Leaning using EGT - Lycoming O-540 (Aztec)

Doug wrote:
Works on my plane (a Husky with Constant Speed prop).

If you can change your engine speed with the mixture then you have a
governor problem.

Cory,

This is what I was concerned about, letting the CHT go over 400 without
realising it, having no CHT installed. In cruise I am running less than
75% so this shouldn't be a problem. Instead of fitting an expensive
engine monitor I may just purchase a digital CHT so I can see what's
going on, however the panel space is pretty tight at present.

Dean

Dean,

Instead of fitting an expensive
engine monitor


Expensive is relative here. The things are cheap compared to one (or,
in your case, two) engine overhauls.

--
Thomas Borchert (EDDH)

Dean,

but how do I know that that
particular EGT is the highest reading. i.e. is it taken off an
individual exhaust outlet or further down the exhaust (i.e.
common/averaged reading).


You don't. But again: You are not looking for the highest value in EGT.
What you are looking for is the first cylinder to reach peak,
regardless of the value it is at. The Deakin columns make all this
clear (after a while...).
The only way to make sure is to install a multi-probe EGT instrument.
Actually, with your kind of engine, I would recommend having one.

But, as long as you don't have one, using the one probe you have will
put you in the ballpark.

--
Thomas Borchert (EDDH)

Dean wrote:
: Cory,

: This is what I was concerned about, letting the CHT go over 400 without
: realising it, having no CHT installed. In cruise I am running less than
: 75% so this shouldn't be a problem. Instead of fitting an expensive
: engine monitor I may just purchase a digital CHT so I can see what's
: going on, however the panel space is pretty tight at present.

Like I was trying to say before, for simple, crude engines like the O-540,
having a whole bunch of readouts probably won't do a whole lot of good. They'll be
all over the map and not much you can do about it.

That said, the first thing I did on my O-360 was install a CHT and EGT probe
for each cylinder. I didn't buy an analyzer, just the Westach gauge and a switch. I
ended up buying the "STC'd" kit, but in reality it's the same thing as the non-kit.
In fact, the rotary switch they supply is pretty cheap and has already become a bit
oxidized internally after 3 years. After switching, you have to wiggle it a bit to
make sure you've got really good internal contact. I'd like to replace it with a
better switch with internal gold-plated contacts.

Depending on how cozy you are with your mechanic (and its corollary of how cozy he is
with your local FSDO), I'd suggest something like this:
http://www.westach.com/images/showca...HT_Pointer.jpg
or maybe
http://www.westach.com/images/showca...8-Dual_CHT.jpg
or
http://www.westach.com/images/showca...al_EGT-CHT.jpg
to conserve panel space.

A rotary switch (all that the STC kit has, anyway) can be wired in to select
whichever jug you want to look at. That makes the primary cost simply that of the
probes. Like I said, I put multiprobes on mine, but in reality I rarely switch. I
found which one was hottest (right-rear, generally) and leave it on that.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************