Message-ID: <003e01c0314e$cce147a0$263132cf@tcac.net>
From: "johnlasher" <johnlasher@msn.com>
To: <lancair.list@olsusa.com>
References: <39DDCBB1.CD54F04@regandesigns.com>
Subject: Re: Re:Lancair IV-P Heating problems climbing through FL 190
Date: Sun, 8 Oct 2000 12:40:06 -0500
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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Mike wrote>
> 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?

Good point mike. The mag was set 24 DBTDC statically and the EI was set 24
DBTDC dynamically with a timing light. Also, the EI has a much hotter spark
and a wider spark gap than the mag. Assuming that they fire together, the
flame front would probably move faster from the EI plug than the mag plug.
Maybe the EI should be retarded slightly.

> 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.

When my heating problems start to occur around 17,000 there is a
simultaneous drop in fuel flow from 30 gph to ~28 gph. Even going to high
boost FULL RICH won't restore the normal 30 gph during climb. I do increase
my climb speed eventually to cruise in order to arrest the situation. How
could I possibly increase my fuel flow? If I could, I'm sure the
temperatures would drop. Why does the fuel flow decrease at this point
during climb? Does your fuel flow change during climb? Fuel vaporization
doesn't seem to be a problem - I have low boost on above 10,000 and the fuel
pressure is stable.

> 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.

Maybe I should go to 20 DBTDC and try that. I do have Dolly Parton cowling
and seem to have very adequate cooling during climb - right up to the point
when my fuel flow starts to decline without any power change.

> 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.


Respectfully,
John Lasher


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