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

On Tue, 10 May 2005 10:01:47 -0700, "Matt Barrow"
wrote:

I hope to hell you cut and pasted all that, rather than typing it in by
hand!! :~)

You'd be right. Copy and paste. :-)

Corky Scott

: 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 *
************************************************** ***********************

In rec.aviation.owning Newps wrote:
: I can lean to that fuel flow without any undue engine sounds, too. But my
: EGTs go well over 1500 degrees, and my CHTs push 350 when I do.

: EGT is irrelavant and 350 is not hot.

Exactly. The absolute value of EGT does not matter... almost all of the
cooling of the exhaust valves is done through the valve seat (and stem in Lycoming).
Thus, the "cold sink" is the cylinder, and CHT is what's important. Lycoming redlines
CHT at 500, recommends 450 as a max, and general wisedom dictates anything under
375-400 in cruise is fine.

Also remember that EGT and CHT probes are often uncompensated thermocouples.
That means they read the difference between the "hot" thing, and the temperature of
the "cold" (where the J thermocouple wires connect to the copper wires going to the
meter, etc). They're generally set to be accurate at about 70 degrees F. If it's 0
F, the temp will read 70 degrees hotter than it actually is. Wintertime temps read
higher for that reason.

I don't know about the fancy JPI, etc, by my dumb gauges definately do this.

-Cory



--

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

I've a feeling I'm not the only one lost on terminology.

Try being a non pilot trying to keep up with you guys!

karel wrote:

Still in all seriousness: shouldn't there be a little
glossary somewhere, perhaps in Ron W's FAQ list?
I've a feeling I'm not the only one lost on terminology.

KA (learning & learning & ....)



Stick around. It'll get worse.


--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

"karel" wrote in message
...

"Corky Scott" wrote in message
...
On Mon, 9 May 2005 18:44:11 -0700, "Matt Barrow"
wrote:

John Deakin has written that if you lean to the lean side of peak and
the engine runs rough, pulling on full carb heat will distribute the
fuel into the air mixture better and give you the ability to lean to
the lean side of peak.

Actually, he says "just a touch" of carb heat.

That was his initial suggestion. In his next column he posted this as
a news flash. I've posted nearly the entire portion of the column
because he has some caveats that are important to understand:

***Begin Quote***

(quote snipped)

***End Quote***
Corky Scott

Corky,

This text must surely be most interesting
and many people might benefit from understanding,
myself not the least.
Unfortunately it is so full of undocumented abbreviations
that I can't really make much from it.
MP must stand for manifold pressure I presume,
and EGT and CHT are wellknown cause there's instruments for them
but what the heck are ROP, ONLY, AMPLE, WOP, JIP, LOP ?

ROP = Rich of Peak
LOP = Lean of Peak

WOP (WOT) + Wide open throttle

ONLY and AMPLE are _emphasis"

"JIP" I don't se in the article



Is there perhaps a glossary web page somewhere for this kind of
terminology?

KA (learning every day)

There's this http://www.gps.tc.faa.gov/glossary.html but much of aviation's
charm is the acronyms we create every day :~)

In article ,
"karel" wrote:

Was mainly the ROP & LOP that worried me,
perfectly clear now!

Still in all seriousness: shouldn't there be a little
glossary somewhere,

Hey, there is a glossary somewhere. It's called www.acronymfinder.com.
Go there and type in ROP, for example, and you'll find the aviation
related definition right there at number 19 in the list.

"karel" wrote in message
...

Still in all seriousness: shouldn't there be a little
glossary somewhere, perhaps in Ron W's FAQ list?
I've a feeling I'm not the only one lost on terminology.


I've seen a book of aviation acronyms and it's several hundred pages. It's
just a part of techical terminology.

Hang around and read as much as you can and you'll discover their terms as
well as their meanings and substance.

Don't feel alone... I didn't know what exactly TSO was until I bought my
first airplane. :~)

KA (learning & learning & ....)

Hang in there!!

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

On Tue, 10 May 2005 20:43:34 +0000 (UTC),
wrote:

Exactly. The absolute value of EGT does not matter... almost all of the
cooling of the exhaust valves is done through the valve seat (and stem in Lycoming).
Thus, the "cold sink" is the cylinder, and CHT is what's important. Lycoming redlines
CHT at 500, recommends 450 as a max, and general wisedom dictates anything under
375-400 in cruise is fine.

Deakin posts a chart from Pratt and Whitney in his "Mixture Magic"
column which verifies this precisely. In the chart is a line
depicting the loss of strength of the aluminum alloy used for cylinder
heads. It starts dipping LONG before 400 degrees is reached and is
plummeting at 450 degrees.

See: http://www.avweb.com/news/columns/182084-1.html

He recommends running at 400 degrees or under for cruise.

Corky Scott