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  • Technical Chat Tips and Advice, including flying the Luscombe
Technical Chat Tips and Advice, including flying the Luscombe

Moderator: HTB

 #8816  by howell
 Wed Dec 31, 2014 8:18 pm
I would like to run a new theme on Mogas as there are many things changing, mainly the cost of Mogas £1.13 a litre down here in sunny Devon.
I have pasted the post from Pete Bush which was very comprehensive.
Hi Tom,
I have heard a rumour that the LAA are not giving out any more Mogas exemptions at the moment as they are worried about future ethenol content.
If you did want to convert your Luscombe for Mogas use and assuming you have a Stromberg carb, probably the most important part to replace is the float needle valve as the originals have a neoprene tip that can swell in mogas and cause engine failure. Aircraft Spruce/LAS do a stainless needle and seat kit (Pt No 07-14222).
This needle is a relatively straight forward job but the seat can be more difficult, the carb float level has to be set up pretty precisely and obviously a new gasket (07-0220) fitted on completion. The disadvantage with a steel needle is that they don't seal as well as the neoprene item and can let fuel through, this is not a problem when the engine is running or if you are in the habit of turning your fuel off after flight but if you have old and leaky fuel taps then you may have a leaky carb.
You then have to consider every rubber item that the fuel contacts in your aircraft including Gascolator seal, tank caps, rubber hoses ect. Mogas tends to attack the standard aviation AN grade hoses and O rings so a mogas proof alternative has to be fitted. Viton is a relatively new kind of rubber that is mogas and avgas proof, LAS do a Viton seal replacement for the ACS type gascolator, I also replaced the O ring primer seals on G-BROO with Viton items.

The LAA used to do a check list for mogas use that your inspector signs off, I suggest you contact your inspector and/or the LAA before starting work. There is plenty to read on the LAA forum regarding fuel.
 #8817  by howell
 Wed Dec 31, 2014 8:30 pm
From the USA.
Run the ethanol test on all the gas you buy.

DO NOT burn fuel with ethanol in your airplane. Revert to 100LL if ethanol free gasoline cannot be found.
•Ethanol fuels can damage the rubber and aluminum components of your aircraft fuel system.
•Ethanol increases the volatility of fuel.
•Ethanol can absorb significant amounts of water in flight.
•Ethanol may vent off at altitude, reducing both range and octane.
•Ethanol has fewer BTUs than conventional gasoline, which further reduces range.

Ethanol has an affinity for water and can pull moisture from inlet air on humid days to such an extent that the engine may malfunction. Allowing gasoline with ethanol to remain in the airplane for extended periods of time has resulted in the need to replace carburetors, hoses, and gaskets. It has also been reported to clean the interior of fuel tanks, leaving the accumulated sludge in the screen. If you cannot find gasoline that you are certain is ethanol free, you must revert to using avgas.
 #8818  by howell
 Wed Dec 31, 2014 8:49 pm
In recent years, due to pressures from the ‘Green’ lobby to use bio-fuel, some petrol supplied through the forecourts has had varying amounts of alcohol added to it. The proportion of alcohol added is gradually increasing over time and the number of outlets supplying alcohol laced petrol is also increasing. Alcohol in the fuel can damage the rubber components in the fuel system, and also cause problems through progressively absorbing water which can suddenly come out of solution later, flood the water trap and fuel sump and stop the engine in flight.
Cap 747, Section 2, Part 4, General Concession 5 makes it mandatory to check that unleaded Mogas fuel does not contain alcohol before it is used in any group A aeroplane. The test method for detecting alcohol in petrol as described in the CAA Safety Sense leaflet 4b is not sensitive to alcohol levels of 5% or less, the current maximum level likely to be found, therefore a test kit has been developed that enables the detection of alcohol down to around 1%. Alcohol detection test kits are available from Airworld UK Ltd.
 #8819  by howell
 Wed Dec 31, 2014 8:52 pm
With these engines, many of which were originally produced many decades ago, there have been a variety of different valve seat and valve materials used over the years, and there is a possibility that some combinations in the field might suffer problems with valve seat recession if deprived of the dry-lubricating effect of tetraethyl lead in leaded fuels. To guard against this possibility it is recommended that all users of Continental and Lycoming engines cleared for
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unleaded Mogas use should either use a fuel mixture with 10% 100LL in it or run a tankful of 100LL through the engine at least every 75 running hours to lubricate the valves and valve seats.
 #8820  by Nige
 Thu Jan 01, 2015 8:07 am
Thanks Chris,
Some good stuff in there and with the potential savings involved, it's well worth looking into, for some.

Happy New Year to all! :)
 #8823  by Nige
 Thu Jan 01, 2015 12:59 pm
Lots of interesting stuff here but I'm worried we're getting a little too nervous (bogged down?) running our machines on Mogas..
I'm finding few instances of hard evidence of Mogas being the main culprit of serviceability problems on our Luscombes and Contintentals in general.. :scratch: I also notice that safety leaflet 4b is no longer in use. If one looks at the LAA website it refers to a blank safety leaflet!
I'd be grateful, therefore, feedback from anyone who has had Mogas related problems either in the air, on the ground or as result of a discovery within the a/c's maintainance. I believe there are instances where pipes/seals didn't meet the correct specs, often accentuated by old parts that should of been replaced?
Nevertheless, it's still an area that should be approached sensibly and with correct advice. Any feedback with problems please?
 #8824  by Steve Martin
 Thu Jan 01, 2015 6:09 pm
Re: Empty weight
Postby Steve Martin » Thu Jan 01, 2015 10:26 am

A Happy New Year to everyone !

If your aircraft logs do not show that your aircraft is signed off for mogas then first step is to talk with your inspector and see what he/she requires for you to get the sign off.

Also you could get the very reasonably priced test kit from Pete Smoothy at Airworld UK Ltd. I have tested our fuel from a number of stations locally to me and some give ethenal readings and some dont. The higher octane stuff tends not too. You need to keep testing (if you are that way inclined) as fuel supplies vary.

You might give up the will to live after awhile and just fly ! :lol:
M 07775712466
 #8825  by Steve Martin
 Thu Jan 01, 2015 6:21 pm
Nige, a few years ago I had to replace hoses on TE in the cockpit footwell as they had become very brittle and were potentially dangerous. This was probably caused by the use of Mogas and also because these hoses had not been replaced every 4-5 yrs as recommended. Use of a completely metal fuel pipe system will help to get the sign off.

I have not heard of any carb problems caused by the use of Mogas, even though some maintenance organisations infer that the jets may get blocked. (ref: past Luscombe Association article).
 #8826  by Vic
 Thu Jan 01, 2015 7:19 pm
I've had some major problems with Petrol powered strimmers, chainsaws and hedge cutters through running on Tesco unleaded with whatever additives they choose to add depending on the time of year! Fuel lines go brittle, rubber gaskets deform and also a white stringy sludge builds up if left for any length of time.

I also had a problem with my MGB where it would would only rev up to about half what it should. I found this to be jelly like sludge in the float bowls and brittle pipe to the main jet.

This stuff grows in the fuel unbelievably and I know of a case where a Europa aircraft force landed due to a blocked fuel filter which on closer inspection had algae growing in it !!!!

I use the BP fuel for everything now despite the 10 or 20p / litre extra

I had my Luscombe signed off a year ago and run on BP Ultimate ever since with no problems. I've been using mogas for about 20 years in various aircraft and no problems

Happy New year to all! :lol:
 #8832  by Rob
 Wed Jan 07, 2015 7:15 pm
I am very, very picky when it comes to fuel. I pre-mix my fuel 25% 100 LL with 75% MoGas. This gives exactly the same lead content as the engine was designed for. (80 grade fuel contained a quarter of the lead 100LL does now).

ALL my fuel goes through a MrFunnel strainer before it goes into my tank with the exception of one trusted 100 LL supplier. The mr Funnel strainer takes out the debris/sludge and water with a 50 micron filter. You can google and will find it. On my past annual of course I opened the carburator screen and took apart the gascolator. A bloody waste of time which I will mandatory repeat every year: because of Mr Funnel there was absolutely nothing there!

Be especialy weary when using containers without Mr Funnel. We had an engine stoppage because of this.

I do an alcohol test (Petersen) before every MoGas purchase. Never, ever, trust a source. There is simply no control over their supply chain like with aviation fuel. I got my MoGas from the same source for a long time. Each time it checked out zero on the Petersen tester. So I got lazy and just bought it. I couldn't get myself to pour it in the Luscombe though and did the check anyway just before refueling. Guess what 5%!

BTW Petersen also advises on an alternative testing method which I have yet to try. He advised me to buy water based soluble food colour drops. Shake and if it mixing with the fuel you got ethanol and your fuel will change colour.

Best regards,

Rob den Hartog
 #8833  by howell
 Wed Jan 07, 2015 7:45 pm
Very interesting Rob, we are not clear here in the UK if its legal to use Mogas with Ethanol in.
Here in the West of England we can no longer purchase Mogas ethanol free, best we can get is 5%.
Chris G-SAGE Luscombe 8A.
 #8839  by howell
 Mon Jan 12, 2015 10:20 pm
From the LAA Forum thread on Mogas.

LAA FoAs far as I am aware, NO! I think the CAA's announcement meant that they no longer object to the use of ethanol laced fuel in principle as long as 1/ your aircraft manufacturer, 2/ your engine manufacturer and 3/ your aircraft regulatory body (the LAA) don't mind either.
As far as I am aware the LAA have NOT yet approved the use of ethanol fuel in any of their aircraft. They made an announcement last year effectively saying that the CAA's announcement gave them the green light to go ahead and look into it and conduct tests with a view to possibly approving it in the future. So at least the LAA can now make their minds up without being hampered by CAA policy.
In my personal case, even if the LAA do give it the green light in the future, I do know that Rotax already approves the 912 to use it but I don't yet know about the position of Europa with regards to ethanol.
This is a link to the announcement that the LAA made following the CAA announcement; I'm not aware of any further progress on it from the LAA yet. ... mogas.html

I apologise if any of the above is wrong, misleading or out of date - it's just how I think the situation is from what I've read over the months!rum has a thread on Mogas with Ethonal.
 #8840  by howell
 Mon Jan 12, 2015 10:22 pm
Brian Hope replied today and there maybe some news in the next issues of the LAA Magazine.

Re: Mogas

Postby Brian Hope » Mon Jan 12, 2015 4:09 pm

Jonathan is correct, this notice from CAA does not mean we can start using mogas with ethanol in aircraft cleared for plain old, common or garden but sadly no longer easy to obtain unleaded mogas. I have asked Francis about it and he has been doing some work on the criteria for aircraft to use mogas with 5% ethanol. I hope we might be able to put something in the next magazine that better explains the situation.
 #8843  by Nige
 Tue Jan 13, 2015 8:33 am
Thanks Chris.
Let's see what developes. As Vic says, it looks like BP 97 is a 'safer' bet. VPower (shell) may well also work - my old motorbikes certainly like it! Pinking disapeared and long term storage much less of an issue. :) similar technology! :shock:
 #8849  by Vic
 Thu Jan 15, 2015 8:15 am
In some parts of the country, BP has ethanol in it, just not here, fortunately for me. The Shell V power near me does have ethanol. Pity it isn't like food packaging where the contents has to be listed. Petrol - Mogas- can be any old cocktail :scratch: