How long is it acceptable to leave mogas in aircraft tanks?
I understand that it has a much shorter life than avgas.
How do you account for the mixing? I mean if your tank is full, then in the next 2 weeks you use half of it, and refill. Is the fuel now considered 2 weeks old, 0 weeks old or a compromise 1 week old?
Is the outside termperature relevant?
Over the three years that I have owned my microlight I have never drained the tanks, never cared, and never had any issues. Only used 95 octane, though the day will come when I get some 100LL for lack of anything cheaper available. For info: the plane is always stored in hangar, and though I sometimes bleed off a bit of fuel from the lowest point (i.e. the header tank) I never found a single drip of water.
Apart from a short period between 4* becoming unavailable, and the approval of EN228 95, we’ve used mogas in our Jodel DR1050s since before I joined the Group in January 1990, with no problems. We fill with avgas only when refuelling away from base. We’ve had our present aircraft since late 1999. We’ve only once drained the rear tank, due to a finger-filter blockage. We’ve never drained the front tank. The aircraft flies about 150 hours per annum.
It’s hangared. The only water-in-fuel problems have been after it was left out over a wet weekend at a Mull FLy-in. I believe the tanks are about 50 years old – the aircraft was a rebuild from a 1961 and a 1964 aircraft after accidents over 35 years ago. We’ve no reason to suspect any tank problem. At an engine top-end mid-life overhaul in 2010, the O-200 looked clean. The plugs looked O.K at the last inspection – we’re starting another inspection tomorrow.
I know other owners who fly less often ,who never drain the tank(s), and have had no problems.
PS the filter blockage was fibrous – not mogas related.
PPS Carb icing with the Continental O-200 and mogas and Scottish air is a regular occurence,.
I fail to see how using mogas instead of Avgas increases the tendency for carb ice to form, but I’m eager to learn…
It’s the Scots air, Bosco, too much alcohol content…
QuoteI fail to see how using mogas instead of Avgas increases the tendency for carb ice to form, but I’m eager to learn…
More volatile. Ethanol is hygroscopic.
If the problem is fuel gumming up over time, I have wondered whether some sort of agitation could be helpful. e.g. you could have some of those rotating magnetic coffee beans in the tank and power them in the hangar in order to keep the fuel fresh.
http://en.wikipedia.org/wiki/Magnetic_stirrer
Or maybe it isn’t an issue and that’s a solution looking for a problem? (not to mention wearing a hole through the bottom of the tank)
What exactly is “gum” made of?
Supposedly it passes through fuel filters, but sticks to things.
Also the fuel pickoff point should be some distance above the bottom of the tank. But I am sure “gum” will stay in suspension for a long time.
What exactly is “gum” made of?
IMO it’s fuel molecules being radicalized by oxidation, then react to form longer hydrocarbon chains
But I am sure “gum” will stay in suspension for a long time.
This paper says gum is soluble, so yes it shoud stay in the solution
Supposedly it passes through fuel filters, but sticks to things.
The problem with gum apparently is that it tends to form hard deposits at hot metal surfaces
I don’t know what the gum (varnish) is made of, but it certainly didn’t pass through the fuel filter of my Dad’s boat.
The problem with gum apparently is that it tends to form hard deposits at hot metal surfaces
Interesting…
I happen to know that none of the fuel system components of an IO540 engine, including right up to the fuel injector(s), get at all warm during flight. The fuel appears to cool them very effectively, even at low power settings and even in thin air (tested to FL125).
(And that works both ways i.e. the airflow doesn’t cool the thin injector pipes significantly, anywhere along that whole pipe run).
The only bit which will get warm is the injector itself (being screwed into the cylinder head) and of course the inlet manifold. There is a procedure for cleaning them – I believe one immerses them in MEK and blows them out with compressed air.
