Is taking off on single mag bad for engine

I inadvertently did not return the ignition switch to "BOTH" after a
preflght mag check cause: distraction, I was an idiot) the other day
departing in my Glasair with my partner. The engine is a 150hp
O-320-E2D. The engine only developed 1900 rpm (2200 is normal for us
on 2 mags with fixed pitch prop) and climbed poorly and ran rough.
After figuring it out in approximately 1 minute, I switch back to
"BOTH" and everything was fine. That was a few months ago. Our
recent annual showed some low compression in #3 (55) and the others
were in the mid 60s, down a few points from last year. Not what I
would like but the engine runs strong. My partner said that the
single mag takeoff could have caused "detonation" or "cylinder
glazing" or "a bad flame front in the cylinders" and ruined the
compression.
I don't think that at that low power setting in a 7:1 compression
engine anything bad could happen. I am not aware of anything bad that
could happen in general from single mag operation at any power
setting, other than rough performance. This would be the same thing
as having a fouled plug in a cylinder, and nothing bad happens then.
Does anyone have any other feelings about this phenomenon.

"flyer" wrote in message om...
My partner said that the single mag takeoff could have caused "detonation"

No. I can't see how it would. Detonation is caused by increased cyl. pressures
and preignition comes from screwing up the timing (or other factors). None of this
I can see how one mag would this effect.

or "cylinder glazing"

Doubtful. Glazing is usually an effect of colder than standard operating temperaturs.

or "a bad flame front in the cylinders"

Well, this is why you get worse performance on one mag. Since there are two plugs
neither one is optimally situated, so running on one is a degredation. But...

and ruined the compression.

I don't think so.

This would be the same thing
as having a fouled plug in a cylinder, and nothing bad happens then.
Does anyone have any other feelings about this phenomenon

I agree with your assesment.

flyer wrote:
: O-320-E2D. The engine only developed 1900 rpm (2200 is normal for us
: on 2 mags with fixed pitch prop) and climbed poorly and ran rough.
Sounds about right, but...

: would like but the engine runs strong. My partner said that the
: single mag takeoff could have caused "detonation" or "cylinder
: glazing" or "a bad flame front in the cylinders" and ruined the
: compression.
Running at only 1900 RPM instead of the normal 2200 RPM on
climbout means that there's more absolute time from the spark (at 25
degrees BTDC) until TDC. For that matter, there's more time from the
beginning of the compression stroke to the spark. That extra time could
cause either preignition or detonation. Not likely, but possible


: I don't think that at that low power setting in a 7:1 compression
: engine anything bad could happen.
7:1 is pretty low compression, granted. BUT, it's rated for a
certain octane gasoline at certain min/max RPM settings.


I am not aware of anything bad that
: could happen in general from single mag operation at any power
: setting, other than rough performance.
Aside from roughness and the potential for lower-than-normal RPM,
I'd agree


This would be the same thing
: as having a fouled plug in a cylinder, and nothing bad happens then.
: Does anyone have any other feelings about this phenomenon.
... except that with one fouled plug, the other three jugs still
run on 2 plugs, so the RPM wouldn't decrease nearly as much.


Just for a bit more clarification... this on avgas (100LL), or cargas?
I'll give you one more data point that might be somewhat related. I've
noticed on my O-360 180 hp 8.5:1 Lycoming with the 91 octane cargas STC
that with a hot (recently flown) engine, it will actually diesel when I
cut the mags off. I was at idle, and rather than cut the mixture, I cut
the mags. It slowly shook to close to a stop, but at 100 rpm or so, it
continued to sputter and run enough to keep shaking and running. I was
very surprised at this, but when I started thinking about it, I realized
that at this (very) low RPM, there was lots of time to get the mixture
burning in the jugs, and also the idle throttle position allowed the MP to
build up to 20" or so (again very small airflow). It's almost like
lugging the engine at full throttle at 100 RPM... pretty tough.

But still... in your situation that 1900 instead of 2200
*shouldn't* have done it.... but it doesn't mean that it didn't. Try a
static RPM runup (and lean if DA is an issue). Make sure the tach is
calibrated, and the runup is within spec as per TCDS (Type certificate...
www.faa.gov)

-Cory


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

COUGARNFW wrote:
:My partner said that the
:single mag takeoff could have caused "detonation" or "cylinder
:glazing" or "a bad flame front in the cylinders" and ruined the
:compression.

: Nonsense. The engine is made to run on one mag, for hours and hours to 'get
: you home' in case one craps out.

: I am astounded at how the helpers are trying to make it appear that one can
: damage an engine when it runs like it is supposed to. Egads!

Hey now... it *is* slightly possible, since there's a *HUGE*
difference in detonation potential between a nice 75% cruise on one plug
and a sea-level takeoff at low airspeeds (read: high CHT), low RPM, high
MP. While it might only be making 75% at 1900/29, that's much tougher
from a detonation perspective than a typical one-mag cruise at 75%
(2400/24).

-Cory

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

Look, folks... I'm not suggesting that it was a very likely
scenario, just that it's slightly possible. As with most things in
aviation, if you dismiss it as categorically impossible, when you think
it through completely you might find out that under the right
circumstances, it could happen. That's one reason why a min RPM static
runup is dictated (although the larger reason is that it indicates engine
power and health).

: The engine (Con?) in the TAYLOR Cub had signle ignition. Took off,
: flew and landed on the one set of plugs, each flight, all ok.

Irrelevant. If an engine is designed to have one ignition, it
will most certainly run properly as designed and tested.


: To the point in question. You need to put the BMEP into play to
: determine if a possibioity of engine damage might occur.

Nice piece of info, but again largely irrelevant. The BMEP
measures the effective pressure, but is dependent on a whole slew of
factors. If detonation or preignition is happening, the BMEP will be
higher. No surprise, no arguments, but it's no more relevant than
saying, "If the pressure is too high and causing damage, then the pressure
must be be too high."

: I went through the 'gate' on a Merlin one time and pulled about 70+
: inches vs the spec of 61. VERY rough engine (detonaton). Engine
: checked out fine after landing and crew chief went through it.

True enough, but again irrelevant. Having one data point where
one engine with one design was abused and survived doesn't extrapolate to
any other circumstances except that one.

: If your on the east coast, keep your head down since you can't fly the
: bird west out of the storm area (like the Military does).

??? Talking Isabel? Not too concerned this far inland (300
miles). Just keep it tied, and hope for the best. Worst case is the
insurance buying us another airplane....

Cheers,
-Cory

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

----------snip--------

Just for a bit more clarification... this on avgas (100LL), or cargas?
I'll give you one more data point that might be somewhat related. I've
noticed on my O-360 180 hp 8.5:1 Lycoming with the 91 octane cargas STC
that with a hot (recently flown) engine, it will actually diesel when I
cut the mags off. I was at idle, and rather than cut the mixture, I cut
the mags. It slowly shook to close to a stop, but at 100 rpm or so, it
continued to sputter and run enough to keep shaking and running. I was
very surprised at this, but when I started thinking about it, I realized
that at this (very) low RPM, there was lots of time to get the mixture
burning in the jugs, and also the idle throttle position allowed the MP to
build up to 20" or so (again very small airflow). It's almost like
lugging the engine at full throttle at 100 RPM... pretty tough.

-----------snip---------

I was present when one of the mechanics, who I respect a lot, told a friend at
FXE that mogas and avgas have significantly different viscosities; and that an
engine will run much richer on one than the other. Me recollection fails me,
but your account indicates that magas has the lower viscosity and will run
rich. A rich mixture at idle, and carbon deposits from rich operation, used to
be the classic causes of "dieseling" in cars--sometimes people had to kill the
engines with the clutch! :-(

My best recollection of the mechanic's advice was to only use mogas if you could
use it all of the time. It might be possible to eliminate the problem by
leaning under all permissible modes of operation; and I plan to explore that
avenue when I have a plane avaible and start flying again.

Peter

flyer wrote:

I inadvertently did not return the ignition switch to "BOTH" after a
preflght mag check cause: distraction, I was an idiot) the other day
departing in my Glasair with my partner. The engine is a 150hp
O-320-E2D. The engine only developed 1900 rpm (2200 is normal for us
on 2 mags with fixed pitch prop) and climbed poorly and ran rough.
After figuring it out in approximately 1 minute, I switch back to
"BOTH" and everything was fine. That was a few months ago. Our
recent annual showed some low compression in #3 (55) and the others
were in the mid 60s, down a few points from last year. Not what I
would like but the engine runs strong. My partner said that the
single mag takeoff could have caused "detonation" or "cylinder
glazing" or "a bad flame front in the cylinders" and ruined the
compression.
I don't think that at that low power setting in a 7:1 compression
engine anything bad could happen. I am not aware of anything bad that
could happen in general from single mag operation at any power
setting, other than rough performance. This would be the same thing
as having a fouled plug in a cylinder, and nothing bad happens then.
Does anyone have any other feelings about this phenomenon.

I dunno. I am not a mechanic, and haven't flown in a long time. However, the
two most probable problems are that you could foul the plugs associated with the
inoperative magneto and that you would have the effect of a slightly retarded
spark--increased head temperature and egt and very slightly reduced power. The
real risk would be the lack of any automatic redundancy in the event the the
operating magneto shold fail. The short answer is that you probably didn't hurt
it any more on one mag than I did climbing out with the carb heat on after a
touch and go.

Try not to make my second, and much more dissastrous mistake as well: After
about the third time in two months that I forgot to turn off the carb heat on a
touch-and-go, I got the idea that about a two month break from flying would
enable me to forget the bad habbits which I had developed and resume the proper
and efficient use of my checklist. The dissastrous result was that two months
became three and three became six and ... and I currently hope to put flying
into next year's budget. What makes that bad decision so bad is that it
happened in 1983! :-(

"Phil Sisson, Litchfield Aerobatic Club" wrote:

For what its worth, the lycoming 0-290-G only had one mag.


That's all it needed for ground power duty...
The O-290 AIRCRAFT engine has two.


--
Richard Lamb

http://www.flash.net/~lamb01/

"Richard Lamb" wrote in message ...


"Phil Sisson, Litchfield Aerobatic Club" wrote:

For what its worth, the lycoming 0-290-G only had one mag.


That's all it needed for ground power duty...
The O-290 AIRCRAFT engine has two.

RIght, but it has no problems with detonation, cylinder glazing,
or other compression-reducing syndromes. The plug isn't even
moved to where you would put a single plug if you'd designed
that engine for only one plug. They just took the 2-plug O-290
cyls and blocked off one side.

For what its worth, the lycoming 0-290-G only had one mag.