Question about mags and horsepower

N2124v

N2124v

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N2124V
Ok, I was having a theoretical debate about this scenario and wonder what you think.

On a Lycoming IO-360 at High rpm one of the mags can not keep up so effectively running on one mag. Do you think there would be a power produced penalty with the one mag not pulling it's weight? Would it be noticeable?
 
N2124v said:
Ok, I was having a theoretical debate about this scenario and wonder what you think.

On a Lycoming IO-360 at High rpm one of the mags can not keep up so effectively running on one mag. Do you think there would be a power produced penalty with the one mag not pulling it's weight? Would it be noticeable?
Click to expand...

Have you ever performed a mag test on a preflight before? Do you understand what is happening?


What do you mean "cannot keep up"? Mags tend to misfire at low RPM if they are weak. If the mag is coked with junk from lack of service it will short out at higher attitudes and may not be noticeable at low altitudes.

There are many failure modes, not what your asking. Yes there is performance loss when even one spark plug isn't firing, if a whole mag dies in flight you'll know right away something is wrong.
 
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If you want a good idea of just how much power you lose on one mag, do a full throttle static run-up on both mags and then on one, and note the RPM's each way. Since HP is pretty much directly related to RPM in that situation, dividing the 1-mag RPM by the 2-mag RPM will tell you pretty closely what percentage of HP you've lost. Just don't run it on one mag very long or you'll need to pull and clean the plugs that were on the "dead" magneto.
 
Like Brian said shut one mag off in the air and see what happens. If you haven't done this you really need to understand why you should. The very reasons you ask the question would be answered by performing this very nessessary "in the air" flight test.

Performace will drop, EGTs go up, (so you have to burn more fuel go maintain engine temps).

It is a good test in the air to see how your plugs and mags are doing. Shut one mag off and feel for vibrations, repeat. Don't forget to turn them both back on. :lol: ;)
 
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This is like the old saw about 'if ya gotta ask ya can't afford it'
In your case, if ya gotta ask you are way past time to have the mags gone over by a mechanic
And it is more than the mag - plugs and wires also
And a weak cylinder will give more symptoms when one plug fails to fire than a strong cylinder will
You asked - so you need to get the engine checked
 
Actually, you'll probably not notice a mag failing either in full or in part (or a plug fowling) in flight unless there's something wrong with the remaining mag. Yeah, you might notice a small decrease in power but that's it.

An intermittent failure of a plug or mag on one side is barely detectable.

Of course, you'll know it in a hurry if you move the mag switch off BOTH.

I've had more than my share of mag and other ignition failures over the years.
 
flyingron said:
Actually, you'll probably not notice a mag failing either in full or in part (or a plug fowling) in flight unless there's something wrong with the remaining mag. Yeah, you might notice a small decrease in power but that's it.

An intermittent failure of a plug or mag on one side is barely detectable.

Of course, you'll know it in a hurry if you move the mag switch off BOTH.

I've had more than my share of mag and other ignition failures over the years.
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I've had my share of mag and ignition failures, and they've all been noticeable. But I'm probably more in-tune with my engines than most pilots are.

Lycomings (especially parallel valve engines) handle mag failures very well and the engines will run indefinitely on one mag. Yes, EGTs will go up, power will go down, but most people probably won't notice it unless they have an engine monitor and are in tune with their engine(s).

Continentals I have found do not handle mag failures well. After about 1-2 hours the engine will get very unhappy and you'll start to get missing on the "good" plugs. I don't know why Continentals suffer this in my experience and not Lycomings, but this is just what I've observed.

If I recall correctly, the regs state that when operating on one mag, an engine may lose "no more than 15% of its rated power." The actual number you'll see is probably more in the realm of under 10%.

Either way, operating a plane that only has one mag that functions as it's supposed to is an extraordinarily dumb move. When that mag goes bad, you've turned into a glider. These engines have two mags for redundancy, performance, and efficiency
 
kinda going off topic, but when do you guys have yours overhauled? at the recommended interval or when they fail a mag check? Mine run great, and I planned to keep going until one starts to give me trouble. Any reason that is wrong? and then do you repair just the one or all of them?
 
rbridges said:
kinda going off topic, but when do you guys have yours overhauled? at the recommended interval or when they fail a mag check? Mine run great, and I planned to keep going until one starts to give me trouble. Any reason that is wrong? and then do you repair just the one or all of them?
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There are two operational wear parts in a mag, the points and the points cam. A mag will rarely need an 'overhaul', typically an IRAN will get it done.
 
rbridges said:
kinda going off topic, but when do you guys have yours overhauled? at the recommended interval or when they fail a mag check? Mine run great, and I planned to keep going until one starts to give me trouble. Any reason that is wrong? and then do you repair just the one or all of them?
Click to expand...

I like doing IRANs at about 500 hours. You'll be seeing signs that they could use some attention by then.

Henning said:
There are two operational wear parts in a mag, the points and the points cam. A mag will rarely need an 'overhaul', typically an IRAN will get it done.
Click to expand...

Don't forget the carbon brush and capacitor too.



Last I checked, if you needed more parts than points, capacitor, points cam, and carbon brush for a Slick magneto you're probably better off buying a new magneto. The parts to repair what you have will cost about the same as the new mag. Bendix magnetos on the other hand are a little more economical to repair. Tempest makes some nice service kits that contain everything you will likely need for a reasonable price. Of course, the labor to repair either could start to push you closer to the cost of just sending them off or buying new.
 
rbridges said:
kinda going off topic, but when do you guys have yours overhauled? at the recommended interval or when they fail a mag check? Mine run great, and I planned to keep going until one starts to give me trouble. Any reason that is wrong? and then do you repair just the one or all of them?
Click to expand...
I've seen recommendations for 'overhaul' at 500 hours for Slicks. They may not need much but I think overhauls are generally offered at a fixed price.

I had a need to open mine up at <200 hours for a Service Bulletin concerning a prematurely wearing part. I feel confident that I can use my repairman's cert to keep them in service with a teardown, inspection and replacement of a few worn parts every 400-500 hours. My intent is to have the overhauled by a specialty shop at 1,000 to 1,500 hours, hopefully before any failures are encountered.
 
rbridges said:
kinda going off topic, but when do you guys have yours overhauled? at the recommended interval or when they fail a mag check? Mine run great, and I planned to keep going until one starts to give me trouble. Any reason that is wrong? and then do you repair just the one or all of them?
Click to expand...


That's a dangerous way to operate. Mags don't just "fail;" they can go rogue on you. Those plastic gears that drive the distributor rotor can wear badly under some conditions (usually poor assembly) and if they slip a few teeth, the mag starts sending spark to plugs at the wrong time. Think spark on the intake stroke, for example. That incoming charge burns and sets fire to the whole intake system, making the engine cough and bark and lose enormous amounts of power.

I've seen those gear really badly worn, and heard an RV go over one morning with its mag doing just that. He was trying to reach the airport. He didn't know, apparently, that the mag switch isn't just for checking mags on runup and shutting them off at shutdown; it's for turning off that rogue magneto when it rebels and starts following its own program.

A worn points cam will retard the spark and drive EGTs up and power down. Worn points will advance the spark and possibly start detonation, busting up the engine. Either case will cost power as the E-gap changes. The magneto's ball bearings can fail when old, too; seen that before, and if they fail badly enough they can cause serious mechanical damage to the engine's accessory case.

False economy to let them go until they start acting up.

Dan
 
mondtster said:
I like doing IRANs at about 500 hours. You'll be seeing signs that they could use some attention by then.



Don't forget the carbon brush and capacitor too.



Last I checked, if you needed more parts than points, capacitor, points cam, and carbon brush for a Slick magneto you're probably better off buying a new magneto. The parts to repair what you have will cost about the same as the new mag. Bendix magnetos on the other hand are a little more economical to repair. Tempest makes some nice service kits that contain everything you will likely need for a reasonable price. Of course, the labor to repair either could start to push you closer to the cost of just sending them off or buying new.
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True, that's in the distribution system not mag in my view, but yeah, it's all in the same housing and definitely causes problems. Actually if this is the thread with problems under power, then the problem may well lie in Cabon deposited in this side of the unit. As power goes up so does resistance at the spark plug. Eventually the carbon dust becomes the path of least resistance and you lose that mag.
 
You have two of them. Unlikely they will both fail at the same time. Some advocate replacing ONE mag. Something to consider.
 
Flying behind mags that you think may have a problem is a very bad idea. As Ted mentioned some engines are better than others. My experience with mag failures on big Continentals makes me want to land immediately when I think something is amiss.

I probably got pretty luck with a certain member's dual magneto setup that **** out on me pretty much the second I landed.

You can learn everything you need to know about fixing magnetos on the tractor forums. At least, that's my strategy with mine, we'll see when I test fly it.
 
I've had double mag failures in the past. I'm certainly not going to take off on just one. Too easy to have a bad mag crop up in flight or have a plug foul or something. There's good reason they are TWO there. It's unsafe and ILLEGAL to depart with only one.
 
I had one fail in an AA-1C Grumman at about 1200 feet above ground shortly after takeoff. My first reactions was to look behind me and smelling for smoke/oil. I though something broke the way the airplane shuttered. Oil pressure and temps were good. It still climbed but not well.

I tuned around then flew a couple circuits above the airport at about 2,000 feet and started troubleshooting, the airborne mag check at about 50% power confirmed an ignition issue.

Landed and taxied to the hangar pulled the cowl and found nothing belatedly wrong. The engine was too hot to work on so we went to lunch. We returned to a cooler engine and ground ran it to find both magnetos now firing again. Now we suspected a bad coil at that point which is what it turned out to be.
 
One thing to consider. If you suspect a mag failure, and you do an airborn mag check, when the faulty mag is tested, the engine will quit. Most engines will almost surely backfire, BIGTIME when you go back to the good magneto. Could damage your muffler or exhaust pipes.
 
coloradobluesky said:
One thing to consider. If you suspect a mag failure, and you do an airborn mag check, when the faulty mag is tested, the engine will quit. Most engines will almost surely backfire, BIGTIME when you go back to the good magneto. Could damage your muffler or exhaust pipes.
Click to expand...

So if it quits, pull the throttle right to idle, wait a second, and turn the mag back on.

Dan
 
All I can say is that if a mag quits on a TSIO- Continental it will get your attention and you will find a landing place really quick. Power loss was prolly about 25% once it was stable, I could maintain altitude but climbing was pretty iffy. Maybe I coulda climbed but it likely would have burned the turbo, TIT was all over the place at normal power settings. IRANs at 500 hours or whenever the engine misses...note engine behavior on roll-out taxi for any sign of a miss.
 
N2124v said:
Ok, I was having a theoretical debate about this scenario and wonder what you think.

On a Lycoming IO-360 at High rpm one of the mags can not keep up so effectively running on one mag. Do you think there would be a power produced penalty with the one mag not pulling it's weight? Would it be noticeable?
Click to expand...

I was asked to check back in, and the first thing I see is this thread where the assumption is one mag is dead. If it passed the mag check prior to take off probably not, it is simply retarded.

For the OP

If you are saying that one mag is running retarded, as many many engines do, there will be no significant loss of power. It will simply shift where the flame front from each mag meets.
 
Dan Thomas said:
So if it quits, pull the throttle right to idle, wait a second, and turn the mag back on.

Dan
Click to expand...

Pull the mixture to idle. Throttle will still introduce fuel.
 
Ted DuPuis said:
Pull the mixture to idle. Throttle will still introduce fuel.
Click to expand...


We do hot mag checks at idle, and never get the bang. That happens at runup power. In flight, at idle, the mixture will be so lean that the bang is unlikely.

Dan
 
Dan Thomas said:
We do hot mag checks at idle, and never get the bang. That happens at runup power. In flight, at idle, the mixture will be so lean that the bang is unlikely.

Dan
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I'd much rather recommend pulling the mixture than the throttle and actually make sure fuel is no longer being introduced to the engine.
 
If you ever forget to go back to "Both" after your pre-flight mag check and then take off, you will get a quick eye opener about how much power you are missing.
 
N2124v said:
Ok, I was having a theoretical debate about this scenario and wonder what you think.

On a Lycoming IO-360 at High rpm one of the mags can not keep up so effectively running on one mag. Do you think there would be a power produced penalty with the one mag not pulling it's weight? Would it be noticeable?
Click to expand...

I just recently had to divert to Idaho Falls (enroute to Kalispell) because of a mag that was dropping out. We could feel the plane (Piper Saratoga) lurch as the mag dropped out. Also, we could see that tachometer twitch when it happened. Definitely noticeable, but you have to know what to be looking for or you might just think its rough air.
 
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