P mag problem

[cguarino]

Originally Posted by Steve Sampson

I think the answer here is make a really good ground strap! Examine it regularly. To my mind it is about the most important wire on the aircraft.

This is extremely important. If the ground strap breaks and you try to start the motor, all of those amps are going to go straight through your PMags. You can guess the rest.

[N941WR]

Originally Posted by Steve Sampson

...I have actually grounded my p-mags to two different places on the engine to make them as independent as possible. A bit of an overkill, but hardly difficult...

Steve, hardly overkill. It is the CORRECT way to wire them. If you put both to a common ground, you might as well only run one ignition system, IMHO.

Originally Posted by cguarino

This is extremely important. If the ground strap breaks and you try to start the motor, all of those amps are going to go straight through your PMags. You can guess the rest.

Charlie, I pointed out to Mike that our chapter's tech advisors recommend a secondary engine to airframe grounding path for all aircraft. This could be either a secondary ground strap or something like a 14 to 16 AWG wire from a case bolt to the common ground.

In my case, the stainless steel oil and fuel lines provide this path. (Think faraday cage.)

Should your plane not have a grounding strap in place and you don't have a secondary path and you hit your starter, the load from your starter motor will probably toast every wire between your engine and the airframe. (CHT's, EGT's, etc.) It gets really ugly.

[Mike Ice]

Fellows,

Thanks for the education.

You can bet the next time I am at the airport I will run the ground wire from the E/P mags to the engine.

Mike Ice

[rv8ch]

Originally Posted by N941WR

...
Charlie, I pointed out to Mike that our chapter's tech advisors recommend a secondary engine to airframe grounding path for all aircraft. This could be either a secondary ground strap or something like a 14 to 16 AWG wire from a case bolt to the common ground.

Seems like wise advice.

Originally Posted by N941WR

In my case, the stainless steel oil and fuel lines provide this path. (Think faraday cage.)

This is flexible hose with stainless steel braiding, right?

[N941WR]

Originally Posted by N941WR

In my case, the stainless steel oil and fuel lines provide this path. (Think faraday cage.)

Yep.

The faraday cage principle will allow the electricity to move along the hose and not hurt what is inside.

[Steve Sampson]

Bill, have you measured the resistance of the stainless hoses? Its a huge current flow (> 200amps?) when you hit the starter.

When I built my -4 I rejected that as an acceptable path in my mind without ever investigating very far. Similarly the control cables.

If either of these paths ever had to take the full load I question if they could accept the heat. Maybe its a lower resistance than I think.

PS Apologies if I drifted your P-mag thread Mike.

[cguarino]

Isn't lectricity is like water? Won't it seek the path of least resistance? Give Brad at Emag a call and asks him what happens on an electronic ignition airplane when the ground strap breaks.

[smithhb]

This is the reason a lot of folks go with dual ground straps. I got mine from B&C http://www.bandc.biz/cgi-bin/ez-cata....cgi?26X358218

[mburch]

Originally Posted by smithhb

This is the reason a lot of folks go with dual ground straps.

Bret,

Not to further hijack this thread, but... Can you share where you connected your second ground strap to the engine? My first one is attached to one of the aux alternator (aka vacuum pad) mounting studs. I'm thinking either a sump bolt or that mystery hole low on the starboard side to mount strap #2.

thanks,
mcb

[smithhb]

Matt,

I haven't installed the straps yet but plan to just grab the nearest accessory case bolt.