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Bulau

Erratic Lift Behaviour

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Recently, I've made a couple of tasks to try out Ian and Wolfgang's new ASH25. I basically took some Open Class tasks from Condor, and recreated them in FSX. Rather than make very long distance tasks, I try, instead, to set lower cloudbase and weaker lift. This means making some custom .CMX files, since the default settings seem rather 'safe'. I confess I've not read enough about all the parameters that CumulusX! controls, and as a result I'm likely making some mistakes.

In the .CMX I mainly changed the thermal strength, and the diameter. In some test flights, I was often getting very erratic behaviour, with the vario swinging wildly from sink to lift, never finding anything steady enough to circle and climb, unless I slewed almost right up to cloudbase. If I was much below cloudbase, impossible to find any lift. So I tried lowering the Weak surface Layer Height, and also lowered the Minimum thermal ceiling (although I have cloud layer set in FSX weather, so this should not be a factor). These changes seem to work, because in our multiplayer on Tuesday past, everything seemed stable...lift strength was in the selected range and no wild fluctuations of vario.

I think also, I need to pay more attention to setting the wind layers to match the cloud height in FSX. In other words, if I have a wind layer change at or near the cloud base, can this contribute to the erratic behaviour I experienced? What other .CMX parameters should I pay closer attention to to keep things as realistic and stable as possible?

CumulusX!.cmx:


1500 ; Minimum Ceiling of AutoThermals [0 ... 10000 m]

3000 ; Maximum Ceiling of AutoThermals [0 ... 10000 m]

2.5 ; Minimum Strength of AutoThermals [0 m/s]

5.5 ; Maximum Strength of AutoThermals [15 m/s]

1000 ; Minimum Diameter of AutoThermals [0.3 ... 3 km]

1800 ; Maximum Diameter of AutoThermals [0.3 ... 3 km]

20 ; Minimum Duration of AutoThermals [10 ... 45 min]

40 ; Maximum Duration of AutoThermals [10 ... 45 min]

5 ; AutoThermals Coverage [1 ... 15 /100km^2]

1 ; AutoThermals Sink Scalar [-1.0 ... 3]

100 ; Weak Surface Layer Height [0 ... 1000 m]

1 ; Thermal Lean Factor [0 ... 3]

-1 ; Wide Spread Sink [-1.0 ... 1]

25 ; Inversion Layer Probability [0 ... 100 %]

25 ; Inversion Layer Weakening [0 ... 50%]

150 ; Minimum Inversion Layer Thickness [150 ... 10000 m]

300 ; Maximum Inversion Layer Thickness [150 ... 10000 m]

300 ; Minimum Inversion Layer Thickness [150 ... 10000 m]

600 ; Minimum Inversion Layer Thickness [150 ... 10000 m]

My Open Class edit:

1000 ; Minimum Ceiling of AutoThermals [0 ... 10000 m]

3000 ; Maximum Ceiling of AutoThermals [0 ... 10000 m]

1.0 ; Minimum Strength of AutoThermals [0 m/s]

2.5 ; Maximum Strength of AutoThermals [15 m/s]

1200 ; Minimum Diameter of AutoThermals [0.3 ... 3 km]

1800 ; Maximum Diameter of AutoThermals [0.3 ... 3 km]

10 ; Minimum Duration of AutoThermals [10 ... 45 min]

40 ; Maximum Duration of AutoThermals [10 ... 45 min]

6 ; AutoThermals Coverage [1 ... 15 /100km^2]

1 ; AutoThermals Sink Scalar [-1.0 ... 3]

50 ; Weak Surface Layer Height [0 ... 1000 m]

1 ; Thermal Lean Factor [0 ... 3]

0 ; Wide Spread Sink [-1.0 ... 1]

25 ; Inversion Layer Probability [0 ... 100 %]

25 ; Inversion Layer Weakening [0 ... 50%]

150 ; Minimum Inversion Layer Thickness [150 ... 10000 m]

300 ; Maximum Inversion Layer Thickness [150 ... 10000 m]

300 ; Minimum Inversion Layer Thickness [150 ... 10000 m]

600 ; Minimum Inversion Layer Thickness [150 ... 10000 m]

Hmm, oh yeah...looks like I also disabled Widespread sink...mistake, or is that the main factor which smoothed everything out?

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My Open Class edit:


1000 ; Minimum Ceiling of AutoThermals [0 ... 10000 m]

3000 ; Maximum Ceiling of AutoThermals [0 ... 10000 m]

1.0 ; Minimum Strength of AutoThermals [0 m/s]

2.5 ; Maximum Strength of AutoThermals [15 m/s]

1200 ; Minimum Diameter of AutoThermals [0.3 ... 3 km]

1800 ; Maximum Diameter of AutoThermals [0.3 ... 3 km]

10 ; Minimum Duration of AutoThermals [10 ... 45 min]

40 ; Maximum Duration of AutoThermals [10 ... 45 min]

6 ; AutoThermals Coverage [1 ... 15 /100km^2]

1 ; AutoThermals Sink Scalar [-1.0 ... 3]

50 ; Weak Surface Layer Height [0 ... 1000 m]

1 ; Thermal Lean Factor [0 ... 3]

0 ; Wide Spread Sink [-1.0 ... 1]

25 ; Inversion Layer Probability [0 ... 100 %]

25 ; Inversion Layer Weakening [0 ... 50%]

150 ; Minimum Inversion Layer Thickness [150 ... 10000 m]

300 ; Maximum Inversion Layer Thickness [150 ... 10000 m]

300 ; Minimum Inversion Layer Thickness [150 ... 10000 m]

600 ; Minimum Inversion Layer Thickness [150 ... 10000 m]

Hmm, oh yeah...looks like I also disabled Widespread sink...mistake, or is that the main factor which smoothed everything out?

That seems to be fairly useful to pinpoint the capabilities of an open class glider. Note, that the lift values in the CumulusX! settings are metereological lift, i.e. you have to subtract the normal sink of the glider. Moreover, it's the lift in the very center of the thermal. Since you can't circle on the spot, your effective lift might be 70% of it (depending on the diameter of the thermal) minus sink of the glider.

If FSX stock cumulus clouds exist, they will override the thermal ceiling setting, so it's only relevant for clear skies situation.

There are several reasons why thermals might appear unsteady. Most likely is that erratic lift is a consequence of the changes in wind conditions. CumulusX! takes wind at 500m AGL and at thermal ceiling to calculate the leaning of the thermals. Whenevery wind changes, leaning will change, too, which might result in the lift column jumping away. Another consequence is, that trigger conditions change also, leading in disappearing of some thermals and popping up of others somewhere else. Unfortunately, FSX behaves sometimes crazy in that. One could ask, why not keeping a thermal once it is there, but this would it make impossible to produce same thermal situation among online player.

If you like to identify the reason for the unsteady thermals, you may out the leaning parameter to 0, which makes the shape of the thermal independent from wind. Not very realistic, though, and even more difficult to stay within, but for trying out it might be worthwhile.

Another reason is the "air-texture" which is a locally distributed pattern of lift and sink which slowly moves along and aligns with wind direction. It's strength is influenced by windspeed. It is superimposed by a pure random noise of up and down of limited amplitude. The strength of this is partly depending on wind and partly on average thermal strength (the high the more). This is indeed influenced in addition by the widespread sink parameters.

However, a widespread sink of 0 doesn't balance the airmasses net-flow anymore, so you will have net-lift if you simple go straight ahead without taking care of any thermals. I propose leaving it at the 1.0. It also has no effect on the steadiness of thermals itself, though on the superimposed air-texture.

A third reason can be that you are flying in lee-side condition. Then you have strong erratic lee-effect superimposed on the thermal. If the basic thermal is rather strong it "punches" through the down-wash, but don't expect good climb values.

Cheers,

Peter

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Thanks, Peter!

OK, I'll put Wide Spread Sink back at 1.0 and see how it is. I read in the manual that disabling it would eliminate the "constant fluctuations due to air texture". Just to clarify, the wild vario swings I experienced were quite rapid, i.e. on the order of 1 second swings between -1 and +1 m/s.

I actually wanted to set even weaker thermal strength for some Open Class tasks, but needed to resolve the erratic behaviour first.

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If FSX stock cumulus clouds exist, they will override the thermal ceiling setting, so it's only relevant for clear skies situation.

Oh yeah, about this...we have always disliked having the FSX 3D clouds interspersed with the CX! clouds, so we have changed our FSX clouds settings to 2D. (SETTINGS...Display settings...Customize...WEATHER tab...select Simple clouds for Cloud detail, and also set Cloud coverage density to Low)) I'm assuming this is not the same as turning them off, or clear skies, but what it does is render the FSX clouds as flat cirrus-like patches, at the same level as the CX! clouds. Not gone, but not as objectionable as the 3D FSX clouds.

Now I know some feel having the FSX clouds in there is a good thing, as it makes it a challenge to find the thermal clouds.

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Hi,

sorry for the confusion, but +1.0 means a constant -1 m/s sink (useful values are around +0.1), while -1.0 is automatically balancing the net-flow of the airmass.

Cheers,

Peter

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