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Mag switches

Jerry Cochran

Well Known Member
When I built my 6a I used Knuckolls' plan for the mags with 2 regular switches and not that crazy rotary thing the certified spam cans have. Now my present project has same and I am confused with it's setup. So if anyone can steer me verbally or with a real diagram towards the proper way to wire same I would vastly appreciate it.

And no, I am not confused just because I turn the big Eight-Oh this november...:D:confused:

email [email protected] or PM.

Jerry
 
Nothing wrong with that setup, and it automates the principle of keeping the non-impulse mag cold while cranking.

But the RV-4 I currently own has been flying since 1992 with just a pair of simple on-off toggles. Mine are the small frame mini toggles with 1/4" bushing mounts. To use simple toggles, you just mount them 'upside down' so that when the handle is up, the contacts are open. This does require the pilot to proactively not turn on the non-impulse mag until after engine start. :)

Charlie
 
Nothing wrong with that setup, and it automates the principle of keeping the non-impulse mag cold while cranking.

But the RV-4 I currently own has been flying since 1992 with just a pair of simple on-off toggles. Mine are the small frame mini toggles with 1/4" bushing mounts. To use simple toggles, you just mount them 'upside down' so that when the handle is up, the contacts are open. This does require the pilot to proactively not turn on the non-impulse mag until after engine start. :)

Charlie

Just curious, what if you have both mags on?
 
If both mags have an impulse coupling, then nothing. But most airplanes have 1 impulse and one non-impulse mag. The impulse mag fires AFTER or AT TDC. If you don't ground out the non-impulse mag for starting then you have the potential for severe kickback because it is timed to fire at 25 degrees BEFORE TDC.

Vic
 
I would like to point out that mags don't fire well at low RPM, like cranking speed. Impulse couplers retard the firing of the mag, and the spring that is wound up before the trip release speeds up the mag enough to get a nice spark.
I have a Pmag and a non-impulse coupled mag on two planes. on my RV-8, I have many times started the engine with both Pmag & mag toggle switches 'hot' and don't get a kick-back.
I try to always start on the Emag, then turn on the Bendix mag, but I have goofed a few times with no problems.
Story; I have a T-18. It has a rotary mag/start switch. It had the standard mag set up with one impulse mag. At an 'away' airport, it wouldn't fire. I got it cranking as fast as the battery wouild turn it, and released the key (activates 'both' mags) and the engine did barely catch and run (third try) so fast cranking speed is 'just' fast enough to get a spark, and also fast enough to not kick back....in my case.
The mag check was fine and I flew off. Once home the mag came off and eventually was replaced with a Pmag.
 
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