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  #11  
Old 12-24-2018, 11:22 AM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by Saville View Post
DIY would cost $100 give or take and some time.

Were I to update the panel the task would take me months just to do the panel. Then there's the question of whether or not I'd have to swap out autopilot servos etc.

I don't have lots of free time to do major projects on the plane.

But I have the time to work in the shop at home on a DIY project for a unit that I don't always need to have in the plane and operational.

The Stratux idea is within the realm of cost vs time considerations.
Yes... it all comes down to a balance of time - money - location....

I did think the sensors would be more expensive.

Which parameters are you thinking of logging?

As I said, DIY is more fun.
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  #12  
Old 12-24-2018, 12:09 PM
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Ed_Wischmeyer Ed_Wischmeyer is offline
 
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If you want to log performance data, you?ll want airspeed altitude. You can derive vertical speed. GPS will be much less important, and not good enough for performance data.
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  #13  
Old 12-24-2018, 12:34 PM
jacoby jacoby is offline
 
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Originally Posted by Saville View Post
But then I remembered my Foreflight/iPad will log flight data and I looked at some of the KML files. I'm wondering if this is accurate enough. This is what I saw:

<altitudeMode>absolute</altitudeMode>

Evidently this means height above sea level. But what does it use for "sea Level"? MSL?


I have to figure out what this line means:

<gx:interpolate>1</gx:interpolate>


What is it interpolating? Successive GPS readings? How does this affect accuracy?
KML uses WGS84 projection and altitude is based on EGM96: "The KML encoding of every kml:Location and coordinate tuple uses geodetic longitude, geodetic latitude, and altitude (in that order) as defined in Annex B. Note that altitude is measured from the vertical datum, which is the WGS84 EGM96 Geoid. The altitude measurement (orthometric H) is illustrated in Figure 1."

http://docs.opengeospatial.org/is/12...-007r2.html#14

gx:interpolate is a google extension (hence the gx prefix). Its documentation is: "Boolean value. If the multi-track contains multiple <gx:Track> elements, specifies whether to interpolate missing values between the end of the first track and the beginning of the next one. When the default value (0) is used, the icon or model stops at the end of one track and then jumps to the start of the next one."

https://developers.google.com/kml/do...#gxinterpolate


I don't know what coordinate system a COTS GPS will use but it's likely to be WGS84.
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  #14  
Old 12-30-2018, 08:45 PM
David Paule David Paule is offline
 
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One feature that might come in handy would be a user-settable flag, that you can use to denote the beginning or end of a test run, or a specific GPS location, or something of that nature.

Dave
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  #15  
Old 12-31-2018, 07:00 AM
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Quote:
Originally Posted by David Paule View Post
One feature that might come in handy would be a user-settable flag, that you can use to denote the beginning or end of a test run, or a specific GPS location, or something of that nature.

Dave
That idea occurred tome as I was flying wind direction determination circles last week and using my Foreflight Track Logger to capture the data:

If I had a Flight Data Recorder (FDR), the wind direction and speed circles would be useless to me because I needed the results during the flight in order to then fly the upwind and downwind legs.

But if I had a simple display for, say, a Raspberry Pi FDR and a button, I could start the circle, press the button to tell the Pi to begin recording. Press the button when the circle was complete, and that would signal the FDR to:

1) Stop recording
2) Determine the min and max GPS ground track speeds
3) Determine the GPS heading for those min/max speeds
4) Display that data on the simple display.
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  #16  
Old 12-31-2018, 07:07 AM
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Saville Saville is offline
 
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So last week I decided to fly some simple tests to determine how useful the Foreflight Track Logger is in capturing data for Flight Tests.

So I flew a simple plan which consisted of taking off, flying wind speed and direction circles at 5000 feet and then again at 8000 feet, then doing some simple aerobatics to see if the Track Logger could also be used to tell me how I'm doing with the acro.

The results were interesting. I downloaded the CSV file from Foreflight and wrote some Python to capture the data and plot it out in 3D.

The short answer is - the Foreflight Track Logger might be useful for Phase 1 flight test of climb, airspeed calibration,best glide, Vx Vy determination etc.

Doesn't seem to be useful in showing a round loop.

This is the 3D plot of the full flight. The roll, loop and roll is the track at the far right of the plot:



This is a plot of speed vs data point from Foreflight. It clearly shows the 4 circles I did at 5000 feet and the 3 I did at 8000 feet. It would be simple to extract the min and max speed from the data as well as the course at those speeds:



But one thing I noticed was that when I executed the loop, the data capture rate seemed to slow down - it didn't show a smoother loop, and also I noticed that the capture rate increased with my speed:



I over-plotted some data points with stars and in red showing the time period just after the entrance to the loop and well after the loop. Notice how the data points are sparse during the loop and increase in data rate during the exit from the loop and the pull up:

I wonder what causes the data capture rate change? Aerobatics causes a loss of signal to the Stratus 1?
General Foreflight Track Logger operation? I have to look at other parts of the data file where the speeds were slower (like take off and landing) to see what happens.
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Last edited by Saville : 12-31-2018 at 07:20 AM.
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  #17  
Old 12-31-2018, 08:11 AM
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DaleB DaleB is offline
 
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Quote:
Originally Posted by Saville View Post
But if I had a simple display for, say, a Raspberry Pi FDR and a button
Like this? https://www.adafruit.com/product/1115
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  #18  
Old 12-31-2018, 08:16 AM
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Saville Saville is offline
 
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Quote:
Originally Posted by DaleB View Post
Yes precisely what I had in mind.
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  #19  
Old 12-31-2018, 09:57 AM
jacoby jacoby is offline
 
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Quote:
Originally Posted by Saville View Post
I wonder what causes the data capture rate change? Aerobatics causes a loss of signal to the Stratus 1?
General Foreflight Track Logger operation? I have to look at other parts of the data file where the speeds were slower (like take off and landing) to see what happens.
Is the data capture rate consistent in normal flight (i.e., when the Stratus maintains LoS to the satellites) or does it change with speed as well?

It's possible the GPS loses its connection to the satellites in a loop due to interference. It's possible the unit could be falling back to sensor data to interpolate at a lower rate.

I could see something like, with a 1Hz sample rate and the unit giving the gps 3 tries, you'd effectively have a 4Hz interp rate or a 1Hz GPS rate.

However, if the data changes sample rate with speed, then it could be distance sampling, which I would think be an unusual approach, or it could actually be changing the sample rate on speed.

You could plot sample rate vs speed vs altitude and look for a correlation.
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  #20  
Old 12-31-2018, 10:26 AM
rv7charlie rv7charlie is offline
 
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Try plotting the points during the loop over horizontal distance. Are they really farther apart, or just appear spread out due to the vertical component?
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