M

morganjp

Well Known Member
I was at a fly-in pancake breakfast yesterday talking about high gas prices with a RV-4 driver. He has a carburated O-320 and says he routinely flies with 100LL in one wing tank and mogas with ethanol in the other. He takes off and lands on 100LL and flies most of his flights on the tank with the mogas. Then as the plane sits between flights the seals etc are soaked in 100LL. He does not mix the 2 fuels. He says he has had no issues with doing this.

Any of you engine experts care to comment on this. Just curious as to the possibilities of doing any damage with this method of lowering flying costs.


John Morgan
 
No engine expert here, but I've been using a similar technique for 5 years and 900 hours; it's not exclusive mogas in one tank, but I'll add 5-10-15 gals of 91-93 oct mogas to one tank and top it with 100LL, so it's a mix, while the other tank is pure 100LL. No issues (yet) with almost 1000 gallons of ethanol mogas used. Of course I'd prefer to use non-ethanol stuff, but here in the Houston area, that ain't happening. Engine is a carbureted O-360-A1D.
 
Mogas E10

Lots of RVs fly this way.
Mogas in one tank and 100LL in the other.
Although I primarily use mogas for cruise, I continue testing for take off
performance on mogas. My goal is to take off and continue Vy climb on a day with 100F OAT and a heat soaked engine to verify my fuel system is vapor lock proof. All of my fuel system components are approved for ethanol except the mechanical fuel pump. This is why I let the aircraft sit in avgas between flights.
Most of my flying is within 2 hours of my home field and I use very little avgas and just keep filling the right tank with 91 octane mogas. Away from home it's
Avgas, because that's all there is available at airports.
The engine runs very well on mogas and probably cleaner and greener than leaded avgas.
 
I have not used 100ll (except for the odd cross country fillup) in over 400 hours.

i use premium mogas with ethanol.

You have to be careful though. The current thinking is the mechanical fuel pump diaphram will not withstand ethanol. Carb seals are questionable as well. need to make sure your fuel lines (if made of rubber are ethanol compliant)

I run two electric fuel pumps (no mechanical pump) and fuel injection which is ethanol compliant.

The engine doesn't care, it runs just fine. The only thing is that it will take about 0.5GPH more to make the same airspeed at cruise as it will when running non ethanol mogas or 100LL.

Mogas is likely to hav a higher vapour pressure than 100LL so vapour lock is more likely.

Much has been written in the forums on the subject I suggest you search the archives.

Frank

7a io360
 
I would not tell anyone to actually act based on internet advice, but I would suggest that you call the current owner of the rights to the mechanical fuel pump & carburetor. I did, & got a very clear and logical explanation of both the risks and possibilities/benefits of alcohol laced mogas, & what can be done to make it work.

Make the call; I think that you'll be pleased.

Charlie
(the biggest issue is the tank sealant supplied with older kits)
 
Charlie,
you are killing me, why the secrecy?

Who is the owner of the rights to the fuel pump and what is his number?
I'd love to talk to him.

I agree with your advice though, if you are going to burn mogas do your homework.
 
The engine does not care one bit - it's the rest of the fuel system you need to think about. Natural rubber components (seals/O-rings/hoses/bladders) do not like ethanol. Switch them to Viton/Teflon, and proceed to proceed. Think about it from the fill nozzle to the intake valve - anything not made of metal needs a good inspection and possible material change.
 
100LL-MOGAS POSSIBILITY

While Lycoming will not vouch for the mechanical fuel pumps ability to withstand ethanol gas, the same pump part number is used in Brazil where the fuel is 89% ethanol! But the bigger issue is the higher vapor pressure of the autogas (and different seasonal blends) AND this pump 'Sucking' the fuel from the tanks. Move the pump closer to the fuel supply, where it's always in wet, cool fuel, and 99% of all issues go away...
This is what the auto industry has done; this is what we need to do..... But if you're going to rely on an electric pump to keep the prop turning, be sure that you have redundant pump capability, and redundant electrical supply to those pumps.....
After a lot of experimenting with autogas, I'm installing a redundent electrical pump system (inside the cabin after the fuel selector) and removing the mechanical engine fuel pump.


frankh said:
I have not used 100ll (except for the odd cross country fillup) in over 400 hours.

i use premium mogas with ethanol.

You have to be careful though. The current thinking is the mechanical fuel pump diaphram will not withstand ethanol. Carb seals are questionable as well. need to make sure your fuel lines (if made of rubber are ethanol compliant)

I run two electric fuel pumps (no mechanical pump) and fuel injection which is ethanol compliant.

The engine doesn't care, it runs just fine. The only thing is that it will take about 0.5GPH more to make the same airspeed at cruise as it will when running non ethanol mogas or 100LL.

Mogas is likely to hav a higher vapour pressure than 100LL so vapour lock is more likely.

Much has been written in the forums on the subject I suggest you search the archives.

Frank

7a io360
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