Primarily for general aviation discussion, but other aviation topics are also welcome.
User avatar
By TheFarmer
#1770559
FAO: LAA Chaps

A hot upcoming few days ahead, and I’m sure there are some LAA’ers with MOGAS sitting in their tanks after a long lay-off.

I’ve just filled with 100LL for a busy few days of aviating and I strongly advise you do the same.

Vapour lock very nearly killed me once, and it wrote off my a/c and put me in a neck brace for six weeks.

Please take it seriously.
Rob L, Nick, G-BLEW and 4 others liked this
By Crash one
#1770563
I tried to start mine after a long wet winter followed by the lockdown.
Stale fuel, Mogas, not so much as a pop out of it.
Fuel replaced, fresh mogas, no problems.
User avatar
By Rob L
#1770569
Further to Farmer's excellent reminder about vapour lock, motor fuel is also not as forgiving as AvGas in terms of storage. MOGAS deteriorates surprisingly quickly (within a few months) and given that it is at or under £1 per litre now, there's no excuse not to drain MOGAS for lawnmower use and use fresh forecourt fuel for the aircraft!
By Nick
#1770573
I aggree I have drained my tanks and replenished. You can go and buy fresh UL91 but as no-one has been flying it could be old stock! The distributor is not going to drain thier tank and dispose of it!

Nick
By Maxthelion
#1770578
Further to this - although the LAA has allowed the use of mogas containing up to 5% ethanol, it's the ethanol and aromatics that are used to boost the octane of forecourt super unleaded that evaporate first on the fuel's transition to becoming stale. Esso have as recently as 2019 communicated with friends of mine in the motorsport world that their forecourt 97 octance fuel is brewed to that octance in the first place, so is far more consistent in terms of actual, rather than claimed octance, and may be stored for far longer than other forecourt fuels without fear of deterioration. It's been measured as still being 97 RON after seven months in storage (though in closed containers rather than an aircraft fuel tank wich vents to atmosphere). Esso's website shows where you can find filling stations stocking their fuel, many of which are Tesco convenience stores cum garages.

This isn't to suggest you ignore the advice above to use fresh fuel or avgas, just a nudge on where to buy petrol from if you must.

Edit: UL91 will, I'm sure, be just fine to use after a few months of being sat in an airfield's tanks. I would use it without reservation. It's very different from mogas in terms of stability in storage.
User avatar
By Smaragd
#1770582
Maxthelion wrote:Further to this - although the LAA has allowed the use of mogas containing up to 5% ethanol,..


.. for a limited number of specific engines.
User avatar
By Trent772
#1770584
Exactly why I run all my little motors on avgas at home. Chain saws, mowers and lawn tractor all run on avgas. never a problem.
Flyin'Dutch' liked this
User avatar
By Flyin'Dutch'
#1770593
Ugh, maybe for a lawn mower not too bad but I would not want to inhale AvGas fumes from a chainsaw etc.

The LL is a total misnomer - there is (IIRCC) 10x more TTL in AvGas than there was in 5 Star Leaded for road use.
User avatar
By Rob L
#1770603
Flyin'Dutch' wrote:Ugh, maybe for a lawn mower not too bad but I would not want to inhale AvGas fumes from a chainsaw etc.

The LL is a total misnomer - there is (IIRCC) 10x more TTL in AvGas than there was in 5 Star Leaded for road use.


It's TEL But you are quite right; Low Lead is a relative term.
Think of the 130 octane used for all those bombers & fighters in WWII.
I confess that I always thought 100LL was about the same as five-star in terms of lead content.

Chainsaws are generally 2-stroke, so the above does not apply.
By andytk58
#1770628
TheFarmer wrote:FAO: LAA Chaps

Vapour lock very nearly killed me once, and it wrote off my a/c and put me in a neck brace for six weeks.

Please take it seriously.


I still think its criminal that aircraft are designed with fuel systems that suck liquid. Particularly a volatile liquid which will flash vapourise at any excuse!!

IMO mogas systems should always have an 'always on' circulating pump at the lowest point in the system, with a pump failed warning lamp on the instrument panel. Cheap insurance against disaster.

[\rantoff] 8)

Andy
By Crash one
#1770632
andytk58 wrote:
TheFarmer wrote:FAO: LAA Chaps

Vapour lock very nearly killed me once, and it wrote off my a/c and put me in a neck brace for six weeks.

Please take it seriously.


I still think its criminal that aircraft are designed with fuel systems that suck liquid. Particularly a volatile liquid which will flash vapourise at any excuse!!

IMO mogas systems should always have an 'always on' circulating pump at the lowest point in the system, with a pump failed warning lamp on the instrument panel. Cheap insurance against disaster.

[\rantoff] 8)

Andy


I fitted one of those for that reason, minus the warning lamp, plus re routed the out feed from the mechanical pump from over the top to underneath to prevent vapour lock.
By riverrock
#1770639
My understanding is that most injected engines essentially have a circulating pump, pushing fuel around much faster than the engine needs (our Bulldog goes anyway), but can still get vapour lock, although its post common when trying to restart a recently running hot engine.
A quick google didn't find the lead content of leaded MOGAS. BS4040 "Specification for leaded petrol (gasoline) for motor vehicles" refers (but I'm not going to pay for that!
I read anecdotally that leaded MOGAs was about 0.2 g/l of lead, 100LL is 0.56g/l, unleaded is max 0.005g/l. However I don't know which star rating that refers to. 5-Star had the highest Octane rating of 101 so I suspect its lead content was close to our 100LL.