Took off on one mag accidentally - did I hurt my engine?

G

Goofball

Guest
Hi,

I made the boneheaded mistake of not going back to BOTH after doing my run up and took off on the L mag. I noticed my climb performance was more sluggish than usual and the engine didn’t sound quite right. Once I climbed to 3,000ft and leveled off, I reduced power, leaned and noticed my EGT gauge was running much hotter than usual. I glanced down and did a check of everything, and found I was on one mag. I switched it to BOTH and bingo, back to normal indications. I would suspect I ran on the single mag for about 5-7 minutes before I noticed it. Did I damage my O360 engine by climbing out and such on one magneto?
 
No, not a good idea to do this, but it probably didn't hurt the engine
 
It shouldn’t,not really a good procedure to adopt.
 
Goofball said:
Funning aside, would this damage the engine?
Click to expand...
To be honest, you should have learned the answer to that during your Private training.

Here are some questions to help you find the answer:

1. How many spark plugs do most non-aircraft engines have per cylinder?
2. What are two reasons why most piston aircraft have dual ignition systems?
3. What are the consequences of running too rich?
 
High egt's do not normally damage an engine. It is more of an indicator that something else is wrong, such as some of the spark plugs being fouled, etc.
 
1) one
2) second as a backup
3) foul the spark plugs (does this mean carbon deposits or they need replacement?)
 
Operating on one mag can put you in the “ Realm of Detonation”.

Whether it WILL occurs is also dependent on compression ratio, power setting and

temperatures. If happens it can trash an engine.
 
Some increase in potential for "knock" which is hard to hear in an aircraft. But if it's still running OK you are most likely OK. It wouldn't hurt to take a quick look at the plugs.

Note: I ain't no A&P
 
Magman said:
Operating on one mag can put you in the “ Realm of Detonation”.

Whether it WILL occurs is also dependent on compression ratio, power setting and

temperatures. If happens it can trash an engine.
Click to expand...
On an o-360? I think that would be unlikely.
 
Flame propagation is reason for two. Running on one isn’t gonna hurt your engine.

This may be controversial… but here goes. You’re gonna lose power… probably manifest itself as a loss of, just shootin from the hip, a hunnert rpm or so.
 
A magneto can fail just as you lift off and have too little runway left to abort, so you climb to safety and land when practicable.

Now, if this was to damage the engine, there would be manufacturers' service bulletins on it, yet I have never seen any.
 
Goofball said:
What’s the point of having two independent mags if running on one will cause engine damage?
Click to expand...
Maybe like a twin engine airplane?
One stops working in the air, really nice to have the second one still operational to let you land nicely on the ground (preferably even a runway).
However that does not mean it would be a smart idea to intentionally then try to take off knowing you only had one (of two) operational.
 
Magman said:
Operating on one mag can put you in the “ Realm of Detonation”.

Whether it WILL occurs is also dependent on compression ratio, power setting and

temperatures. If happens it can trash an engine.
Click to expand...

Capt. Geoffrey Thorpe said:
Some increase in potential for "knock" which is hard to hear in an aircraft. But if it's still running OK you are most likely OK. It wouldn't hurt to take a quick look at the plugs.

Note: I ain't no A&P
Click to expand...

How would a less complete combustion that is caused by running on one plug vs two increase the likelihood of detonation? I disagree with this, but am willing to admit I’m wrong if I learn differently.
 
RyanShort1 said:
To be honest, you should have learned the answer to that during your Private training.

Here are some questions to help you find the answer:

1. How many spark plugs do most non-aircraft engines have per cylinder?
2. What are two reasons why most piston aircraft have dual ignition systems?
3. What are the consequences of running too rich?
Click to expand...
Ryan beat me to it…a pilot should have enough understanding of an engine to know the answer to this question. No worries though, seems now you know.
 
455 Bravo Uniform said:
How would a less complete combustion that is caused by running on one plug vs two increase the likelihood of detonation? I disagree with this, but am willing to admit I’m wrong if I learn differently.
Click to expand...
Detonation happens when fuel spontaneously ignites ahead of the flame front - usually at many places - a slower flame front (since it only starts at one point) increases the time that the unburned mixture heats up and allows the fuel molecules to break down to more detonation prone compounds. On the other hand, the slower flame front can move the peak pressure point further into the expansion cycle which tends to reduce the peak pressures which tends to be anti-detonation. Hard to for me to say for sure which factor will win out - my combustion experience is on the automobile end of things - but I can see the potential.

The probability of significant damage does seem low to me. Plugs do foul and do not seem to end in engine damage. But if one were worried you could check the plugs for damage such as cracked ceramic. If they are good, most likely all is good. IMO.
 
When 1 plug fires the flame front moves across the cylinder. This compresses and

recompresses the fuel/ air mixture. Note this is a rapid burning and NOT an

explosion. Eventually the mixture increases in temp & pressure and may detonate.

This explosion features high temps and pressures that may damage components.

It is similar to a comparison between pushing on the piston and striking it with a

hammer.


To my knowledge this post was not about a particular engine. A high compassion

engine running Lean and advanced timing may experience the phenomenon

but a low compassion engine running Rich may not.
 
Last edited:
I did this once. Only in my case it took me 20 minutes before it dawned on me that my cruise airspeed was a little low...
 
Lndwarrior said:
I did this once. Only in my case it took me 20 minutes before it dawned on me that my cruise airspeed was a little low...
Click to expand...

With a fixed pitch prop, you’ll see low Rpm and reduced acceleration/climb on takeoff.
 
Magman said:
When 1 plug fires the flame front moves across the cylinder. This compresses and
recompresses the fuel/ air mixture. Note this is a rapid burning and NOT an
explosion. Eventually the mixture increases in temp & pressure and may detonate.
This explosion features high temps and pressures that may damage components.
It is similar to a comparison between pushing on the piston and striking it with a
hammer.
Click to expand...
A slow burn increases the time for the complex, detonation-resistant hydrocarbon molecules to break down under the heat and pressure. They can become autoignitable molecules, combusting all at once before the flame front reaches them, and detonation can result. In aircraft engines, the relatively low RPM and large bores increase the burn time, even with both plugs working, so detonation is more likely under certain conditions.

But most engines flown by POAers are low-compression, normally-aspirated affairs that don't easily detonate. That said, you can still get it if you're rough with the engine, such as bashing the throttle open quickly for takeoff. That allows the pressures to rise to detonation territory before the RPM comes up and reduces the time available for it.
 
Someone can correct me if they have a better explanation..

IMO the way we Mag Check newer craft with a rotating Magneto switch is a bit outdated.

Most teach something like, Start the check on Both, got the Left mag (1st click) go back to both, then go to the Right Mag (2nd Click) then back to both. I think this process tends to cause the taking off with one Mag as it is easy to not get the 2 clicks back to both from the right mag position (sorry if I have left and right mixed up, didn't bother to confirm accuracy).

IMO this process is a left over from older aircraft that typically had 2 toggle switches for the 2 ignition system, In that case it makes sense got go back to both in between mag checks to prevent switching both mags off momentarily.

What I teach is in rotating switch airplanes...
1. start the check on both, note the RPM
2, go 2 clicks, note the RPM drop, is it with spec.
3. go back one click to the other Mag, note the difference, is easy to see the difference going from just Right to Left Mag, is it with spec
4. go back to both and verify the RPM goes to the original RPM, if it does not you might be building Carb ice during the runup.

if you note the RPM increase going back to both, you should never take off with one mag turned off.

Brian
CFIIG/ASEL
 
brcase said:
Most teach something like, Start the check on Both, got the Left mag (1st click) go back to both, then go to the Right Mag (2nd Click) then back to both. I think this process tends to cause the taking off with one Mag as it is easy to not get the 2 clicks back to both from the right mag position (sorry if I have left and right mixed up, didn't bother to confirm accuracy).
Click to expand...
This is why I was taught both -> right (2 clicks) -> both -> left (1 click) -> both. With one click at the end, you can't stop short, and with both in between, you see the full rpm before each drop.
 
One other reason to go back to both is to start running on the plugs that were off to make sure they aren't fouled.
 
If running big pistons at low rpm on one spark plug could cause engine damage, then Harley Davidson would have some serious reliability problems.


….oh…..wait.


:stirpot: :smilewinkgrin:
 
Capt. Geoffrey Thorpe said:
Some increase in potential for "knock" which is hard to hear in an aircraft.
Click to expand...
It's quite the opposite. Look at what happens when you do an inflight mag check... the combustion slows, as evidenced by the higher EGT... and power output declines, as evidenced by the lower CHT and lower airspeed. Lower CHT equals LESS chance for detonation. Since the combustion takes longer getting organized, the peak pressure is reduced, because the piston has time to move out of the way as combustion progresses...

If you do experience detonation in flight (CHT climbing 2 degrees a second, let's say) and after you respond by going full rich, full RPM, and reducing throttle some, the next technique is to switch to one mag... that will help quench the detonation.

All this from the Advanced Pilot Seminar course, demonstrated on a real aircraft engine in the test cell at GAMI. The class is still available as computer based training...

https://www.advancedpilot.com/

Paul
 
PaulMillner said:
If you do experience detonation in flight (CHT climbing 2 degrees a second, let's say) and after you respond by going full rich, full RPM, and reducing throttle some, the next technique is to switch to one mag... that will help quench the detonation.

All this from the Advanced Pilot Seminar course, demonstrated on a real aircraft engine in the test cell at GAMI. The class is still available as computer based training...

https://www.advancedpilot.com/
Click to expand...

Sure. But did they try one mag at full throttle?
 
IF you have already increased BMEP either by increasing RPM ( csp) or reducing MAP and Mixture RICH you may have something going on but it wouldn’t be Detonation.

Mags can fail either by not firing or firing at the wrong time.
A mag that is either timed well in advance of spec or is cross firing could well induce problems at Full Power though.

Engine originally certified on 80/87 or even 91/96 fuel ( the other blue) have a little more clearance from Detonation
with 100LL.
 
Note also that with two plugs the ignition timing is slightly later than it would be with a single, centralized plug. You give up some power, and probably fail to burn all of the fuel, and that's about it for consequences of taking off on one mag.
 
The one time I took off on one mag, I didn't notice it until I saw the EGT's shoot through the roof. I was already turning back to the field when I figured out that I was only on one mag. I turned them both on and all was good again.
 
brcase said:
if you note the RPM increase going back to both, you should never take off with one mag turned off.
Click to expand...

Why would you even take your hand off the switch until you go back to both?
What the heck are you testing exactly if you don’t go back to both before stopping?

It doesn’t seem like this situation should be possible.
 
Salty said:
Why would you even take your hand off the switch until you go back to both?
What the heck are you testing exactly if you don’t go back to both before stopping?

It doesn’t seem like this situation should be possible.
Click to expand...

Don’t instruct much I see… oh it’s possible!!

Had a student start up two days ago, AND THEN yelled “clear prop”.
 
Back
Top