John, I need some additional help with your logic for using clock time for your GPH calculation. I calculate fuel consumption based on tach time for the very reason that you state. "if you go by tach time your fuel consumption will be almost the same regardless of engine speed". Or restated; fuel consumption corresponds with the tach and not the clock.
My concern is when will my tanks run dry and that is easily calculated using tach time. It would be a nightmare using elapsed time unless the aircraft is equipped with a Hobbs meter - mine isn't. IMHO Andy Anderson 415-D with C-90 ( 6 GPH tach time) _____ From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of John Cooper Sent: Thursday, January 31, 2008 9:50 AM To: 'Randy Hougham'; [email protected] Subject: RE: [ercoupe-tech] Propeller/Fuel Burn > I never get better than 6 gph. If we're doing touch and goes, etc. I may get 7 gph. I'm using tach time, is that right? No. The tach "time" passes slower when the engine is running slowly and faster when the engine is running fast. A typical C85 tach should record one hour in one hour (i.e. be accurate) at 2500 RPM. Basically, if you go by tach time your fuel consumption will be almost the same regardless of engine speed. It will take a very long hour to burn all that fuel at 1800 rpm, however. Bottom line, measure gallons used verses actual elapsed time. John Cooper Skyport Services 518 797-3064 www.skyportservices.net _,___
