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GROB 109 MOGAS issue - TMGA :: Knowledgebase - Touring MotorGliders
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GROB 109 MOGAS issue

Article ID: 568
Last updated: 12 Jul, 2012
Revision: 2
Views: 9978
Posted: 12 Jul, 2012
by Knapp P.
Updated: 12 Jul, 2012
by Knapp P.

Abstract:    Probably the issue of going away from AVGAS has been debated before - and hence, I'm looking for a summary of that.

Subject: GROB 109 MOGAS issue
From: "johnheeboll" <jh@yahoo.com>
Date: 11/29/11 2:39 AM
To: G109_Pilots@yahoogroups.com

Hi all
I'm new to this group - Danish co-owner of a G109, stationned North Zealand, some 35 km NW of Copenhagen. We use AVGAS, but we consider going to MOGAS.

Probably the issue of going away from AVGAS has been debated before - and hence, I'm looking for a summary of that.

GROB has this to say about the issue of alcohol in MOGAS:
"The G109B with unleaded fuel requires at least 96 Octane,

this means, that (at least in Germany) you'll need SUPER + fuel which comes without ethanol.

So the 10% alcohol addition should not really affect the G109B"

On top of that, a Service Bulletin 817-46 describes details in converting from AVGAS to MOGAS.

As I see it, 96+ octane "super" unleaded MOGAs is a safe solution - as long as alcohol is not added.

Any comments to that?

Subject: Re: GROB 109 MOGAS issue
From: "williamberson" <whodunit@yahoo.com>
Date: 11/29/11 2:49 PM
To: G109_Pilots@yahoogroups.com

I would not use any alcohol in an aircraft. The Grob manual says to avoid fuel additives. My chainsaw won't run with 10% ethanol.

Subject: Re: [G109_Pilots] Re: GROB 109 MOGAS issue
From: lyonbyte@yahoo.com
Date: 11/29/11 5:24 PM
To: G109_Pilots@yahoogroups.com

We have been using 93 octane super unleaded for the last three years in our 109B. We fly out of a small airport in Hawaii and really don't have much of a choice. When we first brought the plane to Hawaii, we did initially use AVGAS 100LL. We had more spark plug fowling with the avgas than with the 10% ethanol super unleaded. We did the same inquiry that you are doing now and we thought we would give it a try. If I could get mogas without ethanol, I would, but we cant get it in Hawaii without a lot of effort.

That being said, we do follow a strict policy of only buying enough gas for the flights planned, we only buy what we need. We do not store it. Gas with ethanol cannot be stored for very long. Given that our aircraft is flown just about everyday, we are constantly using it up. If you think you may let the plane sit for long stretches between flights, then I would think twice about it. We have put about 1500 hrs on the engine using this policy/mogas and have done 1 full overhaul and have seen no ill effects. We regularly fly over open ocean and if we thought we couldn't trust the engine/mogas, believe me, we wouldn't do it!! The tiger sharks are very big in these parts.
Good Luck

Subject: Re: [G109_Pilots] Re: GROB 109 MOGAS issue
From: Christian Mies
Date: 12/1/11 7:12 AM
To: G109_Pilots@yahoogroups.com

Looking at the fuel tubing in the fuselage I would not recommend the use of fuel with more than 1% alcohol. The tubes might be solved by the alcohol, resulting in clogges fuel lines or carburetors.
Another aspect to think about is the higher tendency to vapor locking using alcohol containing fuel.
For these reasons we are only using premium super+ fuels (called "ultimate" in germany; contains no alcohol), aviation mogas or 100LL in our 109b as well as in our SF25.

Just my thoughts ...


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