Single mag operation symptom surprise

[rogerl]

who owns it

Edited March 14, 2021 by rogerl

[StevenL757]

Roger, I'm guessing you own a Missile, Eagle, or Ovation, so can we start with which one you own and how much experience you have in it?  Based on your post, it appears you were on a single mag when you departed, which begs the question of why you didn't run through a scan and notice the key position inflight before you tried leaning and enriching?

Posting a bit of background about your aircraft and place of departure (if different than your home field) would help us better support you and give some guidance.  Believe me, there are a ton o' people here willing to help you operate this thing in peak condition, so you have a great group to work with.  Pictures are always appreciated as well...  :-)

Steve

[Hank]

When my l eft mag failed in flight, my EGT went above redline when it had never been within 100º of it before. So I turned the key to L, it got real quiet and pitched down pretty hard [I was at 9500 msl]. When I turned it back to Both, everything was normal, so I clicked it over to Right and releaned.

That's why we have two magnetos  . . .

It's also the "other" form of single mag operation (besides having the key turned wrong by accident). 

[N601RX]

High EGT and an erratic EGT when LOP. 

[DVA]

Is this "lack of EGT peak before redline" what the more knowledgeable would expect when committing the cardinal sin of inadvertent (as if there's any other) single mag takeoff/operation ?

Hi. Good news... your engine acted as expected. More Good News ... you will now put EGT temps in your pre-flight mag check.

When the engine is running on only a single plug per cylinder (one Mag), the exhaust gas flame front burns slower creating a less power and a hotter exhaust exiting the valve and passing by the probe. Hence the rise in EGT and a much hotter peak if you can even get there. (And you shouldn't try as you can easily exceed TiT in a turbo or you'll start to toast your exhaust system otherwise). Going full rich and landing was the right choice.

With this knowledge, you can use it to easily see if all plugs are working well on the ground during a mag check. And to help insure that you don't accidentally depart on a single mag again.

The technique is simple. Instead of doing a ground Mag check at full rich which really is only slightly diagnostic, lean a bit first. Bring RPM up to anywhere close to POH guidance. Then Lean just to the point of engine roughness and then back off a bit. Switch to the left mag and watch your egt gauge (if you have an engine monitor, scan at all egts) you should all egt temps rise 50-100dF depending on how lean you were. Switch back to both. They should slowly fall back a bit. Then switch to the right mag, you should see all rise again, don't worry about absolute values, they should all rise fairly evenly. Switch back to both. Your done.

If you see any cylinder egt not increase as you expect, or if one falls off, you have an issue. You can read more on this here and elsewhere.

You will likely have a bigger RPM drop on one mag when you do this in a lean mode. Don't worry, that's expected too. However the difference between the two mags should be within POH values. Something different means the ignition system needs to be checked.

Make sure you push the red knob full rich before takeoff.

Dave

[carusoam]

Sounds like memory challenges that I am familiar with...

1) how many clicks of the ignition switch was it? And how to find out where it is now...? Too far left the engine shuts down. Too far right the starter can be engaged...?

2) Screaming EGTs... has only one solution.  Stop the unburned fuel from leaving the cylinder...

3) remembering to return the mixture to full in...  the IO550 may not stumble when lean and accelerating like other engines...

4) checking FF on departure, then Airspeed alive.... 27.2 gph for the 310hp IO550 is the STC set point.  25gph is typical of the mixture left in the 2gph taxi setting...

5) there are some new ignition switches out that separate the functions.  It is very easy to tell if L is on or off, and the same for R.

6) +1 for watching all EGTs rise while doing the run-up...

Stuff I learned as I got 'older'...

 

Best regards,

-a-

[jaylw314]

As an aside, the last time I flew with my instructor, he frowned while I did a mag check using B - L - B - R - B, and pointed out I should turn the key from B - R - B - L - B.  His argument was because L (right key position) is next to B, there is less of a chance you will accidentally miss a notch and leave it on one mag.  I don't know if the Ovation ignition key is laid out the same, but that habit might help prevent that in the future.

Of course, I have an authority problem, so I do it completely differently now   I go from B - R - L - B while watching my EGT's.  Mike Busch noted he does it this way in one of his articles.

[carusoam]

Jay,

i hate long standing traditions... 

Our ignition switch was designed somewhere in the beginning of the last century...

The only modification was the removal of the painful push to start aspect...

I believe my switch positions are: Off, R, L, Both, Start....  (am I right?  The left key position is for the Right mag? The R mag is left of the L mag?)

I begin at one side and and end at the other, hitting B in between... (it matters not whether I test the L or the R mag first)

The goofy part is the Left Mag is on the right side of the engine, isn't it...?

When requesting service, I'll have to check what the label says on the switch and be clear about what I'm asking for.

I would really like two switches and a start button, and have my L mag really be on the pilot's left side of the engine....

Ignition switches only last 50 years or so.  There could be time to get a new styled one....

I probably confused myself...

Best regards,

-a-

[Hank]

On my C, the left mag is on the left side of the engine when sitting inside looking out the windshield. Right there behind the dad-blasted battery box . . . It makes strange sense for the Left key position to be closer to Start, since it cranks on the Left mag, but I won't swear that's how it is off the top of my head. And of course, your thoroughly modern R is probably different from my ancient C.  

[kortopates]

On 7/23/2017 at 7:38 PM, carusoam said:

The goofy part is the Left Mag is on the right side of the engine, isn't it...?

Only if your P-Leads are reversed at the mags - which happens a lot. @Hank says it right. The perspective of Left & Right is from the rear of the engine from the pilots seat. 

[kortopates]

On 7/22/2017 at 3:37 PM, rogerl said:

It was a real surprise to find single magneto operation on the io550 had the symptom of EGT that would not peak before redline.

There really isn't a redline for EGT. Continental did not publish an EGT redline. For whatever reasons, Mooney invented this for their blue-line target EGT sensor that measures EGT on the odd cylinders and  added a 1650F redline on their own, presumably using 1650F since its the most conventional TIT redline for turbo's. But apparently it did do what Mooney intended, as it got your attention that something was wrong in that you couldn't find EGT without continuing beyond 1650F, and if you had kept on leaning you likely would have started flaming out cylinders running on only one plug before seeing a peak unless your gami spread is very small.

Anyway, you're doing fine using your JPI to lean but its also important to know at what approx EGT you can expect to see peak on your richest cylinder (e.g., ~1575F) so that later while in cruise, after leaning it down to 50 LOP at about 1525F, you'll notice if it started creeping up on you so you can make an adjustment. Another easy way to use your monitor to help you better "monitor" in cruise is to put the monitor in "normalize" mode while in cruise. Then any EGT changes, like loosing a mag or plug, will be very obvious to you

On 7/23/2017 at 0:42 PM, carusoam said:

27.2 gph for the 310hp IO550

27.4 is actually the high number from TCM on the 310HP, and at Savvy we prefer to see 0.5 to 1.0 GPH above the high number.

   

[Hank]

22 minutes ago, kortopates said:

Anyway, you're doing fine using your JPI to lean but its also important to know at what approx EGT you can expect to see peak on your richest cylinder (e.g., ~1575F) so that later while in cruise, after leaning it down to 50 LOP at about 1525F, you'll notice if it started creeping up on you so you can make an adjustment.   

This is another area [along with Airspeed, Altitude and VSI] where needles are so much easier than numbers . . .

My EGT gage has a redline. it is likely the gage it left the factory with in 1970.