What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Experimenting With Ignition Timing

logansc said:
Well, I'm late to this party but hearty congratulations and thanks to Michael and all the others who have and continue to, contribute to this important discussion. Fascinating data, I have to say.

Probably not what Ross wants to hear, but I've been waiting on a 6 cylinder P-Mag for so long that I don't see any harm in waiting longer. Am I at least right that as a minimum, its manner of mechanization would at least eliminate flywheel "wiring and installation" damage concerns from the equation?..
Click to expand...

Lee,

I purchased the CPI because I just could not wait for the P-200 any longer. Aside from the configuration between the two systems (unitized vs. distributed), I expected the performance to be comparable (seen one EI, you?ve seen them all, right?) I had some concerns about the front mounted hall sensor for CPI at first, but after installing these massive pieces, as well as armor plating the wires, I think Ross has driven the ?thrown belt? failure mode down to a very acceptable level. I suspect that running out of fuel is a more probable forced landing scenario. However, everyone needs to make their own risk assessment.

Back to performance: As mentioned in other threads, the total adjustability of the CPI is a practical advantage and a genuine product differentiator for Ross. You may not know it yet, but you will find great utility in the ability to set your own cranking retard, idle timing, retard for take off, and yes, an adjustable advance for LOP. To their credit, the P-200 offers the ?LOP? switch that Ross has, but I?m still unclear how ?locked down? the rest of their advance curve is. Brad and the rest of the EI manufacturers have aimed at the fat part of the bell curve to great success, however, we are just beginning to learn that there are limitations to a ?one size fits all? ignition curve.
 
Flexible, Quick Programming

With a couple threads discussing EI and adjustable ignition timing, I wanted to show how easy the CPI is to program compared to the interfaces offered by some of our competitors. Timing is adjustable every 100 rpm in 1 degree increments and reads ACTUAL timing. Scroll to a new range/ window with the < or > buttons, increment or decrement the timing value at that rpm or manifold pressure. Total timing is the composite of rpm timing plus/minus MAP advance or retard. Dead simple. Cranking retard and and advance switch (for LOP operation) amounts are also easily programmable in their own windows.

cpi12_zpsgxqxhrmp.jpg


cpi10_zpsypcyrznc.jpg


cpi13_zpso3xsb6sg.jpg


cpi14_zpsl9sn32p0.jpg
 
So here we are several months after my last "flight test" and I wanted to share some results of a flight yesterday to Sedona, AZ.

Recently, I have been "addicted" to seeing the magic 200 KTAS on my EFIS and as a result I'm running a little less efficiently than I could be at peak EGT and 12 GPH. Prior testing has driven me to set my CPI "LOP switch" at 3 degrees advance, so I decided to play with some "what if" scenarios on my 1.6 hour flight yesterday.

Cruise at peak EGT, 9500 MSL and a sweltering 70 degrees OAT resulted in 12 GPH and just at 200 KTAS. In this rich condition I run without the LOP switch advance active (30 degrees advance). Well stabilized, I advanced the timing to 33 with the LOP switch and within a minute or two I saw zero change in TAS, but the CHT settled in 8 degrees hotter and the oil temp increased a couple of degrees. This is expected behavior based upn my earlier flight test. If you are rich, too much advance only drives more temperature into the engine. after flying in this condition for about 10 minutes, I deactivated the LOP advance to see if the temps would drop to their prior levels. Almost immediately after pulling the advance out, the temps started downhill, settling in at their prior levels after just a few minutes. Ok, that result was confirmed as repeatable.

Next test was LOP cruise. As much as I hated to give up my 200KTAS, I dialed the mixture back to 10 GPH and the speed and temps plummeted, eventually settling in at 188 KTAS and a full 20 degrees cooler on CHT and close to 10 on oil temp. I flew for close to 10 minutes in this configuration to establish stability. Without touching anything else, I activated the CPI LOP advance switch taking the ignition from 30 to 33 degrees. The EGT dropped immediately, and the CHT started climbing. Within 5 minutes, the TAS climbed from 188 to 191 knots and stabilized, with the CHT finally settling in about 8 degrees warmer than before (still a very comfortable 375). I flew the remainder of the mission in this condition and it remained stable for the next 30 minutes until the TOD into Sedona.

So bottom line is even with a new season and new temps, my initial flight testing has been repeated: the optimal ignition advance requrements are highly dependant on the mixture and operating environment of the engine.

I'm even more convinced than before- one ignition advance schedule does NOT fit all.
 
Last edited:
Toobuilder said:
So here we are several months after my last "flight test" and I wanted to share some results of a flight yesterday to Sedona, AZ.

Recently, I have been "addicted" to seeing the magic 200 KTAS on my EFIS and as a result I'm running a little less efficiently than I could be at peak EGT and 12 GPH. Prior testing has driven me to set my CPI "LOP switch" at 3 degrees advance, so I decided to play with some "what if" scenarios on my 1.6 hour flight yesterday.

Cruise at peak EGT, 9500 MSL and a sweltering 70 degrees OAT resulted in 12 GPH and just at 200 KTAS. In this rich condition I run without the LOP switch advance active (30 degrees advance). Well stabilized, I advanced the timing to 33 with the LOP switch and within a minute or two I saw zero change in TAS, but the CHT settled in 8 degrees hotter and the oil temp increased a couple of degrees. This is expected behavior based upn my earlier flight test. If you are rich, too much advance only drives more temperature into the engine. after flying in this condition for about 10 minutes, I deactivated the LOP advance to see if the temps would drop to their prior levels. Almost immediately after pulling the advance out, the temps started downhill, settling in at their prior levels after just a few minutes. Ok, that result was confirmed as repeatable.

Next test was LOP cruise. As much as I hated to give up my 200KTAS, I dialed the mixture back to 10 GPH and the speed and temps plummeted, eventually settling in at 188 KTAS and a full 20 degrees cooler on CHT and close to 10 on oil temp. I flew for close to 10 minutes in this configuration to establish stability. Without touching anything else, I activated the CPI LOP advance switch taking the ignition from 30 to 33 degrees. The EGT dropped immediately, and the CHT started climbing. Within 5 minutes, the TAS climbed from 188 to 191 knots and stabilized, with the CHT finally settling in about 8 degrees warmer than before (still a very comfortable 375). I flew the remainder of the mission in this condition and it remained stable for the next 30 minutes until the TOD into Sedona.

So bottom line is even with a new season and new temps, my initial flight testing has been repeated: the optimal ignition advance requrements are highly dependant on the mixture and operating environment of the engine.

I'm even more convinced than before- one ignition advance schedule does NOT fit all.
Click to expand...

Mike,

Is this with dual CPI's or just one? I thought you added the second one. I have been running 35* when LOP, but I only have one EI. If you are doing well with 33* on two EI's, maybe I'll experiment with throwing more timing at it to see what happens. I am guessing that there should be a 5-7* difference in optimum advance when running one vs. two EI's. I would be curious if you ever documented best advance for both one and two EI's.

Larry
 
Larry,

This is with dual CPI. In a general sense, the single vs dual was about 3 degrees less advance across the board for the dual.
 
You must log in or register to reply here.
Back
Top