MoGas Long Term Test: 5000 gallons and counting...

: The autogas STC is undoubtedly the best thing that has ever happened to
: aircraft owners. If you've got the STC, but aren't using it, you are
: literally flushing thousands of dollars down the toilet.
: --

I agree on that. I will add one more datapoint to the mix here. We put the
Petersen high-compression autogas STC on our Cherokee-180 (requires 91 A.K.I or
better) about two years ago. Due to the difference in fuel ratings, I was concerned
about detonation margin. We've got 93 A.K.I pump-gas here, which is what I use.
Basically, that means the motor octane is probably about 88... less than the 91 the
O-360-A3A was type-certificated at.

I generally run at least 20% 100LL on the takeoff (right) tank, and 100% autogas on
the left for local cruises. I've done enough local flying with long climbs, hot
takeoffs, different mixtures, etc and haven't noticed any ill effects. I'm sure that
you cannot forget to enrichen at *all* when operating on mogas, but I haven't had any
issues. For the record, Petersen said when they did the vapor lock/detonation testing
(in some ridiculously hot desert place at 100+ degrees IIRC), they couldn't get it to
detonate on 89 mid-grade either. The FAA guys insisted on a little "safety-margin"
and made it 91.

On thing I did (rather accidentally) find out about that initially disturbed
me. I shut down the engine with the mags after a flight (I just had to jump out and
get something from my car and didn't want to have to prime it to start). It *almost*
died, but started to diesel at a ridiculously low RPM (100 or so). Dieseling =
preignition = BAD... BUT, the big problems are these:

- Extremely low RPM makes for a *LONG TIME* (20x that of takeoff time) that the
mixture is in the hot cylinders. It's got extra time to decide to light off.
- Extremely low RPM makes even the idle throttle setting "full-throttle." The MP
gauge said basically atmospheric (26-28"), even at idle setting of the throttle. Each
cylinder gets a full-throttle gulp of mixture then which can slow-bake in the jugs.
- Idle mixture is generally set for slightly rich (not super-rich)... best mixture for
preignition.

Concerned, I tried it in a friend's PA-28-150 running 87 autogas. Same thing,
and that engine combo config is identical to Jay's... just 4 rather than 6. Nobody
ever has had issues with octane on the low-compression engines.

Anyway, I'd be interested to hear if you can do the same trick, Jay. I'm
pretty convinced (due to the above reasons) that it's a non-issue for normal
operation. Interesting, though.

-Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

writes:

: The autogas STC is undoubtedly the best thing that has ever happened to
: aircraft owners. If you've got the STC, but aren't using it, you are
: literally flushing thousands of dollars down the toilet.

I'd love to get the STC for my Skylane, but I'm told that all gas sold
in California these days has alcohol in it, so I'm S.O.L.

-jav

"Javier Henderson" wrote in message
...
writes:

: The autogas STC is undoubtedly the best thing that has ever happened
to
: aircraft owners. If you've got the STC, but aren't using it, you are
: literally flushing thousands of dollars down the toilet.

I'd love to get the STC for my Skylane, but I'm told that all gas sold
in California these days has alcohol in it, so I'm S.O.L.

-jav

You should be able to find airports that carry mogas that meets the STC
requirements.

We can find airports that carry mogas that meet the STC requirements with no
problems. Unfortunately, none of them are in California. The closest one
to me is just east of Salt Lake. Die Governator has decreed that all
gasoline shall be contaminated with 5.5% alcohol before it leaves the
refinery. He didn't make any exceptions for old farm vehicles, lawnmowers,
weedwhackers, or aircraft -- all of which to one degree or another get
honked up with alcohol.

The one thing that keeps burning in the back of my head is that they
probably soaked some of these carb seals in pure alcohol for six months and
said, "look, they swell up" and thus forbade gasahol. My sense, and it is
only a gut feeling, is that if you ran your airplane for a couple of days on
gasahol then let it sit for a couple of weeks in 100LL that you wouldn't see
any deterioration at all. However, you are in direct violation of the STC
if you do so.

It might be nice to have EAA and/or Petersen do the same seal test with 1%
gasahol, 2% gasahol and so on over a short, moderate, and long time to see
the exact problems facing us. Whether we like it or not, gasahol is with us
to stay, at least in California.

Jim


"Dave Stadt" wrote in message
. ..

You should be able to find airports that carry mogas that meets the STC
requirements.

The Governor of MN just signed us up for 20% alcohol over the next few
years. Soon we'll be able to drink the stuff......

There is a range and max power output penalty for use of alcohol since
it has only about half the energy density of pure hydrocarbon fuel.

: It might be nice to have EAA and/or Petersen do the same seal test with 1%
: gasahol, 2% gasahol and so on over a short, moderate, and long time to see
: the exact problems facing us. Whether we like it or not, gasahol is with us
: to stay, at least in California.

From what I've read, it's more than just seals in the fuel system. The
alcohol can attack aluminum fuel tanks, IIRC.

-Cory

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

"Dave Stadt" writes:

You should be able to find airports that carry mogas that meets the STC
requirements.

Yes, but none in California. Plus, the gas in CA leaves the refineries
already containing alcohol, so the ideas about using gas meant for farm
equipment, etc., are non starters.

Grumble.

-jav

"Javier Henderson" wrote in message
...
"Dave Stadt" writes:

You should be able to find airports that carry mogas that meets the STC
requirements.

Yes, but none in California. Plus, the gas in CA leaves the refineries
already containing alcohol, so the ideas about using gas meant for farm
equipment, etc., are non starters.

Grumble.

-jav

That sucks.