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  #1  
Old 06-07-2013, 12:40 PM
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walkman walkman is offline
 
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Default EFIS/MFD Airspeed and altimeter disagreement

I have a new HXr and a new Gemini MFD.

They disagree on altitude and airspeed.

The Gemini reads about 4 kias slower, and a couple hundred feet lower at the same baro setting.

I did set the GRT altimeter calibration on installation, to its at least correct on the ground.

Any ideas?
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  #2  
Old 06-07-2013, 12:55 PM
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There are no end user adjustable tweaks that you can make on the Gemini PFD's Altitude and ASI indication.

As far as altitude goes, I have been asking for this since day one. Please join the crusade and ask TT to add this ability into the PFD....

The ASI is a tough one since the sensor signals being dealt with to produce the ASI are very small.

Most aircraft with more than one ASI have slight errors between them. Steam gauges hide this fact more than glass instruments with their digital readings.
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  #3  
Old 06-07-2013, 06:43 PM
AirbusPilot AirbusPilot is offline
 
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Dynon d6 and G3X are within 1kt and 20ft between them
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  #4  
Old 06-07-2013, 08:23 PM
gasman gasman is offline
 
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My XTreme can be adjusted for as,alt & vsi..... but it was only $1000.00
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  #5  
Old 06-08-2013, 06:06 AM
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Question about the xTreme, I see that it will provide GPS derived bank angle when used without the AHRS, what does it do for pitch?
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  #6  
Old 06-08-2013, 07:50 AM
Rainier Lamers Rainier Lamers is offline
 
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Quote:
Originally Posted by Brantel View Post
Question about the xTreme, I see that it will provide GPS derived bank angle when used without the AHRS, what does it do for pitch?
It provides somthing we like to call "flightpath". It is not attitude or AHRS. However, for most flight regimes, it behaves very similar.
The display is based on your flight path in 3D and it assumes that you are flying a three axis aircraft or something that behaves similar. The XTreme has a pretty good GPS which provides some interesting data beyond the normal and this is what we are using.
It shows you a bank angle based on velocity and rate of turn (assuming you will fly more or less a balanced turn). The Pitch angle is based on your true vertical flight path (i.e. forward velocity vs vertical velocity).

Where are the differences to a normal, gyro based AHRS ?

It can't tell if you are upside down (it shows flightpath, not attitude).
It will not show a point roll (your flightpath does not change).
It has a very slight lag, just noticable. We need to use historic data to assemble where you came from and where you are going.
If you stall with high nose up attitude the pitch will show nose down - that is because you are going down !

Other than that it is a valuable reference if used correctly. You can absolutely fly an aircraft with zero external reference with this. This kind of system is "absolute". It does not suffer from gyro drift, rate limitations and never topples.
It's most valuable contribution is as a reference for gyro based AHRS systems. It is a true reference that you can trust as a check on your AHRS and it is much more valuable in that role as a second gyro based AHRS as you would need at least three as a tie breaker if one starts showing a deviation.

Essentially a true gyro AHRS and the GPS based "fake" complement each other in many ways - the weaknesses of one are the strenghts of the other.

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  #7  
Old 06-08-2013, 07:56 AM
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Thanks for the xplainin Rainier, familiar with that method, just wanted to be sure I understood what the xTreme was displaying.
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  #8  
Old 06-08-2013, 08:05 AM
Wayne Gillispie Wayne Gillispie is offline
 
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My GRT HX and Dynon D6 read 1-2 kts off at approach speeds and 30-50 off altitude. Close enough for a backup.
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  #9  
Old 06-08-2013, 05:05 PM
BobTurner BobTurner is online now
 
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Back to OP: Is the Gemini off in altitude even on the ground, with the proper altimeter setting? If so then that would rule out a static line issue.
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  #10  
Old 06-08-2013, 05:19 PM
Wayne Gillispie Wayne Gillispie is offline
 
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If it is off sitting on the ground as well as in flight...You might check and see if it is possible to re-calibrate it with a slight steady positive pressure on the static port. Once calibrated and artificial pressure is removed then it may be more accurate. This may take several tries. That is the only way I could think of since there is no adjustments on mine either.
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