On Fri 6 July 2007 01:41, John Denker wrote:
> On 07/05/2007 06:57 PM, gh.robin wrote:
> > When i opened that topic , it was to know if we could hope any FG update
> > to get an altitude instrument which can be able to indicate more than
> > 61000 ft.
> >
> > We have had a lot of discussion on it , but nothing which could give the
> > right answer.
> > Do we have to stay with that limitation => 61000 ft ?
>
> No, we do not.
>
> Back on 06/19/2007 03:20 PM, I sent a message Gérard off list, including
> a patch to fix this, extending the existing model to over 100,000 feet.
>
> Apparently the message got lost somehow.
>
> As I explained on-list, there is nothing wrong with the altimeter.
> I fixed the altimeter months ago.
>
> The problem is in the model of the atmosphere, in environment.cxx,
> where it computes the ambient pressure.
>
> I will have more to say about this anon, but for now, here is
> the patch again. It applies to today's CVS (offset one line).
Well your patch is right, i have tested it with Blackbird up to 90000 ft
does anybody who has access to CVS source could commit it , both branch ?
here again is the John Denker Patch.
Thanks
--
Gérard
--- src/Environment/environment.cxx 2007/06/19 18:58:22 1.1
+++ src/Environment/environment.cxx 2007/06/19 19:03:22
@@ -48,43 +48,50 @@
// Atmosphere model.
////////////////////////////////////////////////////////////////////////
-// Copied from YASim Atmosphere.cxx, with m converted to ft, degK
-// converted to degC, Pa converted to inHG, and kg/m^3 converted to
-// slug/ft^3; they were then converted to deltas from the sea-level
-// defaults (approx. 15degC, 29.92inHG, and 0.00237slugs/ft^3).
-
-// Original comment from YASim:
-
-// Copied from McCormick, who got it from "The ARDC Model Atmosphere"
-// Note that there's an error in the text in the first entry,
-// McCormick lists 299.16/101325/1.22500, but those don't agree with
-// R=287. I chose to correct the temperature to 288.20, since 79F is
-// pretty hot for a "standard" atmosphere.
+// Calculated based on the ISA standard day, as found at e.g.
+// http://www.av8n.com/physics/altimetry.htm
-// Elevation (ft), temperature factor (degK), pressure factor (inHG)
+// Each line of data has 3 elements:
+// Elevation (ft),
+// temperature factor (dimensionless ratio of absolute temp),
+// pressure factor (dimensionless ratio)
static double atmosphere_data[][3] = {
- { 0.00, 1.00, 1.000 },
- { 2952.76, 0.98, 0.898 },
- { 5905.51, 0.96, 0.804 },
- { 8858.27, 0.94, 0.719 },
- { 11811.02, 0.92, 0.641 },
- { 14763.78, 0.90, 0.570 },
- { 17716.54, 0.88, 0.506 },
- { 20669.29, 0.86, 0.447 },
- { 23622.05, 0.84, 0.394 },
- { 26574.80, 0.82, 0.347 },
- { 29527.56, 0.80, 0.304 },
- { 32480.31, 0.78, 0.266 },
- { 35433.07, 0.76, 0.231 },
- { 38385.83, 0.75, 0.201 },
- { 41338.58, 0.75, 0.174 },
- { 44291.34, 0.75, 0.151 },
- { 47244.09, 0.75, 0.131 },
- { 50196.85, 0.75, 0.114 },
- { 53149.61, 0.75, 0.099 },
- { 56102.36, 0.75, 0.086 },
- { 59055.12, 0.75, 0.075 },
- { 62007.87, 0.75, 0.065 },
+ { -3000.00, 1.021, 1.1133 },
+ { 0.00, 1.000, 1.0000 },
+ { 2952.76, 0.980, 0.8978 },
+ { 5905.51, 0.959, 0.8042 },
+ { 8858.27, 0.939, 0.7187 },
+ { 11811.02, 0.919, 0.6407 },
+ { 14763.78, 0.898, 0.5697 },
+ { 17716.54, 0.878, 0.5052 },
+ { 20669.29, 0.858, 0.4468 },
+ { 23622.05, 0.838, 0.3940 },
+ { 26574.80, 0.817, 0.3463 },
+ { 29527.56, 0.797, 0.3034 },
+ { 32480.31, 0.777, 0.2649 },
+ { 35433.07, 0.756, 0.2305 },
+ { 38385.83, 0.752, 0.2000 },
+ { 41338.58, 0.752, 0.1736 },
+ { 44291.34, 0.752, 0.1506 },
+ { 47244.09, 0.752, 0.1307 },
+ { 50196.85, 0.752, 0.1134 },
+ { 53149.61, 0.752, 0.0984 },
+ { 56102.36, 0.752, 0.0854 },
+ { 59055.12, 0.752, 0.0741 },
+ { 62007.87, 0.752, 0.0643 },
+ { 65000.00, 0.752, 0.0557 },
+ { 68000.00, 0.754, 0.0482 },
+ { 71000.00, 0.758, 0.0418 },
+ { 74000.00, 0.761, 0.0362 },
+ { 77000.00, 0.764, 0.0314 },
+ { 80000.00, 0.767, 0.0273 },
+ { 83000.00, 0.770, 0.0237 },
+ { 86000.00, 0.773, 0.0206 },
+ { 89000.00, 0.777, 0.0179 },
+ { 92000.00, 0.780, 0.0156 },
+ { 95000.00, 0.783, 0.0135 },
+ { 98000.00, 0.786, 0.0118 },
+ { 101000.00, 0.789, 0.0103 },
{ -1, -1, -1 }
};
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