aturner
Well Known Member
There have been a number of excellent threads on VAF regarding optimization of aerodynamic efficiency, and also some valuable threads on measuring true airspeed and static system errors. I think we need to start a thread for those of us interested in efficiency, and accurate measurements of performance....the 20 nautical miles per gallon club. Here is my entry.
Yesterday I flew my RV-10 home to Pennsylvania from a fantastic trip to Leadville Colorado with my two sons (more on that in another post). We climbed high for the return flight, and about four hours into a five hour leg, and with lots of time to study the numbers on the EFIS screens, noted that we were doing 155 knots on 7.5 gallons per hour, which works out to better than 20 nautical miles per gallon:
The other screen would have showed 2100 RPM and 17.3". Being the quantitative sort, I wanted to verify these data, and directed the autopilot to fly four legs 90 degrees from each other, letting the G3X do its once per second data collection thing. Today I entered the GPS ground speed and ground track into Doug Gray's spreadsheet, available from the National Test Pilot School http://www.ntps.edu/information/downloads.html, and got this:
So my true airspeed is 157.1 knots. Mean fuel flow during the test was 7.48 gph (the totalizer consistently agrees with actual fuel burn with 1-2% error, and the error is conservative - actual burn is slightly less than calculated). So, I have a solid 21 nautical miles per gallon, or 24 statute miles per gallon. And this is on a cross-country trip with the family and camping gear, no special preparations. Here is the best part: this is a dead stock setup, with a used Lycoming, Slick mags, and stock Bendix fuel injection. I have tried to pay attention to aerodynamic details, and perhaps that has paid off.
My RV-10 is a work in progress, and I have a list of things that need fine-tuned, so these numbers and just a starting point. In the mean time, it is a testament to the power of simplicity, and it sure is a great family hauling machine.
Yesterday I flew my RV-10 home to Pennsylvania from a fantastic trip to Leadville Colorado with my two sons (more on that in another post). We climbed high for the return flight, and about four hours into a five hour leg, and with lots of time to study the numbers on the EFIS screens, noted that we were doing 155 knots on 7.5 gallons per hour, which works out to better than 20 nautical miles per gallon:
The other screen would have showed 2100 RPM and 17.3". Being the quantitative sort, I wanted to verify these data, and directed the autopilot to fly four legs 90 degrees from each other, letting the G3X do its once per second data collection thing. Today I entered the GPS ground speed and ground track into Doug Gray's spreadsheet, available from the National Test Pilot School http://www.ntps.edu/information/downloads.html, and got this:
So my true airspeed is 157.1 knots. Mean fuel flow during the test was 7.48 gph (the totalizer consistently agrees with actual fuel burn with 1-2% error, and the error is conservative - actual burn is slightly less than calculated). So, I have a solid 21 nautical miles per gallon, or 24 statute miles per gallon. And this is on a cross-country trip with the family and camping gear, no special preparations. Here is the best part: this is a dead stock setup, with a used Lycoming, Slick mags, and stock Bendix fuel injection. I have tried to pay attention to aerodynamic details, and perhaps that has paid off.
My RV-10 is a work in progress, and I have a list of things that need fine-tuned, so these numbers and just a starting point. In the mean time, it is a testament to the power of simplicity, and it sure is a great family hauling machine.
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