Running on mogas?

[QDMQDMQDM]

What's the story in the UK about running on mogas? Operators of 150HP Super Cubs in the US are doing it routinely, as are they in Europe. Is this possible here?

QDM

[FlyingForFun]

It's only allowed for PFA aircraft, not for CofA. The filling points must be appropriately labelled. I suspect you'll need the PFA to agree to it for your type, but I don't know how this works.

Once you have more than a certain percentage of MoGas in your tank (is it 80%? I can't remember) you're not allowed above 6000', and you're not allowed to fly with a tank temperature of over 25 degrees C.

Also, make sure you have a reliable source of MoGas! My Europa had a serious problem of black bits collecting in the fuel filters. We couldn't figure out what it was. Then the petrol station next to the airfield closed. Although the black bits haven't completely gone, there are far fewer of them now - the local petrol station was obviously supplying contaminated fuel.

The PFA are the people to speak to for definitive answers.

FFF
---------------

[QDMQDMQDM]

Shame. I'm on a C of A. Anyone know if the CAA will ever alow this?

QDM

[Them thar hills]

QDM
OK for your PA 18-150 ( if you must !)
Airworthiness notice 98c is where to look !
Unless on public cat C of A

TTH

[Kegbuster]

I use to fly PA 18 150s on mogas in the early 80s glider towing. the best fuel was the old 2 star, lead content i belive. Later we had to fly on 4star as 2 star was not approved.

There were no problems with the Cub but big problems with other types Chipmunks had to leave the cowlings open after shutdown otherwise the fuel will boil in the main pipe next to the engine block. The supermunk was a disaster, lost count how many failours i had with fuel vaporisation. As soon as it vaporised you would lean out till you got to the point where it would rich cut & lean cut at the same time very sporting!:eek:

[QDMQDMQDM]

OK for your PA 18-150

Hey! I think some of my flying costs may just have gone down by 20%. And if I get a Safeway 20p off per litre voucher, can I just taxi up to Safeway?
;)

QDM

[wyrmio]

There are severall aircraft which have STC's to run mogas, but the engine manufacturers do not recommend it and neither do the fuel suppliers.

You might just be cynical and think that this is just a way of making more money out of pilots, but the truth is that the fuels are fundamentally different. Mogas is designed to be used on the road and no consideration is given to the requirements of aircraft in its composition, manufacture or handling.

The most obvious difference is the Octane rating. This is actually around 107 MON lean mixture rating for Avgas 100LL, compared to around 85 for the normal unleaded forecourt gasoline. The 95 octane that is often quoted for Mogas is a RON figure and not comparable to the Avgas octane ratings.

Alright, you may have an engine that does not need all of that octane, so why not use Mogas?

Well there are many differences with the fuels, including:

· Increased Ried Vapour Pressure causing greater potential for engine failure through vapour lock.
· Reduced net specific energy of the fuel (less power).
· Increased risk of elastomer swell and softening in fuel system components.
· Some automotive gasoline can contain ether and / or alcohols, which are not permitted for use in Avgas as they can potentially separate out from the fuel.
· Increased incidence of carburettor icing.
· Poor fuel distribution giving the potential of detonation.
· Fuel washing the lubricating oil off the cylinder wall at low temperatures.
· No consideration for aviation in fuel specifications.
· No consistency in the fuel in different seasons and between countries.
· Ability to change the fuel specification without considering the implication for aviation, or informing aviation customers / authorities.
· Poor storage stability when compared to Avgas.
· No control on the storage and handling of the fuel.
· No control on the water content of the fuel.
· Poor filtration requirements when compared to handling Avgas.

The most incidious of this list is vapour pressure. A high vapour pressure fuel will form a stable vapour at lower altitude and / or lower temperature than a low vapour pressure fuel. Vapours forming in the fuel supply pipes can mean vapour lock and fuel starvation.

Add to this that the road fuels change composition between winter and summer, then you really don't know what you are using. The vapour pressure of winter Mogas is high enough to form a stable vapour at around 30 deg C at ground level (less as you climb).

This temperature sounds high for our climate, but tank temperatures of this level are easily achieved by sitting an aircraft in the sun all day - added to this you have the heat from the engine.....

You really do take a risk when using Mogas, you could be lucky, but the truth is that you have to be careful with this - make no mistake, it does kill people.

[QDMQDMQDM]

wyrmio,

And the DISadvantages are...?

;)

QDM

[Mike Cross]

One is that it can kill you.

A friend of mine had an immaculate restored WW2 trainer that he kept on a private strip.

He went to a rally on a nice warm day and there was a bit of a queue to depart so everything was warm, fuel and engine.

Shortly after take-off he lost power over some trees and stalled it in. He was killed, his passenger seriously injured.

The AAIB found he'd got Mogas in the tank. The a/c was not approved for use with Mogas. The conclusion was that he got vapour lock due to warm fuel, a high ambient, and the long wait at the hold raising teh temperature inside the cowling.

Mogas is more volatile than avgas.

Mike

[QNH 1013]

Some years ago our group used to regularly use MOGAS (the old MOGAS) in our A65 engine. The aircraft used to fly ok, but there were frequent problems with sticking valves etc. When the airfield's MOGAS supply shut the group changed to AVGAS exclusively. After a while, it was noticed that all the previous engine problems had disappeared. Guess which fuel has proved the most economical.

However, I know another owner who has been using MOGAS (unleaded) for over six months now in his C90 engine and (so far) he hasn't had any problems. I've never known him fly above a few thousand feet though.

[QDMQDMQDM]

OK. I know when I'm beaten.

(There, that was easy, wasn't it?)

[FlyingForFun]

Before you accept total defeat, QDM, bear in mind that Rotax recommend that their engines be run on MoGas when possilbe. They'll run off of AvGas, for example when high tank temperatures are expected, or when no source of MoGas is available, but the plugs tend to get fouled up by the lead if you use too much AvGas.

But that's not relevant to your Super Cub, which doesn't have a Rotax, so maybe you should admit defeat! :D

FFF
------------

[nonradio]

Never had a problem in any season with leaded or unleaded in an A65 or Rotax 532

[Philip Whiteman]

Wyrmio and mrcross both make sound technical points. However, I worked in the research department of an oil company in the early 1980s, when Dick Stratton was doing a fine--and technically sound--job in demonstrating that, subject to sensible limitations, there was no problem in running mogas in certain glider-towing types.

On a pragmatic level, I have--let's say--a friend who has been running his A-65 on mogas since 1981. This is in a high-winged type, not unlike QDMQDMQDM's usual mount. My friend has not encountered a single problem with this fuel. Indeed, when he changed to mogas, he suffered much less lead fouling with the aviation plugs he used to run. (Avgas left little lead balls behind the electrodes!)

Now I am not suggesting people go out and blindly copy my friend's approach. Not everybody enjoys gravity-feed from high wings (getting around the vapour lock problem). However, avgas has too much lead for engines like the A-65, and aerodrome fuel storage/throughput can, I suspect, be poor enough to allow more water into the fuel than happens at busy--and well-run--garage forecourts.

Now the price differential has been eroded by changes in fuel duty, there is less pressure to substitute on fuel for the other. However, it is not easy for strip flyers pick up a regular supply of avgas. On the technical side, I would suggest that it is horses for courses: the most expensive and highly-regulated answer is not always the right one!

[gasax]

Read the CAA AD and Note 98.

All the isues which people have raised here have all been addresed within that note and the subsequent approvals.

The simple fact is that low compression engines were not designed to run on 100LL and all this stuff about how dangerous Mogas is in comparison conveniently ignores the fact that these engines were not certified to use 100LL.

They were approved on a paperwork basis because it was the only fuel available.

Anyone remember all the issues flying clubs had with O-235s running on 100LL?

Anyone tried running a Gipsy continuously on 100LL?

I have run my all the aircraft I have owned on it (they all fit within the CAA approved list). No problems, no issues.

Follow the steps outlined in the CAA note and enjoy some flexibilty and cost reduction in your choice of fuel.

[Crossedcontrols]

We run our pa18-95 on mogas never had any probs ( touches wood) it's PFA and a C90 Continental. Always generous with the carb heat. They're supposed to be more iffy at higher altitudes, but who goes up there in a Cub?
Sorry it doesn't help your situation but just letting you know that mogas in some engines is not a problem.

CC

PS Can Dakotas run on mogas? ;-)

[A and C]

The last owner of my aircraft used mogas for the cruse and avgas for take off and landing , when I picked the aicraft up from him it had one tank full of mogas.

When in the cruise I switched from the avgas to the mogas the EGT climbed by about 20F ans the RPM droped by about 25 RPM , I have not used mogas since.

[bottieburp]

Hi Gasax,

I operate 2 Gypsy engines (I call them Pykies!) - a 1 and a 10/2.

THe 1 is unmodded apart from the valve seats, the 10/2 has all the mods.

Both purr away happily on 100LL.

In fact I flew behind the 10/2 to Sweden and back in June (see next issue of Plot) - it was sweltering.

THe thought of Mogas over all those lakes and trees is unthinkable.

Stick it in your car - use aeroplane fuel for aeroplanes.

Too many accidents have occurred as a result of vapour lock.

I feel that there are too many people prepared to take short cuts just to save money. At the end of the day, flying costs. I think you will be surprised how many people don't even insure their aircraft for 3rd party risks.

Pay the money, fly safe. If you can't afford it, join a group.

[Aerohack]

Call them 'Pykies' if you must, bottieburp, but never Gypsies. They're Gipsies, even when installed in Miles aircraft!

[wyrmio]

It's a few days since I have been able to log on to PPRuNe, so quite a few replies on this since I last visited !

I just want to clarify a couple of points.
Gasax says, quite correctly that

The simple fact is that low compression engines were not designed to run on 100LL and all this stuff about how dangerous Mogas is in comparison conveniently ignores the fact that these engines were not certified to use 100LL.

Well true, the early engines were not certified on Avgas 100LL as it did not exist at the time. Neither were these engines certified on Mogas. Avgas 100LL is a closer in its properties to the fuels that the early engines were originally certified on in terms of boiling point range and hydrocarbon content. Believe me, I work in this field.

Don't be fooled into thinking that because Mogas is an unleaded fuel of mid 80's MON octane number then this is a close analogue of leaded Avgas 80/87, or even the pre war unleaded Avgas 80; the base fuel composition and properties are quite different.

All of these engines are now certified to run on Avgas 100LL, but only some aircraft carry limited use STC's to use Mogas. The use of Mogas is not approved at all by the engine manufacturers (Rotax aside). This should tell you something.

As I have said in my earlier posting, Notice 98 does put a limitation on altitude and tank temperature for Mogas use, and notice that it is a tank temperature NOT an air temperature.

Think about this for a minute in this scenario.

You fly on a nice summer's day to visit another airfield and leave your aircraft parked outside in the sun. Air temp can be low 20's, but the sun beating down on the tank can easily raise it's temperature significantly above the air temp. You have no way of measuring the tank temperature, so you have to guess you could be OK, but don't know.

What will you do if you suspect that you are near the limit, drain the fuel and replace it? Postone your flight until the next day? Or will you do what most people do, not even realise that it could be a problem and set off for home. The AAIB will investigate the crash and conclude that you were probably outside the guideance of Notice 98 and so the CAA is in the clear. The fault is yours. Notice 98 does not get changed, as there is no need to -you did not observe the restrictions. People will also continue to read notice 98 and assume that, if their aircraft has an STC then they have carte blanche to use Mogas, but they do not.

As has been said before, Avgas is for aircraft, Mogas is for cars. If you use Mogas for aircraft do not think for one minute that it is as safe and controlled as using Avgas.

This brings me on to another point.

Philip Whiteman makes another point.

However, avgas has too much lead for engines like the A-65, and aerodrome fuel storage/throughput can, I suspect, be poor enough to allow more water into the fuel than happens at busy--and well-run--garage forecourts.

Well fair point on the Lead levels for some engines that run notoriously low combustion temps like A series Continentals, but fiitting a hotter plug and doing an engine run up at the end of a flight is normally enough to let the Lead scavenger in Avgas 100LL to do it's job and clear plugs. The run up involves getting to the parking spot, stabalising the CHT and running at 1800 rpm for 20 - 30 seconds before going back to idle and immediately bringing the mixture lever back for a lean cut.
More info on this can be found in Lycoming's excellent "Flyer" publication - advice that transers to the TCM engines just as well.

As for the water issue - I would have to differ with Philip.

There are rules covering the storage and handling of Avgas in a CAA publication called CAP 434. This stipulates not only equipment standards for storage that are beyond those required for storing Mogas, but also that Avgas tank and filter drains must be checked and cleared of water and debris every day, after a bulk fuel receipt and after rain or snow. Not so for Mogas.

There are also filtration requirements. Speaking for Shell supplied Avgas sites, the final filtration before aircraft delivery is a water absorbant filter. This contains media which chemically reacts and traps any water in the fuel and so Shell can, hand on heart, say that the fuel supplied is filtered to 5 microns for particles (human hair is about 20 microns in diameter) and contains less than 10 parts per million of water.
There are no tank draining or sump inspection criteria for Mogas tanks, and neither is there any filtration requirements for the outflow. If you are lucky your local Mogas forcourt may have a plain mesh filter of about 200 microns. If you are lucky.

There are plenty of people who have run for years on Mogas without a problem, but my point is that it is incurring an additional risk that one day might catch up with you. Remember that no public cat aircraft are allowed to use Mogas. Ask yourself why this might be? It is because inflicting this additional risk on the fare paying public has been deemed unacceptable.

My view is that it is unacceptable for me and my loved ones also.

Good luck.

[MLS-12D]

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/certification/engineering/powerplants/mogas.htm

[Croqueteer]

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.

[MLS-12D]

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

[Rod1]

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

[ShyTorque]

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.

[GTOTO]

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.