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an interesting in flight experiment



 
 
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  #1  
Old October 17th 09, 06:52 PM posted to rec.aviation.piloting
a[_3_]
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Posts: 562
Default an interesting in flight experiment

Next time you're at altitude and in cruise mode, switch from 'both' to
a single bank of spark plugs. It will remind you what happens should
you have one side decide to go in/op when in flight. I had the engine
(IO 360) go rough a couple of weeks ago, but rough was a lot better
than the very smooth and silent effects the left mag only gave me.

  #2  
Old October 17th 09, 08:01 PM posted to rec.aviation.piloting
Peter Dohm
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Default an interesting in flight experiment

"a" wrote in message
...
Next time you're at altitude and in cruise mode, switch from 'both' to
a single bank of spark plugs. It will remind you what happens should
you have one side decide to go in/op when in flight. I had the engine
(IO 360) go rough a couple of weeks ago, but rough was a lot better
than the very smooth and silent effects the left mag only gave me.

Sounds like at least two problems--unless the fault was in the switch.

Peter
Just a thought



  #3  
Old October 17th 09, 08:35 PM posted to rec.aviation.piloting
a[_3_]
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Posts: 562
Default an interesting in flight experiment

On Oct 17, 3:01*pm, "Peter Dohm" wrote:
"a" wrote in message

... Next time you're at altitude and in cruise mode, switch from 'both' to
a single bank of spark plugs. It will remind you what happens should
you have one side decide to go in/op when in flight. I had the engine
(IO 360) go rough a couple of weeks ago, but rough was a lot better
than the very smooth and silent effects the left mag only gave me.


Sounds like at least two problems--unless the fault was in the switch.

Peter
Just a thought


Nope. Engine went rough, stayed just as rough on the right bank, too
quiet on the left. After the repair all was well
again.

Even on run up you lose some RPMs when on a single bank of spark
plugs.
  #4  
Old October 17th 09, 10:30 PM posted to rec.aviation.piloting
Jon Woellhaf
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Default an interesting in flight experiment

"a" wrote in message
...
... Even on run up you lose some RPMs when on a single bank of spark
plugs.


If you don't get an rpm drop when running on a single mag, something's
probably amiss. My engine has never run rough during a mag check, except
when I forgot to lean aggressively before taxi and got lead fouling.


  #5  
Old October 18th 09, 02:06 PM posted to rec.aviation.piloting
twdeckard
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Default an interesting in flight experiment

This test should be part of the run-up pre-flight check.

You are verifying that the P-lead correctly grounds the magneto (by
observing the drop)
and that the firing side is operational. You are also, of course, verifying
that the engine will run on the ungrounded side (and that it is firing that
entire bank of spark plugs by scrutinizing how well it runs).

I am sure you know all of this (grin), I just chimed in becuase its a check
best done on the run-up pad.

Todd

"Peter Dohm" wrote in message
...
"a" wrote in message
...
Next time you're at altitude and in cruise mode, switch from 'both' to
a single bank of spark plugs. It will remind you what happens should
you have one side decide to go in/op when in flight. I had the engine
(IO 360) go rough a couple of weeks ago, but rough was a lot better
than the very smooth and silent effects the left mag only gave me.

Sounds like at least two problems--unless the fault was in the switch.

Peter
Just a thought





  #6  
Old October 18th 09, 02:11 PM posted to rec.aviation.piloting
Morgans[_2_]
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Default an interesting in flight experiment


"twdeckard" wrote

I am sure you know all of this (grin), I just chimed in becuase its a
check best done on the run-up pad.


He did not say you shouldn't do it at run-up. He was just pointing out
that your engine could run very rough if you lose one side while cruising.

--
Jim in NC

  #7  
Old October 18th 09, 03:30 PM posted to rec.aviation.piloting
twdeckard
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Default an interesting in flight experiment

I didn't mean the post to sound too pedantic. I guess I reacted to the OP
phrasing it as a question or a suggestion. I am sure it was rhetorically so
....


"Morgans" wrote in message
...

"twdeckard" wrote

I am sure you know all of this (grin), I just chimed in becuase its a
check best done on the run-up pad.


He did not say you shouldn't do it at run-up. He was just pointing out
that your engine could run very rough if you lose one side while cruising.

--
Jim in NC



  #8  
Old October 18th 09, 03:40 PM posted to rec.aviation.piloting
Peter Dohm
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Posts: 1,754
Default an interesting in flight experiment

"Morgans" wrote in message
...

"twdeckard" wrote

I am sure you know all of this (grin), I just chimed in becuase its a
check best done on the run-up pad.


He did not say you shouldn't do it at run-up. He was just pointing out
that your engine could run very rough if you lose one side while cruising.

--
Jim in NC

I am really not sure exactly what he tried to say; but, in his initial post,
it was clear that he had lost the use of all of one mag and a part of the
other--or the plugs or wires attached to it.

The problem with that is that mags have a couple of failure modes that are
common to all breaker point ignition systems in addition to the failure
modes that are peculiar to magnetos.

As far as I know, it is still a common practice to simply set the timing and
perform a runup type mag check as part of an annual and not open the mags to
gap and visually check the points. That leaves the door a lot farther open
for the failure modes involving erosion of the points--which is related to
one of the two failure modes of the capacitor a/k/a condenser--and also to
wear of the cam follower. Both of those failure modes usually make the
engine harder to start long before they will fail in flight, or at runup
test; but are masked sufficiently by electric starters that they can go
virtually unnoticed--unless the pilot is so dilligent as to carefully prime
and set the throttle and then count the blades on nearly every start.

Peter



  #9  
Old October 18th 09, 04:50 PM posted to rec.aviation.piloting
a[_3_]
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Posts: 562
Default an interesting in flight experiment

On Oct 18, 10:40*am, "Peter Dohm" wrote:
"Morgans" wrote in message

...

"twdeckard" wrote


I am sure you know all of this (grin), I just chimed in becuase its a
check best done on the run-up pad.


He did not say you shouldn't do it at run-up. *He was just pointing out
that your engine could run very rough if you lose one side while cruising.


--
Jim in NC


I am really not sure exactly what he tried to say; but, in his initial post,
it was clear that he had lost the use of all of one mag and a part of the
other--or the plugs or wires attached to it.

The problem with that is that mags have a couple of failure modes that are
common to all breaker point ignition systems in addition to the failure
modes that are peculiar to magnetos.

As far as I know, it is still a common practice to simply set the timing and
perform a runup type mag check as part of an annual and not open the mags to
gap and visually check the points. *That leaves the door a lot farther open
for the failure modes involving erosion of the points--which is related to
one of the two failure modes of the capacitor a/k/a condenser--and also to
wear of the cam follower. *Both of those failure modes usually make the
engine harder to start long before they will fail in flight, or at runup
test; but are masked sufficiently by electric starters that they can go
virtually unnoticed--unless the pilot is so dilligent as to carefully prime
and set the throttle and then count the blades on nearly every start.

Peter


To put several of your minds at ease, of course I did the conventional
both-right-both-left mag check at runup, but at 1900 RPM. I had not
had one bank of spark plugs go in/op ever until the in flight failure
a little while ago, and my post was simply to suggest pilots go to one
mag while at cruise rpm and engine loading to see what happens. In my
case the engine ran a bit rougher -- rpms stayed where they were set,
of course, because prop pitch changed to accommodate the reduction in
power.

I am sure I make lots of inadvertent errors when flying: missing a mag
check is not one of them.

  #10  
Old October 18th 09, 05:02 PM posted to rec.aviation.piloting
Frank Stutzman[_3_]
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Posts: 29
Default an interesting in flight experiment

a wrote:


In my
case the engine ran a bit rougher -- rpms stayed where they were set,
of course, because prop pitch changed to accommodate the reduction in
power.


And if you were flying a 6 cylinder (or larger) engine, you may not have
even noticed the roughness.

(I once failed to get the switch back to "both" after a run-up. Managed
to take-off and fly for ~15 minutes before I noticed it. The roughness
became more pronounced when I started leaning it out).

--
Frank Stutzman
Bonanza N494B "Hula Girl"
Boise, ID

 




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