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Gregg_Seipp

Ground speed wrong in 750?

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I did the update.  Same result.  I'm flying heading 005.  The arrow is indicating an almost direct headwind.  The P3D wind is 276@24...wind coming from my left wing.

 

From DALT/TAS/Winds

  • Track 013
  • TAT -20 (Duke thermometer reads -26C)
  • Wind direction 276
  • Wind Speed 28
  • Headwind component 0KT

EDIT:  Also, in this version the Direct To button doesn't work in the VC...works fine on the popup.  I also "Checked Updates" to make sure the version did, indeed, install correctly.


Gregg Seipp

"A good landing is when you can walk away from the airplane.  A great landing is when you can reuse it."
i7-8700 32GB Ram, GTX-1070 8 Gig RAM

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I concur with 

Gregg. Thanks to FSUIPC auto saves, I was able to resume my flight after lunch.  My wind arrow stayed fixed until I changed the map settings from Track Up to North Up. Then to Heading Up.  The wind pointer changed each time I changed orientation. When I returned to Track Up the wind arrow started showing a direct cross wind. But the actual winds could not be cross winds.  My IAS was 202 knots, TAS was 269 kts, and Ground Speed at only 223 knots.  With the arrow showing a direct crosswind GS would have been the same or very very close to TAS.  

My actual TAS and GS were consistent with winds aloft in my FltPlan.com flight plan.  Approx 300° to 310° and around 46 to 50 knots.  At my indicated 269 TAS my and heading of 282° my indicated GS of 223 knots would have been realistic.

Other than the °C vs °F OAT temperature issue I reported earlier, the calculations in the GTN appear accurate in regard to speeds and enroute times.  i.e the wind arrow appears to be only a false indicator.  My actual winds were accurate in regard to my plan and my chosen weather engine and actual performance.


Frank Patton
MasterCase Pro H500M; MSI Z490 WiFi MOB; i7 10700k 3.8 Ghz; Gigabyte RTX 3080 12gb OC; H100i Pro liquid cooler; 32GB DDR4 3600;  Gold RMX850X PSU;
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VG289 4K 27" Monitor; Honeycomb Alpha & Bravo, Crosswind 3's w/dampener.  
Former USAF meteorologist & ground weather school instructor. AOPA Member #07379126
                       
"I will never put my name on a product that does not have in it the best that is in me." - John Deere

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Ok, here are some preliminary informations to help further find out what is happening:

1) DALT/TAS page shows the Shadin Air Data input. 

'Use Sensor Data' shows actual input from the simulator via our Shadin Computer simulation. Here are some matching infos (field / FltSim simvar):

TAT  <-- "TOTAL AIR TEMPERATURE,celsius"
CAS <-- "AIRSPEED INDICATED,knots"

Using this as reference helps validating the data the GTN computes, and if it matches the simulator data. On the same page, the lower half shows GTN 'computed' TAS, WIND DIR, WIND SPD. They use a very standard e6b like computation that goes similar to this:

dy = (sin(hdg) * tas) - (sin(trk) * grnd_spd);
dx = (cos(hdg) * tas) - (cos(trk) * grnd_spd);
wind_dir = atan2(dy,dx); // vector angle
wind_spd = hypot(dy,dx); // vector length

2) MAP page shows the RXP data. It is WIND DIR and WIND SPD coming from the simulator simvars,  ( "AMBIENT WIND DIRECTION,knots" and "AMBIENT WIND VELOCITY,knots").

3) MAP page OAT field label is "OAT (Total)" and it matches the TAT field in the DALT/TAS page.

 

So, first and foremost, it is important to validate the data source: enable Shadin Air Data and compare your in-sim conditions with the data shown in this page first, validate this matches the simulator. It should. Then, map page wind speed and arrow are direct display of the simulator 'ambient wind' simvars as-is (but I'm reviewing this a little more, not if the source is correctly feeding the GTN, but if the GTN is processing the source correctly).

I'll do some tests in the sim, i.e. check what the FS simvars are outputting and validate they display the same in the aforementioned pages. You might want to do exactly the same too and compare. There is a possibility some FltSim versions have bug with these values, i.e. correct in FSX, buggy in P3D3, correct in P3D4 etc...

 

Addendum: there is a bug in our code that went undetected, we were wrongly feeding the Shadin Air Data pressure altitude with a value, instead of 'marking' it 'unavailable'. It has no impact on the wind dir/spd, only with the TCAD simulation.

Addendum2: both 6.41 and 6.21 are consistent in regard to their values and our input data.

Personal rant: there are still some thinking a product based on a trainer has no merit in regard to price, given the real work is already done in the trainer... obviously, you know better and I thank you for helping us making this a perfect simulation.


Jean-Luc | reality-xp.com
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7 minutes ago, RXP said:

I'll do some tests in the sim, i.e. check what the FS simvars are outputting and validate they display the same in the aforementioned pages. You might want to do exactly the same too and compare. There is a possibility some FltSim versions have bug with these values, i.e. correct in FSX, buggy in P3D3, correct in P3D4 etc...

Jean Luc,

Just to be clear, my problem and the data I provided, was from P3D4.  Like I mentioned, it looked like the data from the DALT/TAS page was correct, pretty much...only the arrow pointed in the wrong direction. 


Gregg Seipp

"A good landing is when you can walk away from the airplane.  A great landing is when you can reuse it."
i7-8700 32GB Ram, GTX-1070 8 Gig RAM

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Not sure from both of the immediately previous messages if it is to be addressed, but the °F vs  °C for OAT needs to be looked at.  My TDv2 reported OAT again was around -29°C.  The GTN reported OAT was -20°C.  So if both are read from the sim then why are they different?  I descended from 20,000 to 16,000. TDv2 OAT was -19°C.  GTN was indicating -9°C.  Both clearly indicated as °C.

FYI, a temp of -29°C corresponds to a temp of -20°F.  C vs F.

 


Frank Patton
MasterCase Pro H500M; MSI Z490 WiFi MOB; i7 10700k 3.8 Ghz; Gigabyte RTX 3080 12gb OC; H100i Pro liquid cooler; 32GB DDR4 3600;  Gold RMX850X PSU;
ASUS 
VG289 4K 27" Monitor; Honeycomb Alpha & Bravo, Crosswind 3's w/dampener.  
Former USAF meteorologist & ground weather school instructor. AOPA Member #07379126
                       
"I will never put my name on a product that does not have in it the best that is in me." - John Deere

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@fppilot 

46 minutes ago, fppilot said:

TDv2 OAT was -19°C.  GTN was indicating -9°C

although -29C is -20.2F, -19C is -2.2F. I think the -20 vs -29 is OAT vs TAT instead of F vs C.

Now, the question remains and I'm trying to look at this: is this an FSX bug (having OAT value when requesting TAT), or a GTN bug, or something like that.

This is puzzling: the simvar used is clearly: "TOTAL AIR TEMPERATURE,celsius"
Our Shadin also feed OAT using the following simvar: "AMBIENT TEMPERATURE,celsius"

Are you flying with FSX? Is this SP2 or ACC? Trainer 6.21 or 6.41 or 6.11


Jean-Luc | reality-xp.com
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1 hour ago, RXP said:

although -29C is -20.2F, -19C is -2.2F. I think the -20 vs -29 is OAT vs TAT instead of F vs C.

Well I had to do some learning about TAT.  More rooted in general aviation aircraft that fly at less than 200 kts I've always used OAT or SAT.  So I read that TAT takes into account ram rise at TAS above 200 knots, and certainly I was well above that. So In my mind that explains the difference between the OAT indicated in the Turbine Duke v2 and the GTN.  TAT should read lower...

I also found that one function mode of my Sporty's E6B electronic calculator has alternate inputs for outside temperature,  (I°C) and (T°C).  The instruction manual simply calls (I°C) "Indicated" and calls (T°C) "True".  So I was not familiar with the term "Total". 

If from my flight today I use 200 knots IAS, 20,000 for pressure altitude, and -20°C for the I°C (indicated) variable in the calculator, it returns true airspeed as 267 kts. Matches what I saw. If I instead input -29°C into the T°C variable (true) it also returns 267 kts. 

Funny, but that would then appear to use I°C for TAT, and T°C for OAT.  Checked the calculator three or four times and clearly for the two results to match the lower value must be input into I°C and the higher into T°C.  Seems to be the use of terms in the calculator.


Frank Patton
MasterCase Pro H500M; MSI Z490 WiFi MOB; i7 10700k 3.8 Ghz; Gigabyte RTX 3080 12gb OC; H100i Pro liquid cooler; 32GB DDR4 3600;  Gold RMX850X PSU;
ASUS 
VG289 4K 27" Monitor; Honeycomb Alpha & Bravo, Crosswind 3's w/dampener.  
Former USAF meteorologist & ground weather school instructor. AOPA Member #07379126
                       
"I will never put my name on a product that does not have in it the best that is in me." - John Deere

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OH! I am using FSX Acceleration and trainer 6.41.  

Also something else I can check on next flight is that from what I read this afternoon Total Air Temp (TAT) reflects ram rise in temperature at or above 200 knots.  OAT does not.  That being true, OAT and TAT should be the same or nearly the same at or below 200 knots.


Frank Patton
MasterCase Pro H500M; MSI Z490 WiFi MOB; i7 10700k 3.8 Ghz; Gigabyte RTX 3080 12gb OC; H100i Pro liquid cooler; 32GB DDR4 3600;  Gold RMX850X PSU;
ASUS 
VG289 4K 27" Monitor; Honeycomb Alpha & Bravo, Crosswind 3's w/dampener.  
Former USAF meteorologist & ground weather school instructor. AOPA Member #07379126
                       
"I will never put my name on a product that does not have in it the best that is in me." - John Deere

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2 hours ago, RXP said:

Now, the question remains and I'm trying to look at this: is this an FSX bug (having OAT value when requesting TAT), or a GTN bug, or something like that.

Still catching up with you.  On this question understand that the OAT is what is being returned by the Turbine Duke v2.  Perhaps RealAir chose OAT over TAT in terms of what to display, while GTN chose TAT.  Don't believe there is a bug. Just one requests one thing and one requests the other.


Frank Patton
MasterCase Pro H500M; MSI Z490 WiFi MOB; i7 10700k 3.8 Ghz; Gigabyte RTX 3080 12gb OC; H100i Pro liquid cooler; 32GB DDR4 3600;  Gold RMX850X PSU;
ASUS 
VG289 4K 27" Monitor; Honeycomb Alpha & Bravo, Crosswind 3's w/dampener.  
Former USAF meteorologist & ground weather school instructor. AOPA Member #07379126
                       
"I will never put my name on a product that does not have in it the best that is in me." - John Deere

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I'm further looking at everything but I'd probably just need you confirm me something:

TAT: It reads sometimes 'True Air Temperature', and other times 'Total Air Temperature'

OAT: it reads sometimes 'Outside Air Temperature' and other times 'Observed Air Temperature'.

Shadin: their doc reads 'True Air Temperature'

GTN: the map tells 'OAT (Total Air Temp)'.

Quite confusing isn't it?

So what is exactly OAT and what is exactly TAT?

Furthermore, what has SAT to do with all this?


Jean-Luc | reality-xp.com
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From Wikipedia:

In aviation, stagnation temperature is known as total air temperature and is measured by a temperature probe mounted on the surface of the aircraft. The probe is designed to bring the air to rest relative to the aircraft. As the air is brought to rest, kinetic energy is converted to internal energy. The air is compressed and experiences an adiabatic increase in temperature. Therefore total air temperature is higher than the static (or ambient) air temperature.

Total air temperature is an essential input to an air data computer in order to enable computation of static air temperature and hence true airspeed.

 

Total air temperature (TAT) is also called: indicated air temperature (IAT) or ram air temperature (RAT)
Static air temperature (SAT) is also called: outside air temperature (OAT) or true air temperature


Bert

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Ok, further on this topic, we've made some additional changes which should better reflect correct computations in the map and the DALT/TAS page. It will be in the next update and I thank you all for your input on this!

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Jean-Luc | reality-xp.com
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Great news...and great service too.  Looking forward to it.


Gregg Seipp

"A good landing is when you can walk away from the airplane.  A great landing is when you can reuse it."
i7-8700 32GB Ram, GTX-1070 8 Gig RAM

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1 hour ago, RXP said:

Ok, further on this topic, we've made some additional changes which should better reflect correct computations in the map and the DALT/TAS page. It will be in the next update and I thank you all for your input on this!

The best and most complete description of Total Air Temp I found yesterday is on the Flying magazine site https://www.flyingmag.com/air-temperature-explained.  

One site I was on yesterday stated that the difference coefficient between OAT/SAT and TAT is called Ram Rise and starts coming into play at about 200 knots TAS.  However other site say that starts to happen at mach 0.2, which is about 134 knots.  

Interesting subject.  Would be interesting to observe the difference between a sim aircraft that provides a tooltip at the temp gauge, such as the TDV2-indicated OAT, and GTN-indicated TAT, as TAS increases from say 150 knots to 250 knots.

I am still not convinced that groundspeed indicated in the GTN is off by any measure as in E6B calculations using  the separate OAT/SAT temp input and then using instead the TAT temp input both produce the same.

 


Frank Patton
MasterCase Pro H500M; MSI Z490 WiFi MOB; i7 10700k 3.8 Ghz; Gigabyte RTX 3080 12gb OC; H100i Pro liquid cooler; 32GB DDR4 3600;  Gold RMX850X PSU;
ASUS 
VG289 4K 27" Monitor; Honeycomb Alpha & Bravo, Crosswind 3's w/dampener.  
Former USAF meteorologist & ground weather school instructor. AOPA Member #07379126
                       
"I will never put my name on a product that does not have in it the best that is in me." - John Deere

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