wyrmio,

I think that Gasax makes a very valid point. Whether you use 100LL or mogas in your 80/87 engine, it's still a compromise, and you are not using the proper fuel for which the engine was designed.

I would never use mogas without a proper STC, but see no problem whatsoever in using it with an STC in place. Every STC is backed up by extensive testing; they don't just hand them out for the asking.

It's quite true that the engine manufacturers discourage the use of mogas. Given their exposure to potential litigation (whether or not they actually have any liability), that's hardly surprising. If they thought that the could get away with it, they would tell you not to use avgas, either ("warning: engine is not designed or intended for actual use")!

It is interesting to note that the FAA has expressly confirmed that (with an STC), mogas is quite safe to use: see http://autofuelstc.com/pa/faa.html

Ultimately, the only truly objective fact regarding aviation use of mogas is that the cost is significantly less than using avgas. Everything else is pretty subjective, with arguments both for and against.

MLS-12D

P.S. Here is an FAQ that may be of some interest:
http://www.ercoupers.com/service/mogas.html#5. See also Transport Canada's document TP10737, available on-line at http://www.tc.gc.ca/CivilAviation/ce...ants/mogas.htm

MLS12D, the main reason for using mogas in the UK is availability. A great many people here operate off private strips and rarely visit airfields with avgas.

Croqueteer,

Sounds like my kind of flying! Nothing like operating off a quiet grass strip on a sunny afternoon. :D Admittedly I don't get to do that so much anymore - especially during the winter - but that's the environment in which I originally learned to fly.

MLS-12D

I have a question for the experts on this.

If I am sat at an airfield with 30L of mogas in my tank and it is a hot day. Say a fuel temp of 30c. I refuel from an underground tank with 40L of avgas. I assume the avgas will be coming out of the ground at about 10c? The fuel temp should then be within minimum and the mix of avgas/mogas will presumably be a lower risk than pure mogas?

Is there any data on the performance of avgas/mogas mix, and is this a half way house as far as risk is concerned?

I would assume that most people who run aircraft on mogas with only one tank would actually be running on mix.

Rod

Rod1,

Interesting point you raised. It makes sense to me to refuel just before departure on a hot day when the aircraft tanks are heated by sunlight, so as to prevent the fuel getting heated too.

It is surprising that the CAA didn't make it mandatory for all aircraft required to use MOGAS to be retrofitted with a fuel tank temperarure gauge.

You may be intersted in this discusion on Mogas from the Cardinal Club Digest.





I have a '68 150HP FG with an EAA STC for Mogas. I have flown the
plane now for 1.5 years (about 165 hours) and have used mogas exclusively
with (up to 10%) and without ethanol.

[Does your STC allow mogas with ethanol? Paul]

I have had oil analyses done after every oil/filter change interval (40Hrs)
and there are no measurable negative effects to the engine from using
mogas. I am not brand loyal and buy the cheapest price I can find. I fly
high and in every season, especially winter. I live between lakes Erie &
Ontario so the moisture content of the air is up there in the winter. I use
no additives to the fuel. I do use Avlube in the oil. The cam is fine.

I have done this to prove to many of the local naysayers that mogas is a
viable alternative for the low compression O320E2D engine, and because I
run an environmental firm I can't justify using any leaded fuels. I have
learned a few things which are helpful.

Firstly, the engine will clean itself of most lead deposits when making the
fuel switch but the plugs will need to be cleaned. Once done they remain
very clean if mogas is the only fuel used.

Second, the engine will run smoother, it will take two or three tanks full
to notice the difference.

Thirdly, mogas gets reformulated for each season to enhance starting
characteristics in cold weather. So use your fuel often, don't let it sit
in the tanks from summer to winter. A fuel formulations engineer told me
that 3-4 months storage is no problem, but don't go longer. He also said
that 80/87 octane contains less additive than the other formulations, and
that buying up one grade to get a higher octane rating for an O320 wasn't
worth the money.

[Both 80/87 and 100/130 have almost no additive package. Paul]

Fourthly, ensure that the fuel lines and associated plumbing have fresh
o-rings installed. Particularly the tank caps, selector, shut off, primer
and strainer. When I switched to mogas some of these o-rings started to
leak and needed replacement. They may have needed it because of old age,
but changing the o-rings solved any leaks. Ensure the fuel tanks have not
been "sloshed" with a sealing compound, as mogas will dissolve some
formulations.

I have not had a single drop of water in the mogas. I constantly saw small
amounts of water in the avgas.

[If you really have ethanol in your mogas, then the water is still there,
it is just that the ethanol is keeping it in solution. Not the best, as it
will come back out of solution when the temperature decreases, like at
altitude, and then potentially freeze in the fuel system.]

Ethanol does seem to decrease the energy available per litre (gallon) so as
a result range is roughly reduced by the percentage of ethanol content. I
have not had any vapour lock, hard or hot start problems. I use the prime,
wait, time based on temp, method for starting, as listed by another CFO'er.

Mogas is good but not perfect. Lugging 5 gal jerry cans up onto the wing is
a pain. Avoiding spills over the wing is an acquired skill. Mogas stinks in
comparison to avgas, so sample cups and dipsticks need to be stowed in zip
lock bags so they don't stink inside the cabin. Disposable gloves are
needed to keep mogas from contacting the skin.

Lastly, most of the myths that surround mogas usage seems to comes from
self proclaimed experts who talk lots and have done little. A local flying
club has run its fleet of 150's and 172's on mogas for over twenty years
without ill effect. I suspect that most of the engine damage theory has
come from those who have not used their aircraft frequently and blamed
mogas usage for the engine ailments.