Thanks Jeff York for the great overview of how mogas is handled. In the case of new builders or a new owner just getting started on running their airplane, I thought it might be useful to relay how I've done it since I bought N335KC. Steve Bennett used to use a "clean" source of mogas he had there in Omaha and when on trips he would use avgas. Once I had the plane, all I've ever used is avgas. The reason for that is mainly that I have a simple mind. I have an airplane so I use airplane gas. I've occasionally put some Chevron Supreme in with the existing avgas in the header (main) tank if topping off to take a trip, but I'm not going to do that anymore. I have a red five gallon plastic container in the hangar I use for this purpose but it sometimes sets there for months. After reading Jeff Scott's recent gas problems, that's the end of that. For all I know, I'm pouring some dissolved plastic in my tank when using "hangar gas". Chevron Supreme in CA has 8% ethanol last time I called their main offices in San Francisco. I had been assuming their premium brand would be ethanol free but that turned out to not be the case. I suspect all mogas has got ethanol in it unless bought from a custom source and where does the custom source get their gas from? What kind of additives are in it? My rationale in using avgas is mainly because I think avgas is more carefully refined and handled and controlled. It's a known value with (hopefully) no variables. Car gas? It's liable to have anything in it.
For those worried about lead, I had the heads off to put new valves and springs in around the 500 hour mark and found heads and piston tops to be a light tan color. Some guys around the airport think it's supposed to look black. Black is "normal". I disagree about that. I think black means the engine has been run rich and all that excess and wasted gas has formed carbon (plus other stuff) deposits that, when extreme, can foul plugs and cause "sticky" valves. Some guys think running rich is being nice to the engine. It's "keeping it cool." They don't understand that combustion temperatures are lower with a lean mixture than a rich one. John Deakin talks all about this in his Pelican Perch columns. I've learned a lot reading Deakin and it was one of his columns that inspired me to put in my oxygen set-up. It was also reading Deakin that I learned to think of the engine as basically just an air pump and as such, runs most efficiently without any obstructions. One of the easiest ways to eliminate an obstruction is to keep the throttle plate wide open. Now, running wide open below about 8 thousand feet in a non-turboed engine will pull way over 75% power and, at least with the VW, will generate a huge amount of heat. Not good. So after take off I pull the power back and run at reduced throttle until reaching that 75% power altitude of 8000'. At that altitude and above and after the engine has cooled off a little after climbing out on a hot day with a full fuel load plus me and my baggage, the throttle goes wide open and the mixture gets pulled way back . . . what Deakin calls "The Big Pull." A wide open throttle, with a 52 x 56 prop on a GP 2180, gives me a max RPM of about 3100, which is right where I want the engine to run at full throttle in the air. A flatter prop would render higher RPM's, but higher RPM's generate lots of internal friction so the increased horsepower gained by turning the prop faster is cancelled out by having to overcome the higher internal friction - so called "friction loss." Generating this wasted power does more than waste gas, it creates a boatload of heat. Since heat is a VW's worst enemy, I've established 3100 as my ideal RPM. It's the pitch of the prop that determines this, not my throttle. I keep the mixture richer than I'd like when climbing out because the excess fuel is needed to cool the valves and heads, but once I reach cruise level - somewhere between 10.5 and 13.5 depending I'm miserly as can be with that mixture knob. Throttle by then is wide open and mixture is just barely enough to keep the engine running smoothly. Even in summer, temps at those altitudes are cool, drag is less, the engine is happy pulling about 50% power and I'm trucking along at 149 MPH for as far as 21 gallons of avgas will take me at 2.8 - 3.5 GPH. I plan on going at least 500 miles even with a bad headwind. Without a bad headwind, leg lengths are normally about 750. I never cease to amaze myself that this flimsy little fiberglass airplane with a VW can go that far, that fast, and be such fun. You need oxygen to fly like this, but that's easy. Mike ____________________________________________________________ Drink This Before Bed, Watch Your Body Fat Melt Like Crazy Celebrity Local http://thirdpartyoffers.juno.com/TGL3141/5b6f45993f09a4599020fst01vuc _______________________________________________ Search the KRnet Archives at https://www.mail-archive.com/krnet@list.krnet.org/. Please see LIST RULES and KRnet info at http://www.krnet.org/info.html. see http://list.krnet.org/mailman/listinfo/krnet_list.krnet.org to change options. To UNsubscribe from KRnet, send a message to krnet-le...@list.krnet.org
