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Date: Fri, 06 Oct 2000 07:55:13 -0500
From: Brent Regan <brent@regandesigns.com>
To: Lancair List <lancair.list@olsusa.com>
Subject: Re:Lancair IV-P Heating problems climbing through FL 190
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John writes

<<I have a single electronic ignition (EI by Klaus Savier) and a mag with
both
ignitions set at 24 degrees BTDC at manifold pressures greater than 25"
<<snip>>
I believe that detonation should be even less likely in my
configuration then standard dual mags. I do like the system, however, it
could be the source of my heating problems during climb. I'm open for any
suggestions.>>

How do you know that both plugs are firing at the same time? The magneto is
set at a static timing point of say 20 DBTDC but that isn't when the plug
fires. When the engine is running there are mechanical and electromagnetic
delays that cause the plug to fire later. How much later is a good question.
With two mags, you can assume that the delay is the same, so how long it is
doesn't really matter, but with one mag and one EI, who knows?

Your fuel flow is dropping because your charge density is falling due to
heat (the intercoolers can't keep up). Remember that you can maintain
manifold pressure while charge density is dropping as the charge gets
hotter. IMHO, if you increase you fuel flows and fly 10-20 KIAS faster in
the climb your ROC will be about the same but cooling will be improved.  I
suspect that in the mid 20s FLs you will need to drop your VSI to 500-700
FPM.

If this doesn't work then you are back to ignition timing and/or improving
cooling through the engine. I tested 25 degrees static advance early in my
flight test program and saw detonation at altitude. I also know that many
conventionally baffled engines have had to resort to increasing the
discharge area ("Dolly Parton" cowl) to get adequate cooling.

Cooling on the IV is marginal, so small changes in speed and attitude can
mean a big change in engine temperatures. During flight testing prior to the
cross country race I would see a 10-20 degree rise in CHTs after a 180
degree standard rate turn at FL270 and 94% power. Talk about touchy.

Regards
Brent Regan



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