N941WR
Legacy Member
On another thread, someone asked how the P-mag will respond with a leak in the MAP line.
This morning I unplugged the MAP line from one P-mag and plugged the system so the right P-mag was operating off of a closed system while the right one remained open to the atmosphere.
All tests were performed with a Fixed Pitch prop. The higher RPM generated with a Constant Speed prop on takeoff or lower RPM in cruise may cause the P-mags to react differently.
What I found was that on startup and initial climb out both P-mags tracked each other exactly.
21, 22.4, 23.8, etc. degrees at low RPM's and MAP.
During the Run up, both the left and right P-mag's stayed at the low end of the setting. (25.2* BTC in my configuration.)
During the takeoff roll and initial climb (My airport elevation is 1064 MSL) both ignitions stayed at 25.2 up to about 4,000'. At that point, the right P-mag started to advance and the open left P-mag stayed right at 25.2 degrees.
The left P-mag's internal MAP sensor started to recognize the reduced atmosphere pressure and started letting the disconnected P-mag start to advance.
As I continued my climb, the open P-mag eventually hit the Max advance limit but it did so after the P-mag that was connected to my MAP system.
What I deducted from this was that should you have a failure in your MAP system, the P-mag will not allow your timing to advance to the point where it will harm your ignition. However, every installation is different and I could very well be mistaken.
(BTW, the EICommander was going crazy because it recognized the timing divergence in my configuration. Normally this wouldn't happen because a leak in the MAP system would impact both P-mag's.)
This morning I unplugged the MAP line from one P-mag and plugged the system so the right P-mag was operating off of a closed system while the right one remained open to the atmosphere.
All tests were performed with a Fixed Pitch prop. The higher RPM generated with a Constant Speed prop on takeoff or lower RPM in cruise may cause the P-mags to react differently.
What I found was that on startup and initial climb out both P-mags tracked each other exactly.
21, 22.4, 23.8, etc. degrees at low RPM's and MAP.
During the Run up, both the left and right P-mag's stayed at the low end of the setting. (25.2* BTC in my configuration.)
During the takeoff roll and initial climb (My airport elevation is 1064 MSL) both ignitions stayed at 25.2 up to about 4,000'. At that point, the right P-mag started to advance and the open left P-mag stayed right at 25.2 degrees.
The left P-mag's internal MAP sensor started to recognize the reduced atmosphere pressure and started letting the disconnected P-mag start to advance.
As I continued my climb, the open P-mag eventually hit the Max advance limit but it did so after the P-mag that was connected to my MAP system.
What I deducted from this was that should you have a failure in your MAP system, the P-mag will not allow your timing to advance to the point where it will harm your ignition. However, every installation is different and I could very well be mistaken.
(BTW, the EICommander was going crazy because it recognized the timing divergence in my configuration. Normally this wouldn't happen because a leak in the MAP system would impact both P-mag's.)
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