Andy asked:
>>>>>>>>>>>>>>>>>>>> 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, My logic in using clock time is this: If things are going badly and I need to worry about remaining fuel, I want to be sure that if I think I have one hour left that I actually have one hour or more remaining. If I look at the map or GPS and figure that the next airport with fuel is 45 minutes ahead, I look at my nose tank wire gauge and see that it's at the four and a half gallons remaining spot, I want to be confident that I have 50 minutes of fuel. (Note that only once did I ever fly into my nose tank on a cross-country flight and I landed with about 45 minutes of reserve.) Since my carefully measured fuel consumption at 2400 rpm was 5.4 gph (based on clock time), I'd have that confidence. (My 415-CD Ercoupe, big venturi, 7146 prop, C-85) Then, I'd slow down to 75-80 mph indicated, get into the slow, mushing flight that provides the best range and be doubly confident that I'd have enough fuel to land at the fuel-stop airport rather than the corn field. If higher than a couple thousand feet, I'd then lean and be triply confident - heck, in that situation, I'd probably lean at any altitude. Suspenders, belt and a hunk of rope in your pocket! Ed 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
