Mixing Mogas and Avgas

[Maoraigh1]

STC is an FAA, and I assume Transport Canada concept. Not an EASA one. Temperature limit under EASA/CAA/LAA is, if I remember, 21C. It's placarded.

[Rod1]

Oh, I see, an STC is an American thing!

UK rules;

Unleaded Mogas fuel is restricted by CAP 747, Appendix 8, General Concessions 4 and 5 to operation with a fuel not exceeding 20° C and an altitude not exceeding 6000 ft.

But then you all knew that, right

Rod1

[Sam Rutherford]

I have a mogas stc for my Maule - involved paperwork and also changing the fuel pump and some piping.

Many STCs though (still costing USD1000 or so) are nothing but a paperwork exercise - nobody goes near the plane at any stage. So, know the rules, do your best, but if you're stuck (and the rebels are running towards you with guns blazing) then your plane will fly fine with mogas (STC or no STC).

As someone said earlier, a mogas/avgvas blend is often really good for your engine.

Safe flights, Sam.

[Pilot DAR]

(and the rebels are running towards you with guns blazing) then your plane will fly fine with mogas (STC or no STC).

Well, if your plane is a Piper Tomahawk, Cessna 185, or 206 (for three examples of aircraft with which I have do Mogas experience back in the testing days), the rebels might catch up to you a mile or so off the end of the runway.

Many aircraft fly fine with Mogas, a few not so well. Don't experiment, unless doing so is your profession....

[EDMJ]

The lack of an STC is an indication that either your aircraft type has been found by someone to not be able to accept Mogas for some engine or airframe reason, and thus not approved. Or very simply, it is an aircraft type which has not been shown to comply with the applicable certification standards with Mogas.

He mentioned earlier that he flies an MCR, which I suspect is powered by a Rotax 912 which in turn (and according to Rotax themselves) should actually be fed with MOGAS rather than AVGAS (they apparently don't like the lead), hence no need for an STC.

[Pilot DAR]

(and according to Rotax themselves) should actually be fed with MOGAS rather than AVGAS

I have zero knowledge of Rotax engines on Mogas. "Should" won't be an aspect though. If the engine is type certified, and installed in a type certified aircraft, the approved fuels will be stated in the TCDS, an STC, or a government policy letter which specifically mentions Mogas use in that engine. If it's not listed in one of those places. it is not approved.

If the aircraft is not type certified, the answer, and degree of certainty, are much less clear - no "approval" is available...

[popobowa]

MOGas for cruise on IO550

A P28-235 (O) has a MOGAS STC, I know that A Beech Debonair IO470 has one...Rotax engines run better on MOGas (they stay much cleaner!). I ran one (Rotax)in Africa until 2000 (TBO) sometimes on 100LL but mostly on (African) MoGAs (which is of very varying Oct and Quality). Running on 100LL showed fouling and heat signs(small molten metal spheres on PLug cathodes).
Running on Af moGas showe dark to black caulifowe-like growth but the engine made 2000tbo time and was still a good runner.
I am tempted to buy a Beech A36 with IO550 (non turbo) and would like to know if I can risc to run it (55-60% cruise) on such MoGas if 100LL isnt availiable (which happens frequently>

[ExSp33db1rd]

I was advised to run the VW in my Turbulent on a mixture of Avgas and Mogas, to replace the lead that used to be in Mogas, but is now unleaded, never had any problem. There was a specific ratio which I can't just quote, but about 25% Avgas if I recall.

I initially ran it on Avgas only - after all, it's an aeroplane, isn't it ? - but then realised that the engine was a cooking standard 1200 cc Beetle, designed to run on the cheapest petrol, so why waste money, but eventually settled on premium petrol with a dash of Avgas.

[Desert185]

Quote:
(and the rebels are running towards you with guns blazing) then your plane will fly fine with mogas (STC or no STC).
Well, if your plane is a Piper Tomahawk, Cessna 185, or 206 (for three examples of aircraft with which I have do Mogas experience back in the testing days), the rebels might catch up to you a mile or so off the end of the runway.

Many aircraft fly fine with Mogas, a few not so well. Don't experiment, unless doing so is your profession....

Only add mogas to one tank. Takeoff with the avgas tank and cruise with the mogas tank while thumbing nose at the rebels.

[Croqueteer]

With the 0-200 and C90 I have experienced sticking valve problems with mogas. I think some on some overhauls the valve guides are done to too tight a clearance.

[Sam Rutherford]

Just to clarify, Mogas and petrol (as found in the motorway service station) are NOT the same thing!

I don't think that there is any Mogas anywhere in Africa, but could be wrong.

Cheers, Sam.



PS of course, you could always go diesel/JET!

[Mariner9]

Sorry Sam, not correct, the terms Mogas, petrol and gasoline are used interchangeably in the oil industry. Indeed, the Tanzanian gasoline specification describes the fuel as "Mogas".

I should know - I helped the Tanzanian Petroleum Import committee draw up their latest set of Fuel import test procedures

Most gasoline in Tanzania is imported into Dar es Salaam from India or the UAE, and the specification was drawn up with the expected Tanzanian climactic conditions in mind (i.e. hot).

Temperature limitations imposed by the CAA/FAA on Mogas use in aircraft are not really relevant to Tanzanian Mogas as the distillation criteria and vapour pressure of Tanzanian Mogas differs from US/European fuels.

[Sam Rutherford]

Oil industry I don't know, but in aviation - petrol is not Mogas (most importantly because Mogas cannot contain ethanol, though there are other differences as well).

I'm just trying to make the point that Mogas certified aircraft are not flying legally if they have taken petrol from the petrol station - something a lot of people don't realise.

Cheers, Sam.

[DaveW]

Sam, CAA Safety Sense Leaflet 4 "Use of MOGAS" is relevant here, and doesn't support that.

It quotes CAP 747, and specifically the General Concessions (GC) contained there.

One GC does indeed say:

Originally Posted by SSL4

e) GC No. 2 permits leaded motor
gasoline (Leaded MOGAS) to be
used with certain engine/aircraft
combinations provided that the fuel
is obtained from an aerodrome
aviation fuel installation in full
compliance with the applicable
requirements of the ANO (equivalent
to the storage and quality control
procedures applied to AVGAS).
Therefore the permissions granted
under GC No. 2 exclude the use of
fuel obtained from a filling station/
garage forecourt.

But the SSL/CAP747 goes on also to say:

Originally Posted by SSL4

f) GC No. 3 provides a partial
exemption from the relevant Article of
the ANO to allow certain light aircraft
to use Leaded MOGAS obtained from
garage forecourts subject to the
conditions contained in the Notice.

g) GC No. 4 provides a partial
exemption from the relevant Article of
the ANO to allow microlight
aeroplanes to use Unleaded MOGAS
obtained from garage forecourts
subject to the conditions
contained in the Notice.

h) GC No. 5 provides a partial
exemption from the relevant Article of
the ANO to allow certain light aircraft
to use Unleaded MOGAS obtained
from garage forecourts subject to
the conditions contained in the
Notice.

So it isn't accurate to state that MOGAS Certified aircraft are flying illegally with petrol station fuel - there's more to it than that.

There's lots more interesting and useful stuff in that SSL for anybody who wishes to operate using MOGAS, including the following relevant to the OP:

Originally Posted by SSL4

If you use a mixture
AVGAS/MOGAS with more than 25%
MOGAS, it will be assumed that your
aircraft is using MOGAS.

[ExSp33db1rd]

With the 0-200 and C90 I have experienced sticking valve problems with mogas.

That's why I was advised to use a cocktail of Mogas and Avgas, the lead has some lubrication properties for the valve guides - I'm told.

(they apparently don't like the lead)

Rotax 912, that is.

Not so much that they don't like it, but after about 10 hours the oil looks like yoghurt. Apparently that's not a problem, but it does look prettty doubtful, and the oil/filter/plug change interval is half the time if run on Mogas. We can't get Mogas, so Premium Petrol from the local filling station on the way to the airport is all we can do, but NZ is threatening to add Ethanol, so then we will be screwed. NZ did something along those lines a few years back - can't remember precisely what - and half the cars on the roads came to a stop with soggy fuel lines, so they had to back-track for "further tests".

"When in doubt, do nowt"

[Sam Rutherford]

Okay, thanks - very interesting. Particulalry as they don't talk about the ethanol 'issue' - which as far as I know is specified in all the STCs (ie the 'Mogas' cannot contain ethanol).

I'm also surprised that NZ fuel is still ethanol free - I thought it was pretty much global to have ethonol there now (in forecourt petrol).

Very interesting thread, thank you for the corrections!

Cheers, Sam.

[cockney steve]

First, the "contamination" bogey.

This is more a figment of imagination, than reality
Yes there was a Supermarket chain that had a batch of"contaminated" fuel.....but that's the only one I know of in over 50 years....I'd venture that deliveries to filling stations will probably be of the order of 100:1 compared to GA._ in terms of volume, it's probably vastly bigger.

Have you bought a fuel-dispensing pump recently?....No, thought not
An operator has to have the pump regularly checked and calibrated -woe betide anyone caught giving wrong measure (the tolerance allowed is ~a teaspoonful per Imp. Gallon) So, nobody will willingly compromise their expensive dispense equipment, which has built in filtration and water-seperators, to protect the metering-head..

UK road-fuel is mandated by law , to have (IIRC) 5% Ethanol...this is the maximum that legacy fuel-systems will reliably tolerate. As with the Lead-free furore, there would be major problems converting the nation's cars to accept higher Ethanol content and given that MPG suffers, any advantage is political,rather than practical.
I'm sure tha vast majority of UK GA activities could quite happily continue on standard Pump Petrol with no percieved difference....Aerobatting on a hot day, might be an exception...that, I don't know. Certain designs, with valve-seats cut straight into cast-iron heads (and some valve-guides too!) relied on the Lead, to coat and lubricate the working surfaces...Aeroengines with hardened seats do not have this problem.. Once you get a petrol-engine warm, it'll run on paraffin.....smokey and lower power, but it'll run Morris Vedette marine engine was built that way, as were many petrol/TVO tractors

That shows that petrol-engines are very robust and very tolerant of fuel-quality PROVIDED THEY ARE MANAGED CORRECTLY.

[Mariner9]

First, the "contamination" bogey.

This is more a figment of imagination, than reality
Yes there was a Supermarket chain that had a batch of"contaminated" fuel.

Agree Steve that fuel contaminations at the pumps is rare, but thankfully for me, (my job depends upon fuel contaminations), they are far from rare in the fuel production/distribution chain. My company investigates and resolves around 2000 cases of fuel quality problems per annum world wide, including the aforesaid supermarket incident .

However, I usually deal with batches of 10's of thousands of tons; fuel contamination at the forecourt pumps is extremely rare - we nearly always catch it before it reaches anywhere near the forecourt - quality control of motor fuels is far better than most lay people realise. If its any consolation to the Mogas users, we investigate far more contaminations to Jet A-1 than we do to Mogas (about 5:1) but that is similarly identified and resolved before it gets near the end users.

UK road-fuel is mandated by law , to have (IIRC) 5% Ethanol.

Not strictly correct, it is mandated by law to comply with EN228, which in fact allows from zero % up to a maximum of 10% ethanol. However, the current RTFO limits set by UK Government are met with Mogas at up to 5% ethanol, and the UK fuels industry has no plans at the moment to increase ethanol content beyond current (max 5%) levels, and the Government say they have no plans to mandate them to do so.

[Maoraigh1]

With the 0-200 and C90 I have experienced sticking valve problems with mogas.

We've used unleaded EN228 on an O200 since it was allowed after 4* went out. We occasionally fill with avgas when away from home, but don't deliberately mix.
However after a top-end overhaul, we were advised to run on Avgas, to build up lead, and did so. I think it was 25 hours on avgas.
We test the fuel for alcohol with the water/fuel technique as specified, and have seldom detected it.

[mayte]

nobody say nothing about magnetos? if you fly with MO GAS magneto timming has to be on 28 BTC , and if you fly with AVGAS magnetos timming has be changed at 24 BTC ,at least CONTINENTAL O200 engines , in the other way if you operate with MO GAS , the restriction about altitud is because MO GAS has alcohol and alcohol contains water if you fly more than 6000 fts of altitud you have the risk the worst thing for pilots , ICE ON CARBURETTOR