Two plugs - Neccessary?

[John Ferrell]

The last full scale I owned was a 1978 Cessna 172 with a Lycoming H2AD 4 
cylinder engine. Absolutely trouble free. It had a Bendix dual mag... both 
in one package, driven from one gear. Redundancy is sometimes how you define 
it.

It is not easy under "normal" conditions to identify a failing plug on a 
carbureted engine. You can hear it but figuring out which one is something 
else.

The P35 Bonanza I had was easy to pick out ignition problems. With dual 
mags, tight mixture control (Fuel injection), and an EGT probe on each 
cylinder, the pilot knew before the mechanic. Like the 182, the basic engine 
was a Continental IO470.

AFAIK, ALL single engine aircraft use a single solenoid to control the 
master electrical power.
That night mine quit at Chicago Meigs I was waiting for IFR clearance time 
to roll around. I sure was glad it did not wait another 20 minutes...

John Ferrell
http://DixieNC.US

----- Original Message ----- 
From: "Bob Richards" <bob at toprudder.com>
To: <discussion at nsrca.org>
Sent: Thursday, April 21, 2005 11:00 AM
Subject: Re: Two plugs - Neccessary?


> John,
>
> If I'm flying in a full-scale, I like having the
> redundancy of two completely separate iginition
> systems. :-)
>
> I'm not sure what you mean about two plugs making the
> troubleshooting more difficult. Should be easy to
> isolate.
>
> OTOH, changing plugs on my Dad's 182 was an expensive
> proposition. Back in the 80's, each plug was $12, and
> there were 12 plugs. :-(  I have no idea what they
> cost now. I guess if you can afford the fuel now, you
> can certainly afford the plugs. The 182 holds 80
> gallons!
>
> Bob R.


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