Flight Data Recorders: Foreflight logger, Arduino, Raspberry Pi

[Saville]

Hi all,

Lately I've gotten the bug to create a Flight Data Recorder using an Arduino or a Raspberry Pi. I've read Nigelspeedy's entries with interest, but he has the use of a system that's well beyond typical amateur finances.

I don't have a modern EFIS system that does the logging and I'm not likely to re-do the instrument panel any time soon.

This posting asks the questions:

1) Is Foreflight data logging data sufficiently accurate for Flight Test/40 hour Phase 1 work?

2) Is an Arduino or Raspberry Pi with GPS and data logger add-ons, fast and accurate enough for Flight Test/40 hour Phase 1 work.

My "yardstick" would be that I want a system that is accurate enough and fast enough to collect data for the Phase I, 40 hour fly off and the POH production.



One can get add-ons for either the Arduino or the Raspberry Pi that supply GPS data - longitude, latitude, and altitude, as well as data loggers which can store the data. So on the face of it it seems possible to build a system that will acquire the necessary data. And I've read article/s blogs, web pages where people have done that.

You could also add an OAT temperature gauge and perhaps even a sensor that's plumbed into the pitot system. That would be very handy.

But I wonder about the speed and accuracy of such systems.


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?


Then there's the data:

<when>2017-05-20T19:11:54.62Z</when>
<gx:coord>-70.911008 42.585208 31.0</gx:coord>

<when>2017-05-20T19:11:56.35Z</when>
<gx:coord>-70.911004 42.585210 32.0</gx:coord>

<when>2017-05-20T19:11:57.88Z</when>
<gx:coord>-70.911004 42.585211 32.0</gx:coord>

<when>2017-05-20T19:12:01.88Z</when>
<gx:coord>-70.911001 42.585216 33.0</gx:coord>

So the readings are not once a second. And here is a big jump of 5 seconds:


<when>2017-05-20T18:56:01.38Z</when>
<gx:coord>-71.471201 42.562610 1719.0</gx:coord>

<when>2017-05-20T18:56:05.02Z</when>
<gx:coord>-71.468250 42.562614 1714.0</gx:coord>


Are these data accurate enough to use to back out course, speed, climb/descent rate, takeoff roll?

I've done a search for Flight+data+recorder in the forum and there are some entries - mostly old.


Any thoughts would be appreciated.

[Brantel]

Check this out for a small, cheap, and easy logger: http://www.vansairforce.com/communit...ghlight=logger

The thread is a bit old but should still work.

It can log most any serial stream.

[Saville]

Originally Posted by Brantel

Check this out for a small, cheap, and easy logger: http://www.vansairforce.com/communit...ghlight=logger

The thread is a bit old but should still work.

It can log most any serial stream.

As I wrote at the start of my post, I don't have an EFIS that supplies the requisite "serial stream".

I'm confident the data logging capabilities of the Pi or an Arduino will work.

it's the data ACCURACY of those systems - as well as the Foreflight data logger - that I'm asking about.

[DaleB]

There are several ways a person gcould attack this, depending on whether you want it to be something quicker and easier, or a "hobby project" for severe geek appeal.

If you were to start with the standard Stratux hardware, you'd be most of the way there. You wouldn't be using the Stratux software, but writing your own. As a bonus, all you need to do is swap out or re-write the SD card and add a couple of receivers, and you have a Stratux.

The Raspberry Pi will provide far more compute power and storage than you're likely to ever need. The AHRS/fan control board gives you a 3-axis accelerometer. The commonly used GPYes sends a position every second by default, but can be configured to send it more often. You could, if you wanted to, add an OAT sensor and differential pressure sensor for airspeed. All the parts are available off the shelf, I think. The code could be pretty simple, especially if you're not doing any fancy graphical display. Al you need to do is collect data from sensors and log in in some sort of text format, like a CSV file - or JSON, or whatever else you want. Analysis with Excel or Splunk after the flight will let you plot out whatever you want to see.

There's also a guy who rolled his own from scratch, if you want to go that route: http://www.dangerpants.com/labs/adi/ I don't think it logs, though, so you'd probably need to modify the firmware and add some sort of external PC-readable storage to do that.

As for accuracy, I guess it depends. I haven't looked at large amounts of flight data to know if there are gaps or inconsistencies. GPS antenna location might be the biggest influencer; if you spend a lot of time upside down or at high bank angles you might lose GPS briefly. Don't know. I'll see if I can get my Stratux to log the GPS data stream to a file the next time I fly. I know Avare will show a smooth and accurate flight path even when I'm having fun, but I really never get past about 80 degrees or so of bank.

[Flying Canuck]

It never made it close to production, but I put together the beginnings of something like this. It consisted of a project box containing an Arduino with 3 sensor boards - a GPS receiver, a 10 DOF sensor (accelerometer, gyroscope, magnetic compass, pressure and temperature) and an extra pressure sensor. I planned to plumb my pitot & static lines to the box (second pressure sensor in an enclosed compartment). The Arduino would have been a complete GPS enabled ADAHRS. I was feeding a serial output of this data to a Raspberry Pi for both data logging and a simple EFIS written in Python. It was ambitious and I ultimately abandoned most of the project and bought a AVMAP UltraEFIS as my backup EFIS. I don't have any doubt that I could have completed this project and it would have functioned reasonably well, the Arduino and the sensors were certainly capable of the processing and were easily providing reliable resolution, I think I had it doing 1 data collection per second.

My second version of this did make it into my plane, although I'm not using it at all. This was just the Raspberry Pi with a 7" touchscreen. I'm getting serial feeds from my Skyview and its GPS receiver. I had plans to make it a data logger, but it proved to be unnecessary as I can get everything I need from the SkyView user data log. I did build a moving map for this and that will be in production in the near future, but I'll be stripping everything else out. The map, based on OpenStreetMap will give me a little bit of extra reference but even that is of limited use with Skyview and Foreflight. Ultimately, this project really wasn't worth consuming the 50 or so square inches of panel space that it did. Definitely worth it on the "geek having fun" scale though.

To your original question, I used my data logs extensively for my test phase. GPS data alone (Foreflight) is of limited value. You need air data - IAS, altitude and OAT. The EMS data is quite helpful as well. Without these, manual data logging will be needed.

Good luck with this endeavor, if you want specifics on what I did on my first attempt, PM me.

[Brantel]

Originally Posted by Saville

As I wrote at the start of my post, I don't have an EFIS that supplies the requisite "serial stream".

I'm confident the data logging capabilities of the Pi or an Arduino will work.

it's the data ACCURACY of those systems - as well as the Foreflight data logger - that I'm asking about.

Serial streams don’t have to come from an EFIS. Also the logger code could be slightly tweaked to log data from thousands of possible sensors at a very high rate.

For home brew sensors...accuracy depends on the resolution of the A to D converter in whatever device you are using has.

You can get some very high accuracy and high update rate GPS units.

Can’t speak to Foreflight because I don’t use it.

[n82rb]

Traveling at 170kts your covering 283 feet a second. Even the worst data logger will give useable data. As stated, its all about the accuracy of the sensors, but even the cheapest sensors nowadays are better than the best of them during the apollo days.

Bob burns
Rv4 n82rb

[humptybump]

If it’s in your price range, you could buy a complete Stratux unit with GPS +AHRS and use its internal logging feature to capture everything. (A complete Stratux is under $250 https://amzn.to/2VbbW3F)

After your flights, you just off-load the log file from the unit. Use of one of its supported apps is optional.

The nice bit about a Stratux is they have already don’t all the heavy lifting of sensor fusion so the AHRS and GPS day is usable without any additional coding.

You also have ADSB-IN for all those cross country flights you’ll take after phase-1

[az_gila]

Costs and time could get interesting for a DIY system.

You could update your panel to a 7" Dynon system and get full engine monitoring too - heck ignore the Dynon flight portion and configure it as an engine monitor only.

Around 6K



But I do have to admit DIY is more fun...

[Saville]

Originally Posted by az_gila

Costs and time could get interesting for a DIY system.

You could update your panel to a 7" Dynon system and get full engine monitoring too - heck ignore the Dynon flight portion and configure it as an engine monitor only.

Around 6K



But I do have to admit DIY is more fun...

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.