Funny thing,
I was just installing a new set of spark plugs and noticed that
there is a set of installation pictures on the stock NGT spark
plug..  the last picture is a big red X through a picture of an
airplane.  Specifically, we should apparently not use these spark
plugs with motor gliders or ultralights.  So I think regular
experimental airplanes should be OK.  :-)

--
David Leonard

Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net

What is that some web sites say?  "Things our lawyers make us say."

I wager this is something the legal department invented to head off a
class of lawsuits.
sdorr

Do not forget about DESIGNED DUTY CYCLE. Automotive spark plugs are designed
with a small % duty cycle. This means they are OK to the max power for short
periods of time. AC use is a lot higher duty cycle. That is also why plugs for
a race car are usually colder heat range than for street. I would expect Dave
uses colder plugs than a car would use. Continuous hiway use also mandates a
cooler plug.
Plugs for certified engines are also subject to fitting into the certified
arena. If you drop an AC plug, you throw it over your shoulder. For
automotive, you pick it up and dust it off. Worst case is you gap it. Also
certified has money put away in the event of the legal beagles becoming involved.

Dale Davies