Flying on 3 or 4 cylinders

"Robert M. Gary" wrote:

Anyway, it got me wondering what would happen if you lost both plugs
in a cylinder during cruise (certainly take off would suck).

I took off from Princeton once in a Cessna 150. She started running rough after
takeoff, but she still had enough power to climb, I was already at altitude, and I
judged that it was safe to make the short trip to Kupper rather than return to
Princeton. About half way to Kupper, the roughness got worse and I lost some more
power, but I was able to maintain altitude at nearly full throttle. When I throttled
back for the landing, the vibration eased up quite a bit.

When the mechanic checked it out, we discovered that the plug wire for the top plug
on one cylinder had died. The other plug had fouled under the combination of a heavy
power demand and cool cylinder.

So. To answer your question. In that aircraft, there was more than enough power to
maintain altitude. There was a great deal of vibration, which could have damaged the
engine mounts had it continued for very long. If it happens to you, you should be
able to make the nearest airport, but you will probably not be able to execute a
go-round if one becomes necessary.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

I had an exhaust valve stick open in a Cessna 150 (O-200, 4 cylinder) cruise
and it resulted in a dead miss that nothing helped. I was able to maintain
altitude at full throttle and made it to a grass field about 10 miles away
(thank you ATC for the suggested heading) - seemed like a half hour, waiting
for something to crater completely.

"They" say a 6 cylinder engine will fly on 5, but it gets iffy with only 3
working in a 4 cylider engine.

CVBreard wrote:

I had an exhaust valve stick open in a Cessna 150 (O-200, 4 cylinder) cruise
and it resulted in a dead miss that nothing helped. I was able to maintain
altitude at full throttle and made it to a grass field about 10 miles away
(thank you ATC for the suggested heading) - seemed like a half hour, waiting
for something to crater completely.

I've also had a stuck valve in a 150 (the same plane). The plane would not quite
maintain altitude in that situation. My conclusion from these two occasions is that
the engine actually put out more power with ignition failure on one cylinder than
with compression failure.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

I believe under slightly different circumstances (a passenger, etc.) I wouldn't
have been able to maintain altitude.

I said:
I had an exhaust valve stick open in a Cessna 150 (O-200, 4 cylinder) cruise
and it resulted in a dead miss that nothing helped. I was able to maintain
altitude at full throttle
------------------------------------------
George commented:
My conclusion from these two occasions is that
the engine actually put out more power with ignition failure on one cylinder
than
with compression failure.

My conclusion from these two occasions is that
the engine actually put out more power with ignition failure on one cylinder than
with compression failure.

Probably because if a valve sticks open, the intake manifold fuel
distribution to the other cylinders also becomes messed up.

If it is an exhaust valve that sticks open (and it probably was),
imagine what happens when the intake dutifuly opens at the same time
every 2 crankshaft revolutions. A big slug of exhaust gas gets sucked
up into the intake manifold, screwing up the mixture on the other
cylinders.

It is important to maintain the integrity of the intake manifold
system to maintain power output.