with high intensity runway lighting - in real life over 2x (RVR = VIS x2).

Second, X-Plane emulates a "shallow ground fog" layer if there are no clouds above - so when you are above this layer during the approach (at minimums) you can see quite a bit further than when down on the runway. This is also a real-life effect, where the distance the light has to travel through a layer of fog increases with the viewing angle getting more shallow.

I think the lowest visibility we can set is 100m (330 feet). If you set this up, and you can REALLY see the lights for over 2 miles when sitting on the runway, please file a bug report. Maybe something got borked with the latest betas.

Cheers, Jan

 

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I just doublechecked myself again and can see what you are saying - if there is no cloud cover above, the visibility (or RVR) will not even be close to what the user specifies.

I also remember there being a discussion about this within Laminar - the problem is that REAL low visibility in the real world does not extend to very high altitudes - so what to do when a user puts in 100m RVR? Keep that all the way to space? I think they went for a middle ground - create a "fogged up soup", but no so dense that you can´t see anything.

To remedy this - set any cloud cover EXCEPT cirrus clouds at any altitude above the airport - and the visibility will drop to the specified value (while RVR at night is still higher, but at least not 20x the specified value)...

Cheers, Jan

 

Edited by Janov

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10 hours ago, Janov said:

Two things coming into effect here:

X-Plane always sets a VISIBILITY - despite the slider saying RVR. There is a big discrepancy, especially at night with high intensity runway lighting - in real life over 2x (RVR = VIS x2).

Second, X-Plane emulates a "shallow ground fog" layer if there are no clouds above - so when you are above this layer during the approach (at minimums) you can see quite a bit further than when down on the runway. This is also a real-life effect, where the distance the light has to travel through a layer of fog increases with the viewing angle getting more shallow.

I think the lowest visibility we can set is 100m (330 feet). If you set this up, and you can REALLY see the lights for over 2 miles when sitting on the runway, please file a bug report. Maybe something got borked with the latest betas.

Cheers, Jan

 

When I say see two miles like I can literally see 2 miles like no fog in that two miles clear as a bell. I had a cloud layer set at 200agl. What’s weird is that when I first set the low vis it’s low vis then over a few seconds the fog clears to a couple miles vis


David Womacks CFI,CFII,MEI

Copilot: Captain have you ever flown a 777 before?

Captain:Nope,but we got a strong tail wind and the bar in Hong Kong stays open till 5am, so lets kick the tires, light the fires and, get the hell outta here.

 

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