Constant speed props

Greg Copeland wrote:

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?

Running on one mag means the fuel air mixture burns slower... so when
the exhaust valve opens, its still burning and the flame front travels
out the valve (or so ive been told).

If you get NO change with a mag check, then the burning characteristics
arent changing, that means the mag is not dropping offline.. which means
its not groundiing out.

I seem to remember this being explained in Deakin's articles but its
been a while since I've read them.

Dave