Kayak Chris wrote:

> but on a trip, how is one supposed to get autofuel? don't a lot of
> airports require you to buy their gas? (I got caught up in that once).

I've found that mogas at airports is typically 87 octane or so....not usually good enough for a high compression engine, especially those with poor combustion chamber design (on VWs and Corvairs this comes in the form of large quench volumes). Most of the online flight planning programs will show fuel prices and even which airports have mogas also. Some flight planners (Airnav, for example) will plan your trip around which stations have mogas, and even space your fuel stops accordingly.

The vast majority of my flying is relatively local, so I take off full of 93 octane autofuel, and usually don't have to fill up again until I'm back home. I get it from the local Raceway station, which keeps their tanks scrupulously clean, and well-filtered at the pump. I've never found any kind of trash in the fuel system of either airplane. I have about eight 6-gallon plastic fuel cans that I carry it around in. It's more convenient than going to the airport fuel pump, especially if there's some guy there filling his Cessna when I need fuel.

Beware of "cheap gas stations" with ethanol-free fuel. I bought some from a local no-name establishment that had a fowl odor to it, but didn't attribute it to the fuel at the time I was filling cans, but as I poured it into the Swfit (which has an autofuel STC), I could smell it again. Within two weeks, the stuff had "blown up" the 1.25" fuel lines connecting the wing tanks to the sump, and all the fuel had drained out onto the hangar floor. Thankfully, I'd never started the engine, so those hoses were the only damage. Autofuel can be a crapshoot. I only buy it from a reputable station, and Raceway near my house is a place I trust. They only sell 93 octane with ethanol, and that's what I burn. My fuel tank is vinylester, so it can take it. Most epoxies cannot take ethanol.

Autofuel is more susceptible to vapor lock, which can ruin your day in a hurry, and it usually happens on takeoff. Proper cooling of the fuel line can mitigate this. N56ML uses a fuel recirculation system and blast cooling of the Ellison's pressure regulator to keep the fuel from vapor locking.

To its credit, 100LL is normally scrupulously tested at airports, well filtered, and turnover is pretty good, whereas mogas at airports tends to sit longer and go "stale" faster due to impurities. Vapor lock isn't as big an issue with 100LL either. There's a lot to be said for 100LL, but you have to manage the lead buildup, as discussed previously.

In N891JF (the VW powered KR2) I normally run a 50/50 mix of 100LL and 93 octane with ethanol, with less autofuel in the summer and more in the winter (out of vapor lock and detonation concerns).

100LL is the safe way....

Mark Langford

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