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

It's possible that the POH's specify rich of peak operation because
that produces the highest cruise speeds, which is often what sells the
airplane.

Corky Scott



The POH (provided by the airframe manufacturer) is not the same as an
operating manual provided by the engine manufacturer.

Dave

"Richard Russell" wrote in message
news
On Thu, 24 Jun 2004 17:47:41 GMT, "Dudley Henriques"
wrote:

I caught that right after I posted it :-) I had cleaned out OE last
night back to four days old and missed the pickup. Thought I had
deleted this but obviously it didn't work!
Anyway.....it looks to me like the IP needs a complete checkout in
this
airplane before flying it. His questions just seem way out of line
for
someone taking delivery of an airplane they are rated and competent
to
fly!
Sorry about the mispost :-)
DH
"Greg Copeland" wrote in message
news
On Thu, 24 Jun 2004 16:08:47 +0000, Dudley Henriques wrote:

I don't wish to sound like a smartass here, but what's your
problem
with
getting a full checkout in this airplane from a competent pilot
current
in the aircraft?
It sounds like you might benefit from a bit of complex training
here!!!
Dudley Henriques


I wondered the same thing, but you're replying to the wrong person.
I'm a
student and GE posted the original question.

Cheers!



I applaud the original poster. He said, " 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." He's trying to learn a little something in advance so he
doesn't start completely cold with the instructor. He is seeking
complex training and proactively preparing in advance for that
training.
Rich Russell

You hope!!!

Could be, and most likely it's an ok scenario, but the correct answer I
believe is still to tell him to get the checkout; at least tell him this
along with supplying the data requested.
This is one of the drawbacks of aviation Usenet. You never know if
someone is taking a "shortcut" or seeking a head start going in the
right direction. You are probably right, but I notice that no one
answering this poster suggested that he get the checkout along with
supplying the data requested. :-)

Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/ CFI Retired
For personal email, please replace
the z's with e's.
dhenriquesATzarthlinkDOTnzt

One other factor to remember is that if you change to high RPM on
final and the engine is idling, you will increase the drag and steepen
your glide path, especially if the prop is 3-blade. That isn't
necessarily something you want to happen on final approach.

Dudley Henriques wrote:

You hope!!!

Granted, he could be lying to us. But he did write "get with my
instructor". Admittedly, this is imprecise, but I took it to mean "...for
a checkout".

- Andrew

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

I can confirm that an engine running on one mag will show a higher EGT than on
both mags.

I went through the preflight, run-up, took off and during full-power climbout,
I noticed a significantly higher EGT than I was used to.

Startled me until I discovered that in the pre-takeoff mag check I had left the
mag switch on only one mag - I took off and was climbing on a single mag. Duh!

Switching to both mags brought the EGT back down to normal.

"PaulH" wrote in message
om...
One other factor to remember is that if you change to high RPM on
final and the engine is idling, you will increase the drag and steepen
your glide path, especially if the prop is 3-blade. That isn't
necessarily something you want to happen on final approach.

Well, by the time you pull the power off enough to slow down for approach,
wouldn't the prop go to full fine pitch anyways (to try and maintain the set
RPM) and then drop farther? At that point you could push the prop control
all the way in without affecting the current RPM... at least, that's how it
works in the RV.

"Andrew Gideon" wrote in message
online.com...
Dudley Henriques wrote:

I caught that right after I posted it :-) I had cleaned out OE last
night back to four days old and missed the pickup. Thought I had
deleted this but obviously it didn't work!
Anyway.....it looks to me like the IP needs a complete checkout in
this
airplane before flying it. His questions just seem way out of line
for
someone taking delivery of an airplane they are rated and competent
to
fly!
Sorry about the mispost :-)


FWIW, I just (today!) completed complex and high performance
checkouts.
Before I started the actual work, though, I read a fair bit on both
the
specific aircraft and constant-speed prop use in general.

[I even posted some questions here, I believe.]

Reading ahead is never a bad idea, in my experience (granted: I don't
read
many mysteries {8^).

- Andrew

Nobody doubts that reading and studying ahead is the right way to go,
and I for one would of course encourage that. I also would encourage
pilots answering requests for this type of information to include as an
integral part of their answering post, the importance of getting this
checkout. I assume that since the poster specified he was preparing for
a proper checkout, this was why pilots answering didn't elaborate on it.
Dealing in flight safety and instruction all my life points any answer I
might give to this type of post toward reminding someone that the REAL
answers being sought will be found there, and not necessarily in the
prep work, which as we both agree, is fine and to be encouraged.
It's a matter of personal emphasis. Mine is ALWAYS on the proper
checkout as supplying the answers needed and NOT the prep work!
Just my style I guess :-)
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/ CFI Retired
For personal email, please replace
the z's with e's.
dhenriquesATzarthlinkDOTnzt

"Andrew Gideon" wrote in message
online.com...
Dudley Henriques wrote:

You hope!!!

Granted, he could be lying to us. But he did write "get with my
instructor". Admittedly, this is imprecise, but I took it to mean
"...for
a checkout".

- Andrew

So did I. I just believe that as important as any pre check flight prep
might be, the actual check flight and checkout procedure is far more
important to emphasize in the answer, as it relates to a specific
aircraft!
Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/ CFI Retired
For personal email, please replace
the z's with e's.
dhenriquesATzarthlinkDOTnzt

"Tom Sixkiller" wrote in message
...

"C J Campbell" wrote in message
...
I think Deakin is worth reading, but some of what he says should be
taken
with a grain of salt. His columns are mostly based on experiments with
his
own highly modified Bonanza, a few high performance radial engines, and
some
theory. In fact, a careful reading of his columns will show no test data
for
the most common engine and propeller combinations in use today.

You've not read hiscolumns about the test beds they've run at GAMI?

I merely point out that his theories are controversial -- they are hardly
universally accepted, as even this thread amply demonstrates. As I said, I
think he has a point, but I have to consider that the engine manufacturers
and aircraft manufacturers might know at least as much about their products
as GAMI does.