Message-ID: <001201bf05ca$c61d39c0$bc818ed1@pavilion>
From: "J. N. Cameron" <CIC@centurytel.net>
To: "Lancair List" <lancair.list@olsusa.com>
Subject: Erring OAT's;  aileron trim tabs
Date: Thu, 23 Sep 1999 08:35:21 -0500
Mime-Version: 1.0

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The OAT sensor in my ES is consistently reading high, but I can't figure out
why.  The probe is a standard thermocouple type, connected as CHT #7 in an
E.I. engine analyzer.  If I heat it slightly on the ramp, it goes up,
indicates about the right ambient in the hangar, and goes to 32 when I put
an ice pack on it.  In flight, however, it rarely goes below 65F.
Yesterday, leaving Wisconsin with an air temp of about 48F on the ground, it
still said 69F at 10,500'.  Not likely.  The probe is presently mounted so
it sticks downward near the top of the nose gear fairing, more or less at
bottom center of the lower cowl assembly.  Looks like it's right in the air
stream.  This is the second location I've tried; the first was just inside
the air intake -- same results.  I've double-checked the plug, but can't see
any problem.   Perhaps heat is being conducted from inside the engine
compartment through the probe housing, biassing the numbers upward.  E.I.'s
tech support say this shouldn't happen, but that's what it looks like.  Any
others out there with similar experience?  Ideas?  Where have most of you
put your OAT probes?

On the subject of aileron trim tabs, I modified the piano hinge that the
manual calls for by adding two pieces of the carbon fiber trimmed off the
elevator skins.  First I drilled both halves of the hinge (swiss cheesed
'em) for better bonding, then bonded carbon fiber skins on both upper and
lower surfaces of the tab (making a composite/metal/composite sandwich)
using Hysol 9309.  This is one of their aerospace epoxies recommended for
metal-to-composite bonding.  Be sitting down when they tell you the price of
it, though -- I paid about $115 for a quart a couple of years ago.  As
always, careful cleaning of the aluminum is critical for a good bond.  The
end result is a trim tab that's the same thickness and appearance as the
trailing edge of the aileron.  Looks better than just the metal hinge tab, I
think.  It may not be as slick as cutting them into the aileron, but it's a
whole lot easier.  My tab is about 10" long by 1.25" fore and aft, which
gives it plenty of authority.

Jim Cameron,  Super ES   N82500

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