Saturday, September 04, 2010
A319 - the final chapter
I've discussed the accelerometer data I gathered on takeoff and landing in Airbus 319's, and I made some calculations with the data involving engine thrust and energy dissipated in braking. The final calculations I've made involve takeoff and landing rolls of the aircraft.
Excel makes it very easy to perform numerical integration of a time series of data such as that gathered by the Pasco Sparkvue software on my iPhone. The basic idea is that the sample rate was set at 20 Hz, so a data point was gathered every 0.05 seconds. I assume that acceleration is constant between samples, multiply the duration of 0.05 seconds and add it to the previous velocity to get the new velocity. Rinse and repeat. Do the same to integrate velocity to get distance.
On takeoff, initial speed is 0 and initial distance is 0. On landing, initial distance is 0 but initial speed is back-calculated by assuming a speed when braking stops. In my earlier posts, I assumed a speed at the end of brake application of 10 knots but that gave fairly unrealistic landing speeds and rolls. I adjusted to 15 knots which is acceptable by the A319 operating manual (max. taxi speed is 20 knots, 10 knots in turns). This gave a more believable touchdown speed and landing roll (though still, I suspect, too low and too short).
I calculated the distance from start of takeoff roll to rotation to be 4,350 feet and, as I mentioned in the earlier post, the rotation speed to be 152 knots. I find these numbers to be pretty credible. For landing, I calculated the touchdown speed to be 99 knots and the landing roll to be 2,800 feet. The latter two numbers are suspect, hopefully an A319 pilot will comment. Or, perhaps, I can install an A319 simulation in MS Flight Simulator and try it myself.