lml@lancaironline.net Mailing List Archive

<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> I mounted the SFS AHRS on the forward face of the 208 bulkhead with good results. I sent Hal a photo directly. The SFS AHRS uses rate gyros, accelerometers and a flux gate to generate it's attitude, heading and inertial navigation information. Of the three, the flux gate is the easiest to screw up followed by the accelerometers. I chose the tail because it provided the cleanest magnetic environment. Locating the AHRS away from the center of gyration causes the inertial algorithms to "work harder" because the accelerometers are now affected by translations AND moments. The rate sensors don't care where they are. The net effect of not mounting the AHRS at the center of gyration is that if you are flying in turbulence WITHOUT a GPS reference you MAY experience a SLIGHT degradation in the inertial navigation derived position data. My gut reaction is that this is less of a problem than having the heading data skewed by stray magnetic fields. I have no hard data to support this but my experience is that the tail mount works just fine. One thing that is worth mentioning (again). Any attitude gyro needs to reference the gravity vector to determine vertical. The problem comes in a turn where the apparent gravity vector is the vector product of the true gravity vector and the centripetal force vector generated by the polar acceleration of the turn. In other words, if you hold a coordinated turn long enough your attitude display will roll back to level and when you roll out to wings level the attitude display will show a turn for several minutes until it recompensates. This is true for mechanical gyros and particularly true for solid state gyros (for reasons only an engineer can love so I won't bore you with). The SFS AHRS is the ONLY system (under $100,000) I know of that uses GPS position information as an input to calculate, and correct for centripetal force. Result, hold the turn as long as you like, roll level and the display shows level. Aint technology swell! Regards Brent Regan >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> LML website: http://www.olsusa.com/Users/Mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>