ALF1

Need Help Deciphering Groundspeed in B200

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Something is troubling me. Yesterday on a flight from KPVU to KBFI Active Sky Next was forecasting a headwind component of about 50 kts at FL 280, getting worse as I neared destination. The indicated airpeed at max cruise power was 170 KIAS. Since there is no way of looking at TAS in this particular King Air, I computed (170x.02)*28+170 to get a True Airspeed of about 265-270 kts. That is pretty close to book values, but the puzzling thing is that the GSP in the Collins HSI and in the Carenado GPS was only 188 kts.

What is going on here ?

Timing the flight, it looks like the flight took well over 3 hours flying to TWF.BOI.BKE.PDL.YKM. Incredulous on the groundspeed deal I briefly switched off ASN and there were jerk reactions in the airplane so it was definitely connected to te sim (I contemplated the possibility that the airplane was taking FSX weather for a moment).

Can anyone chime in on this ?

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Looks like the forecast wind wasn't correct (which happens very often IRL) and it's only a forecasted and no actual reported wind.

Just for testing, suggest to alter the textinfo in the fsx.cfg file to show 'TrueAirspeed'

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High altitude wind forecasts are exactly that, a forecast, not an actual anemometer reading. Unless there happens to be one of these things flying alongside you giving you up to the minute weather reports, a variance or 20-30 knots is pretty much to be expected and actually makes the simulation a lot more like the kind of thing you have to work with for real :cool:

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Hello Scott, the temperature was -49 Celcius, I looked at that too. What I should have done is a 180 degree turn and see if the tailwind component was added correctly to my computed TAS and that way be convinced of the actual wind. I know that forecast winds vary greatly with forecast. Though I never did any real flying at the flight levels with those winds--my real world flying limited to unpressurized piston twins and rarely we did anything over 12,000 feet.

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Hi Alberto,

LOL - Well you're one engine ahead of me...

Just checked the math - 259 KTAS - is what I came up based on your figures - so that's not the source of your discrepancy...

Regards,
Scott

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An issue I've encountered more than once with AS16 is as follows.

When I use the 'Flight Plan' feature with AS16, the temperatures and winds aloft (everything, basically) get fouled up.

I have seen 90 knot winds to the surface; not good. And temps at altitude of +40 instead of -40. The temperature thing will do a number on performance of the aircraft.

Maybe this was a factor?

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OK Scott, so you used 1.8% instead of 2% taking into account OAT. Good, I think guys that actual winds were greater like others have said. I also checked the NOAA AWS forecast at FL 300 before the flight and those guys had double flags on the wind vanes, which means headwinds above 100 kts coming from 275 degrees. That and Scott´s real more accurate TAS calculation could explain everything. I would have had to land at Pendleton or Yakima had this been a real flight, as I was cutting my fuel budget. Destination was VFR but still....

 

Richard, that what you say is REALLY odd. I never had that type trouble with ASN.

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