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Technical Chat Tips and Advice, including flying the Luscombe

Moderator: HTB

 #3077  by Tom
 Wed Dec 17, 2008 8:49 pm
Hi All

Now that i have finally started to do some flying, and the fact Avgas is £1.65 ish up here at the moment, i am considering using Mogas to keep costs down.

Does anyone have any technical tips, ie carb mods etc or other info regarding operating C85 on Mogas?



 #3079  by Pete Bush
 Wed Dec 17, 2008 11:22 pm
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.

Realy good to see your Luscombe in the air again, you have both done a fantastic job.

Pete (G-BROO)

 #3082  by Tom
 Thu Dec 18, 2008 7:58 pm
Thanks Pete/Callum

Some good info thanks. I must admit there is more to it than i first thought :?

I Will speak to my inspector first,


 #3092  by Phil Laycock
 Sun Dec 21, 2008 8:49 pm
Hi Tom

Some good advice there from Pete.

We run 'MI at about 90 to 95 % of the time on regular forecourt Mogas. ( only uplift Avgas when there is no alternative )

The thing to remember is to use the fuel as soon as you buy it...... ie don't store it . Of course unless you drain down the tanks after each flight then there will always be an amount which gets stored in the aircraft, but with careful planning and importantly, regular aircraft use can nullify this.

We had a time when we were operating on 100LL Avgas exclusively...... and had lots of rough running and a occasion of the engine stopping on the landing roll-out ......all caused by plug fouling by globules of lead. Proper cleaning of the plugs and switch to the more Continental friendly Mogas and no re-occurance since.

Another thing to remember is the fuel temperature limitation................ (less of a problem in your northern latitudes :lol: :lol: ) and seeing as you have dark coloured wings / tanks. A good compromise in this case ( if we ever get some decent summer weather ) here would be a policy of one tank with Avgas for TO / Circuit / Landing and the other with Mogas in for the cruise.

Regards Phil

 #3096  by Rob Dyer
 Mon Dec 22, 2008 1:40 pm
Hi all,

I have used a little bit of Mogas recently (never more than 25%).

Had no problems at all, but would like to change my hoses etc. or at least verify they are correct.

From talks with LAA, I get the impression that they are happy with Luscombes running on it, but each plane needs an individual sign off. This was recently (2 months ago) not possible due to their embargo caused by Ethanol. The words I heard was - 'well others use it and the single plane sign off (as opposed to CAA type sign-off) has never been tested in court, so...'

I for one am not sure of my ground here, so if anyone has info on the seals in the carbs and hoses, would appreciate to hear it.


I have also posted a query on the Yahoo site in the US (Doug Combs). That may help. My personal belief is that less than 25% should not be a problem in regards to ethanol or hose degradiation and I have a theory based on the CAA leaflets that they consider that if you use less than 50% Mogas then you are not running on Mogas anyway... This is based on a sentence where it says aircraft using more than 50% mogas are considered to be running totally on Mogas. PLEASE NOTE - just my assumptions here! I may be wrong hence asking Doug Combs and posting this.

Nice flights at the weekend, blimin windy though, landing was about 100 foot I think.

 #3097  by Rob Dyer
 Mon Dec 22, 2008 1:45 pm
Actually just read your message Pete...

So that is where I got the needle bit from...

Not sure if that applies to the Marvel carb, will have to study some more and just put up with visits to airfields with cans in car for now...

 #3098  by dmcneil
 Mon Dec 22, 2008 6:18 pm
Hi All,

There is quite a bit of information on auto fuels (no-lead) available here in the US. I must plead complete ignorance of your regulations regarding the use of auto fuels in your Luscombes. Here we need a Supplemental Type Certificate (STC) to use auto fuel. Two organizations supply those STC's and I've included their websites below. Both organizations sell the respective STCs for a reasonable price. The Petersen Aviation website has a huge amount of information regarding the use of auto fuels and will most likely answer whatever questions you may have. The EAA website is also quite informative. Here are those links...

Petersen Aviation:

EAA Auto Fuels:

In general, no mods are needed to the aircraft. Here in the States, all hoses and fuel system parts remain unchanged. The only caveat, and it's a very important one, is not to use auto fuels if your fuel tank has ever had sloshing compound applied. Many people have reported auto fuels attacking the sloshing compounds. There are sloshing compounds that are resistant to auto fuel but extreme caution is advised before using auto fuel in a previously sloshed tank. And auto fuel that contains alcohol is definitely not allowed!

As Pete Bush mentioned already, the early Stromberg carbs had a Neoprene tipped steel float needle. It was designed to stop the leaks associated with the even earlier all steel needle. It did stop those leaks but later replacement Neoprene needles had quality problems and could swell. Not good. Most needles have been changed out by now (either all steel or newer Delrin needles will work with auto fuel) but the occasional Neoprene tipped needle does turn up. It's worth checking to be sure your needle is not the Neoprene type if you're going to burn auto fuel. The Marvel-Schebler carb has always used an all steel needle.

I would highly recommend reviewing the Petersen website as it really is a fine source of information on the use of auto fuel. Lots of folks here use auto fuel in all kinds of airplanes with no problems. The biggest hassles seem to be hauling the fuel to your airplane as almost no airports have auto fuel pumps...


 #3099  by Tom
 Mon Dec 22, 2008 10:11 pm
Thanks Guys

Some good information there!! I like the idea of one tank for each Phil!!
Not sure what you mean about the weather up here though? :D

 #3100  by Nige
 Tue Dec 23, 2008 12:40 am
I believe, Tom, Phil is refering to the fact we in the Uk live in cool, temperate Latitudes, where Mogas, when operated on 'hot' days{+25c}'may' produce vapour lock, temporarily starving the engine of fuel.

This is very rare in our climate!! However, I believe Alchohol is now a worrying factor in Mogas and the LAA have expressed that concern over the last year. I think keeping the mix 60/40{for those fortunate to have 2 tanks may{?} be the answer.. There doesn't, apart from the 50% criteria, seem to be a difintive answer. May be not such a bad thing.

Please correct me if I'm wrong.


 #3105  by Phil Laycock
 Tue Dec 23, 2008 9:04 pm
You're right Nige, about the vapour lock situation.

It is 20 deg C that you have to remember ( not 25 deg C )

But it is not the OAT thats important , it is the temperature of the fuel you need to be aware of................ a dark coloured tank sitting in the sun all day can absorb a great deal of heat, which results in a fuel temperature significantly higher than the OAT.......So a bright sunny day with temp hovering around, say +18 could result in your tank temperature of + 24 or more.


Conversely , you can use freshly obtained forecourt fuel on a +30 deg C day which because it comes from underground tanks is quite a bit cooler.....around +12 ( when I've checked it ), so long as you uplift it and use it before it has a chance of warming up significantly........
(Yes, I know that north of Watford ,plus 30 days are unheard of :wink:, so it wont be a concern ! )
The temperature within the tank could also vary ........near the top with the warmed up metal exposed to the sun is always going to be more than the lower surfaces where fuel is drawn from

The LAA have withdrawn their info about all this due to the Alcohol / Ethanol issue but I think it was almost a direct copy of the Airworthiness Notice 98 which is still available from the CAA. This is applicable for the poor souls who operate on a C. of A .
AWN 98A listed the limitataions, and AWN98 C ammended these for the use of Unleaded.

There is also the Pressure altitude limit of 6000 feet which again is a attempt to prevent occurances vapour locking.
Both limits are pretty conservative and probably a result of "one size fits all " approach .

rgds Phil ( currently looking at Solar hot water heating systems for the house ! )

 #3108  by rv8or
 Wed Dec 24, 2008 2:32 pm

As one of the two original owners of Kilo Bravo in the UK I would not use mogas as this is what we found when we tried it.
We could get the engine to run but not reliably, on opening the throttle the engine would cut. We could only open it up very slowly and I mean very slowly. That was with a completely overhauled carb. I then gave up and went and consulted the local aircraft engineer and described the symtoms. He he look at me, grinned, said run it on avgas and the problem would go away. He gave me that answer yet I had not told him that I was trying to run on mogas, as it was not approved at the time. We then only ran it on avgas from then on and never had another problem.

I also had a bad experience running an auster on mogas as well.

If I remember KB was 3.8 gas/hr at an economy cruise and 4.2 at a faster get there pace. If you are worried about the extra cost at these burn rates do a couple of hours overtime or better still get your partner to work a couple of hours overtime.

I hope you enjoy KB as much as I did.

p.s. Phil / Lorraine
We will have to met up at some time during the summer.

 #3109  by Nige
 Wed Dec 24, 2008 5:22 pm
As a 100% Avgas operator on Brug I'm intrigued to hear from others who may have experienced problems or, indeed, never suffered a 'glitch' regarding mogas.

I suspect, having met with a few 'users', there are quite a few of us using the juice?


 #3117  by Steve Martin
 Fri Dec 26, 2008 11:10 am
We flew a group aircraft, Lycoming engined mainly on MOGAS for some 5 years with no difficulties. We did ensure the fuel/wing tanks were cool during hot summer ops and if we couldnt cool them we didnt fly. We stored MOGAS in jerry cans in the shady areas of the hangar away from walls that would be heated up by the sun.

I ran "TE" on a mix of MOGAS/100LL (with PFA authorisation) for 2yrs with an A65 engine with no problems(MS carb), but I was always a bit worried about flying on hot days & leaving the aircraft out in the sun before flying back from a destination. Now with a C90 engine installed & stromberg carb (with steel needle) I use 100LL ...the plugs however do clog up surprisingly quickly with carbon deposits. Tried to get MOGAS authorisation earlier this year from LAA, but they were reluctant to issue the paperwork to do this because of the ethanol issue.
Last edited by Steve Martin on Fri Dec 26, 2008 3:03 pm, edited 1 time in total.
 #3120  by Nige
 Fri Dec 26, 2008 2:46 pm
Interesting Steve.

The down side to Avgas{Does it happen with Mogas incidently?} is this 'low lead'{:?: } issue that produces globules of lead balls.. After fitting new plugs to Brug, I was picking out lead balls within 25 hours! - Although I've never suffered a misfire due this problem, I think regular cleaning of the Plugs is the answer. Has anyone else suffered from misfires due to lead build up?

The price of fuel is, at long last, coming down, will this change people's refueling habits?