lml@lancaironline.net Mailing List Archive

<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> I have also seen a discrepancy between the totalizer and the gage after a long flight. The delta is around 2 gallons (2%) and I believe it to be caused by one of four things: 1) Turbulence. I have the sensor mounted horizontally with 6 inches of straight line on each side but it is mounted to the engine (just before the flow divider) so the vibration may be affecting it. 2) Temperature. By the time the fuel has arrived at the transducer it has picked up some heat from the engine and the fuel pumps. This heat would cause the fuel to expand so that the engine is in fact using "more" gallons than are leaving the tank. 3) True density. When I calibrated my fuel probes I used an electronic balance to weigh in the fuel two gallons at a time. I used multiple methods to determine how much two gallons weighed and averaged them. I was surprised to learn that 100LL weighs 5.79 pounds per gallon and not 6 pounds per gallon. Perhaps the lower density is affecting the flow sensor. 4) Tolerance. Manufacturing variances between sensors could account for the difference. The fact that all the sensors have the same K factor (pulses per gallon) would indicate that there is a tolerance band. IMHO we are all fortunate to have the accuracy to know that there is a couple of gallon difference. If you don't agree then go fly a 172 where the fuel indications are "I think the tanks are near full", "There may be some fuel sloshing around" and "If you stare at me long enough I may twitch". If you are determined to have accurate totalizer results then you need to track the performance of the totalizer to determine exactly how much it is off by. Vision should then be able to burn you a new EPROM with a different K factor coefficient to account for the installation variances. Viola! 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. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>