Mag switches

[Ed Haywood]

I have toggle switches on my Decathlon, not a keyed ignition. The current switches are double pole, but only one pole is wired. The wiring diagram shows single pole. Is there a reason double pole switches might be needed instead of smaller and less expensive single pole switches? Could it simply be that the terminals are better protected from accidental contact?

 

[Bell206]

Is there a reason double pole switches might be needed instead of smaller and less expensive single pole switches? Could it simply be that the terminals are better protected from accidental contact?

No. It might be as simple as American Champion buys only double pole switches and gets a better discount. The difference in the pic is only due to switch vendor design.

 

[Ed Haywood]

No. It might be as simple as American Champion buys only double pole switches and gets a better discount. The difference in the pic is only due to switch vendor design.

Both switches in my hand are Bellanca OEM. The single pole on the right was used for lights. The double pole on the left was used for mags and master. Master needs double pole per schematic, but mags do not.

 

[Dan Thomas]

Both switches in my hand are Bellanca OEM. The single pole on the right was used for lights. The double pole on the left was used for mags and master. Master needs double pole per schematic, but mags do not.

But what changes have been made since the airplane left the factory? People do stuff, and maybe they replaced the mag switches with a couple of DPST master switches they had in stock.

 

[Ed Haywood]

But what changes have been made since the airplane left the factory? People do stuff, and maybe they replaced the mag switches with a couple of DPST master switches they had in stock.

Good question, I'll research that further. There are a zillion photos of older electrical panels on the facebook page that the factory hosts, so ought to be able to get an idea what the norm was for Bellanca aircraft back in the 70's.

Mainly I was trying to find out if there was some actual performance reason why someone would need to use DP switches for the mags. Sounds like that is not the case.

 

[Ed Haywood]

A related question about mags: if the switch terminals were shorted to ground in flight, would it kill the engine?

OTOH, if the switch contacts failed, it would have no effect on flight, but would result in a hot mag at shutdown, correct?

 

[Dan Thomas]

A related question about mags: if the switch terminals were shorted to ground in flight, would it kill the engine?

OTOH, if the switch contacts failed, it would have no effect on flight, but would result in a hot mag at shutdown, correct?

Yup.

 

[Ed Haywood]

A little dry fitting answered the question. It is a physical dimension issue. The AN single pole terminals are too deep and would make contact with the frame.

 

[Dan Thomas]

A little dry fitting answered the question. It is a physical dimension issue. The AN single pole terminals are too deep and would make contact with the frame.

View attachment 111078

I see a magnetic hardware tray sitting on the windowsill. I didn't allow that sort of thing around airplanes. It magnetizes hardware and sooner or later one of those nuts gets installed near the compass and drives one mad trying to calibrate it. Get the tray itself close to the compass, and the compass is shot. Instantly. Even more expensive would be getting magnetized stuff near the flux gate used in the wings of glass panel airplanes. Or the tray getting near the AmSafe seatbelt airbag triggers under the cabin floor. They're magnetically triggered. Boom.

 

[Ed Haywood]

I see a magnetic hardware tray sitting on the windowsill. I didn't allow that sort of thing around airplanes. It magnetizes hardware and sooner or later one of those nuts gets installed near the compass and drives one mad trying to calibrate it. Get the tray itself close to the compass, and the compass is shot. Instantly. Even more expensive would be getting magnetized stuff near the flux gate used in the wings of glass panel airplanes. Or the tray getting near the AmSafe seatbelt airbag triggers under the cabin floor. They're magnetically triggered. Boom.

Ok, good tip, thanks.