"Greg Copeland" wrote in message
news
On Thu, 24 Jun 2004 12:30:03 +0000, EDR wrote:

In article , GE
wrote:

I'm taking delivery today of my first aircraft and it had a constant
speed
prop. I have only flown fixed props thus far. I want to have as much
understanding of the c-s prop as possible before I get with my
instructor. I
understand the basic difference in what the controls do, but I don't
really
have a good understanding of the hows and whys of flying with them. Any
general information, explanations, and tips would be greatly
appreciated.

Go to www.avweb.com
on the left side of the screen, select COLUMNS
scroll down to find THE PELICAN"S PERCH
there are articles on fuel injection, manifold pressure, constant speed
props, leaning, etc
Everything you ever want to know about operating a high performance
aircraft engine is in those articles.


Great link!

I started reading this
article, http://www.avweb.com/news/columns/186619-1.html, and have a
question. In the Runup section, when he starts to test for proper mag
operation, somethings seems odd there. Can someone help explain that? He
says, "Are the mags working? The leaner the mixture, the more mag drop
you'll see on one mag, and that's normal." He then goes on to say, "The
EGTs should rise on the first single-mag operation, stay there for the
second, then drop again on the return to BOTH. That rise is proof-positive
the entire ignition system is working, and working well, and the leaner
the mixture, the more diagnostic it is."

Can someone help explain the supporting logic there? If both mags are
working properly and you switch to a single mag, why would the EGT go up?
After all, in theory, you're producing less spark and thusly, a slightly
less effecient ignition of the fuel/air. I would of thought that EGT
would stay the same or go down *just slightly* when running off of one
mag. Likewise, if one mag is not working, I would fully expect to see a
big EGT drop for the given problematic mag, which he does agree with.
But, he further asserts that, "If any of them fail to rise or even drop
during single-mag operation, there is a problem with that plug, the wire,
or the mag."

So, why would running on one mag, versus two, always cause higher EGTs?
And why would no rise in EGT indicate a bad mag, wire or plug?

Anyone?


P.S. I cross posted because this seems like good student pilot material
too.
The key is that with two plugs, the combustion _in the cylinder_ is more
complete, earlier. When one mag cuts, the fuel air mixture still fully
burns, but the burn is continued slightly latter (where it does less work on
the piston). This results in the gas coming out of the exhaust being a
little hotter (in some cases, it may even be still burning).

Best Wishes