Runup mag check

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R-2800-59
Staff Sergeant
Posts: 291
Joined: 23 Jun 2010, 15:45

Runup mag check

Post by R-2800-59 »

Dear community,
this one bothers me for a while now. When checking the mags on the Connie at 30", prop fine and mixture rich, instead of a rpm drop I experience a 3" manifold rise when running on either left or right Mag only. Why is that the case?
Other than that it runs great, just flew LGTS to OMDB and she performed incredibly well.

flapman
Staff Sergeant
Posts: 457
Joined: 10 Oct 2013, 21:35

Re: Runup mag check

Post by flapman »

Just confirming, there was no RPM drop when you switched off a mag?

alan CXA651
Senior Master Sergeant
Posts: 2438
Joined: 15 Mar 2016, 08:23

Re: Runup mag check

Post by alan CXA651 »

Hi.
During mag check it states 2200rpm DO NOT EXCEED 30 man , what was your RPM showing , also at 30man you may have been a tad over this and a drop in RPM may not have been noticed , you are only looking for a drop of 100RPM , which is not a lot.
regards alan. 8)
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R-2800-59
Staff Sergeant
Posts: 291
Joined: 23 Jun 2010, 15:45

Re: Runup mag check

Post by R-2800-59 »

As I've stated, I set the MP to 30" at props full fine, what gives approx. 2200rpm. When switching to single mags I get a MP rise instead of a RPM drop. Just did it again to confirm myself.

Thanks so far!

flapman
Staff Sergeant
Posts: 457
Joined: 10 Oct 2013, 21:35

Re: Runup mag check

Post by flapman »

Here are my test results:

FSX:A (Boxed...yeah, I'm old school)
Had the mechanics wheel the prototype C-69 (Army Air Corps colors) out of the hangar in KBUR(Bob Hope, California) to check out the problem. Flight Engineer is enjoying a day at the beach, and the "Cold Start" button is pressed. Last heavy check reports all engines are in "Excellent" condition... with the selected #3 engine showing 27.3 hours on the Hobbs meter.

A primer-only manual start brings the engine roaring to life flawlessly, and all systems are normal as we wait for the oil to warm up before applying power. Skip the supercharger test. Cycle the prop to get the oil moving.
Now, I personally do a Mag check at 1700 RPM. That's a common figure I use for the wide variety of piston aircraft I fly in the sim (and close to figures I've used in real life), and I figure it is enough power in nearly everything to conduct the test, without creating excessive heat.
The 1700RPM Mag check yields 20RPM loss on each mag. I consider this a good test.

But I see that you're referencing the correct (for this aircraft) value of 2200RPM for the mag check, and you're also noting the MAP increase during it. I personally am not concerned with this MAP change during this test, but I'll do it by the manual and check the readings to see what I find. P. 125 instructs the Engineer, "Increase to 2200 rpm but do not exceed 30 inches Hg. and request pilot to check magnetos. Engines must operate smoothly on either magneto." The pilot's duties are stated, "Check magnetos on request of flight engineer. Maximum normal drop is 100 rpm on going from both to one magneto."

I advance to 2200 and tell the mechanic in the front seat to check the mags on #3. We'll use the FE RPM gauge as it is more accurate. 2200 RPM, 24.5" MAP,
"LEFT!"
20 RPM drop. MAP increases to 26". Smooth operation.
"BOTH!"
Return to 2200 RPM and 24.5" MAP.
"RIGHT!"
2 clicks and #3 slows another 20 RPM, and the MAP climbs again to 26". Purrs like a kitten.
"BOTH!" "GOOD CHECK!"

We idle the engine for about 1 minute before shutting the engine down, turning off the battery, unplugging ground power... then wheeling her back into the hangar for another revenue flight in the (hopefully not to distant) future.

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