It's late, I had a good day flying (two flights with two different CG test points), and I thought some of the more technically-minded might enjoy this little example of what we can do with the modern EFIS capabilty. The GRT folks designed their system with the capability to record flight data, so that you could play it back through the EFIS itself, and "relive" your flights - or give cool demos at trade shows!
Seeing as how I am supposed to be a flight test engineer, I thought "wouldn't it be cool if we could use this capability to record the data in realtime, and then import it into a computer post-flight, allowing easy data reduction?" Surely, it would be more accurate than the traditional method of trying to fly and record data by hand at the same time - or recording the panel on a video camera, and then hand-recording the data back home.
I posed this question to a few folks on the web, and to some of the engineering Coop students at work, and can take no credit at all for the resulting programming - I haven't written code since my early days with Basic and Fortran. But their results are amazing!
Let me share today's products. I went up to fly pitch stability Phugoids - trim for a speed, pull up to slow about ten knots, then go stick free, and watch the results. From this, you can plot the period of oscillations, and determine whether or not the oscillations are damped (ie, the aricraft wants to return to the trimmed condition, and is therefore stable). Do this at several CG's, and as you move aft, you should discover where you go unstable.
I flew two such missions today, one at the forward end of the CG box, and one about 2/3rds of the way aft. Recorded the data, decoded it, and fed it into Excel. Took me about three minutes to produce the following plot. The X-axis is time, in 1 second intervals. The upper "squiggle" (green) is airspeed, the lower squiggles are pitch (pink) and roll (blue) angles. The "spikes" in roll are simple event markers I fly into the data - a quick doublet signals the start of a Phugoid, another, the end. That allows me to quickly find the times of interest in the large data files. The real data is in the pitch oscillation and the IAS.
This plot is for the aft CG positon, with a data take trimmed on about 120 knots, followed by one about 90 knots. For an engineer...this is COOL!
Now you know what engineers do on a Saturday night....
Paul
Seeing as how I am supposed to be a flight test engineer, I thought "wouldn't it be cool if we could use this capability to record the data in realtime, and then import it into a computer post-flight, allowing easy data reduction?" Surely, it would be more accurate than the traditional method of trying to fly and record data by hand at the same time - or recording the panel on a video camera, and then hand-recording the data back home.
I posed this question to a few folks on the web, and to some of the engineering Coop students at work, and can take no credit at all for the resulting programming - I haven't written code since my early days with Basic and Fortran. But their results are amazing!
Let me share today's products. I went up to fly pitch stability Phugoids - trim for a speed, pull up to slow about ten knots, then go stick free, and watch the results. From this, you can plot the period of oscillations, and determine whether or not the oscillations are damped (ie, the aricraft wants to return to the trimmed condition, and is therefore stable). Do this at several CG's, and as you move aft, you should discover where you go unstable.
I flew two such missions today, one at the forward end of the CG box, and one about 2/3rds of the way aft. Recorded the data, decoded it, and fed it into Excel. Took me about three minutes to produce the following plot. The X-axis is time, in 1 second intervals. The upper "squiggle" (green) is airspeed, the lower squiggles are pitch (pink) and roll (blue) angles. The "spikes" in roll are simple event markers I fly into the data - a quick doublet signals the start of a Phugoid, another, the end. That allows me to quickly find the times of interest in the large data files. The real data is in the pitch oscillation and the IAS.
This plot is for the aft CG positon, with a data take trimmed on about 120 knots, followed by one about 90 knots. For an engineer...this is COOL!
Now you know what engineers do on a Saturday night....
Paul