Question about auto gas STC

Dave Stadt wrote:
: Actually it is like shutting off your car. Not a big deal by any means.

Actually, it's not *quite* like that. A car engine:
- Isn't timed to run at "really" low speeds.
- Doesn't have as much inertia as the propeller.
- Doesn't have as much idle load as a propeller at 500 rpm.
- Isn't air-cooled.

I have observed extremely low-speed dieseling on both high-compression and
low-compression aircraft engines when shut down with the mags after flight on cargas.
It initially worried me, but when I thought about it more, the following two things
were important:

- VERY low speeds (50-100 rpm), so 25x more time for the fuel to preignite than at
takeoff conditions (2500 rpm).
- VERY high manifold pressure due to idle throttle at very low RPM... almost full MP.

Both of those equate to serious "lugging" conditions on a hot cylinder head.

YMMV
-Cory



--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

If your worried about it, which there is no reason for, then just mix it
with the 100LL. Operate the plane the same way no matter what kind of gas
you have.



"Carl Orton" wrote in message
...
As long as we're on the subject of mogas STCs...

My still new-to-me '67 172H already had the Petersen STC installed.

But I've been chicken to try it! Guess I'm concerned that vapor lock or
lower quality or whatever other old wives tales will strike me dead.

Is there *anything* I should watch for if I just suddenly decide to fill
'er
up with mogas some day? Like different start procedure, or longer takeoff
run, or ??? Or, is mogas the EXACT same in every other way (yeah, I know
you
guys are gonna chime in with "less bucks, burns cleaner, engine happier,
etc.")

Thanks;
Carl


"JimT96309" wrote in message
...
I am currently interested in an older C-172 (Cont. 0-300 engine) that
has
an
STC for auto gas. My questions a

1. Can I continue to use AVgas instead of auto fuel?

2. I often fly into/out of Big Bear City, Ca. (elev. 6500ft.) I've
been
able
to get out lightly loaded (me and one in the right seat) at a density
altitude
of 8,100 with one of our clubs 172s with the 320H2AD engines at 160 hp.
What
difference would I see with the 15 fewer horses up front?

3. Can you give me a rough idea of cost to add a 2nd Nav-comm with
Glideslope
and then have the whole thing certified for IFR? I would probably try to
find a
good quality used one from one of the local shops.

Thanks for any help you can give to a rookie getting ready to make a
first
purchase.

Jim

Is there *anything* I should watch for if I just suddenly decide to fill
'er
up with mogas some day? Like different start procedure, or longer takeoff
run, or ??? Or, is mogas the EXACT same in every other way (yeah, I know
you
guys are gonna chime in with "less bucks, burns cleaner, engine happier,
etc.")

We use 87 octane unleaded mogas and 100 octane avgas absolutely
interchangeably in our two-year old Lycoming O-540.

No difference has been noted in engine operation, nor is there any
difference in cylinder or exhaust gas temps as noted on our JPI EDM-700
engine analyzer. There is also no difference in fuel flow (as measured with
our JPI FS-450 fuel totalizer), nor is there any difference in engine
leaning at altitude.

In fact, there is precisely no difference in performance at all.

There are really only two differences:

1. Mogas is about a buck a gallon less.
2. We don't fail mag checks (due to lead-fouled plugs) on mogas.

It's the best deal in aviation. If you've got the STC, and are not using
it, you are quite literally burning a 50 dollar bill every time you gas up.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Well, thanks for the assurances, folks. Guess I'll have to give it a try
one of these days. (now to search the archives for Jay's Mighty Grape
contraption!!!).


"Carl Orton" wrote in message
...
As long as we're on the subject of mogas STCs...

My still new-to-me '67 172H already had the Petersen STC installed.

But I've been chicken to try it! Guess I'm concerned that vapor lock or
lower quality or whatever other old wives tales will strike me dead.

Is there *anything* I should watch for if I just suddenly decide to fill
'er
up with mogas some day? Like different start procedure, or longer takeoff
run, or ??? Or, is mogas the EXACT same in every other way (yeah, I know
you
guys are gonna chime in with "less bucks, burns cleaner, engine happier,
etc.")

Thanks;
Carl


"JimT96309" wrote in message
...
I am currently interested in an older C-172 (Cont. 0-300 engine) that
has
an
STC for auto gas. My questions a

1. Can I continue to use AVgas instead of auto fuel?

2. I often fly into/out of Big Bear City, Ca. (elev. 6500ft.) I've
been
able
to get out lightly loaded (me and one in the right seat) at a density
altitude
of 8,100 with one of our clubs 172s with the 320H2AD engines at 160 hp.
What
difference would I see with the 15 fewer horses up front?

3. Can you give me a rough idea of cost to add a 2nd Nav-comm with
Glideslope
and then have the whole thing certified for IFR? I would probably try to
find a
good quality used one from one of the local shops.

Thanks for any help you can give to a rookie getting ready to make a
first
purchase.

Jim

Carl Orton wrote:

Is there *anything* I should watch for if I just suddenly decide to fill 'er
up with mogas some day?

You probably will notice that it starts more easily. That's all I can think of. If
there were things to "look out for", there wouldn't be an STC.

George Patterson
None of us is as dumb as all of us.

Well, thanks for the assurances, folks. Guess I'll have to give it a try
one of these days. (now to search the archives for Jay's Mighty Grape
contraption!!!).

http://alexisparkinn.com/fuel_truck.htm

:-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Thanks, Jay!

"Jay Honeck" wrote in message
newsJRwc.53433$3x.13569@attbi_s54...
Well, thanks for the assurances, folks. Guess I'll have to give it a
try
one of these days. (now to search the archives for Jay's Mighty Grape
contraption!!!).

http://alexisparkinn.com/fuel_truck.htm

:-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

"Dave Stadt" wrote in message om...
"G. Burkhart" wrote in message
newspwwc.8392$HG.7233@attbi_s53...
"Jay Honeck" wrote in message
news:ZFtwc.45447$pt3.6238@attbi_s03...
The J-3 didn't. I believe one of the Chief's didn't. I think mixture
was an optional item on all the 40's 65hp planes. Even when you had
mixture, it didn't do anything on the ground. It only effected you at
cruise power.

Thanks, all, for the info about mixture-less aircraft. I've only flown
a
Cub once, and (apparently) never noticed the lack of a mixture control.
(I
don't think I ever touched the throttle -- the guy in back was working
the
power...) And I sure had no idea that this feature (or lack thereof)
was
universal to so many small-engined, older airplanes.

There's a few features that older aircraft don't have. Some with the
Stromberg (?) carbs have them safety wired fully rich and use the mag
switch
to shut down. It's kind of like shutting off a computer by just pulling
the
power cord out of the wall.

Actually it is like shutting off your car. Not a big deal by any means.

Just don't touch the prop aftewards (unless you want it to start).
When I had the Chief we had to shut it down with the mags. Usually a
20 degree turn on the prop was all we needed to hand start it. Now, if
some line guy were to "move" the prop, he'd have a hand full of his
hands (if the mags didn't ground). At least with a mixture airplane
you shouldn't have as much fireable fuel in the cylinders.

-Robert

"Robert M. Gary" wrote in message
om...
"Dave Stadt" wrote in message
om...
"G. Burkhart" wrote in message
newspwwc.8392$HG.7233@attbi_s53...
"Jay Honeck" wrote in message
news:ZFtwc.45447$pt3.6238@attbi_s03...
The J-3 didn't. I believe one of the Chief's didn't. I think
mixture
was an optional item on all the 40's 65hp planes. Even when you
had
mixture, it didn't do anything on the ground. It only effected you
at
cruise power.

Thanks, all, for the info about mixture-less aircraft. I've only
flown
a
Cub once, and (apparently) never noticed the lack of a mixture
control.
(I
don't think I ever touched the throttle -- the guy in back was
working
the
power...) And I sure had no idea that this feature (or lack
thereof)
was
universal to so many small-engined, older airplanes.

There's a few features that older aircraft don't have. Some with the
Stromberg (?) carbs have them safety wired fully rich and use the mag
switch
to shut down. It's kind of like shutting off a computer by just
pulling
the
power cord out of the wall.

Actually it is like shutting off your car. Not a big deal by any means.

Just don't touch the prop aftewards (unless you want it to start).
When I had the Chief we had to shut it down with the mags. Usually a
20 degree turn on the prop was all we needed to hand start it. Now, if
some line guy were to "move" the prop, he'd have a hand full of his
hands (if the mags didn't ground). At least with a mixture airplane
you shouldn't have as much fireable fuel in the cylinders.

-Robert

I wouldn't bet a plug nickel on your last statement.

"Dave Stadt" wrote in message gy.com...
"Robert M. Gary" wrote in message
om...
"Dave Stadt" wrote in message
om...
"G. Burkhart" wrote in message
newspwwc.8392$HG.7233@attbi_s53...
"Jay Honeck" wrote in message
news:ZFtwc.45447$pt3.6238@attbi_s03...
The J-3 didn't. I believe one of the Chief's didn't. I think
mixture
was an optional item on all the 40's 65hp planes. Even when you
had
mixture, it didn't do anything on the ground. It only effected you
at
cruise power.

Thanks, all, for the info about mixture-less aircraft. I've only
flown
a
Cub once, and (apparently) never noticed the lack of a mixture
control.
(I
don't think I ever touched the throttle -- the guy in back was
working
the
power...) And I sure had no idea that this feature (or lack
thereof)
was
universal to so many small-engined, older airplanes.

There's a few features that older aircraft don't have. Some with the
Stromberg (?) carbs have them safety wired fully rich and use the mag
switch
to shut down. It's kind of like shutting off a computer by just
pulling
the
power cord out of the wall.

Actually it is like shutting off your car. Not a big deal by any means.

Just don't touch the prop aftewards (unless you want it to start).
When I had the Chief we had to shut it down with the mags. Usually a
20 degree turn on the prop was all we needed to hand start it. Now, if
some line guy were to "move" the prop, he'd have a hand full of his
hands (if the mags didn't ground). At least with a mixture airplane
you shouldn't have as much fireable fuel in the cylinders.

-Robert

I wouldn't bet a plug nickel on your last statement.


I wish you'd bet more because I want to get a new GPS for my plane. I
can only speak from years of owning a Chief with no mixture control.
Shutting down (with mag switch) putting gas in, turning the mags back
on, and turning the prop 1/8 turn (no starter), jumping in and flying
away.

-Robert