"Kent, Russell" wrote:
Paul,
I am no engine engineer, but I believe that in the last few messages
titled "Myths from Lycoming" you may have made a serious error. You
repeatedly inserted the following table:
Scenario: Pilot forgets to change the mixture.
Start Operation. Power ...... Fuel Air...... Mixture .. EGT
---------------------------------------------------------------
LOP ..climb .... Reducing ....Same decreasing leaner lower
LOP ..descend .. Increasing ..Same increasing richer higher
ROP ..climb .... Reducing ....Same decreasing leaner maybe the same
due to reduced
power
ROP ..descend .. increasing ..Same increasing Richer lower
You've got the mixture trends reversed. Regardless of the LOP/ROP
starting point, as the aircraft climbs air density decreases, and as the
aircraft descends air density increases. Since the mixture knob
controls the ratio of fuel and air *volumes*, then for a given mixture
setting the fuel mixture enrichens as the aircraft climbs and leans as
the aircraft descends.
This is because as the air density decreases in a climb, the number of
oxygen molecules per unit volume decreases. Same fuel + less oxygen =
richer mixture. And as the air density increases in a descent, the
number of oxygen molecules per unit volume increases. Same fuel + more
oxygen = leaner mixture.
I know the rotary is not at risk by this whole thing, but as you were
trying to point out, conventional piston engines are. While it is very
unlikely that a pilot would operate their engine entirely on the advice
of this newsletter, I would hate for anyone to be confused by the
conflict between it and their POH.
Russell Kent
Yep. I always get it ass backwards with the same result.
You are right Matt. Sorry made a mistake.
This chart is still a work in progress.
Start Operation. Power ...... Fuel Air...... Mixture .. EGT
---------------------------------------------------------------
LOP ..climb .... full ........Same decreasing richer higher
LOP ..descend .. reduced .....Same increasing leaner lower load on engine decreasing
ROP ..climb .... full ... ....Same decreasing richer lower
ROP ..descend .. reduced .. ..Same increasing leaner higher load on engine decreasing
The combination of increased power with richer mixture and higher EGT
while climbing is the valve killer while operating lean of peak.
I would like to make a further point now that I am thinking about it again.
We are trained to richen the mixture when we climb. If you start LOP
and go to rich you may increase the EGT. As you can see starting
with LOP peak is opposite to what we are taught.
There are some secondary effects here.
Pull back the throttle when descending.
Keep the throttle the same.
Increase the prop pitch when descending.
Leave the prop pitch the same.
Decrease the prop pitch.
Perhaps a few others. My point is one must fly all these scenarios
to see what happens to the EGT. A computer controlling the mixture based
on the EGT is the answer.
We in the rotary world don't need.
Paul Lamar
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