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Al,
I'll let Tracy respond to the technical stuff (for obvious reasons). The wires that I separated were the A, B, C, & D wires to each of the six coils, but for only about the last 1.5 - 2' nearest the coils. The rest of the run was impossible to unbundle without major surgery to the harness. I was amazed at how much difference that small change made in how the engine ran, especially in the lower rpm range. Tracy's response stressed the importance of separating the power ground wires from the other coil wires. The area that I separated included the power ground wires, so maybe that explains why there was such a noticable difference.
Mark S.
(I thought I was done with wiring issues)
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From: Rotary motors in aircraft on behalf of Al Gietzen
Sent: Sun 10/15/2006 12:48 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Coil wiring
Mark; Tracy;
I'd like to explore this further. Mark S wrote:
After reading Bob Darrah's post last week where he noticed a big improvement after separating the leads to his coils I gave it a try on my 20B. It made a big difference, but was most noticeable in the lower rpm range. I was only able to separate the wires down near the coils, and then only by a small amount, but it made a substantial improvement. My question for Tracy is, can I leave the grounds and +14v wires bundled together and only separate the trigger leads, or do I need to separate all the wires? Also, if I were to use 3 individual shielded wires and ground the shields, could I then bundle the trigger leads together with the rest of the coil wires?
On a side note, after separating the coil leads, it took a much leaner mixture to get it to run smooth. Before, the best it would idle was about 1200rpm, now it will idle nicely at 900 rpm, not that I want to do that, but it shows that the improvement isn't all in my head.
Clarify for me which leads you separated; the control leads from pins 3, 20, and 21 (C-pins) from each other? I find that below about 1400-1500 rpm the engine begins the occasional miss, and gets progressively rougher as rpm decreases. I've been thinking that it seemed more ignition related then mixture related.
I have the C-pin leads and the B-pins ground bundled together from the box to the firewall penetration (a few feet). These bundles are separate for each set of coils (lead, trail). From the firewall to coils (a few more feet) the power lead (pin-D) joins the bundle. The A-pins are all grounded at the coil mount.
Tracy wrote:
1. How long is the wiring harness between EC2 and coils?
About 6 ft for the trailing and 10 ft for the leading.
2. How is the power ground to the coils (A terminals) routed? (hopefully not in the same harness, if so, there is your problem).
3. Same question as 2. on the power terminals.
Does this say that the power lead (D-pins) should not be bundled with the C or B pin leads? If so, is this just as true if the lead and trailing bundles are separate.
4. I would be surprised if this turned out to be the problem but if coupling between the control lines themselves (C pins) turns out to be the problem, use either twisted pairs or shielded wires to drive the B & C lines to each coil. I would lean toward twisted pairs.
I ran a common B-pin ground for each set; bundled with the C-pin leads but not twisted. Twisted pairs would mean adding more wires - or would twisting 3 control leads with one ground to as well?
5. Are there any other lines routed along with the coil harness (injector drives, etc)?
The coil bundles run with the injector drive bundles from the near the firewall to the top of the engine, maybe 4 ft or so; and run with other wires for a foot or so. One objective is to minimize firewall penetrations, another is to maintain separation between sets of injectors and sets of coils for true redundancy, and another is to separate noisy wires from quiet wires; so further separating isn't a simple matter.
Al
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