Mogas STC & Radial Engines
GLK
My mechanic is against using an automotive fuel and avgas (75/25) combo
on our P&W R-985s. But there is an mogas STC for these engines, and the
mixture would have approx. the same lead content as the 80 octane fuel the
engine were designed to fly with. However there are additives and such in
automotive fuel not present in avgas; the question is whether they are
harmful to the engine, accessories,
hoses or fuel lines.
Any input would be helpful, especially if you've used mogas on radials.
N329DF
We have used mogas in a P&W R-1340 on a T-6, with no problems. The problems
with mogas is that they in some markets, add additive to make it burn cleaner
and that fuel is not allowed by the STC. If you fly your plane enough that the
fuel is not sitting in the tanks for any length of time there will be no
problems, however if your plane sits too long with a tank of mogas it will
start to break down and start to varnish up your fuel system If you are going
to park the plane any length of time make sure you have it filled with Avgas.
Matt Gunsch, A&P, IA
EAA Warbirds of America, GWRRA
Head Crew Chief of the Cactus Squadron Flight Team,
Flying the North American T-6 Texan
owning and Flying a Dragonfly Tri-Gear
Piper Colt project underway
CD195
In reference to your question about mogas and radial engines. I am an A&P, and
have owned a Cessna 195 with a Jacobs 275 radial engine for 22 years. The
engine has a 6.5-to-1 compression ratio and was designed to run on 80 octane
avgas. I have used 100LL with TCP additive religiously since I got the plane
and have never had a problem with either valves or spark plugs. I just ran out
the original engine (that is, the one on the plane when I bought it) last year
and installed a new one. In my opinion (and it's just my opinion, I've not
done a study or accumulated any comparative data) the best way to treat these
old engines is to use an aviation fuel, then adjust the lead burden with TCP.
The additive is approved by the FAA, and a long term study was done at Embry
Riddle which proved its worth. I never use Marvel Mystery Oil nor any other
additive not FAA approved. I do use AvBlend, though I started that recently
and can't tell yet one way or the other whether it will help. We'll see how
this second engine holds up.
Unfortunately, I don't think there's been any definitive study done on this
issue, so most of the advice we get is, like this, anecdotal. I did have many
years of completely reliable service from my first engine. Never stumbled in
flight, ever.
Good luck
Carlos Diaz (CD...@aol.com)
Orval R. Fairbairn
In article <199806070320...@ladder03.news.aol.com>,
cd...@aol.com (CD195) wrote:
I have been using unleaded regular (with the Petersen STC) in my O-435-1
Lycoming for 15 years and 850 hr. I had to pull two cylinders for cracking
at 650 hr and found no wwear and no valve erosion. The stuff is better for
your engine than 100 LL because it doesn't have lead scavengers (which
contain Bromine, which, in turn can form bromic acid) to get into the oil.
In the e3arly 1950's, there was an inleaded 80 octane available and certified.
Both MTBE and ETBE are allowable under both EAA and Petersen STC's.
IMHO, all the talk against mogas is "old mechanics' tales," spread by
FBO's with an interest in selling avgas at $2+ per gallon.
--
To e-mail me remove "o_" from my address
Board member, Ca Pilots' Assn, CRAMP,
EAA Life member
Johnson Rocket Restoration Flying
Mustang IIR under construction
Lar Kaufman
In article <o_orval.fairbairn...@129.197.32.109>,
Orval R. Fairbairn <o_orval....@lmco.com> wrote:
>In article <199806070320...@ladder03.news.aol.com>,
>cd...@aol.com (CD195) wrote:
>> Unfortunately, I don't think there's been any definitive study done on this
>> issue, so most of the advice we get is, like this, anecdotal. I did have many
>> years of completely reliable service from my first engine. Never stumbled in
>> flight, ever.
>> Good luck
>
>I have been using unleaded regular (with the Petersen STC) in my O-435-1
>Lycoming for 15 years and 850 hr. I had to pull two cylinders for cracking
>at 650 hr and found no wwear and no valve erosion. The stuff is better for
>your engine than 100 LL because it doesn't have lead scavengers (which
>contain Bromine, which, in turn can form bromic acid) to get into the oil.
>
>In the e3arly 1950's, there was an inleaded 80 octane available and certified.
>
>Both MTBE and ETBE are allowable under both EAA and Petersen STC's.
>
>IMHO, all the talk against mogas is "old mechanics' tales," spread by
>FBO's with an interest in selling avgas at $2+ per gallon.
Unfortunately, automotive blends can affect things besides the engines
themselves, so you should think carefully about your intended use. I know
from experiments I conducted in the 70s that some automotive additives
(alcohols and light esters, for example) could affect other components.
I induced clouding of tubing used for visual checking of fuel level and
an apparent hardening of a plastic carbureter float in my tests. No actual
failure was induced, but I switched to a different tubing material as
a result of my tests. Couldn't do anything about the carbureter float
issue, though. Sorry, can't recall the aircraft I was testing this for,
probably an Aeronca (this was in context of a maintenance training
facility, so there were lots of possible aircraft) and I suspect that the
specific carb is no longer in common use, either...
Point is, damage to the engine is not the only risk. I know of a homebuilt
whose fuel tank's "slosh-sealant" coating began to bubble and detach after
the pilot switched to autogas, necessitating complete reworking of the
fuel cell. You should also be aware of risks that a service station operator
can substitute off-brand fuels for the fuels they claim to use--even where
the practice is forbidden by law, as a case here in Massachusetts underscores.
So your entire fuel system as well as the engine should be known to be safe
with (at least) all approved automotive fuel additives as well as those that
the producer acknowledges are used.
Prudent care.
-lar
--
While they endure we must note their locations, elevate our gaze above the
level of our immediate concerns, imbibe the sweet air and perfect promise: the
egg miraculous upon the ledge, the bird compact upon the egg, its generous
warmth, its enviable patience, its natural fortitude and grace. - E.B. White
Gary Hillman
Several years ago I worked for a flying school where a customer brought in
Cessna 182 because the engine would quit if her tried clibing higher than
5000'. VAPOR LOCK was the problem. Years later I have learned several things
about MoGas.
1) The Reid Vapor Pressure in auto fuel is at least twice that of avgas,
meaning it will vapor lock more readily. It is more suseptible to carburator
ice.
2) Auto fuel will decay if left in a tank too long. It does not store well
and will gum up the fuel system. Those of us that use motor boats for three
months of summer and snow machines for 5 months of the winter know all too
well that fresh fuel is necessary to get things going at the beginning of the
season.
3) Likewise, the fuel companies will change the formulation of their product
according to the seasonal requirments. Winter fuel is made different than
summer fuel so there is little consitancy in the auto fuel product.
4) Don't be misled by octane rating comparisons. The process used to
identify ground based octanes in auto fuel is different than the octanes
identified in avgas.
I'm not saying not to use mogas, just be aware of the drawbacks and pitfalls
of its use. Watch screens and sumps for the first signs of seal or gasket
deterioration.
Happy Flying
Gary
Ron Natalie
I saw an odd mogas thing the other day. I was talking to a
guy who lives on an airfield. He's got a plastic gas can
that he uses to fill his golf cart with. The thing has a
yellow spout that inverts and gets stored inside the can.
With one recent filling of gas, the spout switched from
being yellow in color to olive drab. Nobodly on the
airfield seems to know what to make of this.
Talbot Ridgway
In article <357D4BC6...@sensor.com> Ron Natalie <r...@sensor.com> writes:
>From: Ron Natalie <r...@sensor.com>
>Subject: Re: Mogas STC & Radial Engines
>Date: Tue, 09 Jun 1998 10:50:46 -0400
_______________________________________________________
Dear Ron;
What is plastic made out of? Petroleum! Color was not stable,
some sun fade is possible. Makes for a custom fuel blend called
"Mellow Yellow" Advice:
Buy better quality Chinese gas cans. Not a problem really.
TV
Talbot V. Ridgway
Irvington Booknook
2825 N.E. 16th AVE.
Portland, Oregon 97212
Telephone 503-284-3051
FAX 503-284-2518
E-Mail tal...@teleport.com
Ron Natalie
Talbot Ridgway wrote:
>
> Dear Ron;
> What is plastic made out of? Petroleum! Color was not stable,
> some sun fade is possible. Makes for a custom fuel blend called
> "Mellow Yellow" Advice:
> Buy better quality Chinese gas cans. Not a problem really.
I didn't say it was a problem. It wasn't sun that changed
the color. We were just curious as to why, after a couple
of years, one batch of gas changed the plastic color. For
all we know it may have been a difference in whatever they
use to dye the gasoline. Was just looking to see if any
body could explain this curiousity.
I try not to buy anything made from the PRC, regardless
of quality.
Orval R. Fairbairn
> Several years ago I worked for a flying school where a customer brought in
> Cessna 182 because the engine would quit if her tried clibing higher than
> 5000'. VAPOR LOCK was the problem. Years later I have learned several things
> about MoGas.
Another possibility is that the fuel filter became clogged. I had this on
my electric fuel pump filter (porous material). It went away when I
switched to the later fine-screen design). This is with a Facet pump. When
you have a fuel pressure guage, pay attention to it! Deviations from
normal indicate that something is wrong.
> 1) The Reid Vapor Pressure in auto fuel is at least twice that of avgas,
> meaning it will vapor lock more readily. It is more suseptible to carburator
> ice.
Not according to EAA data. Mogas USED to have higher RVP but , because of
emissions regs, it no longer does.
> 2) Auto fuel will decay if left in a tank too long. It does not store well
> and will gum up the fuel system. Those of us that use motor boats for three
> months of summer and snow machines for 5 months of the winter know all too
> well that fresh fuel is necessary to get things going at the beginning of the
> season.
True. The solution is to keep flying, which you can do when the fuel costs
half what avgas costs.
> 3) Likewise, the fuel companies will change the formulation of their product
> according to the seasonal requirments. Winter fuel is made different than
> summer fuel so there is little consitancy in the auto fuel product.
As long as it matches ASTM spec, it is OK.
> 4) Don't be misled by octane rating comparisons. The process used to
> identify ground based octanes in auto fuel is different than the octanes
> identified in avgas.
> I'm not saying not to use mogas, just be aware of the drawbacks and pitfalls
> of its use. Watch screens and sumps for the first signs of seal or gasket
> deterioration.
> Happy Flying
> Gary
>
--