Flight Data Recorders: Foreflight logger, Arduino, Raspberry Pi

[Saville]

Originally Posted by rv7charlie

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?

Well I was looking at the data points after the loop - the dip and then the rise. My speed was increasing yet the data points are getting closer together in the dive and then further apart in the climb. One would think that if my speed was increasing and the acquisition rate was constant that the spacing would increase and not decrease. So I'm surmising that the acquisition rate was not constant.

But I confess to not having figured this out yet and further plotting of the data might lead to some insight.

[spatsch]

Originally Posted by Saville

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

I wouldn't rule that out quite as quickly.

I used a Dynon to log my loops and in the first configuration they looked horrible.
Well maybe my loops do look horrible but the recordings looked horrible to a point that it defied physics. I important them into R so you could easily model the dynamics.... .

So I investigated and it turned out that the accuracy of my GPS signal drifted way off when inverted and took a while to come back when in normal flight. Note it's not that I lost tracking completely (maybe that is what happens to you as you mention recording slowing down) but my accuracy just got worse.

Looking at my setup (GPS antenna on dashboard of RV-8) it seems my fuselage was blocking the GPS signal in certain parts of the loop. So I put myself a little GPS data logger together I could move around the airplane easily to find a better spot by combining a serial data logger:

https://www.sparkfun.com/products/13712 15$

with a GPS module

https://www.sparkfun.com/search/results?term=GPS

they don't have the GPS I used any more but above has lots of choices which would all work. All you have to do is to connect RX to TX and vice versa connect both boards to power, write the config file on the memory card and put it in the logger and power it up.

Turns out when I moved it on my wingtip the loops were round. So my theory above seemed to be correct.

When I upgraded my GPS to be 2020 compliant I moved the Dynon puck inside of my wingtip and haven't had an issue since... .

So you might have to just move your GPS around a bit to get round loops... .

Oliver

[Saville]

Originally Posted by spatsch

When I upgraded my GPS to be 2020 compliant I moved the Dynon puck inside of my wingtip and haven't had an issue since... .


Oliver

Very helpful post.

So when you moved the Dynon puck to the wingtip, I take it that the extra wire run inside the wing does not affect antenna performance/signal?

Thanks!

[Saville]

If a GPS receiver antenna puck is moved out to the wingtip, does it's orientation matter? If it's mounted "upright" as if on a glare shield, I take it that being upside down doesn't affect reception?

Or should it be bolted onto the outboard rib so that it is 90 degrees rotated from where it would be on the glare shield?

Thanks!

[Ed_Wischmeyer]

Originally Posted by Saville

If a GPS receiver antenna puck is moved out to the wingtip, does it's orientation matter?

No. The GPS antennae on our planes don't care. Some of the military jam-resistant ones might aim lobes at individual satellites for jam resistance, but not ours. Similarly, VOR antennae don't care about orientation.

ADHRS, that's another story.

Ed

[DrDrift]

What about using a Pixhawk UAV autopilot for a flight data recorder? It has redundant IMU sensors, GPS, internal state estimator (AHRS) and configurable logging/telemetry.

Pixhawk hardware is about $100 for the older models.

I taught a Flight Test Engineering course last semester and mounted a Pixhawk on the tie down loop of a Cessna 210. The location wasnt great for GPS reception, but we got great airspeed data up to 170 kts.

The data is logged to an SD card and can be downloaded by removing the card or downloading through a USB cable or wireless radio. The default rate is 200Hz, which result in giant files for long flights. We have configured it for lower rates for certain tests, and to only log messages that are useful for analysis.