Flying on 3 or 4 cylinders

[Robert M. Gary]

I had to cancel a flight today because one of the plugs in my Mooney
doesn't seem to be firing (tried to burn it clean but no luck).
Anyway, it got me wondering what would happen if you lost both plugs
in a cylinder during cruise (certainly take off would suck). I often
cruise around in my Mooney at 45% power (as indicated on the EDM). I
would like that I would have at least 45%, right? I'm not planning on
flying with a dead plug but really just an academic curiousity.

-Robert

[[email protected]]

I dropped a cylinder in flight. I can tell you, a 4 banger does not run
smooth on 3 cylinders. I don't really think it is a matter of power, but
how much vibration you are going to get. In my case, the engine was running
so rough I made a landing at the nearest airport, which, as luck would have
it, was only 3 miles behind me. After touchdown, the engine ran at 100 RPM,
but when I retarded the throttle, it died and would not restart.


"Robert M. Gary" > wrote in message
om...
> I had to cancel a flight today because one of the plugs in my Mooney
> doesn't seem to be firing (tried to burn it clean but no luck).
> Anyway, it got me wondering what would happen if you lost both plugs
> in a cylinder during cruise (certainly take off would suck). I often
> cruise around in my Mooney at 45% power (as indicated on the EDM). I
> would like that I would have at least 45%, right? I'm not planning on
> flying with a dead plug but really just an academic curiousity.
>
> -Robert

[Mike O'Malley]

"Robert M. Gary" > wrote in message
om...
>I had to cancel a flight today because one of the plugs in my Mooney
> doesn't seem to be firing (tried to burn it clean but no luck).
> Anyway, it got me wondering what would happen if you lost both plugs
> in a cylinder during cruise (certainly take off would suck). I often
> cruise around in my Mooney at 45% power (as indicated on the EDM). I
> would like that I would have at least 45%, right? I'm not planning on
> flying with a dead plug but really just an academic curiousity.

As the other poster mentioned, it ain't very fun if you lose one on a
four-banger. I've lost one under tow before on a PA-12/O-320 combo, was
kind of iffy for a little bit, and defiantly were some vibrations. But was
able to burn the oil off and got home ok. We had a pilot blow a jug clean
off the crankcase, thing was dangling by the plug wires; she made it back ok
too. Of course, we had 150hp engines on airframes designed for 105hp, so we
had a little extra room to play with.

Also lost one in a 182 a couple of times. Worn valve guides this time, only
way I knew was a loss in airspeed and EGT was 0 on #4. Kind of spooked me;
it could have been like that on runup and I wouldn't have noticed. That
plane ended up eating 4 valves before the club finally got around to
replacing that engine.

[G.R. Patterson III]

"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.

[CVBreard]

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.

[G.R. Patterson III]

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.

[CVBreard]

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.
>

[Michael]

(Robert M. Gary) wrote
> I had to cancel a flight today because one of the plugs in my Mooney
> doesn't seem to be firing (tried to burn it clean but no luck).

Usually such problems are resolved by cleaning/regapping. Takes about
15 minutes if you know which plug it is, requires only simple hand
tools, and it's quite legal for an owner to do. It's pretty easy to
figure out which plug is the problem - let the engine cool somewhat,
start it, immediately switch it to the bad mag only, and let warm a
bit. The cold jug is your culprit, and of course you know which plug
based on which mag you have selected. Of course if you have an engine
monitor it's even easier. It's worth learning how - keeps you from
cancelling trips.

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

I actually had that happen. Both plugs fouled. It was in the TwinCo,
so I only lost one jug out of 8 - takeoff was a bit anemic, but it was
a long runway and by the time I noticed anything wrong, I was airborne
and climbing 1000 fpm. In your Mooney, I would expect the takeoff to
approximate what you would get if the density altitude was maybe
5000-7000 ft higher than it actually is.

> I often
> cruise around in my Mooney at 45% power (as indicated on the EDM). I
> would like that I would have at least 45%, right?

Depends on altitude. My estimate is that you would have more than 70%
but less than 75% of whatever is available at that altitude with the
engine working properly. That is certainly consistent with my
experience.

Michael

[[email protected]]

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.