Under the heading of ?knowing how your stuff works?, here?s a bit of trivia on the Dynon ?D?-series, Tru Trak ADI Pilot, and GRT Horizons. We recently had the pitot/static/xpnder/IFR certs done on both of our airplanes. For those who haven?t done this, it involves plugging into the pitot/static systems and using a vacuum pump and a calibrated test set to take the instrumentation system up to a simulated altitude of 20,000? (or greater, in some cases). This checks the static system for leaks, checks the altimeter for calibration, and makes sure that the transponder is reporting codes and altitudes properly. In our case, everything passed with flying colors once again (whew!), but I was able to make an interesting observation that tells me something about the way Attitude is calculated in the systems.
With the test set-up hooked to the RV-6 (Dynon D-10A & D-180, Tru Trak ADI), as we started ?up?, all three attitude indicators showed a significant pitch up ? about 15 degrees nose high with a 2,000 fpm climb rate. This was, of course, with the airplane sitting still, and not changing attitude. Clearly, this is not an expected flight condition, but it does tell me that pitot/static does play a part in the attitude solution for these instruments. A pitch down was indicated during ?descent?, but I don?t think it was quite as pronounced. When we transferred the test rig to the RV-8, with GRT equipment, there was no indication of a pitch change at all, even with a 3,000 fpm climb and descent. So apparently, the attitude algorithms that GRT uses don?t care about pitot/static. I have not seen the attitude determination software code for any of these systems, but I know this has been talked about before on the forums ? how the various electronic attitude systems are ?aided? to get their solution. So this isn?t really new, just an observation that you can see it in action with this kind of a test. Interesting from an engineering standpoint, and good to know that a static leak might affect the attitude solution with some equipment (although I doubt that in real life, it would be a huge error).
Paul
With the test set-up hooked to the RV-6 (Dynon D-10A & D-180, Tru Trak ADI), as we started ?up?, all three attitude indicators showed a significant pitch up ? about 15 degrees nose high with a 2,000 fpm climb rate. This was, of course, with the airplane sitting still, and not changing attitude. Clearly, this is not an expected flight condition, but it does tell me that pitot/static does play a part in the attitude solution for these instruments. A pitch down was indicated during ?descent?, but I don?t think it was quite as pronounced. When we transferred the test rig to the RV-8, with GRT equipment, there was no indication of a pitch change at all, even with a 3,000 fpm climb and descent. So apparently, the attitude algorithms that GRT uses don?t care about pitot/static. I have not seen the attitude determination software code for any of these systems, but I know this has been talked about before on the forums ? how the various electronic attitude systems are ?aided? to get their solution. So this isn?t really new, just an observation that you can see it in action with this kind of a test. Interesting from an engineering standpoint, and good to know that a static leak might affect the attitude solution with some equipment (although I doubt that in real life, it would be a huge error).
Paul