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Date: Sun, 19 Nov 2006 08:23:07 -0600
From: Charlie England <ceengland@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Spark Plugs
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Ed Anderson wrote:

> I agree that the "idea" auto spark plug for the flying rotary is still 
> waiting in the wings.  I am currently using a special lead scavenging 
> formula to see if it can extend the useful life of lead fouled spark 
> plugs (don't ask I don't know what's in it {:>)). Well, see whether it 
> does anything for the problem.
>
> I normally get approx 25 hours on a set before SAG sets in using 
> 100LL.  I speculate that one reason that such things as TCP do not 
> appear to do much for the rotary engine is that the chemical reaction 
> apparently (according to reports) requires the high cylinder head 
> temperatures of air cooled cylinders (like 375F +).  I believe that 
> with our plugs buried within the housing (as opposed to protruding 
> into the combustion chamber (and they had better not or you will clip 
> your apex seals), that the plugs do not reach a sufficiently high 
> temperature to deter fouling or to activate the TCP chemical 
> reaction.  So perhaps a "hotter" plug might help - on the other hand, 
> since we are running WOT for longer periods that many rotary racers - 
> I'm not certain I want a hotter plug.
>
> I have tried fine wire and the stock plugs - but both seemed to have 
> the same problem of lead fouling the ceramic cone and "bleeding" off 
> spark causing misfiring.
>
> My $0.02
>
> Ed 


Back in the bad old days when cars ran leaded gas & transistors were 
only found in spacecraft, there was an after market plug with 
construction known as 'surface gap'. The porcelain filled the area 
between the electrode & thread body. The 'gap' was the distance from the 
electrode to the thread body.

Anyone know whether these plugs are still available? It would seem that 
if nothing else, it might make cleaning the lead a bit easier.

Charlie